Electrolytic cell and method of use

Abstract

In this specification, carbon dioxide (CO x Methods for operating a CO2 reduction reactor (CRR) and associated equipment are provided. In some embodiments, the methods include terminating, reducing, or otherwise controlling current flow during various operational steps, including hydration periods, break-in periods, normal operation periods, planned outage periods, and extended outage or storage periods.

Description

[Technical Field]

[0001] Reference The PCT request form is filed concurrently with this application as part of this application. Each application on which this application claims interest or priority, as identified in the concurrently filed PCT request form, is incorporated herein by reference in its entirety for all purposes. Statement of government support

[0002] This invention was created with government support under grant number DE-AR00000819 from the Advanced Energy Research Projects Agency, grant number DE-FE0031712 from the National Energy Technology Laboratory, and grant number NNX17CJ02C from the National Aeronautics and Space Administration. The government has certain rights to this invention.

[0003] This disclosure relates, in general, to the field of electrolytic carbon oxide reduction, and more specifically to systems and methods for operating electrolytic carbon oxide reactors. [Background technology]

[0004] Electrolytic carbon dioxide reactors require balancing various operating conditions, including the reactant composition at the anode and cathode, the electrical energy delivered to the anode and cathode, and the physicochemical environment of the electrolyte, anode, and cathode. Balancing these conditions can significantly influence the operating voltage, Faraday yield, and the mixing of products generated at the cathode, including carbon monoxide (CO) and / or other carbon-containing products (CCPs) and hydrogen.

[0005] The background and contextual descriptions included herein are generally provided solely for the purpose of presenting the context of this disclosure. While much of this disclosure presents the inventors' research, the mere fact that such research is described in the background section or presented in context elsewhere in this specification does not imply that such research is prior art. [Overview of the project]

[0006] One aspect of this disclosure is CO x This invention relates to a method for operating a membrane electrode assembly (MEA) for reduction. The method involves applying CO to the cathode of the MEA. x A gas containing CO is introduced, and a current is applied to the MEA at a first current density, thereby CO x Reduce CO x The process includes the steps of generating reduction products and automatically pausing the applied current during normal operation according to a current pause schedule.

[0007] In some embodiments, the current pause schedule includes current-on periods at the first current density, separated by current pause periods, wherein the applied current during at least a portion of one current pause period is zero or a second current density lower than the first current density.

[0008] In some embodiments, the duration of the current-on period is 10 to 1000 hours. In some such embodiments, the duration of the current-pause period is 5 minutes to 10 hours.

[0009] In some embodiments, the duration of the current-on period is 1 to 10 hours. In some such embodiments, the duration of the current-pause period is 500 microseconds to 20 minutes.

[0010] In some embodiments, the duration of the current-on period is 3 minutes to 1 hour. In some such embodiments, the duration of the current-pause period is 500 microseconds to 10 minutes.

[0011] In some embodiments, the total current-on duration is at least 3 times, at least 5 times, or at least 10 times longer than the total current-pause duration. According to various embodiments, the current-pause duration and / or the current-on duration may be constant or variable.

[0012] In some embodiments, the step of automatically pausing the applied current includes a single step from the first current density. In some embodiments, the step of automatically pausing the applied current includes multiple steps from the first current density. In some embodiments, the step of automatically pausing the applied current includes a continuous ramp from the first current density.

[0013] In some embodiments, the step of automatically pausing the applied current includes a step of returning to the first current density using a single step. In some embodiments, the step of automatically pausing the applied current includes a step of returning to the first current density using multiple steps. In some embodiments, the step of automatically pausing the applied current includes a step of returning to the first current density using a continuous ramp.

[0014] In some embodiments, the step of automatically pausing the applied current includes the step of reducing the applied current to zero. In some such embodiments, the step of reducing the applied current to zero includes the step of short-circuiting the MEA. In some such embodiments, the MEA has an open-circuit potential when the applied current is zero.

[0015] In some embodiments, the method further includes the step of stopping the flow of the gas while temporarily suspending the current. In some embodiments, the method further includes the step of reducing the flow of the gas while temporarily suspending the current. In some embodiments, the method further includes the step of maintaining the flow of the gas at the same flow rate while temporarily suspending the current.

[0016] In some embodiments, the method further includes the step of introducing anode supply material to the anode of the MEA. In some embodiments, the method further includes the step of stopping the flow of the anode supply material while pausing the current. In some embodiments, the method further includes the step of maintaining but reducing the flow of the anode supply material while pausing the current. In some embodiments, the method further includes the step of maintaining the flow of the anode supply material at the same flow rate while pausing the current.

[0017] In some embodiments, the method further includes a step of performing a break-in procedure, which includes applying current in a multi-step or continuous ramp up to the first current density, before normal operation. In some such embodiments, the method further includes a step of performing a hydration operation, which is performed before the break-in procedure, wherein no current is applied and cathode gas and anode supply material are introduced to the cathode and anode of the MEA, respectively. In some such embodiments, the method further includes a step of changing the temperature in a ramp manner up to the operating temperature during the hydration period.

[0018] Another aspect of this disclosure is a CO2 array comprising one or more membrane electrode assemblies (MEAs) arranged in a stack. x A reduction reactor in which each MEA (i) promotes the reduction of CO x (ii) a cathode containing a reduction catalyst, (ii) an anode containing a catalyst that promotes oxidation, and (iii) a polymer electrolyte membrane (PEM) layer placed between the cathode and the anode, x CO reduction reactor and xA power controller configured to control the current applied to a reduction reactor, the power controller being the above-mentioned CO x During normal operation of the reduction reactor, a power controller configured to automatically pause the applied current according to a current pause schedule, and a system including the power controller are provided.

[0019] In some embodiments, the current pause schedule includes an on-period of current at the first current density separated by current pause periods, and the applied current during at least a portion of one current pause period is zero or a second current density lower than the first current density.

[0020] In some embodiments, the duration of the on-period of current is from 10 hours to 1000 hours. In some such embodiments, the duration of the current pause period is from 5 minutes to 10 hours.

[0021] In some embodiments, the duration of the on-period of current is from 1 hour to 10 hours. In some such embodiments, the duration of the current pause period is from 500 microseconds to 20 minutes.

[0022] In some embodiments, the duration of the on-period of current is from 3 minutes to 1 hour. In some such embodiments, the duration of the current pause period is from 500 microseconds to 10 minutes.

[0023] In some embodiments, the total on-period duration of current is at least 3 times, at least 5 times, or at least 10 times longer than the total current pause period duration. According to various embodiments, the current pause period duration and / or the on-period duration of current may be constant or variable. In some embodiments, the step of automatically pausing the applied current includes a single step from the first current density. In some embodiments, the step of automatically pausing the applied current includes multiple steps from the first current density. In some embodiments, the step of automatically pausing the applied current includes a continuous ramp from the first current density. In some embodiments, the step of automatically pausing the applied current includes a step of returning to the first current density using a single step. In some embodiments, the step of automatically pausing the applied current includes a step of returning to the first current density using multiple steps. In some embodiments, the step of automatically pausing the applied current includes a step of returning to the first current density using a continuous ramp. In some embodiments, the step of automatically pausing the applied current includes the step of reducing the applied current to zero. In some such embodiments, the step of reducing the applied current to zero includes the step of short-circuiting the MEA. In some such embodiments, the MEA has an open-circuit potential when the applied current is zero.

[0024] In some embodiments, the system is configured to perform a break-in procedure before normal operation, which includes applying current in a multi-step or continuous ramp up to the first current density.

[0025] In some embodiments, the system further comprises the CO x The CO includes a cathode subsystem configured to interact with the cathode of the reduction reactor, and xThe system includes a carbon oxide flow controller configured to control the flow of a carbon oxide supply stream to the reactor cathode. In some such embodiments, the carbon oxide flow controller is configured to stop the flow of carbon oxide during current pauses. In some such embodiments, the carbon oxide flow controller is configured to maintain the flow of carbon oxide at the same or a different flow rate during current pauses. In some embodiments, the cathode subsystem is configured to controllly recycle unreacted carbon oxide from the exhaust stream back to the cathode of the MEA.

[0026] In some embodiments, the system further includes CO x The system includes an anode subsystem configured to interact with the reactor anode, and the above CO x The system includes an anode water flow controller configured to control the flow of an anode supply stream to the reactor anode. In some such embodiments, the anode water flow controller is configured to stop the flow of the anode supply stream during a current pause. In some such embodiments, the anode water flow controller is configured to maintain the flow of the anode supply stream at the same or a different flow rate during a current pause.

[0027] In some embodiments, the system further comprises a controller configured to adjust the composition of the anode supply stream during current pause. In some embodiments, the system further comprises a back pressure controller configured to maintain the pressure on the cathode side of the MEA. In some embodiments, the system further comprises an anode water recirculation loop.

[0028] These and other features of the present disclosure are presented in further detail below with reference to the relevant drawings. [Brief explanation of the drawing]

[0029] [Figure 1A] This figure shows an example of a current pause schedule or profile that may be implemented during the operation of a carbon oxide reduction reactor (CRR) according to various embodiments of the present disclosure.

[0030] [Figure 1B] This figure shows schematic examples of current profiles when the current is reduced from the operating current density to the pause current density at the start of a current pause period, according to various embodiments of the present disclosure.

[0031] [Figure 1C] This figure shows schematic examples of current profiles that return to the operating current density at the end of the current pause period, according to various embodiments of the present disclosure.

[0032] [Figure 1D] This figure shows an example of an electrolytic carbon oxide reduction system according to various embodiments of the present disclosure.

[0033] [Figure 2] This is a schematic diagram of a membrane electrode assembly used for COx reduction according to various embodiments of this disclosure.

[0034] [Figure 3] This is a diagram of a bipolar MEA, in which bicarbonate ions and / or carbonate ions can combine with hydrogen ions between the cathode and anode layers to form carbonic acid, which can then decompose to form gaseous CO2.

[0035] [Figure 4] This is a diagram of an MEA in which CO2 gas is supplied to the cathode catalyst layer.

[0036] [Figure 5] This is a diagram of a MEA having a cathode catalyst layer, an anode catalyst layer, and an anion-conducting PEM configured to promote the CO reduction reaction.

[0037] [Figure 6] This is a schematic diagram showing an example of the morphology of a cathode particle having a catalyst supported on a catalyst support particle.

[0038] [Figure 7] This is a diagram of the MEA, similar to the one shown in Figure 3, but providing further information related to mass transfer at the bipolar interface and the generation of CO2 and water.

[0039] [Figure 8A] This figure presents various MEA designs that include features that resist delamination and optionally provide pathways for reaction products to leave the interface area. [Figure 8B] This figure presents various MEA designs that include features that resist delamination and optionally provide pathways for reaction products to leave the interface area. [Figure 8C] This figure presents various MEA designs that include features that resist delamination and optionally provide pathways for reaction products to leave the interface area. [Figure 8D] This figure presents various MEA designs that include features that resist delamination and optionally provide pathways for reaction products to leave the interface area.

[0040] [Figure 9] This is a diagram of a partial MEA comprising an anion-conducting polymer layer, which may be a cathode buffer layer, and a polymer electrolyte membrane, which may be a cationic-conducting polymer layer.

[0041] [Figure 10] This is a schematic diagram showing the main components of a COx reduction reactor (CRR) according to various embodiments of this disclosure.

[0042] [Figure 11] This is a schematic diagram showing the main components of a CRR, with arrows indicating the flow of molecules, ions, and electrons, according to various embodiments of this disclosure.

[0043] [Figure 12]This is a schematic diagram showing the main inputs and outputs of a CRR reactor according to various embodiments of this disclosure.

[0044] [Figure 13] This plot shows the applied current density (J) and the Faraday yield (FY) for H2, CO, CH2CH2, and CH4, obtained from the operation of the MEA including current cycling.

[0045] [Figure 14] This plot shows the applied current density (J) and the Faraday yield (FY) for H2 and CH4, obtained from the operation of an MEA with simulated biogas supply, including current cycling.

[0046] [Figure 15] This plot shows the break-in period of an MEA with a copper cathode catalyst. The applied current density (J) and the Faraday yields for H2, CO, and CH4 are shown.

[0047] [Figure 16] This plot shows the voltage (V), applied current density (J), and Faraday yields for H2 and CO in an MEA configured to generate CO. Three cycles are shown, including a break-in event and two current on / off events.

[0048] [Figure 17] This plot shows the voltage (V), applied current density (J), and Faraday yields for H2 and CO in an MEA configured to produce CO. The current was paused after 95 minutes.

[0049] [Figure 18] This plot compares the performance of two MEA cells configured to generate CO, one operating without current interruption and the other operating with intermittent pulses.

[0050] [Figure 19] The diagram shows two plots with performance data of the MEA stack, each configured to generate CO and operated with a current pause.

[0051] [Figure 20] This figure shows the results of two identical MEAs for generating CO, tested to reach an operating current density of 500 mA / cm² using different ramp programs.

[0052] [Figure 21] This plot compares the performance of an MEA operating in a cell without a lamp to the operating current of a cell with a lamp current.

[0053] [Figure 22] This figure shows the change in the Faraday yield for CO with respect to the duration of current pause (from before to after current pause). [Figure 23] This figure shows the change in voltage (from before to after the current pause) with respect to the duration of the current pause. [Modes for carrying out the invention]

[0054] In this specification, carbon oxide (CO x A method for operating a reduction reactor (CRR) and related equipment is provided. In some embodiments, the method includes steps of stopping, reducing, or otherwise controlling the current during various operating processes, including hydration, break-in, normal operation, planned shutdown, and long-term shutdown or storage periods. Pausing the current during normal operation has advantages, including improved selectivity, as described below and further in the embodiments. Furthermore, the system may be shut down for other purposes, such as maintenance or storage.

[0055] The CRR described herein comprises one or more membrane electrode assemblies (MEAs), the MEAs of which are arranged in a stack. Examples of MEAs are described below with reference to Figures 2 to 9.

[0056] Several challenges exist regarding the reduction in current density or system shutdown. Some of these are specific to CCRs and not found in MEA assemblies for other applications such as fuel cells or water electrolyzers. For example, anion-exchange polymer electrolytes (which are part of either a bipolar membrane or a standalone AEM membrane with a cathode catalyst layer) contain bicarbonate anions during CO2 conversion. Bipolar MEAs and standalone AEM MEAs containing anion-exchange polymer electrolytes are described further below with reference to Figures 2–9. When the system is shut down and CO2 is replaced with another gas within the system, the bicarbonate in the polymer electrolyte may decompose over time into hydroxide and CO2, leaving behind the hydroxide form of the polymer electrolyte. This can affect other aspects of the MEA, including the chemical stability, expansion, water absorption, and durability of the polymer electrolyte. In some embodiments, MEAs containing anion-exchange polymer electrolytes are kept in contact with CO2 during the shutdown period. If this is not possible or cannot be done, it may be beneficial to expose the MEA to CO2 for a certain period of time before the system is restarted to ensure that the MEA is in the bicarbonate form.

[0057] When a bipolar MEA is used for CO2 conversion, water accumulates on the cathode side of the device, and CO x This may prevent water from approaching the catalyst layer. The rate at which water accumulates in the cathode is proportional to the current density. Stopping the system or reducing the current density will decrease the rate at which water accumulates in the cathode. If the CO2 flow rate under typical operating conditions is not sufficient to remove water at a rate faster than the rate at which water accumulates, the rate at which water accumulates can be reduced by stopping or reducing the current while maintaining water removal by the CO2 gas flow to drain excess water out of the cathode, thereby returning to the desired operating conditions that result in high current density and low voltage.

[0058] If a single cell or a stack of cells fails, continuous CO flow through the cathode occurs. x Flow is CO x The reduction products (e.g., CO, CH4, and CH2CH2) and H2 are removed. Only trace amounts of these compounds remain, which are absorbed by the polymer electrolyte, resulting in pure CO. x Along with this, it can slowly diffuse outwards. At the anode, the water is recirculated over time, becoming saturated with O2, and a small amount of CO2 passes through the membrane from the cathode. x It may contain reduction products and H2. When the system is stopped, continuous circulation of water through the anode removes gaseous O2 bubbles from the anode compartment, but the anode is still exposed to O2 and other compounds from the cathode dissolved in the anode water. These compounds diffuse into the cathode during shutdown, and after the current stops, the cathode may be exposed to O2 and other molecules. When the current stops, CO x Or, if the water flow stops, the cathode will contain H2 and other CO2. x It contains a relatively high concentration of [unclear], and the anode contains oxygen bubbles. This means that anode O2 and cathode CO2 are present in the cathode. x This could lead to a relatively large crossover of the products.

[0059] When a stack is started or operated at room temperature, the voltage is higher and the voltage decay is faster than when the stack is operated at a relatively higher temperature (e.g., 40°C). Operation at low temperatures can be avoided by various techniques, such as heating water and circulating it through the stack's anode before initiating current flow. In some embodiments (e.g., when it is not possible to raise the stack to the desired temperature before current flows), the stack may be rapidly raised to a suitable temperature and operation at low temperatures may be minimized by rapidly raising the stack from zero current directly to a desired or higher current in a short time. The operating parameters described below address these challenges.

[0060] In some embodiments, current is applied to the MEA according to a specific current profile. The current profile may vary according to the operating mode, as further described below. Operating modes include hydration (pre-break-in), break-in, normal operation, planned shutdown, and long-term shutdown or storage. In these operating modes, other cell operating parameters that may be adjusted, often when the current is adjusted according to a specific current profile, include (a) cathode gas composition, flow rate, and pressure, (b) anode water composition and flow rate, and (c) temperature. In some embodiments, voltage is controlled.

[0061] The applied current may be paused during cell operation. This pause in current may be referred to as an off / on cycle, where the current is switched off and then on multiple times. Typically, during a current pause, the applied current is reduced to zero (i.e., switched off), but in some embodiments it may be reduced to a non-zero level.

