Electrolysis device and use method

Abstract

The invention relates to an electrolysis device and a use method. Provided herein are methods for operating a carbon oxide (COx) reduction reactor (CRR) and related apparatuses. In some embodiments, the methods involve turning off, reducing, or otherwise controlling current during various operating phases including hydration, run-in, normal operation, planned turning off, and extended turning off or storage periods.

Description

Reference Addition

[0001] This application is a divisional application of Chinese invention patent application No. 201980090689.2 (international application number is PCT / US2019 / 067169), whose priority date is December 18, 2018 and whose invention name is “Electrolysis Device and Method of Use”. Government support statement

[0002] This invention was made with government support under the following awards: Award No. DE-AR00000819 from the U.S. Advanced Research Projects Agency-Energy, Award No. DE-FE0031712 from the National Energy Technology Laboratory, and Award No. NNX17CJ02C from the National Aeronautics and Space Administration. The government has certain rights in this invention. Technical Field

[0003] The present disclosure relates generally to the field of electrolytic carbon oxide reduction and, more particularly, to systems and methods for operating an electrolytic carbon oxide reactor. Background Art

[0004] Electrolysis of carbon dioxide reactors must balance various operating conditions, such as the composition of the reactants at the anode and cathode, the electrical energy provided to the anode and cathode, and the physical and chemical environment of the electrolyte, anode and cathode. Balancing these conditions has a strong impact on the operating voltage of the electrolysis reactor, the Faradaic yield, and the mixing of products generated at the cathode (including carbon monoxide (CO) and / or other carbon-containing products (CCP) and hydrogen).

[0005] The background and context descriptions contained herein are only for the purpose of generally presenting the context of the present disclosure. Most of the content of this disclosure presents the work of the inventor, and just because the work is described in the background section or presented as context elsewhere in this article, it does not mean that the work is prior art. Summary of the invention

[0006] One aspect of the present disclosure relates to a method for operating a membrane electrode assembly (MEA) to achieve CO x The method comprises: x The gas is introduced into the cathode of the MEA and a current is applied to the MEA at a first current density, thereby reducing CO x and produces CO x reduction products; and during normal operation, automatically suspending applied current according to a current suspension schedule.

[0007] In some embodiments, 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 the current-pause periods is zero or at a second current density lower than the first current density.

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

[0009] In some embodiments, the duration of the current on period is between 1 hour and 10 hours. In some such embodiments, the duration of the current off period is between 500 microseconds and 20 minutes.

[0010] In some embodiments, the duration of the current on period is between 3 minutes and 1 hour. In some such embodiments, the duration of the current off period is between 500 microseconds and 10 minutes.

[0011] In some embodiments, the total current-on period duration is at least three times, at least five times, or at least ten times the total current-pause period duration.According to various embodiments, the current-pause period duration and / or the current-on period duration may be constant or variable.

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

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

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

[0015] In some embodiments, the method further comprises stopping the flow of gas while pausing the current. In some embodiments, the method further comprises maintaining but reducing the flow of gas while pausing the current. In some embodiments, the method further comprises maintaining the flow of gas at the same flow rate while pausing the current.

[0016] In some embodiments, the method further comprises introducing an anode feed to the anode of the MEA. In some embodiments, the method further comprises stopping the flow of the anode feed while suspending the current. In some embodiments, the method further comprises maintaining but reducing the flow of the anode feed while suspending the current. In some embodiments, the method further comprises maintaining the flow of the anode feed at the same flow rate while suspending the current.

[0017] In some embodiments, the method further comprises, prior to normal operation, performing a break-in procedure comprising applying current to a first current density in multiple steps or in a continuous gradient. In some such embodiments, the method further comprises, prior to the break-in procedure, performing a hydration operation wherein no current is applied and cathode gas and anode feed are introduced to the cathode and anode of the MEA, respectively. In some such embodiments, the method further comprises raising the temperature to the operating temperature during the hydration period.

[0018] Another aspect of the present disclosure relates to a method comprising: x reduction reactor and power controller system, the CO x The reduction reactor includes one or more membrane electrode assemblies (MEAs) arranged in a stack, each MEA including: (i) a cathode including a CO x reduction catalyst, (ii) an anode including a catalyst promoting oxidation, and (iii) a polymer electrolyte membrane (PEM) layer disposed between the cathode and the anode; the power controller is configured to control the power applied to the CO x reduction reactor current, and the controller is configured to x The application of current is automatically suspended according to the current suspension schedule during normal operation of the reduction reactor.

[0019] In some embodiments, 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 the current-pause periods is zero or at a second current density lower than the first current density.

[0020] In some embodiments, the duration of the current on period is between 10 hours and 1000 hours. In some such embodiments, the duration of the current off period is between 5 minutes and 10 hours.

[0021] In some embodiments, the duration of the current on period is between 1 hour and 10 hours. In some such embodiments, the duration of the current off period is between 500 microseconds and 20 minutes.

[0022] In some embodiments, the duration of the current on period is between 3 minutes and 1 hour. In some such embodiments, the duration of the current off period is between 500 microseconds and 10 minutes.

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

[0024] In some embodiments, the system is configured to perform a run-in procedure prior to normal operation, the run-in procedure comprising applying current to a first current density in multiple steps or in a continuous ramp.

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

[0026] In some embodiments, the system further comprises an anode subsystem configured to communicate with the CO x The anodes of the reactor interact and include an anode water flow controller configured to control the flow of anode feed to the CO x In some such embodiments, the anode water flow controller is configured to stop the flow of the anode feed stream during the current pause. In some such embodiment schemes, the anode water flow controller is configured to maintain the flow of the anode feed stream at the same or different flow rate during the current pause.

[0027] In some embodiments, the system further comprises a controller configured to adjust the composition of the anode feed stream during the 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 invention will be presented in more detail below with reference to the associated drawings. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0030] Figure 1B Schematic examples of current profiles for reducing current from an operating current density to a pause current density at the beginning of a current pause period according to various embodiments of the present disclosure are shown.

[0031] Figure 1C Schematic examples of current distribution of return-to-operation current density at the end of a current pause period according to various embodiments of the present disclosure are shown.

[0032] Figure 1D is a diagram of an example of an electrolytic carbon oxide reduction system according to various embodiments of the present disclosure.

[0033] Figure 2 According to various embodiments of the present disclosure, x Schematic diagram of the reduced membrane electrode assembly.

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

[0035] Figure 4 is a diagram of an MEA supplying CO2 gas to the cathode catalyst layer.

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

[0037] Figure 6 1 is a schematic diagram showing an example form of cathode particles in which a catalyst is supported on catalyst support particles.

[0038] Figure 7 is with Figure 3 A similar diagram of an MEA is shown, but additionally showing information related to the mass transport and generation of CO2 and water at the bipolar interface.

[0039] Figures 8A-8D Various MEA designs are presented that incorporate features that resist delamination and optionally provide a path for reaction products to escape the interfacial region.

[0040] Fig. 9 is a diagram of a partial MEA that includes an anion conducting polymer layer (which may be a cathode buffer layer) and a polymer electrolyte membrane (which may be a cation conducting polymer layer).

[0041] Fig.10 is a diagram showing CO according to various embodiments of the present disclosure x Schematic diagram of the main components of the reduction reactor (CRR).

[0042] Fig.11 is a schematic diagram showing the main components of a CRR according to various embodiments of the present disclosure, where arrows show the flow of molecules, ions, and electrons.

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

[0044] Fig.13 is a graph showing applied current density (J) versus Faradaic yield (FY) for H2, CO, CH2CH2, CH4 obtained from operation of the MEA including current cycling.

[0045] Fig.14 is a graph showing applied current density (J) versus Faradaic yield (FY) for H2 and CH4 obtained from operation of the MEA with simulated biogas feed including current cycling.

[0046] Fig.15is a graph showing the run-in period of an MEA with a copper cathode catalyst. The applied current density (J) and the Faradaic yield for H2, CO and CH4 are shown.

[0047] Fig.16 is a graph showing voltage (V), applied current density (J), and Faradaic yield for H2 and CO for a MEA configured to produce CO. Three cycles are shown, including a run-in and two current on / off events.

[0048] Fig.17 is a graph showing voltage (V), applied current density (J), and Faradaic yield for H2 and CO for a MEA configured to produce CO. The current was paused at 95 minutes.

[0049] Fig.18 is a graph comparing the electrolyser performance of two MEAs configured to produce CO; one operated without current pauses and the other with intermittent pulses.

[0050] Fig.19 Two graphs are shown for performance data of an MEA stack configured to produce CO and each operated with a current pause.

[0051] Fig. 20 Results are shown for two identical MEAs producing CO, tested using different ramping programs to reach 500 mA / cm 2 The operating current density.

[0052] Fig.21 is a graph comparing the performance of an MEA operated in an electrolyzer without a ramp to operating current and the performance of an electrolyzer with a ramped current.

[0053] Fig. 22 shows the change in the Faradaic yield of CO (from before to after the current is suspended) as a function of the duration of the current suspension, and Fig.23 The voltage change (from before and after the current pause) is shown versus the duration of the current pause. DETAILED DESCRIPTION

[0054] This paper provides a method for running carbon oxides (CO x ) reduction reactor (CRR) and related equipment. In some embodiments, the method involves shutting down, reducing or otherwise controlling the current during various operating stages including hydration, running-in, normal operation, planned shutdown and extended shutdown or storage periods. As further described below and in the examples, suspending the current during normal operation has advantages including improved selectivity. In addition, the system can be shut down for other purposes, such as maintenance, storage, etc.

[0055] The CRR described herein includes one or more membrane electrode assemblies (MEAs), wherein a plurality of MEAs are arranged in a stack. Figure 2-9 An example of MEA is described below.

[0056] There are challenges in reducing current density or shutting down the system, some of which are unique to CCR and are not found in MEA components used in other applications such as fuel cells or water electrolysis devices. For example, the anion exchange polymer-electrolyte (either part of the bipolar or only the AEM membrane and cathode catalyst layer) will contain bicarbonate anions during CO2 conversion. Figure 2-9 A bipolar MEA including an anion exchange polymer electrolyte and an AEM-only MEA are further described. If the system is stopped and CO2 is replaced with another gas in the system, the bicarbonate in the polymer-electrolyte may decompose into hydroxide and CO2 over time, thereby leaving the polymer-electrolyte in the hydroxide form. This can affect the chemical stability, swelling, water absorption of the polymer-electrolyte, and other aspects of the MEA that may affect durability. In some embodiments, the MEA including an anion exchange polymer-electrolyte remains in contact with CO2 during the shutdown period. If this is not possible or is not performed, it may be beneficial to expose the MEA to CO2 for a period of time to ensure that it is in the bicarbonate form before the system is started again.

[0057] If a bipolar MEA is used for CO2 conversion, water will accumulate on the cathode side of the device, preventing CO x into the catalyst layer. The rate of water accumulation at the cathode is proportional to the current density. Shutting down the system or reducing the current density will reduce the rate of water accumulation at the cathode. If the flow of CO2 is not sufficient to remove water at a rate equal to or greater than the water accumulation rate under typical operating conditions, shutting down or reducing the current can be used to reduce the rate of water while maintaining water removal through the CO2 gas flow in order to purge excess water from the cathode and return to the desired operating conditions providing high current density and low voltage.

[0058] When a single electrolyzer or a stack of multiple electrolyzers is shut down, the continuous CO x The flow will remove CO x The reduction products (e.g., CO, CH4, and CH2CH2) and H2 leave only trace amounts of these compounds, which can be absorbed in the polymer-electrolyte and transported along with pure CO x At the anode, water is recirculated for a period of time and may be saturated with O2 and contain trace amounts of CO that cross the membrane from the cathode. xWhen the system is shut down, the continued circulation of water through the anode will remove gas-phase O2 bubbles from the anode chamber, but the anode will still be exposed to O2 dissolved in the anode water and other compounds from the cathode. These compounds may diffuse to the cathode during the shutdown period, exposing the cathode to O2 and other molecules after the current stops. If CO x Or if the water flow does not continue, the cathode contains a large concentration of H2 and other CO x , and the anode will contain oxygen bubbles. This can result in anode O2 to the cathode and cathode CO x and a larger crossover of the products to the anode.

[0059] Compared with running the stack at a higher temperature (e.g., 40° C.), turning on the stack or running the stack at room temperature will result in higher voltage and faster voltage decay. Low temperature operation can be avoided by various techniques, such as heating before starting current flow and circulating water through the anode of the stack. In some embodiments (e.g., if it is not possible to increase to the desired temperature before current flows), then the stack can be quickly brought to temperature and the operation of the stack at low temperature can be minimized by using a current from 0 directly to the desired current or above the desired current in a short period of time. The operating parameters described below address these challenges.

[0060] In some embodiments, current is applied to the MEA according to a specific current distribution. The current distribution can be different according to the operating mode, as further described below. The operating mode includes hydration (pre-running-in), running-in, normal operation, planned shutdown, and extended shutdown or storage. Other electrolyzer operating parameters that can be adjusted during these operating modes (usually to adjust the current according to a specific current distribution) include: (a) cathode gas composition, flow and pressure, (b) anode water composition and flow, and (c) temperature. In some embodiments, the voltage is controlled.

[0061] During operation of the electrolyzer, the applied current may be paused. A current pause may also be referred to as an off / on cycle, in which the current is turned off and then on one or more times. Typically, the applied current is reduced to zero (i.e., off) during a current pause, however in some embodiments it may be reduced to a non-zero level.

[0062] The following table describes the current profile, cathode gas composition and flow, anode water composition and flow, temperature and voltage profile during a specific operating mode. Also included are current efficiencies and example electrolyzer configurations. Hydration (pre-break-in)

[0063] In some embodiments, before any current is applied to the electrolyzer, the MEA undergoes a hydration step. This involves starting the reactant flow and heating the electrolyzer (or stack) so that a steady state is reached before applying current. Before stacking or electrolyzer assembly, the MEA is soaked in water to begin hydrating the MEA. After assembly, anode water and cathode CO2 flow and pressure are set. Dry or humidified CO2 flowing in this step may be beneficial, even if dry CO2 is used as input during longer periods of operation. Observe the anode outlet to confirm that no bubbles leave the outlet. If there are, it indicates that there is a significant CO2 crossing (from a pinhole in the membrane) or hardware leakage. If the desired operating temperature is higher than the environment, the electrolyzer is heated to the desired temperature after starting the anode water flow. In this step, the MEA continues to hydrate at the desired temperature.

[0064] Table 1: Example run parameters during hydration Run-in

[0065] The run-in period refers to the process of first applying to an MEA or stack until the operating conditions and performance match the desired long-term settings. In some embodiments, a process different from typical operation may help to achieve better performance when using an MEA for the first time. An MEA that has not been operated before may not be fully hydrated or may have structural changes due to the temperature increase during operation. In some embodiments, the current is ramped from a lower value to a higher value in a series of steps, rather than jumping directly to the desired operating value. A gradual linear ramp up may also be used. An example of a current profile is Figure 1A shown.

