Catalyst-free water electrolysis in graphene oxide and / or graphdiyne oxide

Abstract

The disclosure relates to an electrolysis cell for catalyst-free electrolysis of water molecules from a humid atmosphere to produce hydrogen gas comprising an electrically conductive carbon fiber gas diffusion anode and an electrically conductive carbon fiber gas diffusion cathode. A graphene oxide membrane or a graphdiyne oxide membrane is disposed between the electrically conductive carbon fiber gas diffusion anode and electrically conductive carbon fiber gas diffusion cathode. The temperature of the cell can be varied to increase water molecule adsorption (condensation), dissociation rate, and proton current, hydrogen evolution reaction rate, and hydrogen production. In one practice, humid air is contacted against a surface of the carbon fiber gas diffusion anode that is cooled down to the dew point or slightly lower than the dew point temperature of the humid air, which surface that is opposite the membrane.

Description

CATALYST-FREE WATER ELECTROLYSIS IN GRAPHENE OXIDE AND / OR GRAPHDIYNE OXIDEFIELD

[0001] The disclosure pertains to catalyst-free electrolysis of water molecules adsorbed from a humid atmosphere at its dew point temperature to produce hydrogen gas.BACKGROUND

[0002] Hydrogen is one of the most effective means by which large, grid-scale energy coming from renewable and intermittent power sources can be stored for long durations of time. With the growing capacity of localized renewable energy sources surpassing the gigawatt range, a storage system of equal magnitude is required.

[0003] Electrolysis of water in proton exchange membranes (PEM) provides a sustainable solution for the production of hydrogen, and is well suited to couple with energy sources such as wind and solar. The water vapor electrolysis using PEMs composed of graphene oxide (GO) nanosheets is also known. However, PEM electrolysis requires the use of scarce, expensive materials and components such as noble catalysts (e.g., platinum group metals, e.g., Pt, Ir, and Ru. Fig. 1(a) shows a representative scheme for a prior ail PEM water electrolysis cell.

[0004] Hygroelectricity involves direct electricity generation from interactions between ambient moisture and hydrophilic membranes made out of nanocarbon materials, such as graphene oxide and various metal oxides. Here, water molecules adsorbed on the surface of such a graphene oxide membrane spontaneously dissociate, and diffuse through the membrane due to the gradient of the protons, and create a potential difference of up to about 1 .5 V on the opposite sides of the membrane when the system is exposed to an atmosphere of 80% relative humidity (RH) at 25 °C. Like PEM electrolysis, typical hygroelectrical cells employ catalysts. Use of catalysts increases costs and leads to decreased efficiency over time due to such things as the catalyst poisoning and the like. Fig. 1(b) shows a representative scheme for a prior ail hygroelectric cell.

[0005] Graphene oxide (GO) is known for its use as an electrocatalyst for the oxygen reduction reaction (ORR) in fuel cells. It is also known that hydrogen bonding of bulk water in contact with oxide material surfaces induces proton transfer leading to a reduced activation barrier in the dissociation of water molecules. While GO can at times show a general water dissociating (WD) mechanism with oxides, and because O-H bond reorganization in the presence of an electric field is also involved in the ORR, the nature of its use as a water dissociation catalyst is not specifically known.SUMMARY