[0062] The following table lists the current profile, cathode gas composition and flow rate, anode water composition and flow rate, temperature, and voltage profile for specific operating modes. Current efficiency and cell configuration examples are also included. Hydration (pre-break-in)

[0063] In some embodiments, the MEA is subjected to a hydration process before any current is applied to the cell. This involves initiating the reaction flow and heating the cell (or stack) so that it can reach a steady state before current is applied. Prior to stack or cell assembly, the MEA is immersed in water to initiate the hydration of the MEA. After assembly, the flow rates and pressures of the anode water and cathode CO2 are set. Flowing dry or humidified CO2 may be beneficial in this process, even if dry CO2 is used as input during relatively long-term operation. The anode outlet is observed to ensure that no bubbles are present exiting it. If bubbles are present, this indicates significant CO2 crossover (from pinholes in the membrane) or leakage in the hardware. If the desired operating temperature is higher than the ambient temperature, the cell is heated to the desired temperature after the anode water flow has been initiated. During this process, the MEA continues to hydrate at the desired temperature.

[0064] Table 1: Example of operating parameters during hydration [Table 1] [Table 1] Break-in

[0065] The break-in period refers to the procedure first applied to the MEA or stack until the operating conditions and performance meet the desired long-term settings. In some embodiments, when the MEA is used for the first time, a procedure different from typical operation may be useful to obtain better performance. An MEA that has not been operated before may not be sufficiently hydrated or may undergo structural changes due to the rise in operating temperature. In some embodiments, the current does not jump linearly to the desired operating value, but rather ramps up from a low value to a high value in a series of steps. A gradual linear ramp-up may be used. An example of a current profile is shown in Figure 1A.

[0066] The number of intermediate steps in a multi-step ramp-up may be, for example, 1, 2, 3, 4, 5, or 6. The duration of each step may be the same or different. Examples of durations range from 30 minutes to 5 hours, for example, 1 hour or 2 hours. Figure 20 in the example shows that a gentler ramp may result in higher selectivity, which may be due to better hydration. In some embodiments, each intermediate step is used with a duration of at least 1 hour.

[0067] In embodiments where the operating temperature is reached during pre-break-in (e.g., during the hydration period), the temperature may be maintained constant at this temperature. In other embodiments, the temperature may be ramped up during the break-in procedure.

[0068] Table 2: Example of operating parameters during break-in [Table 2] [Table 2]

[0069] Cycle the stack off and on during normal operation can be useful for maintaining performance over extended periods. Pausing the current for just 5 microseconds, 500 microseconds, 5 seconds, or 30 seconds can improve current efficiency and / or reduce voltage. This is referred to as current pausing. In some embodiments, as shown below, current pausing reduces the current to a non-zero level. For example, a typical operating current density of 300 mA / cm². 2 In this case, the current pause occurs when the current density is 50 mA / cm². 2 This may include reducing the voltage to a certain level. In some embodiments, the voltage is controlled to achieve a similar cyclic action.

[0070] Low or no current reduces the amount of water arriving from the anode to the cathode of the cell (e.g., a bipolar MEA), which can be used to remove excess water that may accumulate at the cathode. Also, low or no current increases the cathode voltage to a point where harmful species that may accumulate on the catalyst surface can be oxidized. Examples of possible impurities include CO2. x Examples include carbon-containing intermediates formed during reduction, metallic impurities such as iron, or impurities introduced into the CO2 stream such as H2S. The same effect can be achieved by directly controlling the stack or cell voltage to a desired value.

[0071] According to various embodiments, the current may be paused at relatively frequent intervals (less than 10 hours, e.g., less than 2 hours) or at relatively infrequent intervals (several tens of hours or more). Examples of operating conditions when the current is paused frequently and when it is paused relatively infrequently are shown below in Tables 3 and 4, respectively.

[0072] Various current profiles can be used when reducing the current from the operating current to zero or a second, lower current density. In some embodiments, a single step is used to immediately transition to the lower level. In alternative embodiments, multiple steps or a continuous, gradual linear ramp may be used. Similarly, when returning to the operating current density, a single step may be used, or the current may be changed in a ramp-like manner using multiple steps or a continuous, gradual ramp program.

[0073] Generally, current profiles or current pause schedules are designed so that the current-on periods are significantly longer than the pause periods. Figure 1A shows a schematic example of a current pause schedule, sometimes referred to as a current profile. Current density is shown on the y-axis, and time is shown on the x-axis. As can be seen in Figure 1A, current-on periods are separated by current pause periods at regular intervals. The interval is the current-on period duration. The current density is reduced during the current pause period from the operating current density (J operating) to the paused current density (J pause), which can be zero or non-zero as shown above. The current pause period duration is significantly shorter than the current-on period for high throughput. For example, the current-on period may be at least 3, 5, 10, 20, 50, 100, or 500 times longer than the current pause period. Improved selectivity correlates with both the current pause duration and the previous selectivity in the current-on duration. Therefore, if the current-on duration is longer, a longer current pause duration may be used. Examples of on / off durations are given below. [Table 3]

[0074] In the example shown in Figure 1A, the current pause schedule is constant for the duration of normal operation. In other embodiments, the intervals and / or pause durations may vary throughout the course of operation. For example, current pauses may be programmed to occur more frequently in advanced operating processes. The current pause schedule is typically implemented automatically using a controller such as those described herein. The controller is programmed or otherwise configured to implement the schedule. In some embodiments, the user may set the schedule to be implemented automatically during operation.

[0075] Furthermore, in the example in Figure 1A, a single step is used to decrease the current density at the start of the pause period and return it to the operating density at the end of the pause period. As with increasing or decreasing the current in other operating modes described herein, the current may change in multiple steps or continuously in a ramp-like manner at the start and / or end of the current pause period. Figure 1B shows a schematic example of the decrease in current from the operating current density to the pause current density at the start of the current pause period. Similarly, Figure 1C shows a schematic example of the return to the operating current density at the end of the current pause period. The current profile at the start may be selected independently of that at the end of the pause period. For example, the current may be decreased in a single step and increased in multiple steps.

[0076] During current suspension, the cell voltage may be maintained at any of a range of values. In some cases, during current suspension, the anode and cathode are short-circuited (e.g., through a power supply or by connecting the electrodes to a metal or other conductor). In this case, the cell voltage is 0 or approximately 0 volts. In some cases, during current suspension, the anode and cathode are made floatable, and the cell voltage is the open-circuit voltage under general conditions, e.g., 0.8V to 1.4V, 0.8V to 1.2V, or 0.9V to 1.1V. The open-circuit voltage represents the potential difference between the electrodes of the cell when no external current is applied to or drawn from the cell. The open-circuit voltage is the manifestation of the half-reaction potential at the anode and cathode. In some cases, during current suspension, the cell voltage is neither 0 volts (short-circuit) nor the open-circuit voltage. Rather, the cell voltage is set to a different voltage by applying a control voltage and / or control current between the anode and cathode. In certain embodiments, during current suspension, the cell voltage is maintained at approximately 0 to 1.4 volts, or 0.9 to 1.1 volts.

[0077] According to various embodiments, the cathode and / or anode flow may be stopped or allowed to continue during current suspension. Table 3: Example of operating parameters during normal operation - Frequent current interruptions [Table 3] [Table 4] Table 4: Example of operating parameters during normal operation - relatively infrequent current pauses [Table 4] [Table 5] Plan cancelled

[0078] Sometimes, CO x Planned shutdowns may be implemented depending on the use of the electrolysis system. During a planned shutdown, the system will be shut down for a short period and then turned back on. Examples of reasons for planned shutdowns include maintenance of a part of the system (e.g., replacement of filters on the anode water recycling loop, replacement of flow controllers, or testing of temperature sensors), planned power outages, and CO2 emissions. x One example is a temporary pause in a downstream process that uses the reduction product. Planned shutdowns have a relatively short duration, ranging from a few minutes to a few days.

[0079] During planned shutdown, the applied current is zero. According to various embodiments, the applied current may drop to zero immediately (i.e., in a single step), or it may ramp down in multiple steps or in a continuous ramp.

[0080] Table 5: Example of operating parameters for planned shutdown [Table 5] [Table 6] Long-term shutdown and storage

[0081] Sometimes, it is desirable for a system or stack to be shut down for an extended period. For example, a facility holiday shutdown, moving a system to a new facility, or CO xSupply interruption. During this time, it is expected that the system can be completely isolated from external inputs. In this case, a gas or aqueous solution different from that used during normal operation can be sealed in the anode or cathode. The startup procedure after a long-term shutdown or storage period can be the same as the break-in procedure described above. Table 6: Example of operating parameters for a long-term shutdown [Table 6] [Table 7] system

[0082] Figure 1D shows a system 101 for controlling the operation of a carbon oxide reduction reactor 103, which may include cells containing any one or more MEAs described herein. The reactor may include multiple cells or MEAs arranged in a stack. The system 101 comprises an anode subsystem that interfaces with the anode of the reduction reactor 103 and a cathode subsystem that interfaces with the cathode of the reduction reactor 103.

[0083] As shown in the figure, the cathode subsystem includes a carbon oxide source 109 configured to provide a supply stream of carbon oxide to the cathode of the reduction reactor 103, which may, during operation, generate an output stream containing the products of the reduction reaction at the cathode. The product stream may contain unreacted carbon oxide and / or hydrogen. See 108.

[0084] The carbon oxide source 109 is connected to a carbon oxide flow controller 113 configured to control the volumetric or mass flow rate of carbon oxide to the reduction reactor 103. One or more other components may be installed in the flow path from the carbon oxide source 109 to the cathode of the reduction reactor 103. For example, an optional humidifier 104 may be provided in the path and configured to humidify the carbon oxide supply stream. Humidified carbon oxide can wet one or more polymer layers of the MEA, thereby preventing such layers from drying out. Another component that may be installed in the flow path is a purge gas inlet connected to a purge gas source 117. In certain embodiments, the purge gas source 117 is configured to provide purge gas for a period of time when the current to the cells of the reduction reactor 103 is paused. In some implementations, flowing purge gas over the MEA cathode promotes the recovery of catalytic activity and / or selectivity. This may be at least partially due to certain reaction intermediates being washed away from the catalytic active site and / or water being removed from the cathode. Examples of purge gases include carbon dioxide, carbon monoxide, hydrogen, nitrogen, argon, helium, oxygen, and any two or more mixtures of these.

[0085] During operation, the output stream from the cathode flows through a conduit 107 connected to a back pressure controller 115, which is configured to maintain the pressure on the cathode side of the cell within a specified range (e.g., approximately 50 to 800 psig, depending on the system configuration). The output stream may provide the reaction product 108 to one or more components (not shown) for separation and / or concentration.

[0086] In certain embodiments, the cathode subsystem is configured to controllly recycle unreacted carbon oxide from the exhaust stream by returning it to the cathode of the reduction reactor 103. In some implementations, the output stream is treated to remove reduction products and / or hydrogen before recycling the carbon oxide. Depending on the configuration and operating parameters of the MEA, the reduction products may be carbon monoxide, hydrogen, methane and / or hydrocarbons such as ethylene, oxygen-containing organic compounds such as formic acid and acetic acid, and any combination thereof. In certain embodiments, one or more components (not shown) for removing water from the product stream are installed downstream of the cathode outlet. Examples of such components include a phase separator configured to remove liquid water from the product gas stream, and / or a condenser configured to cool the product stream gas and thereby provide a dry gas to downstream processes, for example, if needed. In some implementations, the recycled carbon oxide may be mixed with fresh carbon oxide from a source 109 upstream of the cathode.

[0087] As shown in Figure 1D, the anode subsystem is configured to provide an anode supply stream to the anode side of the carbon oxide reduction reactor 103. In certain embodiments, the anode subsystem includes an anode water source (not shown) configured to supply fresh anode water to a recirculation loop including an anode water reservoir 119 and an anode water flow controller 111. The anode water flow controller 111 is configured to control the flow rate of anode water to and from the anode of the reduction reactor 103. In the illustrated embodiment, the anode water recirculation loop is connected to components for adjusting the composition of the anode water. These may include a water reservoir 121 and / or an anode water additive source 123. The water reservoir 121 is configured to supply (and circulate in the anode water recirculation loop) water having a different composition from that in the anode water reservoir 119. In one example, the water in the water reservoir 121 is pure water that can dilute solutes or other components in the circulating anode water. The pure water may be conventional deionized water, or even ultrapure water having a resistivity of, for example, at least about 15 MOhm-cm or greater than 18.0 MOhm-cm. The anode water additive source 123 is configured to supply solutes such as salts and / or other components to the circulating anode water.

[0088] During operation, the anode subsystem may supply water or other reactants to the anode of reactor 103, which at least partially react to produce oxidation products such as oxygen. The products, along with unreacted anode feed material, are supplied to the discharge stream of the reduction reactor. Although not shown in Figure 1D, optional separation components may be provided along the path of the anode discharge stream and configured to condense or separate oxidation products from the anode product stream.

[0089] Other control functions may be included in system 101. For example, a temperature controller may be configured to heat and / or cool the carbon oxide reduction reactor 103 at appropriate points during operation. In the illustrated embodiment, a temperature controller 105 is configured to heat and / or cool the anode water supplied to the anode water recirculation loop. For example, the temperature controller 105 may include or be connected to a heater and / or cooler that can heat or cool the water in the anode water reservoir 119 and / or the water in reservoir 121. In some embodiments, system 101 includes a temperature controller configured to directly heat and / or cool components other than the anode water component. Examples of such other components in the cell or stack, and carbon oxide flowing to the cathode.

[0090] Depending on the phase of electrochemical operation, including whether or not the current to the carbon oxide reduction reactor 103 is paused, certain components of system 101 may operate to control non-electrical operations. For example, system 101 may be configured to regulate the flow rate of carbon oxide to the cathode and / or the flow rate of anode supply material to the anode of reactor 103. Components that can be controlled for this purpose include a carbon oxide flow controller 113 and an anode water controller 111.

[0091] Furthermore, depending on the phase of electrochemical operation, including whether the current is paused or not, certain components of system 101 may operate to control the composition of the carbon oxide supply stream and / or anode supply stream. For example, the water reservoir 121 and / or anode water additive source 123 may be controlled to adjust the composition of the anode supply stream. In some cases, the additive source 123 may be configured to adjust the concentration of one or more solutes, such as one or more salts, in the aqueous anode supply stream.

[0092] In some cases, a temperature controller, such as controller 105, is configured to adjust the temperature of one or more components of the system 101 based on the phase of operation. For example, the temperature of cell 103 may be increased or decreased during break-in, current pause during normal operation, and / or storage.

[0093] In some embodiments, the carbon oxide electrolytic reduction system is configured to facilitate the removal of the reduction cell from other system components. This may be useful when it is necessary to remove the cell for storage, maintenance, or repair. In the illustrated embodiment, isolation valves 125a and 125b are configured to block the fluid communication of the cell 103 to the carbon oxide source and to the cathode and back pressure controller 115, respectively. Furthermore, isolation valves 125c and 125d are configured to block the fluid communication of the cell 103 to the anode water inlet and outlet, respectively.

[0094] The carbon oxide reduction reactor 103 may operate under the control of one or more power supplies and associated controllers. See block 133. The power supplies and controllers 133 may be programmed or otherwise configured to control the current supplied to the electrodes in the reduction reactor 103 and / or the applied voltage. The current and / or voltage may be controlled to perform current schedules and / or current profiles described elsewhere in this specification. For example, the power supplies and controllers 133 may be configured to periodically suspend the current applied to the anode and / or cathode of the reduction reactor 103. Any current profiles described herein may be programmed into the power supplies and controllers 133.

[0095] In certain embodiments, the power supply and controller 133 perform some, but not all, of the operations necessary to achieve a desired current schedule and / or profile in the carbon oxide reduction reactor 103. The system operator or other responsible party may act in conjunction with the power supply and controller 133 to fully define the schedule and / or profile of the current applied to the reduction reactor 103. For example, the operator may establish one or more current pauses in addition to the set of current pauses programmed within the power supply and controller 133.

[0096] In certain embodiments, the power supply and controller operate in coordination with one or more other controllers or control mechanisms that work in conjunction with other components of the system 101. For example, the power supply and controller 133 may operate in coordination with controllers for controlling the delivery of carbon oxide to the cathode, the delivery of anode water to the anode, the addition of pure water or additives to the anode water, and any combination of these functions. In some implementations, one or more controllers are configured to coordinately control or operate to control any combination of the following functions: application of current and / or voltage to reduction cell 103; control of back pressure (e.g., via back pressure controller 115); supply of purge gas (e.g., using purge gas component 117); delivery of carbon oxide (e.g., via carbon oxide flow controller 113); humidification of carbon oxide in the cathode supply stream (e.g., via humidifier 104); flow rate of anode water to and / or from the anode (e.g., via anode water flow controller 111); and anode water composition (e.g., via anode water source 105, pure water reservoir 121, and / or anode water additive component 123).

[0097] In the illustrated embodiment, the voltage monitoring system 134 is used to determine the voltage across the anode and cathode of an MEA cell or across any two electrodes of a cell stack, for example, to determine the voltage across all cells in a multi-cell stack. The voltage thus determined can be used to control the cell voltage during a current pause, to notify the duration of the pause, etc. In certain embodiments, the voltage monitoring system 134 is configured to work in conjunction with the power supply 133 to keep the reduction cell 103 within a specified voltage range. For example, the power supply 133 may be configured to apply current and / or voltage to the electrodes of the reduction cell 103 so as to maintain the cell voltage within a specified range during a current pause. For example, if the open-circuit voltage of a cell deviates from a specified range during a current pause (as determined by the voltage monitoring system 134), the power supply may be configured to apply current or voltage to the electrodes so as to maintain the cell voltage within a specified range.

[0098] An electrolytic carbon oxide reduction system, such as the one shown in Figure 1D, may use a control system comprising one or more controllers and one or more controllable components such as pumps, sensors, dispensers, valves, and power supplies. Examples of sensors include pressure sensors, temperature sensors, flow sensors, conductivity sensors, voltmeters, ammeters, electrolyte composition sensors including electrochemical instruments, chromatography systems, optical sensors such as absorbance measurement tools, etc. Such sensors may be connected to the inlet and / or outlet of the MEA cell (for example, in a flow field) in a storage container for holding anode water, pure water, saline solution, etc., and / or other components of the electrolytic carbon oxide reduction system.

[0099] Various functions that can be controlled by one or more controllers include applying current and / or voltage to a carbon oxide reduction cell, controlling back pressure on the cathode outlet on such a cell, supplying purge gas to the cathode inlet, delivering carbon oxide to the cathode inlet, humidifying carbon oxide in the cathode supply stream, flowing anode water to and / or from the anode, and controlling the anode supply composition. Any one or more of these functions may have a dedicated controller for controlling that function alone. Any two or more of these functions may share a controller. In some embodiments, a controller hierarchy is used in which at least one master controller gives commands to two or more component controllers. For example, the system may have a master controller configured to give high-level control commands to (i) power to the carbon oxide reduction cell, (ii) the cathode supply stream flow controller, and (iii) the anode supply stream flow controller. For example, a programmable logic controller (PLC) may be used to control the individual components of the system.