[0066] For example, the number of intermediate steps in a multi-step ramp up can be 1, 2, 3, 4, 5, or 6. The duration in each step can be the same or different. Example durations range from 30 minutes to 5 hours, such as 1 hour or 2 hours. Fig. 20 It was shown that slower ramps can lead to higher selectivity, possibly due to better hydration. In some embodiments, a duration of at least 1 hour is used at each intermediate step.

[0067] In embodiments where the operating temperature is reached before running-in (eg, during a hydration period), the temperature may be held constant at that temperature. In other embodiments, the temperature may be ramped up during the running-in process.

[0068] Table 2: Example operating parameters during run-in Normal operation

[0069] Cycling the stack off and on during normal operation may help maintain performance over extended periods of time. Stopping the current for as short as 5 microseconds, 500 microseconds, 5 seconds, or 30 seconds may improve current efficiency and / or reduce voltage. This is called a current pause. As shown below, in some embodiments, the current pause reduces the current to a non-zero level. For example, if the typical operating current density is 300 mA / cm 2 , then the current pause may involve reducing the current density to 50 mA / cm 2 In some embodiments, the voltage is controlled to achieve a similar cycling effect.

[0070] Low or no current flow results in less water flowing from the anode to the cathode of the electrolyzer (e.g., bipolar MEA) and can be used to remove water if it accumulates excessively at the cathode of the electrolyzer. Low or no current flow also increases the voltage at the cathode to the point where harmful substances that may accumulate on the catalyst surface can be oxidized. Examples of possible impurities are CO x Carbonaceous intermediates formed during reduction, metallic impurities (e.g. iron) or impurities introduced into the CO2 stream (e.g. H2S). The same effect can be achieved by directly controlling the stack or cell voltage to the desired value.

[0071] According to various embodiments, the current can be suspended at relatively frequent intervals (less than 10 hours, e.g., less than 2 hours) or at relatively infrequent intervals (more than tens of hours). Example operating conditions for frequent current suspension and relatively infrequent suspension are provided below in Tables 3 and 4, respectively.

[0072] When reducing the current from the operating current to zero or a lower second current density, various current profiles can be used. In some embodiments, a single step is used to reach the lower level immediately. In alternative embodiments, multiple steps are used or a continuous and gradual linear gradient can be used. Similarly, when returning to the operating current density, a single step can be used, or multiple steps or a continuous, gradual gradient program can be used to gradient the current.

[0073] Typically, the current profile or current pause schedule is such that the current on period is significantly longer than the pause period. Figure 1A Schematic example of a current pause arrangement, which may also be referred to as a current profile, is shown. Current density is shown on the y-axis and time is shown on the x-axis. Figure 1AAs can be seen in , the current-on period is separated by the current pause period at regular intervals. The interval is the duration of the current-on period. During the current pause period, the current density decreases from the operating current density (Jrun) to the pause current density (Jpause), which can be zero or non-zero, as shown above. For high production (throughput), the duration of the current pause period is significantly less than the current-on period. For example, the current-on period can be at least 3 times, 5 times, 10 times, 20 times, 50 times, 100 times, or 500 times the current pause period. The improvement in selectivity is a function of the previous selectivity of the current pause duration and the current-on duration. Therefore, a longer current pause duration can be used with a longer current-on duration. Example on / off durations are given below: Example current on duration Example Current Pause Duration 10-1000 hours 5 minutes to 10 hours 10-500 hours 5 minutes to 10 hours 10-100 hours 1 second to 1 hour 1-10 hours 500 microseconds to 20 minutes 3-60 minutes 500 microseconds to 10 minutes 3-30 minutes 500 microseconds to 5 minutes

[0074] exist Figure 1A In the example of FIG. 1 , the current pause schedule is constant for the duration of normal operation. In other embodiments, the intervals and / or pause durations can be changed during operation. For example, in advanced stages of operation, the current pauses can be programmed to be more frequent. The current pause schedule is typically implemented automatically using a controller as described herein. The controller is programmed or otherwise configured to implement the schedule. In some embodiments, a user can set a schedule that is automatically implemented during operation.

[0075] Also in Figure 1A In the example of , a single step is used to reduce the current density at the beginning of the pause period and return 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 can be ramped in multiple steps or continuously at the beginning and / or end of the current pause period. Figure 1B 1 shows a schematic example of reducing the current from the operating current density to the pause current density at the beginning of the current pause period. Similarly, Figure 1C A schematic example of returning to the operating current density at the end of the current pause period is shown. The current profile at the start can be selected independently of the current profile at the end of the pause period. For example, the current can be reduced in a single step and increased in multiple steps.

[0076] During the current pause, the cell voltage can be maintained at any value in a variety of values. In some cases, during the current pause, the anode and cathode are shorted (e.g., by a power supply or by connecting the electrodes with a metal or other conductor), in which case the cell voltage is at or near 0 volts. In some cases, during the current pause, the anode and cathode are allowed to float and the voltage of the electrolyzer is its open circuit voltage under the dominant condition, such as 0.8V-1.4V, 0.8V-1.2V or 0.9V-1.1V. The open circuit voltage represents the potential difference between the electrolyzer electrodes when no external current is applied to the electrolyzer or extracted from the electrolyzer. The open circuit voltage is the performance of the half-reaction potential at the anode and cathode. In some cases, during the current pause, the cell voltage is neither 0 volts (short) nor an open circuit voltage. On the contrary, the cell voltage is set to different voltages by applying a controlled voltage and / or a controlled current between the anode and cathode. In certain embodiments, during the pause in current flow, the cell voltage is maintained between about 0 and 1.4 volts, or between 0.9 and 1.1 volts.

[0077] According to various embodiments, flow to the cathode and / or anode may be stopped during the current pause, or allowed to continue. Table 3: Example operating parameters during normal operation - frequent current pauses Table 4: Example operating parameters during normal operation - less frequent current pauses Planned Closure

[0078] Sometimes, according to CO x Depending on the use of the electrolysis system, a planned shutdown may be performed, in which the system is shut down for a short period of time and then reopened. Examples of reasons for a planned shutdown include maintenance of some part of the system (e.g., replacing a filter on the anode water circulation loop, replacing a flow controller, or testing a temperature sensor), planned power outages, and the use of CO x Suspension of downstream processes that reduce products. Planned shutdowns have relatively short shutdown periods, lasting from a few minutes to a few days.

[0079] During the planned shutdown, the applied current is zero. According to various embodiments, it can be dropped to zero immediately (ie, a single step) or in multiple steps or a continuous ramp.

[0080] Table 5: Example operating parameters for a planned shutdown Extended closure and storage

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

[0082] Figure 1D A system 101 for controlling the operation of a carbon oxide reduction reactor 103 is depicted, which can include an electrolyzer containing an MEA, such as any one or more of those described herein. The reactor can include multiple electrolyzers or MEAs arranged in a stack. The system 101 includes an anode subsystem connected to the anode of the reduction reactor 103 and a cathode subsystem connected to the cathode of the reduction reactor 103.

[0083] As depicted, the cathode subsystem includes a carbon oxide source 109 configured to provide a feed stream of carbon oxides to the cathode of the reduction reactor 103, which during operation can produce an output stream comprising the product of the reduction reaction at the cathode. The product stream may also include unreacted carbon oxides and / or hydrogen. See 108.

[0084] The carbon oxide source 109 is connected to a carbon oxide flow controller 113, which is configured to control the volume or mass flow of carbon oxide to the reduction reactor 103. One or more other components can be set on the flow path from the flowing carbon oxide source 109 to the cathode of the reduction reactor 103. For example, an optional humidifier 104 can be provided on the path and configured to humidify the carbon oxide feed flow. The humidified carbon oxide can moisten one or more polymer layers of the MEA, thereby avoiding drying these layers. Another component that can be set on 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 a purge gas to one or more electrolyzers of the reduction reactor 103 during the period when the current is suspended. In some embodiments, allowing the purge gas to flow through the MEA cathode is conducive to the recovery of catalyst activity and / or selectivity. This may be at least partially due to blowing certain reaction intermediates away from the catalyst active site and / or removing water from the cathode. Examples of the purge gas include carbon dioxide, carbon monoxide, hydrogen, nitrogen, argon, helium, oxygen, and a mixture of any two or more of these gases.

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

[0086] In certain embodiments, the cathode subsystem is configured to controllably recycle unreacted carbon oxides from the outlet stream back to the cathode of the reduction reactor 103. In some embodiments, the output stream is treated to remove reduction products and / or hydrogen, and then the carbon oxides are recycled. Depending on the MEA configuration and operating parameters, the reduction products may be carbon monoxide, hydrogen, hydrocarbons (such as methane and / or ethylene), oxygen-containing organic compounds (such as formic acid, acetic acid), and any combination thereof. In certain embodiments, one or more components (not shown) for removing water from the product stream are disposed 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 to provide dry gas to, for example, a downstream process when needed. In some embodiments, the recycled carbon oxides may be mixed with fresh carbon oxides from a source 109 upstream of the cathode.

[0087] As depicted in Figure 1, the anode subsystem is configured to provide an anode feed 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), which is configured to provide fresh anode water to the recirculation loop, and the recirculation loop includes an anode water storage tank 119 and an anode water flow controller 111. The anode water flow controller 111 is configured to control the flow of anode water into or out of the anode of the reduction reactor 103. In the depicted embodiment, the anode water recirculation loop is connected to a component for adjusting the composition of the anode water. These components may include a water storage tank 121 and / or an anode water additive source 123. The water storage tank 121 is configured to supply water having a composition different from that of the water in the anode water storage tank 119 (and circulates in the anode water recirculation loop). In one example, the water in the water storage tank 121 is pure water, which can dilute the solutes or other components in the circulating anode water. The pure water may be regular deionized water or even ultrapure water having a resistivity of, for example, at least about 15 MOhm-cm or exceeding 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 can provide water or other reactant to the anode of reactor 103 where it at least partially reacts to produce an oxidation product such as oxygen. The product is provided in the reduction reactor outlet stream along with unreacted anode feed. Figure 1D Not shown is an optional separation component that may be provided in the path of the anode outlet stream and configured to concentrate or separate the oxidation products from the anode product stream.

[0089] Other control features may be included in the system 101. For example, the temperature controller may be configured to heat and / or cool the carbon oxide reduction reactor 103 at appropriate times during its operation. In the depicted embodiment, the temperature controller 105 is configured to heat and / or cool the anode water provided to the anode water recirculation loop. For example, the temperature controller 105 may include or be coupled to a heater and / or a cooler that can heat or cool the water in the anode water storage tank 119 and / or the water in the storage tank 121. In some embodiments, the system 101 includes a temperature controller that is configured to directly heat and / or cool components other than the anode water components. An example of such other components in an electrolyzer or stack is carbon oxides flowing to the cathode.

[0090] Depending on the stage of electrochemical operation, including whether to suspend the current to the carbon oxide reduction reactor 103, certain components of the system 101 can be operated to control non-electrical operations. For example, the system 101 can be configured to adjust the flow of carbon oxides toward the cathode and / or the flow of anode feed toward the anode of the reactor 103. Components that can be controlled for this purpose can include a carbon oxide flow controller 113 and an anode water controller 111.

[0091] In addition, depending on the stage of electrochemical operation, including whether the current is suspended, certain components of the system 101 can be operated to control the composition of the carbon oxide feed stream and / or the anode feed stream. For example, the water storage tank 121 and / or the anode water additive source 123 can be controlled to adjust the composition of the anode feed stream. In some cases, the additive source 123 can be configured to adjust the concentration of one or more solutes (such as one or more salts) in the aqueous anode feed stream.

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

[0093] In some embodiments, the carbon oxide electrolytic reduction system is configured to facilitate the removal of the reduction electrolyzer from other system components. This can be useful when the electrolyzer needs to be removed for storage, maintenance, refurbishment, etc. In the depicted embodiment, isolation valves 125a and 125b are configured to block the fluid flow from the electrolyzer 103 to the carbon oxide source to the cathode and back pressure controller 115, respectively. In addition, isolation valves 125c and 125d are configured to block the fluid flow from the electrolyzer 103 to the anode water inlet and outlet, respectively.

[0094] The carbon oxide reduction reactor 103 can also be operated under the control of one or more power supplies and associated controllers. See, block diagram 133. The power supply and controller 133 can be programmed or otherwise configured to control the current supplied to the electrodes in the reduction reactor 103 and / or control the voltage applied to the electrodes. The current and / or voltage can be controlled to perform the current arrangement and / or current distribution described elsewhere herein. For example, the power supply and controller 133 can be configured to periodically suspend the current applied to the anode and / or cathode of the reduction reactor 103. Any current distribution described herein can be programmed into the power supply and controller 133.

[0095] In certain embodiments, the power supply and controller 133 performs some, but not all, of the operations necessary to implement a desired current schedule and / or distribution in the carbon oxide reduction reactor 103. A system operator or other responsible personnel may act in conjunction with the power supply and controller 133 to fully define the current schedule and / or current distribution applied to the reduction reactor 103. For example, an operator may establish one or more current pauses beyond the set of current pauses programmed into the power supply and controller 133.

[0096] In certain embodiments, the power supply and controller act in conjunction with one or more other controllers or control mechanisms associated with other components of the system 101. For example, the power supply and controller 133 can act in conjunction with the controller to control carbon oxide delivery to the cathode, anode water delivery to the anode, adding pure water or additives to the anode water, and any combination of these features. In some embodiments, one or more controllers are configured to control or operate in conjunction to control any combination of the following functions: applying current and / or voltage to the reduction tank 103, controlling back pressure (e.g., via back pressure controller 115), supplying purge gas (e.g., using purge gas component 117), delivering carbon oxide (e.g., via carbon oxide flow controller 113), humidifying carbon oxide in the cathode feed stream (e.g., via humidifier 104), anode water flow into and / or out of the anode (e.g., via anode water flow controller 111), and anode water composition (e.g., via anode water source 105, pure water storage tank 121 and / or anode water additive component 123).

[0097] In the depicted embodiment, a voltage monitoring system 134 is used to determine the voltage across the anode and cathode of the MEA electrolyzer or across any two electrodes of the electrolyzer stack, for example, to determine the voltage across all electrolyzers in the multi-electrolyzer stack. The voltage determined in this way can be used to control the electrolyzer voltage during the current pause, the duration of the notification 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 electrolyzer 103 within a specified voltage range. For example, the power supply 133 can be configured to apply current and / or voltage to the electrodes of the reduction electrolyzer 103 in a manner that the electrolyzer voltage is maintained within a specified range during the current pause. For example, if during the current pause, the open circuit voltage of the electrolyzer deviates from a defined range (determined by the voltage monitoring system 134), the power supply can be configured to apply current or voltage to the electrodes so as to maintain the electrolyzer voltage within a specified range.