[0006] In one aspect, the disclosure is directed to an electrolysis cell for catalyst-free water electrolysis (i) an electrically conductive carbon fiber gas diffusion anode and an electrically conductive carbon fiber gas diffusion cathode; and (ii) a graphene oxide (GO) membrane or a graphdiyne oxide (GDY O) membrane disposed between the electrically conductive carbon fiber gas diffusion anode and electrically conductive carbon fiber gas diffusion cathode. In one practice, a power source is used to apply a voltage between the carbon fiber gas diffusion anode and the carbon fiber gas diffusion cathode. In one practice, a temperature control device can be used to control the temperature of the electrically conductive carbon fiber gas diffusion anode, the electrically conductive carbon fiber gas diffusion cathode, or the graphene oxide membrane and / or the graphdiyne oxide membrane to improve operation in various conditions, this includes controlling the surfaces of any one or more of the foregoing. For example, the temperature of the electrically conductive carbon fiber gas diffusion anode, the electrically conductive carbon fiber gas diffusion cathode, or the graphene oxide membrane or the graphdiyne oxide membrane, including the surfaces of same, can be controlled so as to be at the dew point of humid atmosphere that is in contact with one or more of the surfaces of the electrically conductive carbon fiber gas diffusion anode opposite the graphene oxide membrane or the graphdiyne oxide membrane. In one practice, the temperature of one or more of the surfaces, e.g., the surfaces of one or more of the electrically conductive carbon fiber gas diffusion anode, the electrically conductive carbon fiber gas diffusion cathode, and / or the graphene oxide membrane or thegraphdiyne oxide membrane, is controlled so as to be at or about and slightly below the temperature of the dew point to obtain the highest rate of water molecule adsorption (condensation).

[0007] In another aspect, the disclosure is directed to a method for catalyst-free electrolysis of water comprising: (i) providing an electrolysis cell comprising (a) an electrically conductive carbon fiber gas diffusion anode and an electrically conductive carbon fiber gas diffusion cathode; and (b) a graphene oxide membrane or a graphdiyne oxide membrane disposed between the electrically conductive carbon fiber gas diffusion anode and the electrically conductive carbon fiber gas diffusion cathode; (ii) contacting a surface of the electrically conductive carbon fiber gas diffusion anode opposite the graphene oxide membrane or the graphdiyne oxide membrane with a humid atmosphere, such as humid air, preferably the surface is at a temperature equal to or about slightly lower than the dew point of the water vapor in the humid atmosphere, under conditions effective to cause maximum the adsorption (e.g., via condensation) of the water vapor in the humid atmosphere through the electrically conductive carbon fiber gas diffusion anode to the surface of the graphene oxide membrane or the graphdiyne oxide membrane; (iii) dissociating the water adsorbed in step (ii) on the graphene oxide membrane or the graphdiyne oxide membrane under conditions effective to conduct protons from the dissociated water to the electrically conductive carbon fiber gas diffusion cathode; and (iv) generating hydrogen gas and releasing it through the electrically conductive carbon fiber gas diffusion cathode, the hydrogen gas generated as a result of a hydrogen evolution reaction.

[0008] In one practice, the graphene oxide membrane or the graphdiyne oxide membrane comprises oxygen-containing functional groups selected from one or more of the following epoxy, hydroxyl, carbonyl, and carboxyl. In one practice, the graphene oxide membrane and / or the graphdiyne oxide membrane comprises flakes and the majority of the carbonyl and carboxyl groups are located at the edge of the flakes or at vacancy sites, and the majority of the epoxy and hydroxyl groups are located on the basal plane of the flakes.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figs. 1(a) and 1(b) are schematic representations of prior art practices of a PEM water electrolysis cell and a hydroelectric cell, respectively.

[0010] Fig. 2(a) is a schematic of an embodiment of an electrolysis cell for catalyst-free electrolysis of water vapor from a humid atmosphere as per the disclosure. Fig. 2(b) is a schematic of another embodiment of an electrolysis cell for catalyst-free electrolysis of water vapor from a humid atmosphere as per the disclosure.

[0011] Fig. 3 is a graph of the concentration of water molecules (ppm) in air and relative humidity (RH) at 21 °C vs. dew point (Td) (frost Tf) point. The graph can be used as a calibration curve or a moisture conversion graph. The standard range of the sensitivity of the relative humidity sensors from 5% to 95 % at 21 °C corresponds to the dew points from approximately - 20°C to +20°C, which is a very narrow range of the concentrations of the water molecules in air from approx. 103ppm to 104ppm.

[0012] Fig. 4 is a schematic presentation of the coverage function 9 of the surface with water molecules at the dew point. As seen, it is a substantially smooth step-like function 0 changing from 0 to 1 with an inflection point which corresponds to dew point (S-like descending curve).