[0100] In certain embodiments, the control system is configured to apply current to a carbon oxide reduction cell comprising an MEA according to a current schedule which may have any of the characteristics described herein. For example, the current schedule may provide periodic pauses in the applied current. In some cases, the control system provides current pauses having a specified profile such as a ramp and / or step change as described herein.

[0101] In certain embodiments, the control system is configured to control the flow rates of one or more supply streams (e.g., a cathode supply stream and an anode supply stream, such as a carbon oxide stream) in coordination with the current schedule. For example, the carbon oxide or purge gas flow may be switched on, switched off, or otherwise adjusted when the current applied to the MEA cell is paused.

[0102] In certain embodiments, the control system may maintain the salt concentration at a specified level and / or recover and recirculate the anode water. In certain embodiments, the salt concentration is adjusted in coordination with the schedule of temporary pauses in the current applied to the MEA cell. Under the control of the control system, the system may, for example, (a) recirculate the anode water flowing out of the anode, (b) adjust the composition and / or flow rate of the anode water entering the anode, (c) move the water flowing out of the cathode back into the anode water, and / or (d) adjust the composition and / or flow rate of the water recovered from the cathode stream before returning to the anode. Note that (d) may address carbon oxide reduction products in the water recovered from the cathode. However, in some implementations, it is not necessary to consider this, as some reduction products may later oxidize harmless products at the anode.

[0103] The controller may comprise any number of processors and / or memory devices. The controller may include control logic such as software or firmware and / or execute instructions provided from another source. The controller may be integrated with electronic devices for controlling the operation of the electrolytic cell before, during, and after the reduction of carbon oxide. The controller may control various components or sub-parts of one or more electrolytic carbon oxide reduction systems. Depending on the processing requirements and / or type of the system, the controller may be programmed to control any of the processes disclosed herein, such as gas delivery, temperature setting (e.g., heating and / or cooling), pressure setting, power setting (e.g., voltage and / or current delivered to the electrodes of the MEA cell), liquid flow rate setting, fluid delivery setting, and administration of purified water and / or saline solution. These controlled processes may be connected to or interfaced with one or more systems that function in cooperation with the electrolytic carbon oxide reduction system.

[0104] In various embodiments, the controller includes an electronic device having various integrated circuits, logic, memory, and / or software that receive and issue instructions and control the operations described herein. The integrated circuit may include a chip in the form of firmware that stores program instructions, a chip defined as a digital signal processor (DSP), an application-specific integrated circuit (ASIC), and / or one or more microprocessors or microcontrollers that execute program instructions (e.g., software). The program instructions may be instructions communicated to the controller in the form of various individual settings (or program files) that define operating parameters for executing a process on one or more components of an electrolytic carbon oxide reduction system. In some embodiments, the operating parameters may be part of a recipe defined by a process engineer to achieve one or more processing steps when generating specific reduction products such as carbon monoxide, hydrocarbons, and / or other organic compounds.

[0105] In some implementations, the controller may be part of or connected to a computer that is integrated into or connected to the system, or otherwise networked to the system, or a combination thereof. For example, the controller may use and / or execute instructions stored remotely (e.g., in the “cloud”). The computer may allow remote access to the system to monitor the current progress of an electrolytic operation, investigate past electrolytic operation history, investigate trends or performance metrics from multiple electrolytic operations, change parameters of the current process, set up subsequent processes following the current process, or start a new process. In some examples, the remote computer (e.g., a server) may provide process recipes to the system over a network that may include a local network or the internet. The remote computer may have a user interface that allows entry or programming of parameters and / or settings. The parameters and / or settings are then communicated from the remote computer to the system. In some examples, the controller receives instructions in the form of data specifying parameters for each of the processes to be executed during one or more operations.

[0106] The controllers may be distributed, for example, by including one or more separate controllers that are networked together and function for common purposes such as applying current to the MEA cell and other process controls described herein. An example of a distributed control system for such purposes is one or more processors on the system for the electrolytic reduction of carbon oxide, and one or more remotely located processors combined (at the platform level or as part of a remote computer, for example) to control the process.

[0107] In certain embodiments, the electrolytic carbon oxide reduction system is configured and controlled to avoid salt precipitation within the MEA. Precipitated salts can block channels and / or have other effects that degrade the performance of the MEA cell. In some cases, the cell may become excessively dry, for example, on the cathode side, due to the dry gaseous reactants removing excess water from the MEA. This problem, which can lead to salting-out precipitation, can be addressed by controlling the partial pressure of water in the gas inlet stream (e.g., by humidifying the gaseous carbon oxide source gas). In some cases, the salt concentration in the anode water is high enough to promote salting-out precipitation within the MEA. This problem can be addressed by flushing the MEA with pure water during current pauses. MEA Design Embodiment MEA Overview

[0108] In various embodiments, the MEA comprises an anode layer, a cathode layer, an electrolyte, and optionally one or more other layers. These layers may be solid and / or gels. These layers may contain polymers such as ion-conducting polymers.

[0109] When in use, the MEA cathode has three inputs: CO x CO x CO x It promotes the electrochemical reduction of CO. The reduction reaction may produce oxygen and hydrogen containing hydrocarbons and / or organic compounds such as methanol, ethanol, and acetic acid. When in use, the anode of the MEA promotes electrochemical oxidation reactions, such as the electrolysis of water, to produce oxygen and protons. The cathode and anode may each contain catalysts to promote their respective reactions.

[0110] The composition and structure of the layers within the MEA are CO x This can promote high yields of reduction products. For this purpose, MEA is used under the following conditions: (a) parasitic reduction reaction at the cathode (non-CO x(b) Minimal reduction reaction, (b) CO at the anode or other location within the MEA x (c) Minimizing the loss of reactants, (d) Maintaining the physical integrity of the MEA during the reaction (e.g., preventing the peeling of the MEA layer), and (c) CO x Any one or more of the following may be facilitated: (e) preventing crossover of reduction products; (f) preventing crossover of oxidation products (e.g., O2); (g) maintaining a favorable environment at the cathode for oxidation; (h) providing a path for desired ions to move between the cathode and anode while blocking undesirable ions; and (h) minimizing voltage loss. As described herein, the presence of salts or salt ions in the MEA can facilitate some of all of these conditions. COx reduction considerations

[0111] Polymer membrane assemblies such as MEA have been used in various electrolytic systems such as water electrolytic cells, and in various galvanic systems such as fuel cells. However, CO x Reduction presents a problem that is rarely or never encountered in water electrolytic cells and fuel cells.

[0112] For example, in many applications, CO x The MEA for reduction requires a service life of approximately 50,000 hours or more (roughly 5 years of continuous operation), which is significantly longer than the expected lifespan of fuel cells in automotive applications, for example, around 5,000 hours. Furthermore, for various applications, CO x For reduction, the MEA uses electrodes with a relatively larger surface area compared to the MEA used in fuel cells for automotive applications. For example, CO x The MEA required for reduction is at least approximately 500 cm³. 2 An electrode having a surface area (excluding voids and other non-planar shapes) can be used.

[0113] CO xReduction reactions can be carried out in an operating environment that promotes the mass transfer of specific reactants and product species, while suppressing parasitic reactions. Fuel cells and water electrolytic cells (MEAs) often cannot create such an operating environment. For example, such MEAs may promote undesirable parasitic reactions such as the generation of gaseous hydrogen at the cathode and / or gaseous CO2 at the anode.

[0114] In some systems, CO x The rate of the reduction reaction is determined by the gaseous CO at the cathode. x The electrolysis rate is limited by the availability of the reactants. In contrast, the electrolysis rate of water is not significantly limited by the availability of the reactants. Liquid water tends to be easily accessible to the cathode and anode, and the electrolytic cell can operate near the highest possible current density. MEA configuration

[0115] In certain embodiments, the MEA comprises a cathode layer, an anode layer, and a polymer electrolyte membrane (PEM) between the anode and cathode layers. The polymer electrolyte membrane provides ionic communication between the anode and cathode layers while preventing electronic communication, which results in a short circuit. The cathode layer comprises a reduction catalyst and a first ion-conducting polymer. The cathode layer may also contain an ion conductor and / or an electron conductor. The anode layer comprises an oxidation catalyst and a second ion-conducting polymer. The anode layer may also contain an ion conductor and / or an electron conductor. The PEM comprises a third ion-conducting polymer.

[0116] In certain embodiments, the MEA has a cathode buffer layer between the cathode layer and the polymer electrolyte membrane. The cathode buffer comprises a fourth ion-conducting polymer.

[0117] In certain embodiments, the MEA has an anode buffer layer between the anode layer and the polymer electrolyte membrane. The anode buffer contains a fifth ion-conducting polymer.

[0118] In relation to a particular MEA design, there are three available classes of ion-conducting polymers: anionic conductors, cationic conductors, and mixed cationic and anionic conductors. In a particular embodiment, at least two of the first, second, third, fourth, and fifth ion-conducting polymers are made from different classes of ion-conducting polymers. Conductivity and selectivity of ion-conducting polymers for the MEA layer.

[0119] The term “ion-conducting polymer” is used herein to describe polymer electrolytes having a specific conductivity greater than approximately 1 mS / cm for anions and / or cations. The term “anion conductor” describes an ion-conducting polymer that conducts primarily anions (but also some small amounts of cations) and has an anion transport fraction greater than approximately 0.85 at a thickness of approximately 100 microns. The terms “cation conductor” and / or “cation-conducting polymer” describe an ion-conducting polymer that conducts primarily cations (for example, incidental amounts of anions may also be conducted) and has a cation transport fraction greater than approximately 0.85 at a thickness of approximately 100 microns. In the case of an ion-conducting polymer described as conducting both anions and cations ("cation and anion conductor"), neither anions nor cations have a transport fraction greater than approximately 0.85 or less than approximately 0.15 at a thickness of approximately 100 microns. To state that a material conducts ions (anions and / or cations) is to state that the material is an ion-conducting material or ionomer. Examples of ion-conducting polymers in each class are shown in the table below. [Table 8]

[0120] Several Class A ion-conducting polymers are known by trade names such as 2259-60 (Pall RAI), AHA by Tokuyama Co., fumasep® FAA- (fumatech GbbH), Sustanion®, Morgane ADP by Solvay, or Tosflex® SF-17 by Tosoh's anion exchange membrane material. Further Class A ion-conducting polymers include HNN5 / HNN8 by Ionomr, FumaSep by Fumatech, TM1 by Orion, and PAP-TP by W7energy. Several Class C ion-conducting polymers are known by trade names such as Nafion® (DuPont TM It is also known by trade names such as GORE-SELECT(registered trademark)(Gore), fumapem(registered trademark)(fumatech GmbH), and various formulations of Aquivion(registered trademark)PFSA(Solvay). Bipolar MEA for COx reduction

[0121] In certain embodiments, the MEA comprises a bipolar interface having an anion-conducting polymer on the cathode side of the MEA and an interfacial cation-conducting polymer on the anode side of the MEA. In some implementations, the cathode comprises a first catalyst and an anion-conducting polymer. In certain embodiments, the anode comprises a second catalyst and a cation-conducting polymer. In some implementations, a cathode buffer layer is disposed between the cathode and the PEM and comprises an anion-conducting polymer. In some embodiments, an anode buffer layer is disposed between the anode and the PEM and comprises a cation-conducting polymer.

[0122] During operation, the MEA with a bipolar interface allows ions to pass through the polymer electrolyte, electrons to pass through the metal and / or carbon in the cathode and anode layers, and liquids and gases to pass through the vacancies in these layers.

[0123] In embodiments utilizing an anionic conductive polymer in the cathode and / or cathode buffer layer, the MEA can reduce or block undesirable reactions that generate undesirable products and reduce the overall efficiency of the cell. In embodiments utilizing a cationic conductive polymer in the anode and / or anode buffer layer, the MEA can reduce or block undesirable reactions that reduce the generation of desired products and reduce the overall efficiency of the cell.

[0124] For example, at the potential levels used for the cathode reduction of CO2, hydrogen ions can be reduced to hydrogen gas. This is a parasitic reaction. The current that could be used to reduce CO2 is instead used to reduce hydrogen ions. Hydrogen ions can be produced by various oxidation reactions carried out at the anode in the CO2 reduction reactor, travel across the MEA to the cathode, and potentially be reduced there to produce hydrogen gas. The extent to which this parasitic reaction can proceed correlates with the concentration of hydrogen ions present at the cathode. Therefore, the MEA may use anion-conducting material in the cathode layer and / or cathode buffer layer. The anion-conducting material at least partially prevents hydrogen ions from reaching the catalytic site on the cathode. As a result, the parasitic generation of hydrogen gas is reduced, and the rate of CO or other product formation and the overall efficiency of the process are increased.

[0125] Another reaction that can be avoided is the reaction of carbonate or bicarbonate ions at the anode, which produces CO2. At the cathode, aqueous carbonate or bicarbonate ions may be produced from CO2. If such ions reach the anode, they may react with hydrogen ions to produce and release gaseous CO2. The result is a net transfer of CO2 from the cathode to the anode, where the CO2 does not react and is lost along with the oxidation products. To prevent carbonate and bicarbonate ions produced at the cathode from reaching the anode, the anode and / or anode buffer layer may contain a cationic conductive polymer, which at least partially inhibits the movement of negative ions such as bicarbonate ions to the anode.

[0126] Therefore, in some designs, the bipolar membrane structure increases the pH at the cathode to promote CO2 reduction, while a cationic conductive polymer such as a proton exchange layer prevents large amounts of CO2 and CO2 reduction products (e.g., bicarbonates) from passing through to the anode side of the cell.

[0127] CO x An example of MEA200 used for reduction is shown in Figure 2. MEA200 has a cathode layer 220 and an anode layer 240 separated by an ion-conducting polymer layer 260, the ion-conducting polymer layer 260 providing a path for ion movement between the cathode layer 220 and the anode layer 240. In certain embodiments, the cathode layer 220 comprises an anion-conducting polymer, and / or the anode layer 240 comprises a cationic-conducting polymer. In certain embodiments, the cathode layer and / or anode layer of the MEA are porous. The vacancies can facilitate gas and / or fluid movement and increase the amount of catalyst surface area available for the reaction.

[0128] The ion-conducting layer 260 may include two or three sublayers: a polymer electrolyte membrane (PEM) 265, an optional cathode buffer layer 225, and / or an optional anode buffer layer 245. One or more layers in the ion-conducting layer may be porous. In certain embodiments, at least one layer is non-porous to prevent reactants and products from the cathode from passing to the anode and / or vice versa via gas and / or liquid movement. In certain embodiments, the PEM layer 265 is non-porous. Exemplary properties of the anode buffer layer and the cathode buffer layer are provided elsewhere in this specification. In certain embodiments, the ion-conducting layer is either a single layer or includes two sublayers.

[0129] Figure 3 shows a CO2 electrolytic cell 303 configured to receive water and CO2 (e.g., humidified or dry gaseous CO2) as reactants at the cathode 305 and discharge CO as a product. The electrolytic cell 303 is also configured to receive water as a reactant at the anode 307 and discharge gaseous oxygen. The electrolytic cell 303 comprises a bipolar layer having an anion-conducting polymer 309 adjacent to the cathode 305 and a cationic-conducting polymer 311 (shown as a proton exchange membrane) adjacent to the anode 307.

[0130] As shown in the enlarged inset of the bipolar interface 313 in the electrolytic cell 303, the cathode 305 comprises an anion exchange polymer (in this example, the same anion-conducting polymer 309 located in the bipolar layer), conductive carbon-supported particles 317, and metal nanoparticles 319 supported on the supporting particles. CO2 and water are transported through vacancies such as vacancies 321 to the metal nanoparticles 319, where they react with hydroxide ions to produce bicarbonate ions and reduction reaction products (not shown). CO2 may also reach the metal nanoparticles 319 by transport within the anion exchange polymer 309.

[0131] Hydrogen ions are moved from the anode 307 through the cationic conductive polymer 311, eventually reaching the bipolar interface 313, where they are prevented from further movement toward the cathode by the anion exchange polymer 309. At interface 313, hydrogen ions may react with bicarbonate or carbonate ions to produce carbonic acid (H2CO3), which may decompose to produce CO2 and water. As described herein, the resulting CO2 may be provided in the gas phase, and a pathway should be provided within the MEA to return it to the cathode 305 where it can be reduced. The cationic conductive polymer 311 prevents anions such as bicarbonate ions from moving toward the anode. At the anode, anions such as bicarbonate ions may react with protons to release CO2, which is not available to participate in the reduction reaction at the cathode.

[0132] As shown in the figure, a cathode buffer layer having an anion-conducting polymer may function in cooperation with the cathode and its anion-conducting polymer to prevent the movement of protons to the cathode. A MEA using an ion-conducting polymer of an appropriate conductivity type in the cathode, anode, cathode buffer layer, and, if present, the anode buffer layer, can prevent the movement of cations to the cathode and anions to the anode, but cations and anions can still come into contact in internal regions of the MEA, such as the film layer.

[0133] As shown in Figure 3, bicarbonate ions and / or carbonate ions combine with hydrogen ions between the cathode and anode layers to form carbonic acid, which can decompose to form gaseous CO2. The MEA was observed to detach, sometimes, possibly due to the formation of this gaseous CO2, and it was found that it does not have an easy evacuating pathway.