[0098] Electrolytic carbon oxide reduction systems (e.g. Figure 1D The system depicted) may employ a control system including one or more controllers and one or more controllable components (e.g., 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 (e.g., absorbance measurement tools), etc. Such sensors may be connected to the inlet and / or outlet of the MEA electrolyzer (e.g., in the flow field), in a storage tank for containing anode water, pure water, salt solution, etc., and / or in 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 the carbon oxide reduction electrolyzer, controlling the back pressure on the cathode outlet of such electrolyzer, supplying purge gas to the cathode inlet, delivering carbon oxide to the cathode inlet, humidifying carbon oxide in the cathode feed stream, allowing anode water to flow into and / or out of the anode, and controlling the anode feed composition. Any one or more of these functions can have a dedicated controller to control its function separately. Any two or more of these functions can share a controller. In some embodiments, a hierarchy of controllers is adopted, wherein at least one main controller provides instructions to more than two component controllers. For example, the system may include a main controller configured to provide high-level control instructions to (i) a power supply for the carbon oxide reduction electrolyzer, (ii) a cathode feed stream flow controller, and (iii) an anode feed stream flow controller. For example, a programmable logic controller (PLC) can be used to control various components of the system.

[0100] In certain embodiments, the control system is configured to apply current to a carbon oxide reduction electrolyzer including an MEA according to a current arrangement, which may have any of the features described herein. For example, the current arrangement may provide periodic pauses in the applied current. In some cases, the control system provides current pauses with a defined profile, such as the gradual and / or step changes described herein.

[0101] In certain embodiments, the control system is configured to control the flow of one or more feed streams (e.g., cathode feed streams, such as carbon oxide streams, and anode feed streams) in coordination with the current arrangement. For example, when the current applied to the MEA electrolyzer is suspended, the flow of carbon oxide or purge gas can be turned on, off, or otherwise adjusted.

[0102] In certain embodiments, the control system can maintain the salt concentration at a defined level and / or recycle the anode water. In certain embodiments, the salt concentration is adjusted in coordination with the arrangement of the current suspension applied to the MEA electrolyzer. Under the control of the control system, the system can, for example, (a) recirculate the anode water flowing out from the anode, (b) adjust the composition and / or flow of the anode water entering the anode, (c) return the water flowing out from the cathode to the anode water, and / or (d) adjust the composition and / or flow of the water recovered from the cathode stream, and then return to the anode. Note that (d) can explain the carbon oxide reduction products in the recovered water from the cathode. However, in some embodiments, this need not be considered, because some reduction products may be subsequently oxidized to harmless products at the anode.

[0103] The controller may include any number of processors and / or storage devices. The controller may include control logic such as software or firmware and / or may execute instructions provided from another source. The controller may be integrated with an electronic device for controlling the operation of the electrolyzer before, during, and after the reduction of carbon oxides. The controller may control various components or subcomponents of one or more electrolytic carbon oxide reduction systems. Depending on the processing requirements and / or system type, the controller may be programmed to control any process disclosed herein, such as gas delivery, temperature settings (e.g., heating and / or cooling), pressure settings, power settings (e.g., voltage and / or current delivered to the electrodes of the MEA electrolyzer), liquid flow settings, liquid delivery settings, and the quantitative distribution of purified water and / or salt solutions. These controlled processes may be connected or coupled to one or more systems that work in conjunction with the electrolytic carbon oxide reduction system.

[0104] In various embodiments, the controller includes an electronic device having various integrated circuits, logic, storage and / or software, which receive instructions, 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 digital signal processor (DSP), a chip defined as an application-specific integrated circuit (ASIC) and / or one or more microprocessors, or a microcontroller that executes program instructions (e.g., software). The program instructions may be instructions that are communicated to the controller in the form of various separate settings (or program files), thereby defining the operating parameters for executing the process on one or more components of the electrolytic carbon oxide reduction system. In some embodiments, the operating parameters may be part of a recipe defined by a process engineer so as to complete one or more processing steps during the generation of specific reduction products such as carbon monoxide, hydrocarbons, and / or other organic compounds.

[0105] In some embodiments, the controller can be part of or connected to a computer that is integrated with the system, connected to the system, otherwise networked with the system, or a combination thereof. For example, the controller can utilize remotely stored instructions (e.g., in the "cloud") and / or remotely executed. The computer can remotely access the system to monitor the current progress of the electrolysis operation, check the history of past electrolysis operations, check trends or performance indicators from multiple electrolysis operations, change the parameters of the current treatment, set the treatment steps to follow the current treatment, or start a new process. In some examples, a remote computer (e.g., a server) can provide a process recipe to the system via a network that can include a local area network or the Internet. The remote computer may include a user interface that can input or program parameters and / or settings, and then communicate these parameters and / or settings from the remote computer to the system. In some examples, the controller receives instructions in the form of data that specify parameters for each step in the treatment steps to be performed during one or more runs.

[0106] The controller may be distributed, such as by including one or more discrete controllers that are networked together and work toward a common purpose, such as applying current to the MEA electrolyzer and other process control described herein. An example of a distributed control system for such purposes includes one or more processors on the system for electrolytic reduction of carbon oxides and one or more processors located remotely (e.g., at the platform level or as part of a remote computer) that combine to control the process.

[0107] In certain embodiments, the electrolytic carbon oxide reduction system is configured and controlled to avoid salt precipitation in the MEA. Precipitated salts can block passages and / or have other effects that degrade the performance of the MEA electrolyzer. In some cases, the electrolyzer may become too dry, for example on the cathode side, because dry gaseous reactants remove too much water from the MEA, particularly on the cathode side. This problem can cause salt precipitation, which can be solved by controlling the water partial pressure in the gas inlet flow (for example, by humidifying the gaseous carbon oxide source gas). In some cases, the salt concentration in the anode water is high enough that it promotes the salt precipitation in the MEA. This problem can be solved by rinsing the MEA with pure water during the current pause. MEA Design Implementation Plan MEA Overview

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

[0109] When used, the cathode of the MEA promotes CO by combining the following three inputs: x Electrochemical reduction of CO x , and CO x Ions (e.g., protons) and electrons that undergo chemical reactions. The reduction reaction can produce CO, hydrocarbons, and / or organic compounds containing oxygen and hydrogen, such as methanol, ethanol, and acetic acid. When used, the anode of the MEA promotes an electrochemical oxidation reaction, such as electrolysis of water to produce elemental oxygen and protons. The cathode and anode can each contain a catalyst to promote their respective reactions.

[0110] The composition and arrangement of the layers in an MEA can contribute to the CO x To this end, the MEA can promote any one or more of the following conditions: (a) minimal parasitic reduction reactions at the cathode (non-CO x reduction reaction); (b) CO at the anode or elsewhere in the MEA x (c) maintain the physical integrity of the MEA during the reaction (e.g., prevent delamination of the MEA layers); (d) prevent CO x (e) prevent the crossover of the oxidation products (e.g., O2); (f) maintain a suitable environment at the cathode for oxidation; (g) provide a path for the desired ions to travel between the cathode and the anode while blocking the undesired ions; and (h) minimize the voltage loss. As explained herein, the presence of salt or salt ions in the MEA can contribute to some of all of these conditions. CO x Notes on Restoration

[0111] Polymer-based membrane assemblies (e.g., MEAs) have been used in various electrolysis systems (e.g., water electrolysis devices) and various current systems (e.g., fuel cells). However, in water electrolysis devices and fuel cells, CO x There are no or fewer problems encountered with the restore.

[0112] For example, for many applications, the x The reduced MEA requires a lifetime of about 50,000 hours or more (about five years of continuous operation), which is significantly longer than the expected lifetime of a fuel cell for automotive applications; for example, about 5,000 hours. And for various applications, compared with MEAs for fuel cells in automotive applications, the lifetime of a CO x Reduction MEAs use electrodes with relatively large surface areas. For example, for CO x The reduced MEA can use a surface area (excluding pores and other non-planar features) of at least about 500 cm 2 of electrodes.

[0113] CO can be implemented in an operating environment that promotes mass transport of specific reactant and product species and suppresses parasitic reactions. x Reduction reaction. Fuel cell and water electrolyzer MEAs are generally not capable of producing such an operating environment. For example, such MEAs may promote undesirable parasitic reactions, such as gaseous hydrogen evolution at the cathode and / or gaseous CO2 production at the anode.

[0114] In some systems, CO x The rate of the reduction reaction is affected by the gaseous CO x Limitations on reactant availability. In contrast, the rate of water electrolysis is not significantly limited by reactant availability: liquid water tends to readily access both the cathode and the anode, and electrolyzers can be operated at close to the highest possible current density. MEA Configuration

[0115] In certain embodiments, the MEA has a cathode layer, an anode layer, and a polymer electrolyte membrane (PEM) between the anode layer and the cathode layer. The polymer electrolyte membrane provides ionic connectivity between the anode layer and the cathode layer while preventing electronic connectivity that would result in a short circuit. The cathode layer includes a reduction catalyst and a first ion-conducting polymer. The cathode layer may also include an ion conductor and / or an electronic conductor. The anode layer includes an oxidation catalyst and a second ion-conducting polymer. The anode layer may also include an ion conductor and / or an electronic conductor. The PEM includes 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 includes 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 includes a fifth ion-conducting polymer.

[0118] For certain MEA designs, there are three classes of ion conducting polymers available: anion conductors, cation conductors, and mixed cation and anion conductors. In certain embodiments, at least two of the first, second, third, fourth, and fifth ion conducting polymers are from different classes of ion conducting polymers. Conductivity and selectivity of ion-conducting polymers for MEA layers

[0119] The term "ion conducting polymer" is used herein to describe polymer electrolytes having a specific conductivity greater than about 1 mS / cm for anions and / or cations. The term "anion conductor" describes an ion conducting polymer that conducts primarily anions (although there may still be some small amount of cation conduction) and has an anion migration number greater than about 0.85 at a thickness of about 100 microns. The terms "cation conductor" and / or "cation conducting polymer" describe an ion conducting polymer that conducts primarily cations (e.g., there may still be an occasional amount of anion conduction) and has a cation migration number greater than about 0.85 at a thickness of about 100 microns. For ion conducting polymers described as conducting both anions and cations ("cation and anion conductors"), the migration numbers for both anions and cations are no greater than about 0.85 or less than about 0.15 at a thickness of about 100 microns. To say that a material conducts ions (anions and / or cations) is to say that the material is an ion conducting material or ionomer. Examples of each class of ion conducting polymers are provided in the following table.

[0120] Some of the A-type ion-conducting polymers are known by trade names such as: 2259-60 (PallRAI), AHA from Tokuyama Co, FAA-(fuma tech GbbH), Solvay's Morgane ADP or Tosoh anion exchange membrane materials SF-17. Other Class A ion-conducting polymers include: Ionomr's HNN5 / HNN8, Fumatech's FumaSep, Orion's TM1, and W7energy's PAP-TP. Some Class C ion-conducting polymers are known by trade names such as: (DuPont TM ), (Gore), (fuma tech GmbH), and Various formulations of PFSA (Solvay). For CO x Reduced bipolar MEA

[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 certain embodiments, 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 certain embodiments, the cathode buffer layer between the cathode and the PEM comprises an anion conducting polymer. In certain embodiments, the anode buffer layer between the anode and the PEM comprises a cation conducting polymer.

[0122] During operation, an MEA with a bipolar interface moves ions through the polymer-electrolyte, electrons through the metal and / or carbon in the cathode and anode layers, and liquids and gases through the pores in the layers.

[0123] In embodiments where an anion conducting polymer is used in the cathode and / or cathode buffer layer, the MEA can reduce or prevent undesirable reactions that produce undesirable products and reduce the overall efficiency of the electrolyzer. In embodiments where a cation conducting polymer is used in the anode and / or anode buffer layer, undesirable reactions that reduce the production of desired products and reduce the overall efficiency of the electrolyzer can be reduced or prevented.

[0124] For example, at potential levels used for 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 of the CO2 reduction reactor, and can move across the MEA and reach the cathode, where they can be reduced to produce hydrogen gas. The extent to which this parasitic reaction can proceed is a function of the concentration of hydrogen ions present at the cathode. Therefore, the MEA can use anion conductive materials in the cathode layer and / or the cathode buffer layer. The anion conductive material at least partially blocks the hydrogen ions from reaching the catalytic sites on the cathode. Therefore, the parasitic production of hydrogen gas generation is reduced, and the production rate of CO or other products and the overall efficiency of the process are improved.

[0125] Another reaction that can be avoided is the reaction of carbonate or bicarbonate ions at the anode to produce CO2. Hydrated carbonate or bicarbonate ions can be produced from CO2 at the cathode. If these ions reach the anode, they can react with hydrogen ions to produce and release gaseous CO2. The result is a net movement of CO2 from the cathode to the anode, where it does not react and is lost with the oxidation products. In order to prevent carbonate and bicarbonate ions produced at the cathode from reaching the anode, the anode and / or the anode buffer layer may include a cation-conducting polymer that at least partially blocks the transport of negative ions such as bicarbonate ions to the anode.

[0126] Therefore, in some designs, the bipolar membrane structure raises the pH at the cathode to promote CO2 reduction, while the cation-conducting polymer (e.g., proton exchange layer) prevents the migration of large amounts of CO2 and CO2 reduction products (e.g., bicarbonate) to the anode side of the electrolyzer.

[0127] Figure 2 Shown for CO x Example MEA 200 for reduction. MEA 200 has a cathode layer 220 and an anode layer 240 separated by an ion conducting polymer layer 260 that provides a path for ions to travel between the cathode layer 220 and the anode layer 240. In certain embodiments, the cathode layer 220 includes an anion conducting polymer and / or the anode layer 240 includes a cation conducting polymer. In certain embodiments, the cathode layer and / or the anode layer of the MEA are porous. The pores can facilitate gas and / or fluid transport and can increase the amount of catalyst surface area available for reaction.

[0128] Ion conducting layer 260 may include two or three sublayers: polymer electrolyte membrane (PEM) 265, optional cathode buffer layer 225 and / or 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 so that reactants and products of the cathode cannot reach the anode through gas and / or liquid transport, and vice versa. In certain embodiments, PEM layer 265 is non-porous. Example properties of anode buffer layer and cathode buffer layer are provided elsewhere herein. In certain embodiments, the ion conducting layer includes only a single layer or two sublayers.

[0129] Figure 3 A CO2 electrolyzer 303 is shown, which is configured to receive water and CO2 (e.g., humidified or dry gaseous CO2) as reactants at a cathode 305 and to emit CO as a product. The electrolyzer 303 is also configured to receive water as a reactant and to emit gaseous oxygen at an anode 307. The electrolyzer 303 includes a bipolar layer having an anion conducting polymer 309 adjacent to the cathode 305 and a cation conducting polymer 311 (illustrated as a proton exchange membrane) adjacent to the anode 307.

[0130] As shown in the enlarged inset of the bipolar interface 313 in the electrolyzer 303, the cathode 305 includes an anion exchange polymer (in this example, it is the same anion conducting polymer 309 in the bipolar layer) conductive carbon support particles 317, and metal nanoparticles 319 supported on the support particles. CO2 and water are transmitted through pores such as pores 321 and reach the metal nanoparticles 319, where they react, in this case with hydroxide ions, to produce bicarbonate ions and reduction reaction products (not shown). CO2 can also reach the metal nanoparticles 319 by being transmitted within the anion exchange polymer 315.