[0013] Fig. 5(a) is a graph of a MATLAB calculation of the coverage of adsorbed water molecules at condensation 0(T) as defined by equation (3) herein. The parameters C and To, are related to dew point and the activation energy for adsorption. Fig. 5(b) is a graph showing the temperature dependence of the conductance of GO membrane experimentally measured at condensation of water in N2 flow with the dew point TD~+14°C, TD~+18°C and TD~+24°C while the temperature is decreasing.

[0014] Figs. 6(a), 6(b), 6(c), 7(d) are graphs showing open circuit potential difference generated between top and bottom of g-GO membrane electrodes in response to the intermittent periodic variation of the humidity. In Fig. 6(a), TD varies from min value at about -40°C to max value from TD = -10°C to +5°C. In Fig. 6(b) three hygroelectric pulses zoomed in from min value at or about -40°C to the max humidity level TD = +5°C. In Fig. 6(c), one of three of the hygroelectric pulses in Fig. 6(b) at the humidity level variation TD from approximately -40°C to +5°C. Fig. 6(d) is the same as Fig. 6(c) with zoomed in front of the hygroelectric pulse, which allows to roughly estimate the proton diffusion time through the membrane thickness as the delay of the hygroelectric pulse in respect to the humidity saturation tDiff ~60sec.

[0015] Fig. 7(a) is a graph showing representative behavior of the proton current vs. time with the step like variation of the humidity TD from -15°C to +15°C. Fig. 7(b) is a graph of the proton current vs. humidity measured in dew points TD, Fig. 7(c) is a graph showing the linear dependence of the proton current vs. humidity in TD in semi-log scale.

[0016] Fig. 8(a) is a graph showing a double potential step and the current response, and Fig. 8(b) is a graph showing a current response in linear coordinates and in insert: the current response Cottrell coordinates (see equation 6 herein) is linear.

[0017] Figs.9(a), 9(b), 9(c) are graphs of the temperature scan signal (proton current vs. time) in an embodiment of the GO membrane of the disclosure at a dew point TD= -12°C (lower than 0°C)(See Fig. 9(a)) and at TD= +5°C (higher than 0°C)(See Fig. 9(b)), both in linear scale vs time and vs. T (See Fig. 9(c)).

[0018] Figs.10(a) and 10(b) are graphs showing temperature dependences of the proton current membrane at a dew point Tj>- -12°C (lower than 0°C)(see Fig. 10(a)) and TD= +5°C (higher than 0°C)(see Fig. 10(b)) in Arrhenius coordinates. The activation energy EA of the proton current was found to be about leV.

[0019] Fig. 11 is a schematic representation of a potential mechanism for proton transport through a 2D graphene crystal due to the hopping of protons between epoxy groups on both sides of the basal plane of graphene oxide. The red curve represents the potential profile along the direction of proton permeation.DETAILED DESCRIPTION

[0020] As used herein terms such as “a,” “an,” and “the” are not intended to refer to only a single entity but include the general class of which a specific example may be used for illustration. Terms defined herein in the singular are intended to include those terms defined in the plural and vice versa.

[0021] Reference to any numerical range as used herein expressly includes each numerical value (including fractional numbers and whole numbers) encompassed by that range and including endpoints of that range. For illustrative purposes only, a reference to a range of “0.0001 to 5000” includes whole numbers such as 5000, 4999, 4998...3, 2, 1; and includes fractional numbers such as 0.00011, 0.00012...0.1, 0.2, 0.3...1.1, 1.2, 1.3....100.5, 100.6...4900.5, 4990.6, 4990.7 etc.

[0022] As used herein, the term “about” includes the value listed and indicates that the value listed may be somewhat altered, as long as the alteration does not result in nonconformance of the article or method or system herein described. For example, the term “about” as used herein can refer to a variation of between ±1% up to ±10%, including any value therebetween, including without limitation ranges within same, such as between ±1% up to ±8%, between ±1% up to ±5%, between ±1% up to ±3% and the like. The term “at about slightly lower than” as used herein can refer to a variation of between -1% to -10%, including any value therebetween, including without limitation ranges within same, such as between -1% to -8%, and between -1% to -5%, between -1% to -3% and the like. The term “majority” as used herein means more than 50%.