[0134] The problem of delamination can be addressed by using a cathode buffer layer having an inert filler and associated vacancies. One possible explanation for its effectiveness is that the vacancies create a pathway for gaseous carbon dioxide to escape back to the cathode, where it can be reduced. In some embodiments, the cathode buffer layer is porous, while at least one layer between the cathode and anode layers is non-porous. This prevents the passage of gases and / or bulk liquids between the cathode and anode layers while still preventing delamination. For example, a non-porous layer can prevent the direct passage of water from the anode to the cathode. The porosity of various layers within the MEA is described further elsewhere in this specification. Example of bipolar MEA

[0135] As an example, the MEA comprises a cathode layer containing a reduction catalyst and a first anion-conducting polymer (e.g., Sustainion, FumaSep FAA-3, Tokuyama anion exchange polymer), an anode layer containing an oxidation catalyst and a first cationic-conducting polymer (e.g., PFSA polymer), a film layer containing a second cationic-conducting polymer and disposed between the cathode layer and the anode layer to conductively connect the cathode layer and the anode layer, and a cathode buffer layer containing a second anion-conducting polymer (e.g., Sustainion, FumaSep FAA-3, Tokuyama anion exchange polymer) and disposed between the cathode layer and the film layer to conductively connect the cathode layer and the film layer. In this example, the cathode buffer layer may have a porosity of about 1 to 90 volume percent, but may also or alternatively have any suitable porosity (e.g., non-porous). In other examples, the cathode buffer layer can have any suitable porosity (e.g., 0.01-95%, 0.1-95%, 0.01-75%, 1-95%, 1-90%, etc.).

[0136] Excessive porosity can reduce the ionic conductivity of the buffer layer. In some embodiments, the porosity is 20% or less, and in specific embodiments, it is 0.1–20%, 1–10%, or 5–10%. Porosity within these ranges may be sufficient to allow the movement of water and / or CO2 without impairing ionic conductivity. Porosity may be measured as further described below.

[0137] In related examples, the membrane electrode assembly may include a third cationic conductive polymer and an anode buffer layer positioned between the membrane layer and the anode layer to provide a conductive connection between the membrane layer and the anode layer. The anode buffer layer preferably has a porosity of about 1 to 90 volume percent, but may have any suitable porosity (e.g., non-porous). However, in other configurations and examples, the anode buffer layer may have any suitable porosity (e.g., 0.01 to 95%, 0.1 to 95%, 0.01 to 75%, 1 to 95%, 1 to 90%). Similar to the cathode buffer layer, in some embodiments, the porosity is 20% or less, for example, 0.1 to 20%, 1 to 10%, or 5 to 10%.

[0138] In one example, the anode buffer layer may be used in a MEA having a cathode catalyst layer with an anion exchange polymer, a cathode buffer layer with an anion exchange polymer, a membrane with a cation exchange polymer, and an anode buffer layer with an anion exchange polymer. In such a structure, the anode buffer layer may be porous to facilitate water migration to the membrane / anode buffer layer interface. At this interface, the water separates, producing protons that pass through the membrane and hydroxides that move to the anode catalyst layer. One advantage of this structure is the use of a low-cost hydroxide catalyst (e.g., NiFeO) that is stable only under basic conditions. x It is possible to use ).

[0139] In another specific example, the membrane electrode assembly comprises a cathode layer containing a reduction catalyst and a first anion-conducting polymer (e.g., Sustainion, FumaSep FAA-3, Tokuyama anion exchange polymer), an anode layer containing an oxidation catalyst and a first cationic-conducting polymer, a membrane layer containing a second anion-conducting polymer (e.g., Sustainion, FumaSep FAA-3, Tokuyama anion exchange polymer) and disposed between the cathode layer and the anode layer to provide a conductive connection between the cathode layer and the anode layer, and an anode buffer layer containing a second cationic-conducting polymer and disposed between the anode layer and the membrane layer to provide a conductive connection between the anode layer and the membrane layer.

[0140] A MEA containing an anion exchange polymer membrane and an anode buffer layer containing a cation exchange polymer can be used for CO reduction. In this case, water is formed at the membrane / anode buffer layer interface. Vacuities in the anode buffer layer can facilitate water removal. One advantage of this structure is its acid stability (e.g., IrO x This involves the use of a hydroxide catalyst.

[0141] In related examples, the membrane electrode assembly may include a cathode buffer layer positioned between the cathode layer and the membrane layer to conductively connect the cathode layer and the membrane layer, comprising a third anion-conducting polymer. The third anion-conducting polymer may be the same as or different from the first and / or second anion-conducting polymer. The cathode buffer layer preferably has a porosity of about 1 to 90 volume percent, but may further or alternatively have any suitable porosity (e.g., non-porous). However, in other configurations and examples, the cathode buffer layer may have any suitable porosity (e.g., 0.01 to 95%, 0.1 to 95%, 0.01 to 75%, 1 to 95%, 1 to 90%). In some embodiments, the porosity is 20% or less, and in certain embodiments, it is 0.1 to 20%, 1 to 10%, or 5 to 10%.

[0142] In one example, the cathode catalyst layer is supported on Vulcan XC72R carbon and consists of 4 nm diameter Au nanoparticles mixed with TM1 (mTPN-1) anion exchange polymer electrolyte (manufactured by Orion). The layer is approximately 15 μm thick, with Au / (Au+C) = 20 wt%, a mass ratio of TM1 to catalyst of 0.32, a material packing density of 1.4-1.6 mg / cm² (total Au+C), and an estimated porosity of 0.56. The anion exchange polymer layer is composed of TM1 and PTFE particles. The PTFE particles are approximately 200 nm in diameter. The molecular weight of TM1 is 30 k to 45 k. The layer thickness is approximately 15 μm. The PTFE can introduce a porosity of approximately 8%. The proton exchange membrane layer is composed of a perfluorosulfonic acid polymer (e.g., Nafion 117). Its thickness is approximately 125 μm. The film forms a continuous layer that prevents significant movement of gases (CO2, CO, H2) through the layer. The anode catalyst layer is 10 μm thick Ir or IrO x It is composed of nanoparticles (aggregates of 100-200 nm). CO x Anion exchange membrane alone for reduction MEA

[0143] In some embodiments, the MEA does not include a cationic conductive polymer layer. In such embodiments, the electrolyte does not include a cationic conductive polymer if it includes an ionic conductive polymer instead of a cationic conductive polymer and an anode. Examples are provided herein.

[0144] A single-layer AEM MEA allows for the conduction of anions across the MEA. In embodiments where none of the MEA layers have significant cationic conductivity, hydrogen ions have limited mobility in the MEA. In some implementations, a single-layer AEM film can provide a high pH environment (e.g., at least about pH 7) and promote CO2 and / or CO reduction by suppressing hydrogen evolution parasitic reactions at the cathode. As with other MEA designs, a single-layer AEM MEA allows ions, particularly anions such as hydroxide ions, to pass through the polymer electrolyte. The pH may be lower in some embodiments, and a pH of 4 or higher is considered sufficiently high to suppress hydrogen evolution. A single-layer AEM MEA also allows electrons to move to and pass through the metals and carbon in the catalyst layer. In embodiments with vacancies in the anode layer, cathode layer, and / or PEM, a single-layer AEM MEA allows liquids and gases to pass through the vacancies.

[0145] In certain embodiments, the AEM-only MEA comprises an anion-exchange polymer electrolyte membrane having electrocatalytic layers on both the cathode and anode sides. In some embodiments, one or both of the electrocatalytic layers contain an anion-exchange polymer electrolyte.

[0146] In certain embodiments, an AEM-only MEA is formed by depositing cathode and anode electrolytic catalyst layers on a porous conductive carrier such as a gas diffusion layer to form a gas diffusion electrode (GDE), and sandwiching an anion exchange film between the gas diffusion electrodes.

[0147] In certain embodiments, AEM alone is used for CO2 reduction. Using an anion exchange polymer electrolyte avoids the low pH environment unsuitable for CO2 reduction. Furthermore, when AEM is used, water is moved away from the cathode catalyst layer, thereby preventing water accumulation (flooding) that could block reactant gas movement at the cell cathode.

[0148] Water transport in MEAs occurs through various mechanisms, including diffusion and electroosmotic drag. In some embodiments, at the current densities of the CO2 electrolytic cells described herein, electroosmotic drag is the dominant mechanism. Water is pulled along with ions as it passes through the polymer electrolyte. In cation exchange membranes such as Nafion membranes, the amount of water transport is well characterized and understood to depend on the membrane pretreatment / hydration. Protons move from positive to negative potential (anode to cathode), each carrying 2-4 water molecules, depending on the pretreatment. The same type of effect occurs in anion exchange polymers. Hydroxide ions, bicarbonate ions, or carbonate ions passing through the polymer electrolyte "pull" water molecules. In anion exchange MEAs, ions move from negative to positive voltage, and therefore from cathode to anode, carrying water molecules in this process and moving water from cathode to anode. In certain embodiments, AEM-only MEAs are used in CO reduction reactions. Unlike the CO2 reduction reaction, CO reduction does not produce carbonate anions or bicarbonate anions that can travel to the anode and release beneficial reactants.

[0149] Figure 4 shows the configuration of an example of a CO2 reduction MEA401 comprising a cathode catalyst layer 403, an anode catalyst layer 405, and an anion-conducting PEM 407. In certain embodiments, the cathode catalyst layer 403 includes metal catalyst particles (e.g., nanoparticles) that are not supported or are supported on a conductive substrate such as carbon particles. In some implementations, the cathode catalyst layer 403 further comprises an anion-conducting polymer. The metal catalyst particles can catalyze CO2 reduction, particularly at pH above 7. In certain embodiments, the anode catalyst layer 405 includes metal oxide catalyst particles (e.g., nanoparticles) that are not supported or are supported on a conductive substrate such as carbon particles. In some implementations, the anode catalyst layer 403 further comprises an anion-conducting polymer. Examples of metal oxide catalyst particles for the anode catalyst layer 405 include iridium oxide, nickel oxide, nickel-iron oxide, iridium ruthenium oxide, platinum oxide, and the like. Anion-conducting PEM407 may contain any of the various anion-conducting polymers, such as HNN5 / HNN8 by Ionomr, FumaSep by Fumatech, TM1 by Orion, PAP-TP by W7energy, and Sustainion by Dioxide Materials. These and other anion-conducting polymers may be used that have an ion exchange capacity (IEC) in the range of 1.1 to 2.6, a functional pH range of 0 to 14, durable solubility in some organic solvents, reasonable thermal stability, and mechanical stability, good ionic conductivity / ASR and an acceptable water absorption / expansion ratio. The polymer may be chemically exchanged for a specific anion rather than a halogen anion before use.

[0150] As shown in Figure 4, CO2 such as CO2 gas may be supplied to the cathode catalyst layer 403. In certain embodiments, CO2 may be supplied via a gas diffusion electrode. In the cathode catalyst layer 403, the CO2 reacts to form C x O y H zThe reduction product shown is produced. The anions produced in the cathode catalyst layer 403 may include hydroxides, carbonates, and / or bicarbonates. These may diffuse, move, or otherwise move to the anode catalyst layer 405. In the anode catalyst layer 405, oxidation reactions such as the oxidation of water may occur to produce diatomic oxygen and hydrogen ions. In some applications, hydrogen ions may react with hydroxides, carbonates, and / or bicarbonates to produce water, carbonic acid, and / or CO2. The fewer interfaces there are, the lower the resistance. In some embodiments, a more basic environment is maintained for C2 and C3 hydrocarbon synthesis.

[0151] Figure 5 shows an example configuration of a CO reduction MEA501 comprising a cathode catalyst layer 503, an anode catalyst layer 505, and an anion-conducting PEM 507. Overall, the configuration of the MEA501 may be the same as that of the MEA401 in Figure 4. However, the cathode catalyst may be selected to promote the CO reduction reaction, that is, different reduction catalysts may be used in the CO and CO2 reduction embodiments.

[0152] In some embodiments, AEM-only MEA may be advantageous for CO reduction. The number of water absorption cycles of the AEM material can be selected to help regulate moisture at the catalyst interface, thereby improving CO availability to the catalyst. For this reason, AEM-only membranes may be preferable for CO reduction. Bipolar membranes may be preferable for CO reduction because they are better resistant to CO2 dissolution and crossover in basic anode liquid media.

[0153] In various embodiments, the cathode catalyst layer 503 includes metal catalyst particles (e.g., nanoparticles) that are not supported or are supported on a conductive substrate such as carbon particles. In some implementations, the cathode catalyst layer 503 further includes an anion-conducting polymer. In certain embodiments, the anode catalyst layer 505 includes metal oxide catalyst particles (e.g., nanoparticles) that are not supported or are supported on a conductive substrate such as carbon particles. In some implementations, the anode catalyst layer 503 further includes an anion-conducting polymer. Examples of metal oxide catalyst particles for the anode catalyst layer 505 include those specified with respect to the anode catalyst layer 405 in Figure 4. The anion-conducting PEM 507 may include any of the various anion-conducting polymers, such as those specified with respect to the PEM 407 in Figure 4.

[0154] As shown in Figure 5, CO gas may be supplied to the cathode catalyst layer 503. In certain embodiments, CO may be supplied via a gas diffusion electrode. In the cathode catalyst layer 503, CO reacts to form C x O y H z It produces the reduction product shown as follows.

[0155] The anions generated in the cathode catalyst layer 503 may include hydroxide ions. These may diffuse, migrate, or otherwise move to the anode catalyst layer 505. In the anode catalyst layer 505, oxidation reactions such as the oxidation of water may occur to produce diatomic oxygen and hydrogen ions. In some applications, hydrogen ions may react with hydroxide ions to produce water.

[0156] The overall composition of MEA501 is similar to that of MEA401, but there are certain differences between these MEAs. Firstly, the MEA may be more wetted for CO reduction to help the catalyst surface have more -H atoms. Also, in AEM-only MEAs such as those shown in Figure 4, a large amount of CO2 may be dissolved for CO2 reduction and then moved to the anode. Significant CO gas crossover is unlikely to occur for CO reduction. In this case, the reaction environment can be very basic. The MEA material containing the catalyst may be selected to have good stability in a high pH environment. In some embodiments, a thinner film may be used for CO reduction than for CO2 reduction. Example of AEM-only MEA

[0157] 1.Copper metal (USRN 40nm thick Cu, approx. 0.05mg / cm 2 ) were deposited on a porous carbon sheet (Sigracet 39BC gas diffusion layer) via electron beam deposition. Ir metal nanoparticles were deposited at a rate of 3 mg / cm³ via drop casting. 2 Anion exchange membrane made of Ionomr (25-50 μm, 80 mS / cm²) was deposited on a porous titanium sheet with the following packing amount. 2 OH conductivity: 2-3 mS / cm 2 HCO3 - A conductive material (with a water absorption rate of 33-37%) was sandwiched between a porous carbon sheet and a titanium sheet, with the electrolytic catalyst layer facing the film.

[0158] 2. Sigma Aldrich's 80 nm spherical Cu nanoparticles were mixed with Famatech's FAA-3 anion exchange solid polymer electrolyte, with a mass ratio of FAA-3 to catalyst of 0.10, as described above.

[0159] U.S. Patent Application Publication No. 2017 / 0321334, published on November 9, 2017, and U.S. Patent Application Publication No. 20190226103, published on July 25, 2019, describe various features and examples of MEAs, which are incorporated herein by reference in their entirety. All published documents referenced herein are incorporated by reference in their entirety as if they were fully described herein. Cathode catalyst layer - general structure

[0160] As shown above, the cathode of the MEA, also called the cathode layer or cathode catalyst layer, is CO x It promotes conversion. x This is a porous layer containing a catalyst for the reduction reaction.

[0161] In some embodiments, the cathode catalyst layer comprises a blend of reducing catalyst particles, electron-conducting support particles providing a support for the reducing catalyst particles, and a cathode ion-conducting polymer. In some embodiments, the reducing catalyst particles are blended with the cathode ion-conducting polymer without a support.

[0162] Examples of materials that can be used for reduction catalyst particles include, but are not limited to, transition metals such as V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Au, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, and Hg, and combinations thereof, and / or any other suitable materials. Other catalyst materials include alkali metals, alkaline earth metals, lanthanides, actinides, and post-transition metals such as Sn, Si, Ga, Pb, Al, Tl, Sb, Te, Bi, Sm, Tb, Ce, Nd, and In, or combinations thereof, and / or any other suitable catalyst materials. The selection of catalyst depends on the specific reaction performed at the cathode of the CRR.

[0163] The catalyst can be in the form of nanoparticles with a size range of approximately 1 to 100 nm, or particles with a size range of approximately 0.2 to 10 nm, or particles with a size range of approximately 1 to 1000 nm or any other suitable range. In addition to nanoparticles and larger particles, films and nanostructured surfaces may be used.

[0164] When used, the electron-conducting support particles in the cathode can be various forms of carbon particles. Other possible conductive support particles include boron-doped diamond or fluorine-doped tin oxide. In one configuration, the conductive support particles are Vulcan carbon. The conductive support particles can be nanoparticles. The size range of the conductive support particles is approximately 20 nm to 1000 nm or any other suitable range. It is particularly useful when the conductive support particles are compatible with the chemicals present in the cathode during CRR operation, are stable with respect to reduction, and have a high hydrogen-generating overpotential, so as not to participate in any electrochemical reactions.

[0165] Regarding composite catalysts such as Au / C, the size of the exemplified metal nanoparticles may be in the range of approximately 2 nm to 20 nm, and the size of the carbon as a supporting material may be approximately 20 to 200 nm. Regarding pure metal catalysts such as Ag or Cu, the particles have a wide range of crystal grain sizes from 2 nm to 500 nm. Aggregation can be even larger, in the micrometer range.

[0166] Generally, such conductive supported particles are larger than the reducing catalyst particles, and each conductive support particle can support many reducing catalyst particles. Figure 6 is a schematic diagram showing possible configurations of two different types of catalysts supported on catalyst support particles 610, such as carbon particles. First type catalyst particles 630 and second type catalyst particles 650 are bonded to the catalyst support particles 610. In various configurations, only one type of catalyst particle or more than two types of catalyst particles are bonded to the catalyst support particles 610.

[0167] Using two types of catalysts may be useful in certain embodiments. For example, one catalyst may be adept at one reaction (e.g., CO2 → CO), and the second at another (e.g., CO → CH4). Overall, the catalyst layer performs the conversion of CO2 to CH4, but different steps occur in the reaction on different catalysts.

[0168] The electronically conductive support may be in a form other than particles, including tubes (e.g., carbon nanotubes) and sheets (e.g., graphene). Structures with a large surface area relative to their volume are useful for providing sites for catalyst particles to bind.