[0131] Hydrogen ions are transported from the anode 307 and pass through the cation conducting polymer 311 until they reach the bipolar interface 313, where the anion exchange polymer 309 blocks their further transport to the cathode. At the interface 313, the hydrogen ions can react with bicarbonate or carbonate ions to form carbonic acid (H2CO3), which can decompose to produce CO2 and water. As explained herein, the CO2 produced can be provided in the gas phase and a path should be provided in the MEA back to the cathode 305, where it can be reduced. The cation conducting polymer 311 blocks anions such as bicarbonate ions from transporting to the anode, where they can react with protons and release CO2, which will not be able to participate in the reduction reaction at the cathode.

[0132] As shown, a cathode buffer layer having an anion conducting polymer can work in conjunction with the cathode and its anion conducting polymer to block proton transport to the cathode. Although an MEA using ion conducting polymers of the appropriate conductivity type in the cathode, anode, cathode buffer layer, and (if present) anode buffer layer can block cation transport to the cathode and anion transport to the anode, cations and anions may still be in contact in the interior regions of the MEA (e.g., in the membrane layers).

[0133] like Figure 3 As shown, bicarbonate 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. It has been observed that MEAs sometimes delaminate, which may be due to the production of this gaseous CO2, which has no easy escape path.

[0134] The stratification problem can be solved by using a cathode buffer layer with an inert filler and associated pores. A possible explanation for its effectiveness is that the pores provide a path for gaseous carbon dioxide to escape back to the cathode, where it can be reduced. In some embodiments, the cathode buffer layer is porous, but at least one layer between the cathode layer and the anode layer is non-porous. This can prevent gas and / or bulk liquid from passing between the cathode layer and the anode layer while still preventing stratification. For example, a non-porous layer can prevent water from flowing directly from the anode to the cathode. The porosity of the various layers in the MEA is further described elsewhere in this article. Example of a bipolar MEA

[0135] For example, the MEA includes a cathode layer, an anode layer, a membrane layer, and a cathode buffer layer, the cathode layer including a reduction catalyst and a first anion conductive polymer (e.g., Susta inion, FumaSep FAA-3, Tokuyama anion exchange polymer), the anode layer including an oxidation catalyst and a first cation conductive polymer (e.g., PFSA polymer), the membrane layer including a second cation conductive polymer and disposed between the cathode layer and the anode layer to conductively connect the cathode layer and the anode layer, the cathode buffer layer including a second anion conductive polymer (e.g., Susta inion, FumaSep FAA-3, Tokuyama anion exchange polymer) and disposed between the cathode layer and the membrane layer to conductively connect the cathode layer and the membrane layer. In this example, the cathode buffer layer may have a porosity of about 1 to 90% by volume, but may additionally or alternatively have any suitable porosity (including, for example, no porosity). In other examples, the cathode buffer layer can have any suitable porosity (eg, 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 less than 20%, and in specific embodiments, 0.1-20%, 1-10%, or 5-10%. Porosity within these ranges is sufficient to allow water and / or CO2 to move without loss of ionic conductivity. Porosity can be measured as described further below.

[0137] In a related example, the membrane electrode assembly may include an anode buffer layer that includes a third cation-conducting polymer and is disposed between the membrane layer and the anode layer to conductively connect the membrane layer and the anode layer. The porosity of the anode buffer layer is preferably about 1 to 90 volume %, but may additionally or alternatively have any suitable porosity (including, for example, no porosity). However, in other arrangements and examples, the anode buffer layer may have any suitable porosity (e.g., 0.01-95%, 0.1-95%, 0.01-75%, 1-95%, 1-90%). As with the cathode buffer layer, in some embodiments, the porosity is less than 20%, such as 0.1-20%, 1-10%, or 5-10%.

[0138] In one example, the anode buffer layer can be used in an MEA having: a cathode catalyst layer having an anion exchange polymer, a cathode buffer layer having an anion exchange polymer, a membrane having a cation exchange polymer, and an anode buffer layer having an anion exchange polymer. In such a structure, the anode buffer layer can be porous to facilitate water transport to the membrane / anode buffer layer interface. Water will split at this interface, thereby generating protons that pass through the membrane and hydroxides that move to the anode catalyst layer. One advantage of this structure is that a low-cost water oxidation catalyst that is only stable under alkaline conditions (e.g., NiFeO x ).

[0139] In another specific example, the membrane electrode assembly includes a cathode layer, an anode layer, a membrane layer and an anode buffer layer, the cathode layer includes a reduction catalyst and a first anion conductive polymer (e.g., Sus tainion, FumaSep FAA-3, Tokuyama anion exchange polymer), the anode layer includes an oxidation catalyst and a first cation conductive polymer, the membrane layer includes a second anion conductive polymer (e.g., Sus ta inion, FumaSep FAA-3, Tokuyama anion exchange polymer) and is arranged between the cathode layer and the anode layer to conductively connect the cathode layer and the anode layer, and the anode buffer layer includes a second cation conductive polymer and is arranged between the anode layer and the membrane layer to conductively connect the anode layer and the membrane layer.

[0140] An 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 will form at the membrane / anode buffer layer interface. The pores in the anode buffer layer can facilitate water removal. One advantage of this structure is the use of acid-stable (e.g., IrO x ) water oxidation catalyst.

[0141] In a related example, the membrane electrode assembly may include a cathode buffer layer, which includes a third anion conductive polymer and is disposed between the cathode layer and the membrane layer to conductively connect the cathode layer and the membrane layer. The third anion conductive polymer may be the same as or different from the first and / or second anion conductive polymer. The porosity of the cathode buffer layer is preferably about 1 to 90 volume %, but may additionally or alternatively have any suitable porosity (including, for example, no porosity). However, in other arrangements and examples, the cathode buffer layer may have any suitable porosity (e.g., 0.01-95%, 0.1-95%, 0.01-75%, 1-95%, 1-90%). In some embodiments, the porosity is less than 20%, and in specific embodiments is 0.1-20%, 1-10%, or 5-10%.

[0142] In one example, the cathode catalyst layer consisted of 4 nm diameter Au nanoparticles supported on Vulcan XC72R carbon and mixed with TM1 (mTPN-1) anion exchange polymer electrolyte (from Orion). The layer thickness was ~15 um, Au / (Au+C) = 20 wt%, the mass ratio of TM1 to catalyst was 0.32, and the mass loading was 1.4-1.6 mg / cm 2 (Total Au+C), estimated porosity 0.56. The anion exchange polymer layer is composed of TM1 and PTFE particles. The diameter of PTFE is about 200nm. The molecular weight of TM1 is 30k-45k. The layer thickness is ~15um. PTFE can introduce a porosity of about 8%. The proton exchange membrane layer is composed of perfluorosulfonic acid polymer (such as Nafion 117). The thickness is about 125um. The membrane forms a continuous layer that prevents the large-scale movement of gases (CO2, CO, H2) through the layer. The anode catalyst layer is composed of 10um thick Ir or IrOx nanoparticles (100-200nm agglomerates). For CO x Reduced anion exchange membrane-only MEA

[0143] In some embodiments, the MEA does not include a cation conducting polymer layer. In such embodiments, the electrolyte is not a cation conducting polymer and the anode (if it includes an ion conducting polymer) does not include a cation conducting polymer. Examples are provided herein.

[0144] Only the MEA of AEM allows negative ions to conduct across the MEA. In embodiments where there is no MEA layer with significant conductivity to cations, hydrogen ions have limited mobility in the MEA. In some embodiments, only the membrane of AEM provides a high pH environment (e.g., at least about pH 7), and can promote CO2 and / or CO reduction by suppressing the parasitic reaction of hydrogen evolution at the cathode. Like other MEA designs, only the MEA of AEM allows ions (especially negative ions, such as hydroxide ions) to move through the polymer-electrolyte. In some embodiments, the pH value may be lower; pH values ​​of 4 or higher may be sufficient to suppress hydrogen precipitation. Only the MEA of AEM also allows electrons to move to and through the metal and carbon in the catalyst layer. In embodiments, there are holes in the anode layer, cathode layer and / or PEM, and only the MEA of AEM allows liquid and gas to move through the holes.

[0145] In certain embodiments, the AEM-only MEA comprises an anion exchange polymer electrolyte membrane with an electrocatalyst layer on either side: cathode and anode. In some embodiments, one or both electrocatalyst layers further comprise an anion exchange polymer electrolyte.

[0146] In certain embodiments, an AEM-only MEA is formed by depositing cathode and anode electrocatalyst layers onto porous conductive supports such as gas diffusion layers to form gas diffusion electrodes (GDEs), and sandwiching an anion exchange membrane between the gas diffusion electrodes.

[0147] In certain embodiments, only AEM's MEA is used for CO2 reduction. The use of anion exchange polymer electrolytes avoids low pH environments that are not conducive to CO2 reduction. In addition, when AEM's are used, water is removed from the cathode catalyst layer, thereby preventing water accumulation (flooding), which can block the transport of reactant gases in the electrolyzer cathode.

[0148] The transport of water in the MEA occurs through a variety of mechanisms, including diffusion and electroosmotic drag. In some embodiments, at the current density of the CO2 electrolysis device described herein, electroosmotic drag is the main mechanism. When ions move through the polymer electrolyte, water is dragged along with the ions. For cation exchange membranes, such as Nafion membranes, the amount of water transport is well characterized and is understood to depend on the pretreatment / hydration of the membrane. Protons move from positive potential to negative potential (anode to cathode), each of which carries 2-4 water molecules, depending on the pretreatment. In anion exchange polymers, the same type of effect occurs. Hydroxide, bicarbonate or carbonate ions "drag" water molecules as they move through the polymer electrolyte. In anion exchange MEA, ions move from negative voltage to positive voltage, therefore from cathode to anode, and they carry water molecules along with them, moving water from cathode to anode in the process. In certain embodiments, only the MEA of the AEM is used for the CO reduction reaction. Unlike the CO2 reduction reaction, CO reduction does not produce carbonate or bicarbonate anions, which are transported to the anode and release valuable reactants.

[0149] Figure 4 An example configuration of a CO2 reduction MEA 401 having a cathode catalyst layer 403, an anode catalyst layer 405, and an anion conducting PEM 407 is shown. In certain embodiments, the cathode catalyst layer 403 includes metal catalyst particles (e.g., nanoparticles) that are not supported or supported on a conductive substrate (e.g., carbon particles). In some embodiments, the cathode catalyst layer 403 additionally includes an anion conducting polymer. The metal catalyst particles can catalyze CO2 reduction, particularly at a pH greater than 7. In certain embodiments, the anode catalyst layer 405 includes metal oxide catalyst particles (e.g., nanoparticles) that are not supported or supported on a conductive substrate (e.g., carbon particles). In some embodiments, the anode catalyst layer 403 additionally includes 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. The anion conducting PEM 407 may comprise any of a variety of anion conducting polymers, such as HNN5 / HNN8 from Ionomr, FumaSep from Fumatech, TM1 from Orion, PAP-TP from W7energy, Sustainion from Dioxide Materials, etc. These and other anion conducting polymers may be used with an ion exchange capacity (IEC) of 1.1 to 2.6, a working pH range of 0-14, tolerable solubility in certain organic solvents, reasonable thermal and mechanical stability, good ionic conductivity / ASR, and acceptable water absorption / swelling ratios. The polymer may be chemically exchanged prior to use to replace the halogen anions with certain anions.

[0150] like Figure 4 As shown, CO2, such as CO2 gas, can be provided to the cathode catalyst layer 403. In certain embodiments, CO2 can be provided via a gas diffusion electrode. At the cathode catalyst layer 403, CO2 reacts to produce a gas generally represented by C x O y H zThe anions produced at the cathode catalyst layer 403 may include hydroxide, carbonate and / or bicarbonate. These anions may diffuse, migrate or otherwise move to the anode catalyst layer 405. At the anode catalyst layer 405, an oxidation reaction may occur, such as oxidation of water to produce diatomic oxygen and hydrogen ions. In some applications, hydrogen ions may react with hydroxide, carbonate and / or bicarbonate to produce water, carbonic acid and / or CO2. Fewer interfaces produce lower resistance. In some embodiments, a strongly alkaline environment is maintained to achieve C2 and C3 hydrocarbon synthesis.

[0151] Figure 5 An example configuration of a CO reduction MEA 501 is shown having a cathode catalyst layer 503, an anode catalyst layer 505, and an anion conducting PEM 507. In general, the configuration of the MEA 501 may be similar to Figure 4 However, the cathode catalyst may be selected to promote the CO reduction reaction, which means that different reduction catalysts will be used in the CO and CO2 reduction embodiments.

[0152] In some embodiments, an AEM-only MEA may be advantageous for CO reduction. The water absorption of the AEM material may be selected to help regulate moisture at the catalyst interface, thereby improving the CO availability of the catalyst. For this reason, an AEM-only membrane may be advantageous for CO reduction. Bipolar membranes are more advantageous for CO reduction due to better resistance to CO2 dissolution and crossover in alkaline anolyte media.

[0153] In various embodiments, cathode catalyst layer 503 includes metal catalyst particles (e.g., nanoparticles) that are not supported or supported on a conductive substrate (e.g., carbon particles). In some embodiments, cathode catalyst layer 503 also includes an anion conducting polymer. In certain embodiments, anode catalyst layer 505 includes metal oxide catalyst particles (e.g., nanoparticles) that are not supported or supported on a conductive substrate (e.g., carbon particles). In some embodiments, anode catalyst layer 503 also includes an anion conducting polymer. Examples of metal oxide catalyst particles for anode catalyst layer 505 may include about Figure 4 The anion conducting PEM 507 may include any of a variety of anion conducting polymers, such as Figure 4 Those identified by PEM 407.

[0154] like Figure 5 As shown, CO gas may be provided to the cathode catalyst layer 503. In certain embodiments, CO may be provided through a gas diffusion electrode. At the cathode catalyst layer 503, CO reacts to produce ax O y H z of the reduction product.

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

[0156] While the general configuration of MEA 501 is similar to that of MEA 401, there are certain differences in the MEA. First, for CO reduction, the MEA may be wetter, thereby helping to have more -H on the catalyst surface. Also, for CO2 reduction, a large amount of CO2 may dissolve and then transfer to the anode of the AEM-only MEA, such as Figure 4 As shown. For CO reduction, it is unlikely that there is significant CO gas transition. In this case, the reaction environment can be very alkaline. MEA materials (including catalysts) can be selected to have good stability in high pH environments. In some embodiments, thinner membranes can be used for CO reduction rather than CO2 reduction. Example of MEA with AEM only

[0157] 1. Copper metal (USRN 40nm thick Cu, ~0.05mg / cm 2 ) was deposited onto a porous carbon sheet (Sigracet 39BC gas diffusion layer). Ir metal nanoparticles were drop cast at a concentration of 3 mg / cm 2 The anion exchange membrane (25-50 μm, 80 mS / cm 2 OH- conductivity, 2-3mS / cm 2 HCO3 - conductivity, 33-37% water absorption) sandwiched between a porous carbon sheet with an electrocatalyst layer and a titanium sheet, where the electrocatalyst layer faces the membrane.