[0023] Referring to Fig. 2(a), thereat is a schematic representation of an embodiment of an electrolysis cell 100 for catalyst-frcc water electrolysis comprising an electrically conductive carbon fiber gas diffusion anode 110 and an electrically conductive carbon fiber gas diffusion cathode 120. A membrane 130, which can comprise a graphene oxide membrane and / or a graphdiyne oxide membrane, is disposed between the electrically conductive carbon fiber gas diffusion anode 110 and the electrically conductive carbon fiber gas diffusion cathode 120. In one practice, at least a portion of either or both of surfaces 150 and 160 of conductive carbon fiber gas diffusion anode 110 and the electrically conductive carbon fiber gas diffusion cathode 120, respectively facing membrane 130, is in contact with membrane 130. In another practice, substantially the entirety of surfaces 150 and 160 are in contact with membrane 130. In the practice shown, a power source 140 is used to apply a voltage between the electrically conductive carbon fiber gas diffusion anode 110 and the electrically conductive carbon fiber gas diffusion cathode 120. In one practice, the power source 140 is configured to supply a voltage less than the voltage of electrolysis threshold, for example and without limitation, less than about 1.23V. As depicted, the GO membrane is sandwiched between the two carbon fiber gas diffusion electrodes. The positive electrode 110 is exposed to moist air. Water molecules penetrate through the carbon fiber electrode (anode) 110 and are adsorbed at the GO membrane surface.

[0024] Graphene oxide (GO) is a carbon-based material which in a particular embodiment is covalently functionalized by oxygen-containing functional groups selected from one or more of the following: epoxy, hydroxyl, carbonyl, and carboxyl. In one practice, the GO membrane comprises flakes, as known in the art, see e.g., W.W. Cai, et al. Synthesis and solid-state NMR structure characterization of C 13 labeled graphite oxide. Science 321 , 1815-1817 (2008); A. Lerf, H.Y. He, M. Forster, J. Klinowski. Structure of graphite oxide revisited. J. Phys. Chem. B 102, 4477-4482 (1998); H.Y. He, J. Klinowski, M. Forster, A. Lerf. A new structural model for graphite oxide. Chem. Phys. Lett. 287, 53-56 (1998). In another practice, all or most of the epoxy and hydroxyl groups are located on the basal plane of the GO membrane flakes. In still another practice, the carbonyl and carboxyl groups are located on the edge of the GO membrane flakes and / or at vacancy sites of either the GO membrane flakes or of the GDYO membrane flakes. Due to the presence of these groups the adsorbed water molecules can be spontaneously dissociated on the GO surface. The free protons H+ are driven by the applied electric field to the other side of the GO membraneand interact with free electrons supplied by the cathode. H2 molecules are being formed then due to the hydrogen evolution reaction and collected in the attached to the membrane volume.

[0025] GO is an efficient water dissociation material, lowering the overpotential by 75% compared to a control membrane. It is known that the water molecule can be spontaneously dissociated on GO supported by the (111) surface of the copper substrate. This process involves a proton transferring from water to the interfacial oxygen groups. The water dissociation barrier is decreased so as to be less than or comparable to thermal fluctuations. This enhances the reaction activity of interfacial oxygen groups along the basal plane of GO for water dissociation. The proton transport through monocrystalline membranes made from a mono- and a few-layer graphene, hBN, and molybdenum disulphide (M0S2) is known. As a result, a controllable flow of H2 (hydrogen molecules) can be observed out of the other side of the membrane.