[0169] In addition to reducing catalyst particles and electron-conducting support particles, the cathode catalyst layer may contain an ion-conducting polymer. There are trade-offs in the selection of the amount of cathode ion-conducting polymer in the cathode. It may be important that there is enough cathode ion-conducting polymer to provide sufficient ion conductivity. However, it is also important that the cathode be porous so that reactants and products can pass through easily, and to maximize the amount of catalyst surface area available for the reaction. In various configurations, the cathode ion-conducting polymer occupies any of the ranges of 30-70 wt%, 20-80 wt%, or 10-90 wt%, or any other suitable range, of the material in the cathode layer. The wt% of the ion-conducting polymer in the cathode is CO x The cathode layer porosity and ionic conductivity are selected to provide the best current density for reduction. In some embodiments, this may be 20–60 wt% or 20–50 wt%. Examples of cathode catalyst layer thicknesses range from approximately 80 nm to 300 μm.

[0170] In addition to reduction catalyst particles, a cathode ion conductive polymer, and an electronically conductive support if present, the cathode catalyst layer may contain other additives such as PTFE.

[0171] In addition to the polymer:catalyst mass ratio, the catalyst layer has a material filling amount (mg / cm³). 2The material can be characterized by its density and porosity. Porosity can be determined by various methods. In one method, the amount of each component (e.g., catalyst, support, and polymer) is multiplied by its density. These are summed up to determine the thickness that these components occupy in the material. This is then divided by the known total thickness to obtain the percentage of the layer filled with the material. The resulting percentage is then subtracted from 1 to obtain the percentage of the layer assumed to be filled with air, i.e., the porosity. Methods such as mercury porosimetry or image processing on TEM images may be used.

[0172] Examples of cathode catalyst layers for CO, methane, and ethylene / ethanol production are given below. ●CO generation: 4 nm diameter Au nanoparticles are supported on Vulcan XC72R carbon and mixed with Orion's TM1 anion exchange polymer electrolyte. The layer is approximately 15 μm thick, with an Au / (Au+C) ratio of 30%, a TM1 mass ratio to catalyst of 0.32, and a material packing amount of 1.4-1.6 mg / cm³. 2 The estimated porosity is 0.47. ● Methane Production: Cu nanoparticles with a size of 20-30 nm are supported on Vulcan XC72R carbon and mixed with Fumatech's FAA-3 anion exchange solid polymer electrolyte. The mass ratio of FAA-3 to catalyst is 0.18. The estimated Cu nanoparticle load is in a broader range of 1-100 μg / cm³. 2 Within approximately 7.1 μg / cm³ 2 That is the case. ● Ethylene / ethanol production: Cu nanoparticles with a size of 25-80 nm are mixed with Famatech's FAA-3 anion exchange solid polymer electrolyte. The mass ratio of FAA-3 to catalyst is 0.10. It is deposited either on Sigracet39BC GDE for pure AEM or on an MEA electrode assembly. Estimated Cu nanoparticle load is 270 μg / cm³ 2 That is the case.

[0173] The functions, materials, and structures of the cathode catalyst layer components are further described below. Water management (cathode catalyst layer)

[0174] The cathode catalyst layer can facilitate the movement of water and prevent water from becoming trapped within the cathode catalyst layer. Trapped water can become trapped in CO x This may prevent the reaction product from approaching the catalyst and / or from moving out of the cathode catalyst layer.

[0175] Water management challenges are unique to CRRs in many respects. For example, CRRs use much lower gas flow rates compared to the oxygen electrodes of PEM fuel cells. Vapor phase water removal is determined by the volumetric flow rate of the gas, and therefore, much less vapor phase water removal is performed in CRRs. CRRs may operate at higher pressures than fuel cells (e.g., 100 psi to 450 psi). Higher pressures result in lower volumetric flow rates and less vapor phase water removal at the same molar flow rate. As a result, liquid water present in the MEA of a CRR is removed. For some MEAs, the ability to remove water from the vapor phase is further limited by temperature constraints that do not exist in fuel cells. For example, the reduction of CO2 to CO may be performed at around 50°C, and the production of ethylene and methane may be performed at 20°C to 25°C. This is compared to the typical operating temperature of 80°C to 120°C for fuel cells. As a result, more liquid phase water is removed.

[0176] Properties that affect the water removal ability of the cathode catalyst layer include porosity, pore size, pore size distribution, hydrophobicity, relative amounts of ion-conducting polymer, metal catalyst particles, and electronically conductive support, layer thickness, catalyst distribution throughout the layer, and distribution of ion-conducting polymer around the catalyst through the layer.

[0177] The porous layer provides a water drainage pathway. In some embodiments, the cathode catalyst layer has a pore size distribution including pores having a size of 1 nm to 100 nm and pores having a size of at least 1 micron. This size distribution can assist in water removal. The porous structure can be formed by one or more of the following: pores in the carbon-supported material, pores stacked between stacked spherical carbon nanoparticles, pores secondarily stacked between aggregated carbon spheres (on a micrometer scale), or pores into which an inert filler (e.g., PTFE) has been introduced, which also creates irregular pores in the range of several hundred nm to micrometers at the interface between PTFE and carbon.

[0178] The cathode catalyst layer may have a thickness that contributes to water management. Using a thicker layer allows the catalyst, and consequently the reactants, to be dispersed in a larger volume. This broadens the water distribution and makes its management easier.

[0179] An ion-conducting polymer having a non-polar hydrophobic skeleton may be used in the cathode catalyst layer. In some embodiments, the cathode catalyst layer may contain a hydrophobic polymer such as PTFE in addition to the ion-conducting polymer. In some embodiments, the ion-conducting polymer may be a component of a copolymer that also includes a hydrophobic polymer. Gas transfer (cathode catalyst layer)

[0180] The cathode catalyst layer may be structured for gas transfer. Specifically, CO x The reaction is carried to the catalyst, and the gas-phase reaction products (e.g., CO, ethylene, methane, etc.) are moved out of the catalyst layer.

[0181] Specific challenges related to gas transfer are unique to CRR. The gas is transferred both inside and outside the cathode catalyst layer, i.e., CO x In a PEM fuel cell, products such as CO, ethylene, and methane are moved to the outside. In a PEM fuel cell, gas (O2 or H2) is moved in, but nothing is released to the outside, or water is released as a product. In a PEM water electrolytic cell, water is a reaction product of O2 and H2 gas products.

[0182] Operating conditions, including pressure, temperature, and flow rate through the reactor, affect gas transfer. Properties of the cathode catalyst layer that affect gas transfer include porosity, pore size and distribution, layer thickness, and ionoma distribution.

[0183] In some embodiments, contact between the ionomer and the catalyst is minimized. For example, in embodiments using a carbon support, the ionomer may form a continuous network along the carbon surface with minimal contact with the catalyst. The ionomer, support, and catalyst may be designed such that the ionomer has a higher affinity for the support surface than for the catalyst surface. This allows the ionomer to conduct ions between the catalyst and the support while facilitating gas transfer between the catalyst and the support surface without being blocked by the ionomer. Ionomer (cathode catalyst layer)

[0184] Ionomers can have multiple functions, including holding together the particles of the catalyst layer and moving ions through the cathode catalyst layer. In some cases, the interaction between the ionomer and the catalyst surface allows CO x A favorable environment for reduction is created, increasing selectivity for the desired product and / or reducing the voltage required for the reaction. Importantly, the ionomer is an ion-conducting polymer to allow ion movement through the cathode catalyst layer. For example, hydroxide ions, bicarbonate ions, and carbonate ions are used in CO x It migrates away from the catalyst surface where reduction occurs. In the following description, the ionomer in the cathode catalyst layer can be referred to as the first ion-conducting polymer.

[0185] The first ion-conducting polymer may include at least one ion-conducting polymer that is an anion conductor. This may be advantageous because it increases the pH compared to a proton conductor.

[0186] In some embodiments, the first ion-conducting polymer may include one or more covalently bonded, positively charged functional groups configured to transport negatively charged mobile ions. The first ion-conducting polymer can be selected from the group consisting of amination tetramethylpolyphenylene, poly(ethylene-co-tetrafluoroethylene)-based quaternary ammonium polymers, quaternary polysulfones, blends thereof, and / or any other suitable ion-conducting polymers. The first ion-conducting polymer may be configured to solubilize bicarbonates or hydroxide salts.

[0187] In some embodiments, the first ion-conducting polymer may include at least one ion-conducting polymer that is a cation and anion conductor. The first ion-conducting polymer can be selected from the group consisting of polyethers capable of transporting cations and anions, and polyesters capable of transporting cations and anions. The first ion-conducting polymer can be selected from the group consisting of polyethylene oxide, polyethylene glycol, polyvinylidene fluoride, and polyurethane.

[0188] Cationic and anionic conductors increase pH (compared to pure cationic conductors). Furthermore, in some embodiments, it may be advantageous to use cationic and anionic conductors to promote acid-base recombination in larger volumes rather than at the 2D interface of anionic and cationic conductive polymers. This can potentially reduce the resistance of the membrane by spreading water and CO2 formation, and decreasing the barrier to acid-base reactions. All of these may be advantageous in reducing resistance losses in the MEA, which helps avoid product accumulation, heat, and leads to a decrease in cell voltage.

[0189] Typical anionic conductive polymers have a polymer backbone with covalently bonded, positively charged functional groups. In some embodiments, these may include positively charged nitrogen groups. In some embodiments, the polymer backbone is nonpolar, as described above. The polymer may have any suitable molecular weight, e.g., 25,000 g / mol to 150,000 g / mol, although polymers outside this range may also be used.

[0190] Specific challenges with ion-conducting polymers in CRRs include the possibility that CO2 can dissolve or solubilize the polymer electrolyte, reducing its mechanical stability, making it prone to swelling, and allowing the polymer to move more freely. This reduces the mechanical stability of the catalyst layer and the entire polymer electrolyte membrane. In some embodiments, polymers that are less susceptible to CO2 plasticization are used. Also, unlike in water electrolyzers and fuel cells, conductive carbonate and bicarbonate ions are important parameters for CO2 reduction.

[0191] The introduction of polar functional groups such as hydroxyl and carboxyl groups, which can form hydrogen bonds, leads to the formation of a pseudo-crosslinked network. Crosslinking agents such as ethylene glycol and aluminum acetylacetonate can be added to strengthen the anion-exchange polymer layer and suppress polymer CO2 plasticization. Additives such as dimethylpolysiloxane copolymer may also help mitigate CO2 plasticization.

[0192] According to various embodiments, the ion-conducting polymer may have a bicarbonate ion conductivity of at least 12 mS / cm, be chemically and mechanically stable at temperatures below 80°C, and be soluble in organic solvents used in the manufacture of methanol, ethanol, and isopropanol. The ion-conducting polymer is CO xIt is stable in the presence of reduction products (has chemically stable solubility). Ion-conducting polymers can also be characterized by their ion exchange capacity, i.e., the total number of active sites or functional groups responsible for ion exchange, which may range from 2.1 mmol / g to 2.6 mmol / g in some embodiments.

[0193] Examples of anionic conductive polymers are given above as Class A ionic conductive polymers in the table above. A specific example of anionic conductive polymer is Orion mTPN1, which has an m-triphenylfluorialkylene as its backbone and a trimethylammonium (TMA+) cationic group. Its chemical structure is shown below. [ka]

[0194] Further examples include anion exchange membranes manufactured by Fumatech and Ionomr. Fumatech FAA-3 ionomer is available in Br-form. Anion exchange polymer / membrane based on polybenzimidazole manufactured by Ionomr is available in I-form as AF-1-HNN8-50-X.

[0195] The polymer as it was received contains anions (for example, I - , Br - It may be prepared by replacing (etc.) with bicarbonate.

[0196] Furthermore, as shown above, in certain embodiments, the ionomer may be a cationic and ion-conducting polymer. Examples are given in the table above as Class B ion-conducting polymers. Metal catalyst (cathode catalyst layer)

[0197] Metal catalysts are CO xThe catalyst catalyzes the reduction reaction. The metal catalyst is typically a nanoparticle, but in some embodiments, larger particles, films, and nanostructured surfaces may be used. Depending on the specific form of the nanoparticle, a more active site may be exposed and stabilized.

[0198] Metal catalysts are often composed of pure metals (e.g., Cu, Au, Ag), but certain alloys or other dimetallic systems may have high activity and be used for specific reactions. The selection of a catalyst can be guided by the desired reaction. For example, Au may be used for CO production, and Cu may be used for methane and ethylene production. Other metals, including Ag, alloys, and dimetallic systems, may be used. CO2 reduction has a high overpotential compared to other well-known electrochemical reactions such as hydrogen and oxygen evolution on known catalysts. Small amounts of contaminants can poison the catalyst for CO2 conversion. Also, as mentioned above, metal catalysts such as Cu, Au, and Ag are less developed than catalysts such as platinum used in hydrogen fuel cells.

[0199] Properties of the metal catalyst that affect the performance of the cathode catalyst layer include size, size distribution, uniformity of coverage on the supported particles, shape, packing density (characterized as weight of metal / weight of metal + weight of carbon or mass of particles per unit geometric area of ​​the catalyst layer), surface area (actual metal catalyst surface area per unit volume of the catalyst layer), purity, and the presence of toxic surface ligands from synthesis.

[0200] Nanoparticles may be synthesized by any suitable method, such as those described in Phan et al., "Role of Capping Agent in Wet Synthesis of Nanoparticles," J.Phys.Chem.A 2018, 121, 17, 3213-3219; Bakshi, "How Surfactants Control Crystal Growth of Nanomaterials," Cryst.Growth Des. 2016, 16, 2, 1104-1133; and Morsy, "Role of Surfactants in Nanotechnology and Their Applications," Int.J.Curr.Microbiol.App.Sci. 2014, 3, 5, 237-260, which are incorporated herein by reference.

[0201] In some embodiments, metal nanoparticles are provided without toxic surface ligands. This can be achieved by using an ionomer as a ligand to induce the synthesis of a nanocrystalline catalyst. The surface of the metal nanocatalyst is directly connected to the ion-conducting ionomer. This avoids the need to treat the catalyst surface to allow the ionomer to contact the metal, and improves contact.

[0202] In some embodiments, the metal catalyst may be placed on a carbon support. For CO production, examples include Premetek 20wt%Au supported on Vulcan XC-72R carbon having an Au particle size of 4-6 nm, and 30%Au / C supported on Vulcan XC-72R having an Au particle size of 5-7 nm. For methane, an example is Premetek 20wt%Cu supported on Vulcan XC-72R carbon having a Cu particle size of 20-30 nm. In some embodiments, the metal catalyst may not be supported. For ethylene production, examples of unsupported metal catalysts include SigmaAldrich unsupported Cu with a particle size of 80 nm, and a thin Cu layer of 10-100 nm deposited by electron beam or sputtering. Support (cathode catalyst layer)

[0203] The support for the cathode catalyst layer may have various functions. It can prevent the aggregation of metal nanoparticles and stabilize the metal nanoparticles in a state where the catalytic sites are dispersed throughout the entire catalyst layer volume, thereby mitigating reactant loss and product formation. It can also electronically form conductive pathways to the metal nanoparticles. Carbon particles, for example, may aggregate so that contacting carbon particles provide conductive pathways. The voids between particles form a porous network through which gases and liquids can pass.

[0204] In some embodiments, carbon supports developed for fuel cells can be used. Many different types have been developed. These are typically 50 nm to 500 nm in size and can be obtained in various shapes (spheres, nanotubes, sheets (e.g., graphene)), porosity, surface area per unit volume, conductivity, and functional groups (N-doped, O-doped, etc.).

[0205] The support may be hydrophobic and also have an affinity for metal nanoparticles.

[0206] Examples of carbon black that can be used include: ●Vulcan XC-72R - density 256 mg / cm2, 30 - 50 nm ●Ketjen Black - hollow structure, density 100 - 120 mg / cm2, 30 - 50 nm ●Printex Carbon, 20 - 30 nm can be mentioned. Anode catalyst layer

[0207] The anode of the MEA, also referred to as the anode layer or anode catalyst layer, promotes the oxidation reaction. It is a porous layer containing a catalyst for the oxidation reaction. Examples of the reaction are as follows. 2H2O → 4H + + 4e - + O2 (in the acidic environment of the proton exchange polymer electrolyte - bipolar membrane), or, 4OH - → 4e - + O2 + 2H2O (in the basic environment of the anion exchange polymer electrolyte)

[0208] Oxidation of other materials such as hydrocarbons may be carried out to create CO2 or chloride ions to produce chlorine gas.

[0209] In some embodiments, referring to FIG. 2, the anode 240 contains a blend of an oxidation catalyst and an anode ion - conductive polymer. There are various oxidation reactions that can occur at the anode depending on the reactants supplied to the anode and anode catalyst. In one configuration, the oxidation catalyst is selected from the group consisting of metals and oxides of Ir, Pt, Ni, Ru, Pd, Au and their alloys, IrRu, PtIr, Ni, NiFe, stainless steel, and combinations thereof. The oxidation catalyst can further contain conductive support particles selected from the group consisting of carbon, boron - doped diamond, and titanium.

[0210] The oxidation catalyst can be in the form of a structured mesh or in the form of particles. When the oxidation catalyst is in the form of particles, the particles can be supported by electronically conductive carrier particles. The conductive support particles can be nanoparticles. It is particularly useful if the conductive support particles are compatible with the chemicals present in the anode 240 during the operation of the CRR and are oxidatively stable so as not to participate in any electrochemical reaction. It is particularly useful when the conductive support particles are selected taking into account the voltage and reactants at the anode. In some configurations, the conductive support particles are titanium suitable for high voltages. In other configurations, the conductive support particles are carbon which may be most useful at low voltages. Generally, such conductive support particles are larger than the oxidation catalyst particles, and each conductive support particle can support many oxidation catalyst particles. An example of such a configuration is shown in FIG. 3 and has been discussed above with respect to the cathode catalyst layer. In one configuration, the oxidation catalyst is iridium ruthenium oxide. Examples of other materials that can be used for the oxidation catalyst include, but are not limited to, those listed above. It should be understood that many of these metal catalysts can be in the form of oxides, particularly under the reaction conditions.

[0211] In some embodiments, the MEA comprises an anode layer comprising an oxidation catalyst and a second ion-conductive polymer. The second ion-conductive polymer can include one or more polymers comprising covalently bonded negatively charged functional groups configured to transport positively charged mobile ions. The second ion-conductive polymer can be selected from the group consisting of ethanesulfonic acid fluoride, 2-[1-[difluoro-[(trifluoroethenyl)oxy]methyl]-1,2,2,2-tetrafluoroethoxy]-1,1,2,2,-tetrafluoro- with tetrafluoroethylene, tetrafluoroethylene-perfluoro-3,6-dioxa-4-methyl-7-octanesulfonic acid copolymer, other perfluorosulfonic acid polymers, and blends thereof. Examples of cation-conductive polymers include, for example, Nafion 115, Nafion 117, and / or Nafion 211.