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

[0159] Various features and examples of MEAs are described in U.S. Patent Application Publication No. US 2017 / 0321334, published on November 9, 2017, and U.S. Patent Application Publication No. 20190226103, published on July 25, 2019, which are incorporated herein by reference in their entirety. All publications mentioned herein are incorporated by reference in their entirety, as if fully set forth herein. Cathode Catalyst Layer - General Structure

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

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

[0162] Examples of materials that can be used to reduce 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 material. Other catalyst materials may 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 material. The choice of catalyst depends on the specific reaction being performed at the cathode of the CRR.

[0163] The catalyst may be in the form of nanoparticles ranging in size from about 1-100 nm, or particles ranging in size from about 0.2-10 nm, or particles ranging in size from about 1-1000 nm, or any other suitable range. In addition to nanoparticles and larger particles, thin films and nanostructured surfaces may also be used.

[0164] If used, the conductive 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 arrangement, the conductive support particles are Vulcan carbon. The conductive support particles can be nanoparticles. The size range of the conductive support particles is about 20nm to 1000nm or any other suitable range. It is particularly useful if the conductive support particles are compatible with the chemicals present in the cathode when the CRR is running, are reduction stable, and have a high hydrogen production overpotential so that they do not participate in any electrochemical reaction.

[0165] For composite catalysts such as Au / C, example metal nanoparticle sizes can be in the range of about 2nm-20nm and carbon size as a supporting material can be in the range of about 20-200nm. For pure metal catalysts such as Ag or Cu, particles can have a wide range of grain sizes from 2nm to 500nm. Agglomerates can even be larger to the micrometer range.

[0166] Typically, such conductive support particles are larger than reducing catalyst particles, and each conductive support particle may carry many reducing catalyst particles. Figure 6 6 is a schematic diagram showing possible configurations of two different types of catalysts supported on catalyst support particles 610 (e.g., carbon particles). A first type of catalyst particles 630 and a second type of second catalyst particles 650 are attached to the catalyst support particles 610. In various configurations, only one type of catalyst particles or more than two types of catalyst particles are attached to the catalyst support particles 610.

[0167] In certain embodiments it may be useful to use two types of catalysts. For example, one catalyst may be good at one reaction (e.g. CO2→CO), while a second catalyst is good at another reaction (e.g. CO→CH4). Overall, the catalyst layer will perform the conversion of CO2 to CH4, but different steps in the reaction will be performed on different catalysts.

[0168] The conductive support can also be in forms other than particles, including tubes (eg, carbon nanotubes) and sheets (eg, graphene). Structures with a high surface area to volume ratio can be used to provide attachment sites for catalyst particles.

[0169] In addition to the reducing catalyst particles and the conductive support particles, the cathode catalyst layer may include an ion-conducting polymer. There is a trade-off in selecting the amount of cathode ion-conducting polymer in the cathode. It is important to include enough cathode ion-conducting polymer to provide sufficient ionic conductivity. But it is also important that the cathode is porous so that reactants and products can easily move through the cathode and maximize the amount of surface area of ​​the catalyst available for the reaction. In various arrangements, the cathode ion-conducting polymer accounts for 30-70wt%, 20-80wt% or 10-90wt% of the material in the cathode layer or any other suitable range. The wt% of the ion-conducting polymer in the cathode is selected to produce cathode layer porosity and ionic conductivity, thereby providing the highest current density for COx reduction. In some embodiments, it may be 20-60wt% or 20-50wt%. An exemplary thickness range for the cathode catalyst layer is about 80nm-300μm.

[0170] In addition to the reducing catalyst particles, the cathode ion-conducting polymer, and (if present) the conductive support, the cathode catalyst layer may include other additives, such as PTFE.

[0171] In addition to the polymer:catalyst mass ratio, the catalyst layer can be characterized by the mass loading (mg / cm 2 ) and porosity. Porosity can be determined in a variety of ways. In one method, the loading of each component (e.g., catalyst, support, and polymer) is multiplied by its respective density. These are added together to determine the thickness of the material occupied by these components. This is then divided by the known total thickness to obtain the percentage of the layer filled by the material. The resulting percentage is then subtracted from 1 to obtain the percentage of the layer that is considered to be filled with air, i.e., the porosity. Methods such as mercury intrusion or image processing of TEM images can also be used.

[0172] Examples of cathode catalyst layers for CO, methane and ethylene / ethanol production are given below. CO production: Au nanoparticles with a diameter of 4 nm were loaded on Vulcan XC72R carbon and mixed with TM1 anion exchange polymer electrolyte from Orion. The layer thickness was about 15 μm, Au / (Au+C)=30%, the mass ratio of TM1 to catalyst was 0.32, and the mass loading was 1.4-1.6 mg / cm 2 , the estimated porosity is 0.47 Methane production: Cu nanoparticles of 20-30 nm size were supported on Vulcan XC72R carbon and mixed with FAA-3 anion exchange solid polymer electrolyte obtained from Fumatech. The mass ratio of FAA-3 to catalyst was 0.18. The estimated Cu nanoparticle loading was ~7.1 μg / cm 2, 1-100 μg / cm 2 In a wider range Ethylene / ethanol production: Cu nanoparticles of 25-80 nm size, mixed with FAA-3 anion exchange solid polymer electrolyte obtained from Fumatech. The mass ratio of FAA-3 to catalyst was 0.10. Deposited on Sigracet 39BC GDE for neat AEM or on MEA electrode assembly. Estimated Cu nanoparticle loading was 270 μg / cm 2 .

[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 promotes the movement of water and prevents it from being trapped in the cathode catalyst layer. The trapped water will hinder the CO x Entering the catalyst and / or hindering the reaction products from moving out of the cathode catalyst layer.

[0175] Water management challenges are unique to CRRs in many ways. For example, CRRs use much lower gas flow rates than the oxygen electrode of a PEM fuel cell. Gas-phase water removal is determined by the gas volume flow rate, so much less gas-phase water removal is performed in a CRR. CRRs can also operate at higher pressures than fuel cells (e.g., 100 psi-450 psi); at higher pressures, the same molar flow rate results in lower volume flow rates and lower gas-phase water removal. As a result, liquid water in the MEA of the CRR will be removed. For some MEAs, the ability to remove gas-phase water is further limited by temperature limitations, which do not exist in fuel cells. For example, the reduction of CO2 to CO can be carried out at about 50°C, while the production of ethylene and methane can be carried out at 20°C-25°C. This is compared to the typical operating temperature of a fuel cell, which is 80°C to 120°C. As a result, there is more liquid-phase water to remove.

[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 conductive support; layer thickness; distribution of catalyst throughout the layer; and distribution of ion-conducting polymer across the layer and around the catalyst.

[0177] The porous layer allows an outflow path for water. In some embodiments, the pore size distribution of the cathode catalyst layer includes pores with a size of 1nm-100nm and pores with a size of at least 1 micron. This size distribution can help remove water. The porous structure can be formed by one or more of the following: pores within the carbon support material; stacking pores between stacked spherical carbon nanoparticles; secondary stacking pores (micrometer scale) between agglomerated carbon spheres; or porosity introduced by an inert filler (e.g., PTFE), wherein the interface between PTFE and carbon also produces irregular pores ranging from hundreds of nanometers to microns.

[0178] The cathode catalyst layer can have a thickness that aids in water management. Using a thicker layer allows the catalyst, and thus the reaction, to be distributed over a larger volume. This spreads out the distribution of water and makes it easier to manage.

[0179] Ion-conducting polymers with non-polar hydrophobic backbones can be used in the cathode catalyst layer. In some embodiments, the cathode catalyst layer can include a hydrophobic polymer such as PTFE in addition to the ion-conducting polymer. In some embodiments, the ion-conducting polymer can be a component of a copolymer that also includes a hydrophobic polymer. Gas transport (cathode catalyst layer)

[0180] The cathode catalyst layer can be configured for gas transport. Specifically, CO x is transported to the catalyst, and the gas-phase reaction products (such as CO, ethylene, methane, etc.) are transported outside the catalyst layer.

[0181] Certain challenges associated with gas transport are unique to CRR. Gas transport to and from the cathode catalyst layer—CO x Input and output of products such as CO, ethylene and methane. In a PEM fuel cell, a gas (O2 or H2) is input, but no material or product water is output. In a PEM water electrolysis device, water is the reactant and O2 and H2 are the gaseous products.

[0182] Gas transport is affected by operating conditions including pressure, temperature, and flow rate through the reactor. Properties of the cathode catalyst layer that affect gas transport include: porosity; pore size and distribution; layer thickness; and ionomer distribution.

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

[0184] The ionomer can have several functions, including holding the particles of the catalyst layer together and allowing ions to move through the cathode catalyst layer. In some cases, the interaction between the ionomer and the catalyst surface can produce a favorable CO x The cathode catalyst layer is a catalyst that is used to generate a reducing environment, thereby increasing the selectivity for the desired product and / or reducing the voltage required for the reaction. Importantly, the ionomer is an ion-conducting polymer that allows ions to move across the cathode catalyst layer. For example, hydroxide, bicarbonate, and carbonate ions are removed from the cathode catalyst layer by the CO generation. x The reduced catalyst surface is removed. In the following description, the ionomer in the cathode catalyst layer may be referred to as a first ion-conducting polymer.

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

[0186] In some embodiments, the first ion-conducting polymer may include one or more covalently bound positively charged functional groups configured to transport mobile negatively charged ions. The first ion-conducting polymer may be selected from aminated tetramethylpolyphenylene; poly(ethylene-co-tetrafluoroethylene)-based quaternary ammonium polymer; quaternized polysulfone), blends thereof, and / or any other suitable ion-conducting polymer. The first ion-conducting polymer may be configured to dissolve a salt of bicarbonate or hydroxide.

[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 may be selected from polyethers capable of transporting cations and anions and polyesters capable of transporting cations and anions. The first ion-conducting polymer may be selected from polyethylene oxide, polyethylene glycol, polyvinylidene fluoride, and polyurethane.

[0188] Cationic and anionic conductors will increase the pH (compared to pure cationic conductors). In addition, in some embodiments, it may be advantageous to use cationic and anionic conductors to promote acid-base recombination in a larger volume rather than at the 2D interface of the anionic and cation conductive polymers. This can disperse the formation of water and CO2, heat generation, and potentially reduce membrane resistance by reducing barriers to acid-base reactions. All of these can be beneficial in helping to avoid accumulation of products, heat, and reducing resistive losses in the MEA, resulting in lower cell voltages.

[0189] Typical anion conducting polymers have a polymer backbone to which covalently bound positively charged functional groups are attached. In some embodiments, these may include positively charged nitrogen groups. In some embodiments, the polymer backbone is non-polar, as described above. The polymer may be of any suitable molecular weight, e.g., 25000 g / mol-150000 g / mol, but it will be appreciated that polymers outside this range may be used.

[0190] Special challenges for ion-conducting polymers in CRRs include: CO2 can dissolve or solubilize polymer electrolytes, making them less mechanically stable, prone to swelling, and allowing the polymers to move more freely. This reduces the mechanical stability of the entire catalyst layer and polymer electrolyte membrane. In some embodiments, polymers that are not susceptible to CO2 plasticization are used. In addition, unlike water electrolysis devices and fuel cells, conductive carbonate and bicarbonate ions are key parameters for CO2 reduction.

[0191] The introduction of polar functional groups, such as hydroxyl and carboxyl groups that can form hydrogen bonds, leads to the formation of a pseudo-crosslinked network. Crosslinkers such as ethylene glycol and aluminum acetylacetonate can be added to strengthen the anion exchange polymer layer and inhibit polymer CO2 plasticization. Additives such as polydimethylsiloxane copolymers 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 of 80° C. and below, and be soluble in organic solvents used during manufacturing, such as methanol, ethanol, and isopropanol. x The ion conducting polymer is stable (chemically stable and has stable solubility) in the presence of the reduction product. The ion conducting polymer is also characterized by its ion exchange capacity, the total number of active sites or functional groups responsible for ion exchange, which in some embodiments can range from 2.1 mmol / g to 2.6 mmol / g.

[0193] Examples of anion conducting polymers are given in the table above as type A ion conducting polymers. A specific example of an anion conducting polymer is Orion mTPN1, which has meta-terphenyl fluoroalkylene as the backbone and trimethylammonium (TMA+) as the cationic group. The chemical structure is shown below.

[0194] Additional examples include anion exchange membranes produced by Fumatech and Ionomr. Fumatech FAA-3 ionomer exists in the Br-form. Ionomr's polybenzimidazole-based anion exchange polymer / membrane exists in the I-form, such as AF-1-HNN8-50-X.

[0195] By exchanging anions (e.g. I - Br - etc.) to prepare the received polymer.

[0196] Furthermore, as mentioned above, in certain embodiments, the ionomer can 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 catalyze CO x Reduction reaction. Metal catalysts are typically nanoparticles, but larger particles, films, and nanostructured surfaces may be used in some embodiments. The specific morphology of the nanoparticles may expose and stabilize active sites with greater activity.

[0198] Metal catalysts are usually composed of pure metals (e.g., Cu, Au, Ag), but specific alloys or other bimetallic systems may be highly active and used for certain reactions. The choice of catalyst can be guided by the desired reaction. For example, for CO production, Au can be used; for the production of methane and ethylene, Cu can be used. Other metals, including Ag, alloys, and bimetallic systems can be used. Compared with other well-known electrochemical reactions (such as hydrogen and oxygen evolution on known catalysts), CO2 reduction has a high overpotential. Small amounts of pollutants can poison the catalyst used for CO2 conversion. And as mentioned above, metal catalysts such as Cu, Au, and Ag are not as developed as catalysts used in hydrogen fuel cells (e.g., platinum).

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

[0200] Nanoparticles can be synthesized by any suitable method, such as 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 in the absence of toxic surface ligands. This can be achieved by using ionomers as ligands to guide the synthesis of nanocrystal catalysts. The surface of the metal nanocatalyst is directly connected to the ion-conducting ionomer. This avoids having to treat the catalyst surface to allow ionomers to contact and improve contact with the metal.

[0202] In some embodiments, the metal catalyst can be disposed on a carbon support. For CO production, examples include Premetek 20wt% Au supported on Vulcan XC-72R carbon, with an Au particle size of 4-6nm, and 30% Au / C supported on Vulcan XC-72R, with an Au particle size of 5-7nm. For methane, examples include Premetek 20wt% Cu supported on Vulcan XC-72R carbon, with a Cu particle size of 20-30nm. In some embodiments, the metal catalyst can be unsupported. For ethylene production, examples of unsupported metal catalysts include SigmaAldrich unsupported Cu 80nm particle size and 10nm to 100nm thin Cu layers deposited by electron beam or sputtering. Support (cathode catalyst layer)

[0203] The support of the cathode catalyst layer can have various functions. It can stabilize the metal nanoparticles to prevent them from agglomerating and distribute the catalytic sites throughout the catalyst layer volume to disperse the loss of reactants and the formation of products. It can also form a conductive path to the metal nanoparticles electronically. For example, carbon particles are stacked together so that the contacting carbon particles provide a conductive path. The spaces between the particles form a porous network through which gases and liquids can travel.