[0026] In a practice of the disclosure, the adsorption of water molecules, their dissociation on the hydrophilic nanocarbon surfaces, and proton current through GO membranes is effectuated. This transport shows exponential Arrhenius-type dependence of conductivity of protons versus temperature with the activation energy of ~ 1.0 eV (similar to the proton transport through monocrystalline graphene membranes). In one practice, the disclosure utilizes one of more hydrophilic nanocarbon materials in the form of electronically insulating graphene oxide, possessing extremely high controllable water molecules adsorption (condensation) and dissociation on its surface. In one aspect of this practice, at low water coverage, molecularly adsorbed water is metastable and dissociates readily by a kinetically preferred pathway.Observations at higher water coverage effectuate more rapid dissociation and collective effects, including water-catalyzed dissociation and proton transport. In the practice of the disclosure, by electronically insulating GO, e.g., by using catalyst free carbon fiber gas diffusion anodes and cathodes, pure proton transport is realized across the membrane for proton harvesting and for a hydrogen evolution reaction for hydrogen production.

[0027] In one practice of the disclosure, the rate of hydrogen generation is determined solely by the proton current in GO membrane. In one instance, since current is defined as the flow ofprotons and a hydrogen molecule ass only two protons and two electrons, an equivalent number of hydrogen molecules will be generated. Since hydrogen production is dictated by current, this is a convenient way to control production rates without actually having to measure the gas production or rely on other parameters that may change with time. With a protonic current density” j” of 0.12 A / cm2, the number of protons coming out of the GO membrane of 1 cm2per second is:N- j / c -0. 12 A / cm2 / 1.6xl0"19C = 0.75xl018protons sec"1cm"2.This proton generation rate has to be decreased by a factor Yi due to H2 molecules evolving out of two protons. As a result, the rate of hydrogen molecule formation per 1 second from 1 cm2GO membrane is:R= 0.375 xlO18sec"1cm"2or 0.6*10"6mol sec"1cm"2or 1.2*10"9kg sec"1cm"2.

[0028] In one practice, the membrane comprises graphene oxide (GO) which is known to be a nonspecifically oxidized derivative of graphene, and which is composed of macromolecular, one atom-thick sheets of sp2 -hybridized carbon. In one practice, a number of carbon sites are sp3 - hybridized with a variety of functional groups such as one of more of epoxy, hydroxyl, carbonyl, or carbonyl, wherein the majority (over 50%) of the epoxy and / or hydroxyl groups are located on the basal plane and the carbonyl and / or carboxyl groups are located at the edge or vacancy sites. GO is also water dispersible, enabling the production of continuous films from GO, which procedures are known in the art. The basal plane and edges of GO platelets (also referred to herein as flakes) are composed of distributed chemical groups containing oxygen, which increases the hydrophilicity of GO and consequently enhance the sensitivity of the sensors to water. Moreover, these chemical groups make GO electronically insulating. The proton conductivity mechanism in GO is initiated by water adsorbed molecules, interacting with hydrophilic functional groups in GO, generating protons (H+). In one aspect, the disclosure is based on the direct current (DC) measurements versus temperature at fixed and well-defined humidity levels, introducing specific values of protonic concentrations in GO films, initiated by water molecules adsorbed and dissociated on the GO surface.

[0029] In one practice, the graphene oxide membrane or the graphdiync oxide membrane 130comprises oxygen-containing functional groups selected from one or more of the following groups: epoxy, hydroxyl, carbonyl, or carboxyl. Without limitation, the oxygen-containing groups are located on the basal plane and / or on the edge of the graphene oxide membrane or of the graphdiyne oxide membrane 130.