[0212] There are trade-offs in selecting the amount of ion-conducting polymer in the anode. It is important that the anode contains enough ion-conducting polymer to provide sufficient ion conductivity. However, it is also important that the anode is porous to allow reactants and products to pass through easily, and to maximize the amount of catalyst surface area available for the reaction. In various configurations, the ion-conducting polymer in the anode occupies approximately 50 wt%, or approximately 5-20 wt%, 10-90 wt%, 20-80 wt%, 25-70 wt%, or any preferred range. It is particularly useful if anode 240 can withstand high voltages, such as voltages exceeding approximately 1.2 V relative to the reversible hydrogen electrode. It is particularly useful if anode 240 is porous to maximize the amount of catalyst surface area available for the reaction and to promote gas and liquid transfer.

[0213] In one example of a metal catalyst, Ir or IrOx particles (100-200 nm) and Nafion ionomer form a porous layer approximately 10 μm thick. The amount of metal catalyst packed is approximately 0.5-3 g / cm³. 2 That is the case.

[0214] In some embodiments, NiFeOx is used in the basic reaction. PEM

[0215] The MEA includes a polymer electrolyte membrane (PEM) positioned between the anode catalyst layer and the cathode catalyst layer, and conductively coupled to them. Referring to Figure 2, the polymer electrolyte membrane 265 has high ionic conductivity (over approximately 1 mS / cm) and is mechanically stable. Mechanical stability can be demonstrated by various means, such as high tensile strength, elastic modulus, elongation at break, and tear resistance. Many commercially available membranes can be used for the polymer electrolyte membrane 265. Examples, but not limited to, include various Nafion® formulations, GORE-SELECT, FumaPEM® (PFSA) (FuMA-Tech GmbH), and Aquivion® (PFSA) (Solvay).

[0216] In one configuration, the PEM comprises at least one ion-conducting polymer that is a cation conductor. The third ion-conducting polymer may contain one or more covalently bonded, negatively charged functional groups configured to transport positively charged mobile ions. The third ion-conducting polymer can be selected from the group consisting of ethanesulfonic acid fluoride, 2-[1-[difluoro-[(trifluoroethenyl)oxy]methyl]-1,2,2,2-tetrafluoroethoxy]-1,1,2,2,-tetrafluoro-, tetrafluoroethylene-perfluoro-3,6-dioxa-4-methyl-7-octanesulfonic acid copolymer, other perfluorosulfonic acid polymers, and blends thereof. Cathode buffer layer

[0217] Referring to Figure 2, it can be noted that if the polymer electrolyte membrane 265 is both a cation conductor and a proton conductor, it will contain a high concentration of protons during CRR operation, while the cathode 220 will operate best in the presence of a low concentration of protons. It may be useful to provide a cathode buffer layer 225 between the polymer electrolyte membrane 265 and the cathode 220 to provide a transition region from high-concentration protons to low-concentration protons. In one configuration, the cathode buffer layer 225 is an ion-conducting polymer having many of the same properties as the ion-conducting polymer in the cathode 220. The cathode buffer layer 225 provides a region where the proton concentration transitions from the polymer electrolyte membrane 265 having a high concentration of protons to the cathode 220 having a low proton concentration. Within the cathode buffer layer 225, protons from the polymer electrolyte membrane 265 encounter anions from the cathode 220, and they neutralize each other. The cathode buffer layer 225 helps ensure that a harmful number of protons from the polymer electrolyte membrane 265 do not reach the cathode 220 and increase the proton concentration. If the proton concentration at cathode 220 is too high, CO x No reduction occurs. High proton concentrations are considered to be in the range of approximately 10 to 0.1 moles, while low concentrations are considered to be less than approximately 0.01 moles.

[0218] The cathode buffer layer 225 may contain a single polymer or multiple polymers. If the cathode buffer layer 225 contains multiple polymers, the multiple polymers may be mixed together or placed in separate adjacent layers. Examples of materials that can be used for the cathode buffer layer 225 include, but are not limited to, FumaSep FAA-3, Tokuyama anion exchange membrane materials, and polyether polymers such as polyethylene oxide (PEO), as well as blends thereof. Further examples are given above in the discussion of the cathode catalyst layer.

[0219] The thickness of the cathode buffer layer is due to the low proton concentration of CO x The cathode buffer layer is selected to be sufficiently high in reducing activity. This sufficiency may differ for different cathode buffer layer materials. Generally, the thickness of the cathode buffer layer is approximately 200 nm to 100 μm, 300 nm to 75 μm, 500 nm to 50 μm, or any preferred range.

[0220] In some embodiments, the cathode buffer layer is less than 50 μm thick, for example, 1 to 25 μm, such as 1 to 5 μm, 5 to 15 μm, or 10 to 25 μm. By using a cathode buffer layer with a thickness in this range, the proton concentration in the cathode can be reduced while maintaining the overall conductivity of the cell. In some embodiments, an ultrathin layer (100 nm to 1 μm, and in some embodiments, submicron) may be used. Also, as discussed above, in some embodiments, the MEA does not have a cathode buffer layer. In some such embodiments, the anion-conducting polymer in the cathode catalyst layer is sufficient. The thickness of the cathode buffer layer can be characterized against that of a PEM.

[0221] Water and CO2 formed at the interface between the cathode buffer layer and the PEM can cause delamination of the MEA at the point where the polymer layers connect. The delamination problem can be addressed by using a cathode buffer layer with inert filler particles and associated vacancies. One possible explanation for its effectiveness is that the vacancies create pathways for gaseous carbon dioxide to escape back to the cathode where it can be reduced.

[0222] Suitable materials for inert filler particles include, but are not limited to, TiO2, silica, PTFE, zirconia, and alumina. In various configurations, the size of the inert filler particles is 5 nm to 500 μm, 10 nm to 100 μm, or any suitable size range. The particles may generally be spherical.

[0223] If the volume of PTFE (or other filler) is too high, it dilutes the polymer electrolyte to the point where the ionic conductivity is low. The volume of excess polymer electrolyte dilutes the PTFE to the point where it does not contribute to the porosity. In many embodiments, the mass ratio of polymer electrolyte / PTFE is 0.25 to 2, and more specifically, 0.5 to 1. The volume ratio of polymer electrolyte / PTFE (or, more generally, polymer electrolyte / inert filler) can be 0.25 to 3, 0.5 to 2, 0.75 to 1.5, or 1.0 to 1.5.

[0224] In other configurations, porosity is achieved by using specific processing methods when the layer is formed. One example of such processing methods is laser ablation, where nano- to micro-sized channels are formed in the layer. Another example is mechanically perforating the layer to form channels through it.

[0225] In one configuration, the cathode buffer layer has a porosity of 0.01% to 95% (for example, by weight, volume, mass, etc.). However, in other configurations, the cathode buffer layer can have any suitable porosity (e.g., 0.01 to 95%, 0.1 to 95%, 0.01 to 75%, 1 to 95%, 1 to 90%). In some embodiments, the porosity is 50% or less, for example, 0.1 to 50%, 5 to 50%, 20 to 50%, 5 to 40%, 10 to 40%, 20 to 40%, or 25% to 40%. In some embodiments, the porosity is 20% or less, for example, 0.1 to 20%, 1 to 10%, or 5 to 10%.

[0226] Porosity may be measured for the catalyst layer as described above, including using the material packing amount and thickness of the components, by methods such as mercury porosimetry, X-ray diffraction (SAXS or WAXS), and image processing on TEM images for calculating packed space versus cavity space. Since the material expands to a different degree when exposed to water during operation, porosity should be measured when the MEA is completely dry.

[0227] The porosity in the MEA layer, including the cathode buffer layer, is described further below. Anode buffer layer

[0228] In some CRR reactions, bicarbonates are formed at cathode 220. It may be useful to have a polymer somewhere between cathode 220 and anode 240 that inhibits bicarbonate migration, preventing the bicarbonates from moving far away from the cathode. As bicarbonates migrate, they take up some CO2, which can reduce the amount of CO2 available for the reaction at the cathode. In one configuration, the polymer electrolyte membrane 265 contains a polymer that inhibits bicarbonate migration. Examples of such polymers, but not limited to, Nafion® formulations, GORE-SELECT, FumaPEM® (PFSA) (FuMA-Tech GmbH), and Aquivion® (PFSA) (Solvay). In another configuration, an anode buffer layer 245 is present between the polymer electrolyte membrane 265 and anode 240, which inhibits bicarbonate migration. If the polymer electrolyte membrane is an anion conductor or does not inhibit bicarbonate migration, an additional anode buffer layer to inhibit bicarbonate migration may be useful. Materials that can be used to inhibit bicarbonate migration include, but are not limited to, Nafion® formulations, GORE-SELECT, FumaPEM® (PFSA) (FuMA-Tech GmbH), and Aquivion® (PFSA) (Solvay). Naturally, if bicarbonates are not present in the CRR, it is not particularly desirable to include bicarbonate-inhibiting features in the ion exchange layer 260.

[0229] In another embodiment of the present invention, the anode buffer layer 245 provides a region where the proton concentration transitions between the polymer electrolyte membrane 265 and the anode 240. The proton concentration in the polymer electrolyte membrane 265 depends on both its composition and the ions it conducts. For example, a Nafion polymer electrolyte membrane 265 that conducts protons has a high proton concentration. A FumaSep FAA-3 polymer electrolyte membrane 265 that conducts hydroxides has a low proton concentration. For example, if the desired proton concentration at the anode 240 differs from that of the polymer electrolyte membrane 265 by more than three orders of magnitude, the anode buffer layer 245 may be useful in transitioning the proton concentration of the polymer electrolyte membrane 265 to the desired proton concentration at the anode. The anode buffer layer 245 may contain a single polymer or multiple polymers. If the anode buffer layer 245 contains multiple polymers, the multiple polymers may be mixed together or placed in separate adjacent layers. Materials that may be useful in providing a region for pH transitions include, but are not limited to, Nafion®, FumaSep FAA-3, Sustainion®, Tokuyama anion exchange polymers, and polyether polymers such as polyethylene oxide (PEO), blends thereof, and / or any other suitable materials. High proton concentrations are considered to be in the range of approximately 10 to 0.1 moles, and low concentrations are considered to be approximately less than 0.01 moles. Ion-conducting polymers can be sorted into different classes based on the type of ions they conduct. This is discussed in more detail above. Three classes of ion-conducting polymers are listed in Table 4 above. In one embodiment of the present invention, at least one of the ion-conducting polymers in the cathode 220, anode 240, polymer electrolyte membrane 265, cathode buffer layer 225, and anode buffer layer 245 is of a different class from at least one of the others. porosity of the layer

[0230] It may be useful if some or all of the following layers: cathode 220, cathode buffer layer 225, anode 240, and anode buffer layer 245 are porous. In some configurations, the porosity is achieved by binding inert filler particles to the polymer within these layers. Suitable materials for the inert filler particles include, but are not limited to, TiO2, silica, PTFE, zirconia, and alumina. In various configurations, the size of the inert filler particles is from 5 nm to 500 μm, from 10 nm to 100 μm, or any suitable size range. In other configurations, the porosity is achieved by using a specific processing method when the layer is formed. One example of such a processing method is laser ablation, where nano- to micro-sized channels are formed in the layer. Further or alternatively, laser ablation can achieve the porosity within the layer by subsurface ablation. By subsurface ablation, when the focus of the beam is set at a point within the layer, voids are formed within the layer, thereby vaporizing the material of the layer in the vicinity of the point. This process is repeated to form voids throughout the layer, thereby achieving the porosity within the layer. The volume of the voids is preferably determined by the laser output (e.g., a high laser output corresponds to a larger void volume), but further or alternatively, it can be determined by the focus size of the beam or any other suitable laser parameter. Another example is mechanically perforating the layer to form channels through the layer. The porosity can have any suitable distribution within the layer (e.g., uniform, porosity gradient increasing through the layer, random porosity gradient, porosity gradient decreasing through the layer, periodic porosity, etc.).

[0231] The porosity of the examples described above and in other examples and modifications (e.g., of the cathode buffer layer, anode buffer layer, film layer, cathode layer, anode layer, other suitable layers, etc.) preferably has a uniform distribution, but can also or alternatively have any suitable distribution (e.g., randomized distribution, increasing pore size gradient through or across layers, decreasing pore size gradient through or across layers, etc.). Porosity can be formed by any suitable mechanism, such as inert filler particles (e.g., diamond particles, boron-doped diamond particles, polyvinylidene fluoride / PVDF particles, polytetrafluoroethylene PTFE particles, etc.) and any other suitable mechanism that forms substantially unreactive regions within the polymer layer. The inert filler particles can have any suitable size, such as a minimum of about 10 nanometers and a maximum of about 200 nanometers, and / or any other suitable dimensions or dimensional distribution.

[0232] As discussed above, the cathode buffer layer preferably has a porosity of about 1 to 90 volume percent, but can have any suitable porosity (e.g., non-porous). However, in other configurations and examples, the cathode buffer layer can have any suitable porosity (e.g., 0.01 to 95%, 0.1 to 95%, 0.01 to 75%, 1 to 95%, 1 to 90%, etc.). In some embodiments, the porosity is 20% or less, for example, 0.1 to 20%, 1 to 10%, or 5 to 10%.

[0233] In some embodiments, the cathode buffer layer is porous, while at least one layer between the cathode and anode layers is non-porous. This prevents gases and / or bulk liquids from passing between the cathode and anode layers while still preventing delamination. For example, the non-porous layer can prevent the direct passage of water from the anode to the cathode. MEA manufacturing

[0234] CO xMEA for reduction can be manufactured using various techniques. In various embodiments, multiple steps are used in the production of MEA. Even small differences in the parameters of the manufacturing process can result in significant differences in performance.

[0235] In certain embodiments, the production of a MEA involves the steps of depositing or otherwise forming a polymer electrolyte membrane (e.g., Nafion PEM) layer, an anion-exchange polymer electrolyte layer and a cathode catalyst layer on the cathode, and depositing or otherwise forming an anode catalyst layer on the anode. An alternative method involves forming a catalyst layer on a porous gas diffusion layer (e.g., carbon for the cathode or titanium for the anode) and sandwiching a membrane (which may include an anion-exchange layer) between the catalyst-containing porous layers. In certain embodiments, the catalyst layer is formed by dispersing a solid catalyst and supported particle ink and a polymer electrolyte in a solvent. The ink can be applied to the polymer electrolyte membrane or GDL by various methods. The solvent then evaporates, leaving the porous solid catalyst layer.

[0236] Imaging methods may be used to characterize thickness and uniformity. Thickness should be consistent and controllable, and uniformity should be smooth and as defect-free as possible.

[0237] Various techniques can be used to form individual layers of MEA. Typically, these techniques form layers on a substrate such as a PEM layer or GDL as referred to herein. Examples of such techniques include ultrasonic spray deposition, doctor blade application, gravure printing, screen printing, and transfer.

[0238] Catalyst inks used with anion exchange polymers (particularly with respect to certain polymers) are not well studied and do not have the same solution structure as typical Nafion-based inks used in fuel cells and electrolytic cells. The formulations and processes necessary to form well-dispersed and stable catalyst inks were unknown. Nafion is thought to form a micelle-like structure that allows for relatively easy suspension in aqueous media. Other ion-conducting polymers, especially some anion-conducting polymers, do not form such a structure and are therefore more difficult to provide in suspension.

[0239] In certain embodiments, the catalyst layer ink is prepared by mixing a metal supported on a metal or carbon catalyst with an ion-conducting polymer (e.g., an anion-conducting polymer) and diffusing the mixture into a solvent (such as alcohol) by sonication.

[0240] As shown in the illustration, certain manufacturing techniques utilize methods such as doctor blade application, screen printing, transfer printing, and electrospinning. For high-throughput processing, roll-to-roll techniques such as gravure printing or microgravure printing may be used. MEA post-processing

[0241] After the MEA is manufactured, additional processing may be used to enhance its performance. Examples of performance improvements include lifespan and voltage. In some embodiments, post-processing introduces salts or specific salt ions into the MEA. In some embodiments, post-processing produces an MEA with structural modifications resulting from the processing, including better interlayer adhesion.

[0242] Hot pressing: The MEA is heated under pressure to bond the layers together. Hot pressing helps prevent delamination by "melting" the layers together. ●Time: Approximately 2-10 minutes (MEA only), 1.5-2 minutes (MEA + gas dispersion layer (GDL)). The "MEA + GDL" may be pressed at least twice to form a stable assembly. ●Temperature: Approximately 100℃~150℃, ●Pressure: Approximately 300 psi to 600 psi (for a 3x3 inch 1 / 2 MEA), but the MEA can withstand approximately 2500 psi without GDL.

[0243] Hydration: The MEA is immersed in water or an aqueous solution to wet the polymer electrolyte before cell assembly. In some embodiments, the aqueous solution is a salt solution as described herein.

[0244] Boiling Nafion or other polymer electrolytes (MEAs) permanently alters the macrostructure of the polymer electrolyte, increasing the amount of water in the polymer matrix. This not only increases the ionic conductivity but also increases the water transfer rate.

[0245] Heating and drying reduces the water content, thereby decreasing the amount of water transferred through the polymer electrolyte during operation. Stabilization interface between MEA layers

[0246] Water and CO2 formed at the interface between an anion-conducting layer (e.g., a cathode buffer layer) and a cation-conducting film (e.g., a PEM) can cause separation or delamination of the two layers at the point where the polymer layers connect. Reactions at the bipolar interface are shown in Figures 3 and 7.

[0247] Furthermore, it is desirable that the CO2 returns to the cathode of the cell where it can be reduced, rather than being lost to the anode. Therefore, pathways (e.g., vacancies) within the anion exchange layer (e.g., cathode buffer layer and / or cathode layer) provide both pathways for removing water and CO2 from the interface to prevent delamination and for returning CO2 to the cathode where it can react.