[0204] In some embodiments, carbon supports developed for fuel cells can be used. Many different types have been developed; their sizes are typically 50nm-500nm, and they are available in different shapes (spheres, nanotubes, flakes (e.g., graphene)), porosity, surface area / volume, conductivity, functional groups (N-doped, O-doped, etc.).

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

[0206] Examples of carbon blacks that may be used include: Vulcan XC-72R - density 256mg / cm 2 ,30-50nm Ketjen Black-hollow structure, density 100-120mg / cm 2 , 30-50nm ·Pretex Carbon, 20-30nm Anode catalyst layer

[0207] The anode of the MEA, also called the anode layer or anode catalyst layer, promotes the oxidation reaction. It is a porous layer containing a catalyst for the oxidation reaction. An example of a reaction is: 2H2O→4H + +4e - +O2 (in the acidic environment of a proton exchange polymer electrolyte - bipolar membrane); or 4OH - →4e - +O2+2H2O (in the alkaline environment of anion exchange polymer electrolyte)

[0208] Oxidation of other materials may also be performed, such as oxidation of hydrocarbons to produce CO2 or oxidation of chloride ions to produce chlorine.

[0209] In some embodiments, reference Figure 2, anode 240 comprises a blend of an oxidation catalyst and an anode ion conducting polymer. A variety of oxidation reactions may occur at the anode, depending on the reactants supplied to the anode and the anode catalyst. In one arrangement, the oxidation catalyst is selected from the following metals and oxides: Ir, Pt, Ni, Ru, Pd, Au, and alloys thereof, IrRu, Pt Ir, Ni, NiFe, stainless steel, and combinations thereof. The oxidation catalyst may also comprise conductive support particles selected from carbon, boron-doped diamond, and titanium.

[0210] The oxidation catalyst may be in the form of a structured mesh or may be in the form of particles. If the oxidation catalyst is in particulate form, the particles may be supported by conductive carrier particles. The conductive carrier particles may be nanoparticles. It is particularly useful if the conductive carrier particles are compatible with the chemicals present in the anode 240 during CRR operation and are oxidatively stable so that they do not participate in any electrochemical reactions. It is particularly useful if the conductive carrier particles are selected with consideration of the voltage and reactants at the anode. In some arrangements, the conductive carrier particles are titanium, which is well suited for high voltages. In other arrangements, the conductive carrier particles are carbon, which may be most useful at low voltages. Typically, such conductive carrier particles are larger than the oxidation catalyst particles, and each conductive carrier particle may carry many oxidation catalyst particles. Examples of such arrangements are Figure 3 As shown in FIG. 1 and discussed above with respect to the cathode catalyst layer. In one arrangement, 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 has an anode layer comprising an oxidation catalyst and a second ion-conducting polymer. The second ion-conducting polymer may comprise one or more polymers comprising covalently bound, negatively charged functional groups configured to transport mobile positively charged ions. The second ion-conducting polymer may be selected from: ethanesulfonyl fluoride, 2-[1-[difluoro-[(trifluorovinyl)oxy]methyl]-1,2,2,2-tetrafluoroethoxy]-1,1,2,2,-tetrafluoro-, copolymers with tetrafluoroethylene, tetrafluoroethylene-perfluoro-3,6-dioxa-4-methyl-7-octenesulfonic acid, other perfluorosulfonic acid polymers and blends thereof. Examples of cation-conducting polymers include, for example, Nafion 115, Nafion 117 and / or Nafion 211.

[0212] There is a tradeoff in selecting the amount of ion-conducting polymer in the anode. It is important to include enough anode ion-conducting polymer to provide sufficient ionic conductivity. But it is also important that the anode is porous so that reactants and products can easily move through it and maximize the amount of catalyst surface area available for reaction. In various arrangements, the ion-conducting polymer in the anode accounts for about 50 wt %, or about 5 wt % to 20 wt %, 10 wt % to 90 wt %, 20 wt % to 80 wt %, 25 wt % to 70 wt %, or any suitable range of the layer. It is particularly useful if the anode 240 can withstand high voltages, such as voltages greater than about 1.2 V relative to the reversible hydrogen electrode. It is particularly useful if the anode 240 is porous so as to maximize the amount of catalyst surface area available for reaction and facilitate gas and liquid transport.

[0213] In one example of a metal catalyst, Ir or IrOx particles (100-200 nm) and Nafion ionomer form a porous layer about 10 μm thick. The metal catalyst loading is about 0.5-3 g / cm 2 .

[0214] In some embodiments, NiFeOx is used for alkaline reactions. PEM

[0215] The MEA includes a polymer electrolyte membrane (PEM) disposed between and conductively coupled to an anode catalyst layer and a cathode catalyst layer. Figure 2 The polymer electrolyte membrane 265 has high ionic conductivity (greater than about 1 mS / cm) and is mechanically stable. Mechanical stability can be demonstrated in a variety of ways, such as by 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 include, but are not limited to, various Preparation, GORE-SELECT, (PFSA) (FuMA-Tech GmbH) and (PFSA)(Sol lvay).

[0216] In one arrangement, the PEM comprises at least one ion-conducting polymer that is a cation conductor. A third ion-conducting polymer may comprise one or more covalently bound negatively charged functional groups configured to transport mobile positively charged ions. The third ion-conducting polymer may be selected from: ethanesulfonyl fluoride, 2-[1-[difluoro-[(trifluorovinyl)oxy]methyl]-1,2,2,2-tetrafluoroethoxy]-1,1,2,2,-tetrafluoro-, copolymers with tetrafluoroethylene, tetrafluoroethylene-perfluoro-3,6-dioxa-4-methyl-7-octenesulfonic acid, other perfluorosulfonic acid polymers and blends thereof. Cathode buffer layer

[0217] refer to Figure 2 , it can be noted that when the polymer electrolyte membrane 265 is a cation conductor and conducts protons, it contains a high concentration of protons during CRR operation, while the cathode 220 operates best when a low concentration of protons is present. It can be useful to include a cathode buffer layer 225 between the polymer electrolyte membrane 265 and the cathode 220 to provide a transition region from a high proton concentration to a low proton concentration. In one arrangement, the cathode buffer layer 225 is an ion-conducting polymer that has 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 proton concentration 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 of the cathode 220 is too high, COx reduction will not occur. High proton concentrations are considered to be in the range of about 10 to 0.1 molar, while low concentrations are considered to be less than about 0.01 molar.

[0218] The cathode buffer layer 225 may include a single polymer or multiple polymers. If the cathode buffer layer 225 includes multiple polymers, the multiple polymers may be mixed together or may be arranged 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), and blends thereof. Further examples are given in the discussion of the cathode catalyst layer above.

[0219] Since the proton concentration is low, a sufficient cathode buffer layer thickness is selected to allow high COx reduction activity. This sufficiency may be different for different cathode buffer layer materials. Typically, the thickness of the cathode buffer layer is about 200nm to 100μm, 300nm to 75μm, 500nm to 50μm, or any suitable range.

[0220] In some embodiments, the cathode buffer layer is less than 50 μm, for example, between 1-25 μm, such as 1-5 μm, 5-15 μm or 10-25 μm. By using a cathode buffer layer within this thickness range, the proton concentration in the cathode can be reduced while maintaining the overall conductivity of the electrolyzer. In some embodiments, ultra-thin layers (100 nm-1 μm, in some embodiments, submicron) can be used. And as mentioned 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 relative to the thickness of the PEM.

[0221] Water and CO2 formed at the interface of the cathode buffer layer and PEM can cause delamination of the MEA at the junction of the polymer layers. This delamination problem can be solved by using a cathode buffer layer with inert filler particles and associated pores. One possible explanation for its effectiveness is that the pores create a path for gaseous carbon dioxide to escape back to the cathode, where it can be reduced.

[0222] Materials suitable as inert filler particles include, but are not limited to, TiO2, silica, PTFE, zirconium oxide, and aluminum oxide. In various arrangements, 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 large, it will dilute the polymer electrolyte to the point where the ionic conductivity is low. Too much polymer electrolyte volume will dilute the PTFE to the point where it does not contribute to porosity. In many embodiments, the mass ratio of polymer electrolyte / PTFE is 0.25 to 2, 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 arrangements, porosity is achieved by using specific processing methods when the layer is formed. An example of such a processing method is laser ablation, where nanometer to micrometer sized channels are formed in the layer. Another example is mechanical puncturing of the layer to form channels through it.

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

[0226] Porosity can be measured as described above for the catalyst layer, including using the mass loading and thickness of the components, by methods such as mercury intrusion, X-ray diffraction (SAXS or WAXS), and image processing of TEM images to calculate the filled space versus the void space. Porosity is measured when the MEA is completely dry, as the material will swell to varying degrees when exposed to water during operation.

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

[0228] In some CRR reactions, bicarbonate is produced at the cathode 220. It may be useful if there is a polymer that blocks the transport of bicarbonate somewhere between the cathode 220 and the anode 240, thereby preventing the bicarbonate from migrating away from the cathode. It may be that the bicarbonate carries some CO2 with it as it migrates, which reduces the amount of CO2 available for reaction at the cathode. In one arrangement, the polymer electrolyte membrane 265 includes a polymer that blocks the transport of bicarbonate. Examples of such polymers include, but are not limited to: Preparation, GORE-SELECT, (PFSA) (FuMA-Tech GmbH), and (PFSA) (Solvay). In another arrangement, there is an anode buffer layer 245 between the polymer electrolyte membrane 265 and the anode 240 that blocks the transport of bicarbonate. If the polymer electrolyte membrane is an anionic conductor, or does not block the transport of bicarbonate, then it may be useful to use an additional anode buffer layer to prevent the transport of bicarbonate. Materials that can be used to block the transport of bicarbonate include, but are not limited to: Preparation, GORE-SELECT, (PFSA) (FuMA-Tech GmbH) and (PFSA) (Solvay) Of course, if bicarbonate is absent from the CRR, then including bicarbonate blocking features in the ion exchange layer 260 is not particularly desirable.

[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, the Nafion polymer electrolyte membrane 265 that conducts protons has a high proton concentration. The FumaSep FAA-3 polymer electrolyte membrane 265 that conducts hydroxide has a low proton concentration. For example, if the desired proton concentration at the anode 240 differs from the polymer electrolyte membrane 265 by more than 3 orders of magnitude, then the anode buffer layer 245 can be used to achieve a transition from the proton concentration of the polymer electrolyte membrane 265 to the desired proton concentration of the anode. The anode buffer layer 245 may include a single polymer or multiple polymers. If the anode buffer layer 245 includes multiple polymers, the multiple polymers may be mixed together or may be arranged in separate adjacent layers. Materials that can be used to provide a pH transition region include, but are not limited to: Nafion, FumaSep FAA-3, Tokuyama anion exchange polymers and polyether polymers, such as polyethylene oxide (PEO), blends thereof, and / or any other suitable material. High proton concentrations are considered to be in the range of about 10 to 0.1 molar, while low concentrations are considered to be less than about 0.01 molar. Ion conducting polymers can be divided into different categories based on the type of ions they conduct. This has been discussed in more detail above. There are three categories of ion conducting polymers described in Table 4 above. In one embodiment of the present invention, at least one of the ion conducting polymers in cathode 220, anode 240, polymer electrolyte membrane 265, cathode buffer layer 225, and anode buffer layer 245 is from a category different from at least one of the others. Layer porosity

[0230] It may be useful if some or all of the following layers are porous: cathode 220, cathode buffer layer 225, anode 240, and anode buffer layer 245. In some arrangements, porosity is achieved by combining inert filler particles with polymers in these layers. Materials suitable as inert filler particles include, but are not limited to, TiO2, silicon oxide, PTFE, zirconium oxide, and aluminum oxide. In various arrangements, the size of the inert filler particles is between 5 nm and 500 μm, between 10 nm and 100 μm, or any suitable size range. In other arrangements, porosity is achieved by using a specific treatment method when the layer is formed. An example of such a treatment method is laser ablation, in which nanometer to micron-sized channels are formed in the layer. In addition or as an alternative, laser ablation can achieve porosity in the layer by subsurface ablation. Subsurface ablation can form voids in the layer: when the beam is focused at a certain point in the layer, the layer material near the point is vaporized. This process can be repeated to form voids everywhere in the layer, thereby achieving porosity in the layer. The volume of the voids is preferably determined by the laser power (e.g., higher laser powers correspond to larger void volumes), but may additionally or alternatively be determined by the focal size of the beam or any other suitable laser parameter. Another example is mechanically piercing a layer to form a channel through the layer. The porosity may have any suitable distribution in the layer (e.g., uniform, a porosity gradient that increases across the layer, a random porosity gradient, a porosity gradient that decreases across the layer, periodic porosity, etc.).

[0231] The porosity of the above examples and other examples and variations (e.g., the porosity of the cathode buffer layer, the anode buffer layer, the membrane layer, the cathode layer, the anode layer, other suitable layers, etc.) preferably has a uniform distribution, but in addition or as an alternative, may have any suitable distribution (e.g., a randomized distribution, an increasing pore size gradient through or across the layer, a decreasing pore size gradient through or across the layer, etc.). The porosity may 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 for forming substantially non-reactive regions within the polymer layer. The inert filler particles may have any suitable size, such as a minimum of about 10 nanometers and a maximum of about 200 nanometers, and / or any other suitable size or size distribution.

[0232] As described above, the cathode buffer layer preferably has a porosity of about 1 to 90% by volume, but in addition or as an alternative, may have any suitable porosity (including, for example, no porosity). However, in other arrangements and examples, the cathode buffer layer may have any suitable porosity (e.g., 0.01-95%, 0.1-95%, 0.01-75%, 1-95%, 1-90%, etc.). In some embodiments, the porosity is less than 20%, such as 0.1-20%, 1-10%, or 5-10%.

[0233] In some embodiments, the cathode buffer layer is porous, but at least one layer between the cathode layer and the anode layer is nonporous. This can prevent gas and / or bulk liquid from passing between the cathode layer and the anode layer while still preventing stratification. For example, the nonporous layer can prevent water from passing directly from the anode to the cathode. MEA Manufacturing

[0234] For CO x The reduced MEA can be manufactured using a variety of techniques. In various embodiments, MEA manufacturing uses multiple steps. Small differences in the parameters of the manufacturing process can lead to large differences in performance.