[0030] Fig. 2(b) is a schematic representation of another embodiment of an electrolysis cell 200 for catalyst-free electrolysis of water vapor molecules, the cell 200 comprising an electrically conductive carbon fiber gas diffusion anode 210 , an electrically conductive carbon fiber gas diffusion cathode 220, and a membrane 230 comprising a graphene oxide membrane and / or a graphdiyne oxide membrane which is disposed between the electrically conductive carbon fiber gas diffusion anode 210 and the electrically conductive carbon fiber gas diffusion cathode 220. In the practice depicted, cell 200 comprises a power source 240 to apply a voltage between the electrically conductive carbon fiber gas diffusion anode 210 and the electrically conductive carbon fiber gas diffusion cathode 220. In one practice, the power source 240 is configured to supply a voltage less than the voltage of electrolysis threshold, which in one non-limiting instance, such voltage is less than about 1.23V. Electrically conductive carbon fiber gas diffusion anode 210 and electrically conductive carbon fiber gas diffusion cathode 220 are free of any catalytic materials, e.g., metals such as platinum and the like. In one embodiment, the gas diffusion anode 210 consists essentially of electrically conductive carbon fiber. In another embodiment, the gas diffusion anode 210 consists of electrically conductive carbon fiber. In one embodiment, the gas diffusion cathode 220 consists essentially of electrically conductive carbon fiber. In another embodiment, the gas diffusion cathode 220 consists of electrically conductive carbon fiber. In one embodiment, the membrane 130 consists essentially of graphene oxide membrane and / or of the graphdiyne oxide membrane. In another embodiment, the membrane 130 consists of graphene oxide membrane and / or of the graphdiyne oxide membrane.

[0031] As shown in Fig. 2(b), an electrically conductive carbon fiber gas diffusion anode 210 has surface 211 in contact with a first surface 212 of membrane 230, and an electrically conductivecarbon fiber gas diffusion cathode 220 has surface 221 in contact with a second surface 222 of membrane 230, which second surface 222 is on the opposite side of first surface 212 of membrane 230. In one practice, at least a portion of either or both of surfaces 211 and 221 are in respective contact with first and second membrane surfaces 212 and 222; in another practice, substantially the entirety of either or both of surfaces 211 and 221 are in respective contact with first and second membrane surfaces 212 and 222. In one embodiment, membrane 230 (comprising the graphene oxide membrane and / or the graphdiyne oxide membrane either one or both of which comprises flakes) comprises oxygen-containing functional groups selected from one or more of the following groups: epoxy, hydroxyl, carbonyl or carboxyl. In another embodiment, the oxygen-containing groups are located on the basal plane and / or the edge of the graphene oxide flakes of the graphene oxide membrane or of the graphdiyne oxide membrane, 230.

[0032] In the practice shown at Fig. 2(b), a surface 213 of the electrically conductive carbon fiber gas diffusion anode 210 located opposite the graphene oxide membrane or the graphdiyne oxide membrane is configured to be in contact with a humid atmosphere at or about its dew point, denoted in Fig. 2(b) as air @ T DEW POINT. A humid atmosphere includes, without limitation, humid air, and can include other water vapor containing gases. Fig. 2(b) further comprises an accumulation vessel 260 having interior space 270 wherein hydrogen gas (H2) created by cell 200 is accumulated. In the practice depicted, a surface 250 of the electrically conductive carbon fiber gas diffusion cathode 220 opposite the graphene oxide membrane (or the graphdiyne oxide membrane) 230 is configured to release hydrogen gas generated thereat into the accumulation vessel, e.g., through openings 271 in storage vessel 260. Vessel 260 can further comprise conduit 280 and valve 290 through which hydrogen gas in vessel 260 can be removed for use or for storage.