[0248] The structure shown in Figure 7 is similar to that shown in Figure 3, but Figure 7 includes additional information related to mass transfer at the bipolar interface and the generation of CO2 and water. For example, it shows that hydroxide and CO2 react on the cathode side to produce bicarbonate ions, which then move toward the bipolar interface 713. On the anode side, hydrogen ions produced by the oxidation of water move toward the bipolar interface 713, where they react with bicarbonate ions to produce water and CO2, both of which should be able to leach out without damaging the bipolar layer.

[0249] Furthermore, the water transport pathway is also shown in Figure 7, which includes (a) electroosmotic drag on anions from the cathode toward interface 713, (b) electroosmotic drag on cations from the anode toward interface 713, and (c) diffusion. Water evaporates at the anode and cathode.

[0250] Various MEA designs include features that resist delamination and optionally provide pathways for reaction products to leave the interface area. In some embodiments, the bipolar interface is flat. However, in some designs, the interface is provided to have a compositional gradient and / or interlocking structure. These are further described below with reference to Figures 8A, 8B, 8C, and 8D, which show bipolar interfaces of MEA designs configured to resist delamination.

[0251] In some embodiments, the interface includes a gradient. For example, a gradient may be formed by using two nozzles during spray deposition to add a relative amount of polymer to the anion exchange polymer, which varies during the deposition of the cation exchange layer. Similarly, the cation exchange polymer may be added during the deposition of the anion exchange layer. Referring to Figure 7, for example, the gradient may extend substantially through all or part of the anion exchange region and the cation exchange region, such that the anion exchange region has the anion exchange polymer mainly adjacent to the cathode, and the relative amount of the cation exchange polymer increases as it moves from the cathode toward the interface 713. Similarly, the cathode exchange region has the cation exchange polymer mainly adjacent to the anode, and the relative amount of the anion exchange polymer increases as it moves from the anode toward the interface 713. In some embodiments, there are pure anion exchange regions and pure cation exchange regions, and a gradient exists between the two.

[0252] In some embodiments, the bipolar film layers are melted together. This can be achieved by selecting a suitable solvent. For example, Nafion is at least slightly soluble in a water / ethanol mixture. By using the mixture (or another solvent in which the cationic conductive polymer is soluble) as the solvent for the anionic conductive polymer, Nafion or other cationic conductive polymer can gain at least slight solubility and dissolve into the interface. In some embodiments, this results in a smaller gradient, for example, extending 0.5–10% into the thickness of the anionic conductive polymer layer.

[0253] In some embodiments, the interface includes a mixture of polymers. Figure 8A shows a bipolar interface 813 in which a cationic conductive polymer 821 and an anionic conductive polymer 819 are mixed. The example in Figure 8A shows a portion of the anionic conductive polymer layer 809 and a portion of the cationic conductive polymer layer 811. The anionic conductive polymer layer 809 may be a pure anionic conductive polymer, and the cationic conductive polymer layer 811 may be a pure cation exchange polymer. The cationic conductive polymer 821 may be the same or a different cationic conductive polymer as that in the cationic conductive polymer layer 811. The anionic conductive polymer 819 may be the same or a different anionic conductive polymer as that in the anionic conductive polymer layer 809.

[0254] In some embodiments, the interface includes a third material that physically reinforces the interface. For example, Figure 8B shows an example of a material 830 spanning interface 813. That is, material 830 is partially present in the anionic conductive polymer layer 809 and the cationic conductive polymer layer 811. Thus, material 830 can bond the two layers to resist delamination. In one example, material 830 is a porous inert material such as porous PTFE. Such an interface may be formed, for example, by pouring or otherwise coating cationic conductive polymers and anionic conductive polymers on both sides of a PTFE or similar porous film, followed by hot pressing.

[0255] Figure 8C shows a bipolar interface 813 having protrusions 840 of a cationic conductive polymer extending from a cationic conductive polymer layer 811 into an anionic conductive polymer layer 809. These protrusions can mechanically reinforce the interface 813 to prevent delamination when CO2 and water are generated at the interface. In some embodiments, the protrusions extend from the anionic conductive polymer layer 809 into the cationic conductive polymer layer 811. In certain embodiments, the protrusions extend in both directions. Exemplary dimensions are 10 μm to 1 mm in in-plane dimensions, but smaller dimensions (e.g., 500 nm to 1 μm) are also possible. Out-of-plane dimensions may be, for example, 10 to 75% or 10 to 50% of the total thickness of the polymer layer in which they extend. The protrusions may be formed by any suitable technique, such as lithography, or by spraying the polymer onto a patterned mesh that is later removed. Roughening techniques may be used to create the protrusions. In some embodiments, the protrusions may be formed from different materials, such as metal, to help interlock the polymer layers and mechanically reinforce the interface.

[0256] Figure 8D shows a bipolar interface 813 having a third material 850 placed between a cationic conductive polymer layer 811 and an anionic conductive polymer layer 809, or mixed with one or more of them. In some embodiments, for example, the third material 850 may be an additive as further discussed below. In some embodiments, the third material 850 may be a blend of anionic conductive ionomer and cationic conductive ionomer at the interface. For example, it may be a mixture of Nafion 5 wt% ionomer and Orion 2 wt% mTPN1. In some embodiments, the third material may include an ion acceptor and a donor, which may be mixed together or provided as separate layers.

[0257] In some embodiments, the interface contains additives to promote acid-base reactions and prevent delamination. In some embodiments, the additives may promote the spread of acid-base recombination not only at the 2D interface of anionic and cationic conductive polymers but also in larger volumes. This can lead to the formation of water and CO2, the spread of exothermic reactions, and a decrease in the film's resistance due to a reduced barrier to acid-base reactions. These effects may be advantageous in that they help avoid product accumulation, heat, and thus reduce resistance losses in the MEA, which can lead to a decrease in cell voltage. Furthermore, this helps avoid material degradation at the interface due to heat and gas generation.

[0258] Examples of additives that promote acid-base reactions include molecules that are both proton acceptors and anion acceptors, such as hydroxide-containing ionic liquids (a specific example being 1-butyl-3-methyllimidazolium hydroxide). Other ionic liquids may also be used. In some embodiments, ions different from those of the anion-conducting polymer layer and the cationic-conducting polymer layer may be used. For example, relatively high-conductivity anion exchange materials such as Sustainion may be used. Such anion exchange materials may not be sufficiently selective for use as a cathode buffer layer, but they can be used at the interface.

[0259] Further examples of materials that may be present at the interface include block copolymers having different charge groups (e.g., both cationic and anionic stationary charge groups), cationic and anionic conductive polymers, resin materials, ion donors such as oxides including graphene oxide, catalysts for acid / base recombination, catalysts that react with H2 and O2 diffusing from the anode and cathode, water splitting catalysts, CO2 absorbents, and H2 absorbents.

[0260] In some embodiments, a crosslinking agent may be added to covalently crosslink two polymers of a bipolar film. An example of a crosslinking group is xylene, which may be provided on an ionomer. Other crosslinking groups may be used. For example, a crosslinking agent may be provided on a cationic conductive polymer, an anionic conductive polymer may be spray-deposited on top of it, and then heated to induce a crosslinking reaction, resulting in crosslinking across the interface.

[0261] In some embodiments, the anionic conductive polymer and the cationic conductive polymer of the bipolar film have the same backbone with different statically charged groups. For example, an Orion ionomer may be used with different statically charged groups. The ionomer offers better compatibility and is less prone to delamination.

[0262] In the above example, the interface 813 may be a three-dimensional volume having a thickness of 1% to 90% of the total thickness of the bipolar film, or 5% to 90%, 10% to 80%, 20% to 70%, or 30% to 60% of the total thickness of the bipolar film. In some embodiments, it is less than half of the total thickness, including 1% to 45%, 5% to 45%, 5% to 40%, or 5% to 30%.

[0263] Hot pressing may be used to manufacture any of the bipolar interface designs described above. Relative size of the MEA layer

[0264] In certain embodiments, the polymer electrolyte membrane and the adjacent cathode buffer layer or other anion-conducting polymer layer may have a relative thickness that facilitates the fabrication and / or operational performance of the MEA.

[0265] Figure 9 shows an example of a partial MEA comprising an anion-conducting polymer layer (AEM) 903, which may be a cathode buffer layer, and a polymer electrolyte membrane (PEM) 905, which may be a cationic-conducting polymer layer (e.g., a proton-exchange polymer layer) or anion-conducting polymer layer. In this example, the PEM 905 is relatively thicker than the anion-conducting polymer layer 903, which may be a cathode buffer layer, and the polymer electrolyte membrane (PEM) 905 may be a cationic-conducting polymer layer (e.g., a proton-exchange polymer layer) or anion-conducting polymer layer. In this example, the PEM 905 is relatively thicker than the anion-conducting polymer layer 903. For example, the PEM 905 may be 120 micrometers thick, compared to approximately 10-20 micrometers thick for the AEM 903.

[0266] In some cases, anionic conductive polymers, such as those used in the anionic conductive polymer layer 903, have substantially lower conductivity than cationic conductive polymers, such as those used in the PEM 905. Therefore, a relatively thin cathode buffer is used to provide the benefits of the cathode buffer layer (e.g., the anionic conductive polymer layer 903) without substantially increasing the total resistance of the MEA. However, if the cathode buffer layer is too thin, it becomes difficult to handle during the manufacturing of the MEA and under other circumstances. Therefore, in certain embodiments, a thin cathode buffer layer is formed on top of a relatively thick PEM layer, such as a cationic conductive polymer layer. The anionic conductive polymer layer may be fabricated on the PEM layer, for example, using any of the manufacturing techniques described elsewhere in this specification.

[0267] In various embodiments, the polymer electrolyte membrane layer is approximately 20 to 200 micrometers thick. In some embodiments, the polymer electrolyte membrane layer is approximately 60 to 120 micrometers thick. In some embodiments, a thin polymer electrolyte membrane layer of approximately 20 to 60 micrometers thick is used. In some embodiments, a relatively thick polymer electrolyte layer of approximately 120 to 200 micrometers thick is used.

[0268] In some embodiments, a thinner cathode buffer layer is used along with a thinner polymer electrolyte membrane. This facilitates the migration of CO2 formed at the interface back to the cathode rather than the anode. In some embodiments, a thicker cathode buffer layer is used along with a thicker polymer electrolyte membrane. As a result, in some embodiments, the cell voltage may decrease.

[0269] Factors that may affect the thickness of the cathode buffer layer include the ion selectivity of the anion-conducting polymer, the porosity of the anion-conducting polymer, and the conformability of the anion-conducting polymer coating the polymer electrolyte membrane.

[0270] Many anion-conducting polymers exhibit selectivity in the 95% range for anions, with approximately 5% of the current being cation-conducting. More selective anion-conducting polymers, exhibiting selectivity exceeding 99% for anions, can enable significant thickness reductions while providing sufficient buffer.

[0271] The mechanical strength of the anion-conducting layer can also affect its thickness; higher layer strength allows for a thinner layer. The thickness of the anion-conducting layer can be reduced by decreasing the porosity of the anion-conducting polymer.

[0272] In some implementations, the cathode buffer layer or other anion-conducting polymer layer in contact with the polymer electrolyte membrane is approximately 10 to 20 micrometers thick. In some embodiments, the cathode buffer layer can be reduced to 2 to 10 microns by using a polymer with selectivity exceeding 99%.

[0273] In some cases, the ratio of the thickness of the polymer electrolyte membrane to the thickness of the adjacent anion-conducting polymer layer is approximately 3:1 to 90:1, where the higher ratio is used for the more selective anion-conducting polymer layer. In some embodiments, the ratio is approximately 2:1 to 13:1, approximately 3:1 to 13:1, or approximately 7:1 to 13:1.

[0274] In certain embodiments, a relatively thin PEM improves some aspects of MEA performance. Referring to Figure 9, for example, the polymer electrolyte membrane 905 may have a thickness of about 50 micrometers, and the anion-conducting layer may have a thickness of about 10-20 micrometers. With a thin PEM, water generated at the AEM / PEM interface is more likely to move toward the anode. The gas pressure on the cathode side of the cell can be about 80-450 psi, which causes the water at the interface to move toward the anode. However, in some examples, a thick PEM may allow most of the water to pass through the AEM to the cathode, which leads to flooding. Flooding can be avoided by using a thin PEM. CO x Reduction reactor (CRR)

[0275] Figure 10 shows an embodiment of the present disclosure of CO x This is a schematic diagram showing the main components of the reduction reactor (CRR) 1005. The CRR 1005 has a membrane electrode assembly 1000, such as any of those described elsewhere in this specification. The membrane electrode assembly 1000 has a cathode 1020 and an anode 1040 separated by an ion exchange layer 1060. The ion exchange layer 1060 may include sublayers. The illustrated embodiment has three sublayers: a cathode buffer layer 1025, a polymer electrolyte membrane 1065, and an optional anode buffer layer 1045. The CRR 1005 also has a cathode support structure 1022 adjacent to the cathode 1020 and an anode support structure 1042 adjacent to the anode 1040.

[0276] The cathode support structure 1022 has, for example, a cathode electrode plate 1024 made of graphite, to which a voltage can be applied. Flow field channels, such as meandering channels, can be present on the inner surface of the cathode electrode plate 1024. A cathode gas diffusion layer 1026 is also present adjacent to the inner surface of the cathode electrode plate 1024. In some configurations, there are more than one cathode gas diffusion layer (not shown). The cathode gas diffusion layer 1026 promotes the flow of gas in and out of the membrane electrode assembly 1000. An example of the cathode gas diffusion layer 1026 is carbon paper having a carbon microporous layer.

[0277] The anode support structure 1042 typically has a metal anode plate 1044 to which a voltage can be applied. Flow field channels, such as meandering channels, can be present on the inner surface of the anode plate 1044. An anode gas diffusion layer 1046 is also present adjacent to the inner surface of the anode plate 1044. In some configurations, there are more than one anode gas diffusion layer (not shown). The anode gas diffusion layer 1046 promotes the flow of gas in and out of the membrane electrode assembly 1000. An example of the anode gas diffusion layer 1046 is a titanium mesh or titanium felt. In some configurations, the gas diffusion layers 1026 and 1046 are microporous.

[0278] Inlet and outlet ports (not shown) are also present, which are linked to the support structures 1022 and 1042, allowing for the flow of reactants and products to the respective membrane electrode assemblies 1000. Various gaskets (not shown) are also present to prevent leakage of reactants and products from the cell.

[0279] In one embodiment, a direct current (DC) voltage is applied to the membrane electrode assembly 1000 through the cathode plate 1024 and the anode plate 1042. Water is supplied to the anode 1040 and oxidized on the oxidation catalyst to form molecular oxygen (O2), releasing protons (H+) and electrons (e-). The protons move toward the cathode 1020 through the ion exchange layer 1060. The electrons flow through an external circuit (not shown). In one embodiment, the reaction is represented as follows: 2H2O → 4H + +4e - +O2

[0280] In other embodiments, other reactants can be supplied to the anode 1040, and other reactions may occur.

[0281] The illustrated embodiment shows an ion exchange layer having three sublayers, but in certain embodiments, an ion exchange layer having only one layer (e.g., a cation-conducting polymer layer or an anion-conducting polymer layer) is used. Other embodiments have only two sublayers.

[0282] Figure 11 shows the flow of reactants, products, ions, and electrons through the CRR1105 reactor according to one embodiment. The CRR1105 has a membrane electrode assembly 1100, such as one of the MEAs described elsewhere in this specification. The membrane electrode assembly 1100 has a cathode 1120 and an anode 1140 separated by an ion exchange layer 1160. In a particular embodiment, the ion exchange layer 1160 has three sublayers: a cathode buffer layer 1125, a polymer electrolyte membrane 1165, and an optional anode buffer layer 1145. The CRR1105 also has a cathode support structure 1122 adjacent to the cathode 1120 and an anode support structure 1142 adjacent to the anode 1140.

[0283] The cathode support structure 1122 has a cathode plate 1124, which may be made of graphite, to which a voltage can be applied. Flow field channels, such as meandering channels, may be present on the inner surface of the cathode plate 1124. A cathode gas diffusion layer 1126 is also present adjacent to the inner surface of the cathode plate 1124. In some configurations, there are more than one cathode gas diffusion layer (not shown). The cathode gas diffusion layer 1126 promotes the flow of gas in and out of the membrane electrode assembly 1100. An example of the cathode gas diffusion layer 1126 is carbon paper having a carbon microporous layer.

[0284] The anode support structure 1142 has an anode plate 1144, which can be made of metal, to which a voltage can be applied. Flow field channels such as serpentine channels can be provided on the inner surface of the anode plate 1144. An anode gas diffusion layer 1146 also exists adjacent to the inner surface of the anode plate 1144. In some configurations, more than one anode gas diffusion layer (not shown) exists. The anode gas diffusion layer 1146 promotes the flow of gas into and out of the membrane electrode assembly 1100. An example of the anode gas diffusion layer 1146 is a titanium mesh or titanium felt. In some configurations, the gas diffusion layers 1126, 1146 are microporous.

[0285] Inlets and outlets can also exist in cooperation with the support structures 1122, 1142, which allow the flow of reactants and products to the membrane electrode assembly 1100, respectively. Various gaskets can also exist to prevent the leakage of reactants and products from the cell.

[0286] CO x is supplied to the cathode 1120 and can be reduced on a reduction catalyst in the presence of protons and electrons. x CO x can be supplied to the cathode 1120 at a pressure of 0 psig to 1000 psig or any other suitable range. x CO x can be supplied to the cathode 1120 at a concentration of less than 100% or any other suitable percentage, together with a mixture of other gases. In some configurations, the concentration of

[0287] In one embodiment, approximately 10% to 100% of the unreacted x CO is collected at the outlet adjacent to the cathode 1120, separated from the reduction reaction products, and then recycled back to the inlet adjacent to the cathode 1120. In one embodiment, the oxidation products at the anode 1140 are compressed to a pressure of 0 psig to 1500 psig.

[0288] In one embodiment, a plurality of CRRs (such as those shown in FIG. 10, etc.) are arranged as an electrochemical stack and operated together. The CRRs that make up the individual electrochemical cells of the stack can be electrically connected in series or in parallel. Reactants are supplied to the individual CRRs, and the reaction products are then collected.

[0289] FIG. 12 shows the inputs and outputs to the reactor according to some embodiments. CO x An anode feed material and electricity are supplied to the reactor. CO x Reduction products and any unreacted CO x leave the reactor. Unreacted CO x is separated from the reduction products and can be recycled back to the input side of the reactor. Anode oxidation products and any unreacted anode feed material leave the reactor in a separation stream. Unreacted anode feed material can be recycled back to the input side of the reactor.