[0235] In certain embodiments, MEA manufacture uses polymer-electrolyte membrane (e.g., Nafion-PEM) layer, and deposits or otherwise forms anion exchange polymer electrolyte layer and cathode catalyst layer on cathode, and deposits or otherwise forms anode catalyst layer on anode. An alternative approach is to manufacture catalyst layer on porous gas diffusion layer (e.g., carbon for cathode or titanium for anode), and sandwich the membrane (which may include anion exchange layer) between porous layers containing catalyst. In certain embodiments, catalyst layer is manufactured by manufacturing ink in which solid catalyst and carrier particles and polymer electrolyte are dispersed in solvent. Ink can be applied to polymer electrolyte membrane or GDL by a variety of methods. The solvent evaporates subsequently, leaving a porous solid catalyst layer.

[0236] Imaging methods can 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 the various layers of the MEA. Typically, these techniques form layers on a substrate (such as a PEM layer or GDL as described herein). Examples of such techniques include ultrasonic spray deposition, doctor blade application, gravure printing, screen printing, and decal transfer.

[0238] Catalyst inks using anion exchange polymers are not well studied (especially for some polymers) and do not have the same solution structure as the typical Nafion-type inks used in fuel cells and electrolyzers. The formulation and steps required to form a well-dispersed and stable catalyst ink are not well understood. It is thought that Nafion forms a micelle-like structure that can be suspended in aqueous media relatively easily. Other ion-conducting polymers, especially some anion-conducting polymers, do not form this structure and are therefore more difficult to provide in suspension.

[0239] In certain embodiments, the catalyst layer ink is prepared by mixing a metal or a metal supported on a carbon catalyst with an ion conducting polymer (eg, an anion conducting polymer) and dispersing in a solvent (ethanol, etc.) by ultrasonic treatment.

[0240] As previously mentioned, some manufacturing techniques utilize doctor blade application, screen printing, decal transfer, electrospinning, etc. Roll-to-roll techniques such as gravure or micro-gravure printing can be used for high throughput processing. MEA post-processing

[0241] After manufacturing the MEA, additional treatments may be used to improve performance. For example, examples of types of performance improvements include life and voltage. In some embodiments, post-treatment introduces salt or certain salt ions into the MEA. In some embodiments, post-treatment produces an MEA with structural changes caused by the treatment, including better interlayer adhesion.

[0242] Heat Pressing: The MEA is heated under pressure to bond the layers together. Heat pressing will help "melt" the layers together to prevent delamination. Time: about 2min to 10min (MEA only); 1.5min to 2min (MEA + gas distribution layer (GDL)); "MEA + GDL" can be pressed at least twice to form a stable component Temperature: about 100℃ to 150℃; Pressure: about 300 psi to 600 psi (for a 3×3 inch 1 / 2 MEA), but without a GDL, the MEA can withstand about 2500 psi;

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

[0244] Boil Nafion or other polymer electrolyte MEA. This permanently changes the macrostructure of the polymer electrolyte and increases the amount of water in the polymer matrix. This improves ionic conductivity and increases water transport.

[0245] Heat drying. This reduces the water content and can reduce the amount of water transported across the polymer electrolyte during operation. Stable interface between MEA layers

[0246] Water and CO2 formed at the interface of an anion conducting layer (e.g., cathode buffer layer) and a cation conducting membrane (e.g., PEM) can cause the two layers to separate or delaminate at the junction of the polymer layers. Reactions at the bipolar interface such as Figure 3 and Figure 7 shown.

[0247] Additionally, it is desirable to return the CO2 to the cathode of the electrolyzer where it can be reduced rather than lost to the anode, so pathways (e.g., pores) in the anion exchange layer (e.g., cathode buffer layer and / or cathode layer) provide a means to remove water and CO2 from the interface to prevent stratification, as well as return the CO2 to the cathode where it can react.

[0248] Figure 7 The structure depicted in Figure 3 Similar to the structure depicted in Figure 7 Includes additional information related to the mass transport and generation of CO2 and water at the bipolar interface. For example, it shows that hydroxide and CO2 react on the cathode side to form bicarbonate ions, which move toward the bipolar interface 713. On the anode side, hydrogen ions generated by water oxidation move toward the bipolar interface 713, where they react with bicarbonate ions to form water and CO2, both of which should be allowed to escape without damaging the bipolar layers.

[0249] Figure 7 Also depicted are water transport pathways, including (a) electroosmotic drag of anions from the cathode to the interface 713, (b) electroosmotic drag of cations from the anode to the interface 713, and (c) diffusion. Water evaporates at the anode and cathode.

[0250] Various MEA designs include features that resist delamination and optionally provide a path for reaction products to leave the interface region. In some embodiments, the bipolar interface is flat. However, in some designs, the interface has a composition gradient and / or an interlocking structure.

[0251] In some embodiments, the interface comprises a gradient. For example, a gradient can be formed by using two nozzles during jet deposition and adding an anion exchange polymer, wherein the relative amount of the polymer is changed during deposition of the cation exchange layer. Similarly, a cation exchange polymer can be added during deposition of the anion exchange layer. For example, reference Figure 7, the gradient can extend through substantially all or a portion of the anion exchange zones and cation exchange zones, such that the anion exchange zones have primarily anion exchange polymer adjacent to the cathode, wherein the relative amount of cation exchange polymer increases as one moves from the cathode toward the interface 713. Similarly, the cathode exchange zones have primarily cation exchange polymer adjacent to the anode cathode, wherein the relative amount of anion exchange polymer increases as one moves from the anode toward the interface 713. In some embodiments, there are pure anion exchange zones and pure cation exchange zones with a gradient between them.

[0252] In some embodiments, the layers of the bipolar membrane are melted together. This can be achieved by selecting an appropriate solvent. For example, Nafion is at least slightly soluble in a water / ethanol mixture. By using this mixture (or other solvents that can dissolve cation-conducting polymers) as a solvent for the anion-conducting polymer, it is possible to cause the Nafion or other cation-conducting polymer to at least slightly dissolve and blend into the interface. In some embodiments, this results in a thin gradient, for example, a gradient that extends 0.5-10% into the thickness of the anion-conducting polymer layer.

[0253] In some embodiments, the interface comprises a mixture of polymers. Fig. 8A A bipolar interface 813 is shown where a cation conducting polymer 821 and an anion conducting polymer 819 are mixed. Fig. 8A In the example of FIG. 8 , a portion of anion conducting polymer layer 809 and a portion of cation conducting polymer layer 811 are shown. Anion conducting polymer layer 809 can be a pure anion conducting polymer, while cation conducting polymer layer 811 can be a pure cation exchange polymer. Cation conducting polymer 821 can be the same or different cation conducting polymer as in cation conducting polymer layer 811. Anion conducting polymer 819 can be the same or different anion conducting polymer as in anion conducting polymer layer 809.

[0254] In some embodiments, the interface includes a third material that physically enhances the interface. For example, Figure 8B An example of material 830 is shown that spans interface 813. That is, material 830 is partially located in anion conducting polymer layer 809 and cation conducting polymer layer 811. Thus, material 830 will bind the two layers in a manner that resists delamination. In one example, material 830 is a porous, inert material, such as porous PTFE. The interface can be made, for example, by casting or otherwise applying a cation conducting polymer and anion conducting polymer on opposite sides of a PTFE or similar porous membrane, followed by heat pressing.

[0255] Figure 8CA bipolar interface 813 is shown having protrusions 840 of cation conducting polymer extending from the cation conducting polymer layer 811 into the anion conducting polymer layer 809. These protrusions can mechanically strengthen the interface 813 so that it does not delaminate when CO2 and water are produced at the interface. In some embodiments, the protrusions extend from the anion conducting polymer layer 809 into the cation conducting polymer layer 811. In certain embodiments, the protrusions extend in both directions. Example dimensions are in-plane dimensions of 10 μm–1 mm, but smaller dimensions (e.g., 500 nm-1 μm) are also possible. The out-of-plane dimensions can be, for example, 10-75% or 10-50% of the total thickness of the polymer layer into which it extends. For example, the protrusions can be made by any suitable technique (e.g., photolithography) or by spraying a polymer into a patterned grid and then removing the grid. Surface roughening techniques can also be used to create the protrusions. In some embodiments, the protrusions can be formed of different materials (e.g., metals) to help interlock the polymer layers and mechanically strengthen the interface.

[0256] Fig.8D A bipolar interface 813 is shown having a third material 850 disposed between or mixed into one or more cation conducting polymer layers 811 and anion conducting polymer layer 809. For example, in some embodiments, the third material 850 can be an additive, as discussed further below. In some embodiments, the third material 850 can be a blend of an anion conducting ionomer and a cation conducting ionomer at the interface. For example, it can be a mixture of Nafion 5wt% ionomer and Orion 2wt% mTPN1. In some embodiments, the third material can include ion acceptors and donors mixed together or provided as different layers.

[0257] In some embodiments, the interface includes additives that promote acid-base reactions and prevent stratification. In some embodiments, the additives can promote the expansion of acid-base complexes to a larger volume, rather than just at the 2D interface of the anion-conducting polymer and the cation-conducting polymer. This disperses the formation of water and CO2, heat generation, and may reduce membrane resistance by lowering the barrier to acid-base reactions. These effects help avoid the accumulation of products, heat, and reduce resistance losses in the MEA, resulting in lower electrolyzer voltage. In addition, it helps avoid degradation of materials 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, of which 1-butyl-3-methylimidazolium hydroxide is a specific example. Other ionic liquids may also be used. In some embodiments, ionomers different from the ionomers in the anion conductive polymer layer and the cation conductive polymer layer may be used. For example, relatively high conductivity anion exchange materials such as Susta inion may be used. The selectivity of such anion exchange materials may not be sufficient to be used as a cathode buffer layer, but may be used at the interface.

[0259] Additional examples of materials that may be present at the interface include block copolymers having different charged groups (e.g., cationic and anionic fixed charge groups), cation and anion conductive polymers, resin materials, ion donors (e.g., oxides including graphene oxides), catalysts for acid / base complexation, catalysts for reacting H2 and O2 diffused from the anode and cathode, water splitting catalysts, CO2 absorbing materials, and H2 absorbing materials.

[0260] In some embodiments, a crosslinking agent may be added to covalently crosslink the two polymers of the bipolar membrane. Examples of crosslinking groups include xylene, which may be provided on the ionomer. Other crosslinking groups may be used. For example, a crosslinking agent may be provided on a cation conducting polymer, an anion conducting polymer may be spray deposited on top, and then heated to initiate the crosslinking reaction and introduce crosslinking across the interface.

[0261] In some embodiments, the anion conducting polymer and cation conducting polymer of the bipolar membrane have the same backbone with different fixed charge groups. For example, Orion ionomers can be used with different fixed charge groups. Ionomers are more compatible and less prone to delamination.

[0262] In the above examples, the interface 813 can be a three-dimensional volume with a thickness of 1% to 90% of the total thickness of the bipolar membrane, or 5% to 90%, or 10% to 80%, or 20% to 70%, or 30% to 60% of the total thickness of the bipolar membrane. 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 can be used to fabricate any of the bipolar interface designs described above. Relative dimensions of the MEA layers

[0264] In certain embodiments, the polymer electrolyte membrane and the adjoining cathode buffer layer or other anion conducting polymer layer can have relative thicknesses that facilitate the manufacturing and / or operating performance of the MEA.

[0265] Fig. 9An example of a partial MEA is depicted, which includes: 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 cation conducting polymer layer (e.g., a proton exchange polymer layer) or an 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 cation conducting polymer layer (e.g., a proton exchange polymer layer) or an 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 microns, while the thickness of the AEM 903 is about 10-20 microns.

[0266] In some cases, the conductivity of anion conducting polymers (e.g., those used in anion conducting polymer layer 903) is significantly less than that of cation conducting polymers (e.g., those used in PEM 905). Therefore, in order to provide the benefits of a cathode buffer layer (e.g., anion conducting polymer layer 903) without significantly increasing the overall resistance of the MEA, a relatively thin cathode buffer layer is used. However, when the cathode buffer layer becomes too thin, it becomes difficult to handle during the manufacture of the MEA and in other situations. Therefore, in some embodiments, a thin cathode buffer layer is manufactured on top of a relatively thick PEM layer (e.g., a cation conducting polymer layer). The anion conducting polymer layer can be manufactured on the PEM layer using any of the manufacturing techniques described elsewhere herein, for example.

[0267] In various embodiments, the polymer electrolyte membrane layer thickness is about 20 microns to 200 microns. In some embodiments, the polymer electrolyte membrane layer thickness is about 60 microns to 120 microns. In some embodiments, a thin polymer electrolyte membrane layer is used, and its thickness is about 20 microns to 60 microns. In some embodiments, a relatively thick polymer electrolyte layer is used, and its thickness is about 120 microns to 200 microns.

[0268] In some embodiments, a thinner cathode buffer layer is used with a thinner polymer electrolyte membrane. This helps to move the CO2 formed at the interface back to the cathode instead of moving to the anode. In some embodiments, a thicker cathode buffer layer is used with a thicker polymer electrolyte membrane. In some embodiments, this reduces the electrolyzer voltage.

[0269] Factors that can 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 conformality of the anion conducting polymer coating the polymer electrolyte membrane.

[0270] Many anion conducting polymers have selectivity for anions in the 95% range, with about 5% of the current being cations. Higher selective anion conducting polymers (greater than 99% selectivity for anions) allow for significant reductions in thickness while providing adequate buffering.

[0271] The mechanical strength of the anion conducting layer also affects its thickness, with stronger layers being thinner. Reducing the porosity of the anion conducting polymer can reduce the thickness of the anion conducting layer.

[0272] In some embodiments, the thickness of the cathode buffer layer or other anion conducting polymer layer adjacent to the polymer electrolyte membrane is about 10 to 20 microns. In some embodiments, the use of polymers with >99% selectivity can allow the cathode buffer layer to be reduced to 2 to 10 microns.

[0273] In some cases, the thickness ratio of the polymer electrolyte membrane and the adjacent anion conducting polymer layer is about 3:1-90:1, with higher ratios used with highly selective anion conducting polymer layers. In some embodiments, the ratio is about 2:1-13:1, about 3:1-13.1, or about 7:1-13.1.

[0274] In certain embodiments, a relatively thin PEM improves some aspects of MEA performance. Fig. 9 , for example, the thickness of the polymer electrolyte membrane 905 can be about 50 microns, while the thickness of the anion conducting layer can be about 10 to 20 microns. Thin PEMs facilitate the movement of water generated at the AEM / PEM interface toward the anode. The gas pressure on the cathode side of the electrolyzer can be about 80-450 psi, which causes the water at the interface to move toward the anode. However, in some cases, thick PEMs can cause most of the water to move through the AEM to the cathode, which causes overflow. By using thin PEMs, overflow can be avoided. CO x Reduction Reactor (CRR)

[0275] Fig.10 is a diagram showing CO according to an embodiment of the present disclosure x Schematic diagram of the major components of a reduction reactor (CRR) 1005. CRR 1005 has a membrane electrode assembly 1000, such as any membrane electrode assembly described elsewhere herein. 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 depicted embodiment has three sublayers: a cathode buffer layer 1025, a polymer electrolyte membrane 1065, and an optional anode buffer layer 1045. In addition, CRR 1005 has a cathode support structure 1022 adjacent to cathode 1020 and an anode support structure 1042 adjacent to anode 1040.

[0276] The cathode support structure 1022 has a cathode plate 1024, such as made of graphite, to which a voltage can be applied. There can be flow field channels, such as serpentine channels, cut into the inner surface of the cathode plate 1024. There is also a cathode gas diffusion layer 1026 adjacent to the inner surface of the cathode plate 1024. In some arrangements, there is more than one cathode gas diffusion layer (not shown). The cathode gas diffusion layer 1026 facilitates gas flow into and out of the membrane electrode assembly 1000. An example of a cathode gas diffusion layer 1026 is carbon paper with a carbon microporous layer.

[0277] The anode support structure 1042 has an anode plate 1044, which is typically made of metal, to which a voltage can be applied. There may be flow field channels, such as serpentine channels, cut into the inner surface of the anode plate 1044. There is also an anode gas diffusion layer 1046 adjacent to the inner surface of the anode plate 1044. In some arrangements, there is more than one anode gas diffusion layer (not shown). The anode gas diffusion layer 1046 facilitates the flow of gas into 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 arrangements, the gas diffusion layers 1026, 1046 are microporous.

[0278] There are also inlets and outlets (not shown) associated with the support structures 1022, 1042 that allow reactants and products, respectively, to flow to the membrane electrode assembly 1000. There are also various gaskets (not shown) that prevent reactants and products from leaking out of the electrolyzer.

[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 the water is oxidized on the oxidation catalyst to form molecular oxygen (O2), releasing protons (H + ) and electron (e - ). The protons migrate through the ion exchange layer 1060 toward the cathode 1020. The electrons flow through an external circuit (not shown). In one embodiment, the reaction is described as follows: 2H2O→4H + +4e - +O2

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

[0281] Although the depicted embodiment shows an ion exchange layer having three sublayers, certain embodiments use an ion exchange layer having only a single layer (eg, a cation conducting polymer layer or an anion conducting polymer layer). Other embodiments have only two sublayers.

[0282] According to one embodiment, Fig.11 1105. The flow of reactants, products, ions, and electrons through the CRR 1105 reactor is shown in FIG. The CRR 1105 has a membrane electrode assembly 1100, such as any MEA described elsewhere herein. The membrane electrode assembly 1100 has a cathode 1120 and an anode 1140 separated by an ion exchange layer 1160. In certain embodiments, 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. In addition, the CRR 1105 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 may be applied. There may be flow field channels, such as serpentine channels, cut into the inner surface of the cathode plate 1124. There is also a cathode gas diffusion layer 1126 adjacent to the inner surface of the cathode plate 1124. In some arrangements, there is more than one cathode gas diffusion layer (not shown). The cathode gas diffusion layer 1126 facilitates gas flow into and out of the membrane electrode assembly 1100. An example of a cathode gas diffusion layer 1126 is carbon paper with a carbon microporous layer.

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

[0285] There may also be inlets and outlets associated with the support structures 1122, 1142 that allow reactants and products, respectively, to flow to the membrane electrode assembly 1100. There may also be various gaskets that prevent reactants and products from leaking out of the electrolyzer.

[0286] CO x supplied to the cathode 1120, and in the presence of protons and electrons in CO x Reduction on a reduction catalyst. x The pressure may be supplied to cathode 1120 at a range of 0 psig to 1000 psig or any other suitable range. x The CO may be supplied to cathode 1120 in a mixture with other gases at a concentration less than 100% or any other suitable percentage.x The concentration may be as low as about 0.5%, as low as 5%, or as low as 20% or any other suitable percentage.

[0287] In one embodiment, about 10% to 100% of the unreacted CO x It 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, multiple CRRs (e.g. Fig.10 The CRRs shown in FIG. 1 are arranged in an electrochemical stack and run together. The CRRs constituting each electrochemical cell in the stack can be electrically connected in series or in parallel. Reactants are supplied to each CRR, and then the reaction products are collected.

[0289] According to some embodiments, the input and output of the reactor are as follows Fig.12 As shown. x Anode feed and power supply to the reactor. CO x The reduction products and any unreacted CO x Leaving the reactor. Unreacted CO x The anode feed and the reduced product may be separated and recycled back to the input side of the reactor. The anodized product and any unreacted anode feed leave the reactor in separate streams. The unreacted anode feed may be recycled back to the input side of the reactor.

[0290] Various catalysts in the CRR cathode lead to the conversion of CO x The reduction reaction forms different products or product mixtures. CO x An example of a reduction reaction is 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, running CO x The method of reducing the reactor (as described in the above embodiment) involves applying a DC voltage to the cathode plate and the anode plate, supplying an oxidizing reactant to the anode and allowing an oxidation reaction to occur, supplying a reducing reactant to the cathode and allowing a reduction reaction to occur, collecting an oxidizing reaction product from the anode; and collecting a reducing reaction product from the cathode. The current or voltage is controlled to perform a cycle according to the above arrangement.

[0292] In one arrangement, the DC voltage is greater than about -1.2 V. In various arrangements, the oxidation reactant can be any of hydrogen, methane, ammonia, water, or a combination thereof, and / or any other suitable oxidation reactant. In one arrangement, the oxidation reactant is water. In various arrangements, the reduction reactant can be any of carbon dioxide, carbon monoxide, and a combination thereof, and / or any other suitable reduction reactant. In one arrangement, the reduction reactant is carbon dioxide. Example :

[0293] Faradaic efficiency, sometimes called Faradaic yield, Coulombic efficiency, or current efficiency, is the efficiency of charge transfer in a system that facilitates an electrochemical reaction. The Faraday constant is used in Faradaic efficiency to relate charge to the number of moles of a substance and electrons. Faradaic losses occur when electrons or ions participate in undesirable side reactions. These losses manifest as heat and / or chemical byproducts. The following examples include Faradaic yield plots for various products. Improved methane selectivity

[0294] Build an MEA with a copper cathode catalyst at 5 cm 2 100 mA / cm is applied to MEA 2 After running for about one hour, a cycle of implementing a 1-minute current shutdown (i.e., current pause) for every 4.5-minute current application was established. Fig.13 is a graph showing applied current density (J) and Faradaic yield (FY) for H2, CO, CH2CH2, CH4 and the total. Each point in this graph is 5.5 minutes apart, so current pauses are not shown. However, as shown, the current cycle begins at 1 hour.

[0295] In the first hour after running-in, the methane selectivity dropped from 13% to 7%. After the start of the current cycle, the methane selectivity rose to 23%. The hydrogen selectivity dropped, and the selectivities of ethylene and carbon monoxide remained at a low level.

[0296] Possible mechanisms for the improvements described (and other observed improvements described in this disclosure) include: 1) allowing removal of hydrogen from the catalyst surface, thereby improving CO2 ingress, 2) allowing removal of water from the local environment of the catalyst, 3) desorption of other reaction byproducts or impurities from the catalyst surface, and 4) changes in membrane / double layer resistance / conductivity. Improved methane selectivity using simulated biogas feed

[0297] MEA with copper cathode catalyst was used to test simulated biogas with up to 1500ppm H2S injection, initially at 100mA / cm 2 Constant current is applied to start. Fig.14 is a graph showing the Faradaic yield (FY) of H2 and CH4. H2S injection is also shown. The initial yield of methane (before any current pause) dropped from 20% to 10%. When the applied current was paused for 5 minutes and then resumed, the performance of the MEA improved significantly, but continued to decline. When the test was paused for 1 minute again and restarted, the MEA recovered performance but continued to decline. After regular 1 minute pauses for every 4.5 minutes of applied current, the MEA maintained a stable 30% selectivity for methane and was able to withstand up to 1500ppm of H2S exposure without obvious signs of poisoning. Improved methane selectivity during run-in

[0298] Fig.15 is a graph showing the run-in period of an MEA with a copper cathode catalyst. The applied current density is shown, as well as the Faradaic yields for H2, CO, and CH4. During the entire duration of the run, the current was applied for 4.5 minutes and then paused for 1 minute. Fig.13 As with the graph above, the points are 5.5 minutes apart, so no pauses are visible on the graph. Fig.15 It also shows that for current cycling, the slope of the FY CH4 curve is positive, which is consistent with Fig.13 and 14 The FY CH4 curve in the Fig.13 and 14 The FY CH4 curve in FIG. 1 decreases in the period before the current cycle. Improved CO selectivity

[0299] The MEA with gold cathode catalyst for CO production was shut down for more than 4 days after two duration periods of 50-300 hours each. Fig.16 As shown, when the electrolyzer is restarted, the Faradaic yield of CO increases, while the Faradaic yield of H2 decreases compared to the value when the electrolyzer was shut down for the previous cycle. Specifically, the Faradaic yield of CO increases by about 10% at the beginning of cycle 2 compared to the end of cycle 1, and increases by about 5% at the beginning of cycle 3 compared to the end of cycle 2.

[0300] Fig.17 The electrolyser performance of a single MEA for long term testing is shown with the shutdown / on current pauses indicated. Fig.17 As shown, pausing the electrolyzer operation for 15 minutes at 95 hours improved the electrolyzer performance. FY CO increased by 8% from 86% to 94%, while FY H2 was halved from 13% to 6%.

[0301] Fig.18 The electrolyzer performance of two MEAs is shown, one running continuously without current pauses and the other running with intermittent current pulses, where the electrolyzer was running for 55 minutes and then turned off for 5 minutes. This off / on cycle was repeated during the pulse period, as shown by the dashed bands on the graph. Between these pulse periods, the current was running continuously. Reference Fig.18 , different curves for FY CO and FY H2 are marked. Intermittent pulses lead to better CO selectivity. This figure illustrates the improvement in reactor stability when intermittent pulses are applied during operation. For the electrolyzer with intermittent pulses, the selectivity decay (dFY_CO / dt) between 30 and 134 hours is -0.0070% / hr, compared to -0.055% / hr for the electrolyzer with continuous current.

[0302] These examples demonstrate that suspending electrolyser operation for both short and extended periods improves electrolyser performance by increasing CO selectivity. Improved CO selectivity—MEA stack

[0303] The examples above used a single MEA; however, improvements in selectivity were observed using a stack of MEAs. Fig.19 Performance data for two stacks are shown: At 1901, operating data for an MEA stack with a current pause of about 32 hours for a duration of about 63 hours. The 32 hour break is not shown in this figure; however, at 1910, an increase in FY_CO produced is observed. At 1902, operating data with a current pause of about 13 hours at 1912 is shown. An increase in selectivity is observed as evidenced by an increase in FY CO at 1914. The increase is about 20%. Running-in—Current Gradual Change

[0304] Fig. 20Results are shown for two identical MEAs for CO production tested using different ramping procedures to reach 500 mA / cm 2 The filled points correspond to the operation current density at each intermediate current density (100 mA / cm 2 , 200mA / cm 2 、300mA / cm 2 , 400mA / cm 2 ) for an electrolyzer that was run for 1 hour, and the unfilled points correspond to electrolyzers that were run for 30 minutes at each intermediate current density. (In some cases, unfilled points obscure filled points on the graph, and vice versa). Fig. 20 It is shown that for the electrolyser operated at a slower ramp rate (filled points), the Faradaic yield of CO is higher than for the electrolyser operated for a shorter period of time at each current density. These results suggest that slower current ramps can promote hydration, leading to higher performance.

[0305] Fig.21 The performance of two MEAs at high CO2 utilization is shown. One MEA (filled point) was operated in the electrolyzer without current ramping and directly at 300 mA / cm 2 The other MEA (unfilled point) was tested at a current ramp of 100, 200, and 250 mA / cm 2 The electrolyzer was run for 2, 2, and 2 hours respectively until it reached 300 mA / cm 2 .like Fig.21 As shown, a current ramp was used to reach 300 mA / cm 2 , which improves the voltage by about 100mV. Effects of gradient programs

[0306] Running the electrolyzer with different ramp-up or ramp-down programs resulted in different decay rates of selectivity and voltage. 2 During operation of the test MEA for CO production, the current density was reduced to 0 within 30 min and maintained at 0 for 15 min, and then immediately increased to 300 mA / cm 2 Restarting the device resulted in a much better Faradaic yield decay than a test in which the current was immediately stopped and held at 0 for 15 minutes, and then the current density was slowly ramped from 0 to 300 mA / cm over 30 minutes. 2 . Current pause duration

[0307] Fig. 22 The change in the Faradaic yield for CO (from before to after the current pause) is shown relative to the duration of the current pause, Fig.23The voltage change (from before to after the current pause) is shown relative to the duration of the current pause. Fig. 22 As shown in Figure 2, the duration of the current pause during the long-term test affects the change in CO Faradaic yield, while no effect of the duration of the current pause on the voltage change is observed ( Fig.23 ). Open circuit voltage relative to the electrolytic cell short circuit

[0308] Two CO-producing MEAs were run with intermittent current pulses, with the electrolyzer running for 45 minutes and then shut down for 15 minutes. This cycle was repeated for 14 hours. For one MEA, the electrolyzer was short-circuited to 0V during the current pause. For the other MEA, the electrolyzer was at an "open circuit voltage" (OCV), which was about 1-1.2V, during the current pause. The voltage stability of the electrolyzer at OCV (1-1.2V) was higher than that of the electrolyzer running at 0V during the current pause. For the electrolyzer running at 0V during the current pause, the voltage decay was 0.6mV / hr. For the electrolyzer at OCV, the voltage increased at a rate of 3.7mV / hr. The CO selectivity of both tests also increased over time, at a rate of about 0.07% / hr. Other Implementations

[0309] Although omitted for brevity, embodiments of the systems and / or methods may include every combination and arrangement of various system components and various method processes, wherein one or more instances of the methods and / or processes described herein may be performed asynchronously (e.g., sequentially), simultaneously (e.g., in parallel), or in any other suitable order by and / or using one or more instances of the systems, elements and / or entities described herein.

[0310] Those skilled in the art will recognize from the previous detailed description and from the drawings and claims that modifications and changes may be made to the preferred embodiments of the invention without departing from the scope of the invention as defined in the following claims.

Claims

1. A method for operating a membrane electrode assembly (MEA) to achieve CO x A method of restoring, comprising: Will contain CO x The gas is introduced into the cathode of the MEA and a current is applied to the MEA at a first current density, thereby reducing CO x and produces CO x Reduction products; and During normal operation, the applied current is automatically suspended according to the current suspension schedule.

2. The method of claim 1 , wherein the current pause schedule comprises current on periods at a first current density separated by current pause periods, wherein the current applied during at least a portion of the current pause periods is zero or at 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. A method according to claim 3, wherein the duration of the current suspension period is between 5 minutes and 10 hours. 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 pause 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. The method of claim 7, wherein the duration of the current pause period is between 500 microseconds and 10 minutes.

9. The method of any one of claims 2-8, wherein the total current-on period duration is at least three times the total current-off 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.

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