[0290] The various catalysts within the cathode of the CRR cause x the reduction reaction to form various products or mixtures of products. Examples of possible CO x reduction reactions at the cathode are described below. CO2 + 2H + + 2e - → CO + H2O 2CO2 + 12H + + 12e - → CH2CH2 + 4H2O 2CO2 + 12H + + 12e - → CH3CH2OH + 3H2O CO2 + 8H + + 8e - → CH4 + 2H2O 2CO + 8H + + 8e - → CH2CH2 + 2H2O 2CO + 8H + + 8e - → CH3CH2OH + H2O CO + 6H + + 8e - → CH4 + H2O

[0291] In some embodiments, CO xA method for operating the reduction reactor includes, as described in the above embodiments, the steps of: applying a DC voltage to the cathode plate and the anode plate; supplying an oxidation reactant to the anode to cause an oxidation reaction; supplying a reduction reactant to the cathode to cause a reduction reaction; collecting the oxidation reaction product from the anode; and collecting the reduction reaction product from the cathode. The current or voltage may be controlled to cycle according to the schedule described above.

[0292] In one configuration, the DC voltage is approximately greater than -1.2V. In various configurations, the oxidizing reactant may be hydrogen, methane, ammonia, water, or a combination thereof, and / or any other suitable oxidizing reactant. In one configuration, the oxidizing reactant is water. In various configurations, the reducing reactant may be carbon dioxide, carbon monoxide, or a combination thereof, and / or any other suitable reducing reactant. In one configuration, the reducing reactant is carbon dioxide. Examples

[0293] Faraday efficiency, sometimes also called Faraday yield, Coulomb efficiency, or current efficiency, is the efficiency with which charge is transferred to a system that facilitates an electrochemical reaction. The use of the Faraday constant in Faraday efficiency correlates charge with the moles of matter and electrons. Faraday losses occur when electrons or ions participate in undesirable side reactions. These losses manifest as heat and / or chemical byproducts. The following examples include plots of Faraday yields for various products. Improved selectivity for methane

[0294] A copper cathode catalyst-assisted MEA was set to have a current of 100 mA / cm² applied to a 5 cm² MEA with selectivity for methane. After approximately 1 hour of operation, a cycle was applied in which a current was applied for 4.5 minutes followed by a 1 minute current off (i.e., current pause). Figure 13 is a plot showing the applied current density (J) and the Faraday yield (FY) for H₂, CO, CH₂CH₂, CH₄, and total. Each dot on the plot is separated by 5.5, and therefore the current pause is not shown. However, as shown in the plot, the current cycle begins at 1 hour.

[0295] During the first hour after break-in, methane selectivity decreased from 13% to 7%. After the application of current cycling began, methane selectivity increased to 23%. Hydrogen selectivity decreased, and selectivity for ethylene and carbon monoxide remained at low levels.

[0296] Possible mechanisms for improvement (and other observed improvements described herein) include: 1) enabling the removal of hydrogen from the catalyst surface and thus improving the access of CO2; 2) enabling the removal of water from the local environment of the catalyst; 3) desorbing other reaction by-products or impurities from the catalyst surface; and 4) changing the resistance / conductivity of the film / bilayer. Improved selectivity for methane through simulated biogas supply

[0297] An MEA with a copper cathode catalyst for testing simulated biogas with a maximum H2S injection of 1500 ppm was initially set to 100 mA / cm². 2The experiment was started with a constant current applied. Figure 14 is a plot showing the Faraday yields (FY) for H2 and CH4. H2S injection is also shown. The initial yield of methane (before any current pause) decreased from 20% to 10%. When the applied current was paused for 5 minutes and then resumed, the MEA's performance improved significantly, but the decline continued. Subsequently, when the experiment was paused again for 1 minute and restarted, the MEA recovered its performance, but the decline continued. After establishing regular 1-minute pauses of the applied current every 4.5 minutes, the MEA was able to maintain a stable selectivity of 30% for methane and withstand exposure to up to 1500 ppm of H2S without any signs of significant toxicity. Improved selectivity for methane during break-in

[0298] Figure 15 is a plot showing the break-in period for an MEA with a copper cathode catalyst. The applied current density and the Faraday yields for H2, CO, and CH4 are shown. The applied current is paused for 1 minute for every 4.5 minutes applied during the entire duration of operation. Similar to the plot in Figure 13, the dots are spaced 5.5 minutes apart, and therefore no pauses are observed on the plot. Figure 15 shows that a significant break-in period exists. It also shows that in this current cycle, the slope of the FY CH4 curve is upward, in contrast to the FY CH4 curves in Figures 13 and 14 which decrease in the period prior to the current cycle. Improved selectivity for CO

[0299] The MEA, with a gold cathode catalyst for CO generation, was shut down for over 4 days after two periods of 50–300 hours each. As shown in Figure 16, when the cell was restarted, the Faraday yield for CO increased, while the Faraday yield for H2 decreased compared to the value at which the cell was stopped in the previous cycle. In particular, the Faraday yield for CO increased by approximately 10% at the start of cycle 2 compared to the end of cycle 1, and by approximately 5% at the start of cycle 3 compared to the end of cycle 2.

[0300] Figure 17 shows the cell performance in a long-term test of a single MEA, with off / on current pauses indicated. As shown at 95 hours in Figure 17, pausing cell operation for 15 minutes improved cell performance. FY CO increased by 8% from 86% to 94%, while FY H2 was halved from 13% to 6%.

[0301] Figure 18 shows the performance of two MEA cells, one of which was operated continuously without current pauses, and the other operated with intermittent current pulses, where the cell was operated for 55 minutes and then switched off for 5 minutes. This on / off cycle was repeated during the pulse period, as indicated by the striped dots in the figure. Between these pulse periods, the current flowed continuously. Referring to Figure 18, different curves for FY CO and FY H2 are labeled. The intermittent pulses improve CO selectivity. The plot shows the improvement in reactor stability when intermittent pulses are applied during operation. For the cell with intermittent pulses, the selectivity decay (dFY_CO / dt) over 30–134 hours was -0.0070% / hr, compared to -0.055% / hr for the cell with continuous current.

[0302] These examples demonstrate that cell performance can be improved by increasing selectivity for CO through short-term and long-term pauses in cell operation. Improved selectivity for CO - MEA stack

[0303] The above example uses a single MEA. However, improved selectivity is observed with an MEA stack. Figure 19 shows performance data for two stacks, with 1901 showing data for the operation of an MEA stack with approximately 32 hours of current pause at approximately 63 hours of duration. The 32-hour pause is not shown in the plot. However, at 1910, the resulting increase in FY_CO is observed. At 1902, data for operation with approximately 13 hours of current pause at 1912 is shown. Improved selectivity is observed, as demonstrated by the increased FY_CO at 1914. The increase was approximately 20%. Break-in current lamp

[0304] Figure 20 shows 500 mA / cm². 2 The image shows the results of two identical MEAs for generating CO, tested using different ramp programs to reach the operating current density (100 mA / cm²). The black dots represent each intermediate current density (100 mA / cm²). 2 , 200mA / cm 2 , 300mA / cm 2 , 400mA / cm 2 The white dots correspond to cells operated for 1 hour at the intermediate current density, and the white dots correspond to cells operated for 30 minutes at each intermediate current density (in some examples, the white dots obscure the black dots on the plot, and vice versa). Figure 20 shows that the Faraday yield of CO was higher for cells operated at a slower ramp rate (black dots) than for cells operated for relatively shorter periods at each current density. These results suggest that a slower current ramp promotes hydration and can lead to higher performance.

[0305] Figure 21 shows the performance of two MEAs with high CO2 utilization rates. One MEA (black dot) was operated in a cell without a current lamp, at 300 mA / cm². 2 Start directly with this. The other MEA (white dot) is 300mA / cm 2It took 2 hours, 2 hours, and 2 hours respectively for the current to settle at 100, 200, and 250 mA / cm². 2 The device was operated in a cell with a current lamp. As shown in Figure 21, using a current lamp up to 300 mA / cm² improves the voltage by approximately 100 mV. The effect of the lamp program

[0306] Operating the cells with different ramp-up or ramp-down programs results in different selectivity and voltage decay rates. Specifically, in a test where an MEA for CO was operated at 300 mA / cm², ramped down to 0 within 30 minutes, maintained at 0 for 15 minutes, and then immediately restarted at 300 mA / cm², it yielded better Faraday yield decay than a test where the current was immediately stopped, maintained at 0 for 15 minutes, and then gradually ramped up from 0 to 300 mA / cm² within 30 minutes. Current pause duration

[0307] Figure 22 shows the change in Faraday yield for CO as a function of current pause duration (from before to after current pause), and Figure 23 shows the change in voltage as a function of current pause duration (from before to after current pause). As shown in Figure 22, the duration of current pause during long-term testing affects the change in CO Faraday yield, but no effect of the duration of current pause on voltage change is observed (Figure 23). Open-circuit voltage vs. cell short circuit

[0308] Two MEAs generating CO were operated with intermittent pulses of current, and the cells were operated for 45 minutes, then switched off for 15 minutes. This cycle was repeated for 14 hours. For one MEA, the cell was short-circuited to 0V during the current pause. For the other MEA, the cell was kept at an "open-circuit voltage" (OCV) of approximately 1–1.2V during the current pause. Voltage stability was higher for the cells kept at OCV (1–1.2V) compared to the cells operated at 0V during the current pause. For the cells operating at 0V during the current pause, the voltage decay was 0.6mV / hr. For the cells at OCV, the voltage increased at a rate of 3.7mV / hr. For both tests, CO selectivity also increased over time at a rate of approximately 0.07% / hr. Other Embodiments

[0309] For simplicity, the embodiments of the system and / or method may include any combination and substitution of various system components and various method processes, and one or more examples of such methods and / or processes described herein may be executed asynchronously (e.g., sequentially), simultaneously (e.g., in parallel), or in any other preferred order by one or more examples of the systems, elements, and / or entities described herein and / or using such examples.

[0310] As can be understood by those skilled in the art from the above detailed description, the drawings and the claims, modifications and changes can be made to preferred embodiments of the present invention without departing from the scope of the present invention as defined by the following claims.

Claims

1. CO ｘ 1. A method of operating a membrane electrode assembly (MEA) for reduction, comprising: The cathode of the MEA is CO ｘ and applying a current to the MEA at a first current density while introducing a gas containing CO ｘ is reduced to CO ｘ generating a reduction product; automatically suspending the applied current during normal operation according to a current suspension schedule; A method comprising:

2. 2. The method of claim 1, wherein the current pause schedule includes current-on periods at the first current density separated by current pause periods, and the applied current during at least a portion of a current pause period is zero or a second current density lower than the first current density.

3. The method of claim 2, wherein the duration of the current-on period is between 10 hours and 1000 hours.

4. 4. The method of claim 3, wherein the duration of the current suspension period is between 5 minutes and 10 hours.

5. The method of claim 2, wherein the duration of the current-on period is between 1 hour and 10 hours.

6. The method of claim 5, wherein the duration of the current suspension period is between 500 microseconds and 20 minutes.

7. The method of claim 2, wherein the duration of the current-on period is between 3 minutes and 1 hour.

8. 8. The method of claim 7, wherein the duration of the current suspension period is between 500 microseconds and 10 minutes.

9. The method according to any one of claims 2 to 8, wherein the total current on period duration is at least three times longer than the total current pause period duration.

10. The method according to any one of claims 1 to 9, wherein the current pause period duration is constant and the current on period duration is constant.

11. The method of any one of claims 1 to 9, wherein one or both of the current pause period duration and the current on period duration are varied.

12. The method of any one of claims 1 to 11, wherein the step of automatically pausing the applied current comprises a single step from the first current density.

13. The method of any one of claims 1 to 11, wherein automatically pausing the applied current comprises multiple steps from the first current density.

14. The method of any one of claims 1 to 11, wherein automatically pausing the applied current comprises a continuous ramp from the first current density.

15. The method of any one of claims 1 to 14, wherein automatically pausing the applied current comprises returning to the first current density using a single step.

16. The method of any one of claims 1 to 14, wherein automatically pausing the applied current comprises returning to the first current density in multiple steps.

17. The method of any one of claims 1 to 14, wherein automatically pausing the applied current comprises returning to the first current density using a continuous ramp.

18. A method according to any preceding claim, wherein suspending the applied current comprises reducing the applied current to zero.

19. 20. The method of claim 18, wherein reducing the applied current to zero comprises short-circuiting the MEA.

20. 20. The method of claim 18, wherein the MEA has an open circuit potential when the applied current is zero.

21. The method of any one of claims 1 to 20, further comprising stopping the flow of gas while suspending the electrical current.

22. 21. The method of any one of claims 1 to 20, further comprising maintaining but reducing the flow of gas while suspending the electrical current.

23. The method of any one of claims 1 to 20, further comprising the step of maintaining the flow of gas at the same rate while suspending the electric current.

24. The method of any one of claims 1 to 23, further comprising introducing an anode feed material to the anode of the MEA.

25. 25. The method of claim 24, further comprising stopping the flow of the anode feed material while suspending the current.

26. 25. The method of claim 24, further comprising maintaining but reducing the flow of the anode feed material while suspending the current.

27. 25. The method of claim 24, further comprising maintaining the flow of the anode feed material at the same rate while suspending the current.

28. 28. The method of any one of claims 1 to 27, further comprising the step of performing a break-in procedure prior to normal operation, comprising applying current in a multi-step or continuous ramp up to said first current density.

29. 29. The method of claim 28, further comprising, prior to the break-in procedure, performing a hydration operation, wherein no electrical current is applied and a cathode gas and an anode feed material are introduced to the cathode and anode of the MEA, respectively.

30. 30. The method of claim 29, further comprising ramping the temperature to an operating temperature during the hydration operation.

31. CO2 containing one or more membrane electrode assemblies (MEA) arranged in a stack ｘ In a reduction reactor, each MEA comprises: (i) a CO ｘ a CO2 fuel cell comprising: (i) a cathode including a reduction catalyst; (ii) an anode including a catalyst that promotes oxidation; and (iii) a polymer electrolyte membrane (PEM) layer disposed between the cathode and the anode. ｘ a reduction reactor; and CO ｘ a power supply controller configured to control a current applied to a reduction reactor, the power supply controller ｘ a power supply controller configured to automatically suspend the applied current according to a current suspend schedule during normal operation of the reduction reactor; A system comprising:

32. 32. The system of claim 31 , wherein the current pause schedule includes current-on periods at a first current density separated by current pause periods, and the applied current during at least a portion of a current pause period is zero or a second current density lower than the first current density.

33. 33. The system of claim 32, wherein the duration of the current-on period is between 10 hours and 1000 hours.

34. 34. The system of claim 33, wherein the duration of the current suspension period is between 5 minutes and 10 hours.

35. 33. The system of claim 32, wherein the duration of the current-on period is between 1 hour and 10 hours.

36. 36. The system of claim 35, wherein the duration of the current suspension period is between 500 microseconds and 20 minutes.

37. 33. The system of claim 32, wherein the duration of the current-on period is between 3 minutes and 1 hour.

38. 38. The system of claim 37, wherein the duration of the current suspension period is between 500 microseconds and 10 minutes.

39. A system according to any one of claims 32 to 38, wherein the total current on period duration is at least three times longer than the total current pause period duration.

40. A system according to any one of claims 31 to 39, wherein the current pause period duration is constant and the current on period duration is constant.

41. 40. The system of any one of claims 31 to 39, wherein one or both of the current suspend period duration and the current on period duration are varied.

42. 40. The system of any one of claims 32 to 39, wherein automatically pausing the applied current comprises a single step from the first current density.

43. 40. The system of any one of claims 32 to 39, wherein automatically pausing the applied current comprises multiple steps from the first current density.

44. 40. The system of any one of claims 32 to 39, wherein automatically pausing the applied current comprises a continuous ramp from the first current density.

45. The system of any one of claims 32-39 and 42-44, wherein automatically pausing the applied current comprises returning to the first current density using a single step.

46. The system of any one of claims 32-39 and 42-44, wherein automatically pausing the applied current comprises returning to the first current density using multiple steps.

47. 45. The system of any one of claims 32-39 and 42-44, wherein automatically pausing the applied current comprises returning to the first current density with a continuous ramp.

48. The system of any one of claims 31 to 47, wherein suspending the applied current comprises reducing the applied current to zero.

49. 49. The system of claim 48, wherein reducing the applied current to zero comprises shorting the MEA.

50. 49. The system of claim 48, wherein the MEA has an open circuit potential when the applied current is zero.

51. 48. The system of any one of claims 32-39 and 42-47, wherein the system is configured to perform a break-in procedure prior to normal operation, the break-in procedure including application of current in a multi-step or continuous ramp up to the first current density.

52. Furthermore, the CO ｘ a cathode subsystem configured to interact with a cathode of the reduction reactor, ｘ 52. The system of any one of claims 31 to 51, comprising a carbon oxide flow controller configured to control the flow of the carbon oxide feed stream to the cathode of the reduction reactor.

53. 53. The system of claim 52, wherein the carbon oxide flow controller is configured to stop the flow of the carbon oxide supply stream during a current pause.

54. 53. The system of claim 52, wherein the carbon oxide flow controller is configured to maintain the flow of carbon oxide at the same or a different flow rate during a current pause.

55. Furthermore, CO ｘ an anode subsystem configured to interact with an anode of the reactor, ｘ 55. The system of any one of claims 31 to 54, comprising an anode water flow controller configured to control flow of the anode feed stream to the anode of the reactor.

56. 56. The system of claim 55, wherein the anode water flow controller is configured to stop the flow of the anode supply stream during a current pause.

57. 56. The system of claim 55, wherein the anode water flow controller is configured to maintain the flow of the anode supply stream at the same or a different flow rate during a current pause.

58. 56. The system of claim 55, further comprising a controller configured to adjust the composition of the anode supply stream during a current pause.

59. The system of any one of claims 31 to 58, further comprising a backpressure controller configured to maintain pressure on the cathode side of the MEA.

60. 53. The system of claim 52, wherein the cathode subsystem is configured to controllably recycle unreacted carbon oxides from an exhaust stream back to the cathode of the MEA.

61. 61. The system of any one of claims 31 to 60, further comprising an anode water recirculation loop.

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