[0033] In another embodiment, cell 200 further comprises a temperature control device (not shown) configured to control the temperature of the electrically conductive carbon fiber gas diffusion anode 210, the electrically conductive carbon fiber gas diffusion cathode 220, and either the graphene oxide membrane or the graphdiyne oxide membrane, 230. For example,electrically conductive carbon fiber gas diffusion anode 210, the electrically conductive carbon fiber gas diffusion cathode 220, and cither the graphene oxide membrane or the graphdiync oxide membrane, 230, can be located on the surface of a cooling unit, e.g., a Peltier 3-stage cooler or on the surface of a copper (Cu) stage of the cold finger cooled down by thermal conductance with the other side immersed in a refrigeration liquid, e.g., liquid nitrogen. In one practice, such a temperature control device comprises a stage located inside a vacuum sealed chamber having intake port and an exhaust ports for the mixture of dry nitrogen flow from a liquid nitrogen tank and moist nitrogen from a water bubbler, mixture comprising specific flow rates to create a defined level of humidity (e.g., the dew point) in the chamber. The humidity level can be controlled by a flow rate control unit (for the mixture) and a pressure controller, and is measured by a commercially available dew point meter. In one practice, the temperature of the electrically conductive carbon fiber gas diffusion anode 210, the electrically conductive carbon fiber gas diffusion cathode 220, and either of the graphene oxide membrane or the graphdiyne oxide membrane, 230, is controlled to be at or about the dew point of the humid atmosphere, e.g., humid air, that is in contact with the surface 213 of the carbon fiber gas diffusion anode 210 opposite the graphene oxide membrane or the graphdiyne oxide membrane, 230.

[0034] In another aspect, the disclosure relates to a method for the catalyst-free electrolysis of water vapor from the atmosphere. Referring without limitation to the embodiment depicted in Fig. 2(b), discussed above and provided as representative, the method comprises (i) providing an electrolysis cell 200 comprising an electrically conductive carbon fiber gas diffusion anode 210 being open to a humid atmosphere, the humid atmosphere being a source of water molecules at a concentration corresponding to the dew point, and an electrically conductive carbon fiber gas diffusion cathode 220; and a graphene oxide membrane and / or a graphdiyne oxide membrane, 230, disposed between the electrically conductive carbon fiber gas diffusion anode 210 and the electrically conductive carbon fiber gas diffusion cathode 220. In one practice, the graphene oxide membrane or the graphdiyne oxide membrane 230 comprises oxygen-containing functional groups selected from one or more of the following: epoxy, hydroxyl, carbonyl, or carboxyl. In one practice, the GO membrane 230 (or the graphdiyne membrane) comprises flakesand the oxygen-containing groups are located on the basal plane and / or the edge of the graphene oxide flakes of the GO membrane (or the graphdiync membrane), 230.

[0035] The method comprises a step (ii) of contacting a surface 213 of the electrically conductive carbon fiber gas diffusion anode 210 opposite the graphene oxide membrane or the graphdiyne oxide membrane 230 with air at the dew point (shown in Fig. 2(b) as AIR @ Toew point) or air that has been cooled down to the dew point of the humid atmosphere, e.g., humid air (if an atmosphere, e.g., air, is at a temperature other than dew point is used it can be cooled down or one or more surfaces of the device can be cooled down such that they are at the dew point) under conditions effective to transfer at least a portion of the water (denoted in Fig. 2(b) as H2O) in the humid atmosphere from the electrically conductive carbon fiber gas diffusion anode 210 to the graphene oxide membrane or the graphdiyne oxide membrane 230. In one practice, at least a portion of the water in the humid atmosphere condenses on the surface 213 of the electrically conductive carbon fiber gas diffusion anode 210 and on the surface of the graphene oxide membrane or the graphdiyne oxide membrane, 230.

[0036] The method comprises a step (iii) of dissociating at least a portion of the water transferred in step (ii) on the surface of the graphene oxide membrane or the graphdiyne oxide membrane 230 under conditions effective to conduct protons (denoted in Fig. 2(b) as H+) from the dissociated water to the electrically conductive carbon fiber gas diffusion cathode 220. The method comprises a step (iv) of generating hydrogen gas (denoted in Fig. 2(b) as H2) from the protons at the electrically conductive carbon fiber gas diffusion cathode 220. In one practice, the method comprises providing a power source 240 and applying a voltage between the electrically conductive carbon fiber gas diffusion anode 210 and the electrically conductive carbon fiber gas diffusion cathode 220. In one instance, the voltage applied is less than about 1.23 V.

[0037] In one practice, shown at Fig. 2(b), the method further comprising a step of collecting the hydrogen gas accumulated in step (iv) in an accumulation vessel 260. As shown, the hydrogen gas passes into vessel 260 via openings 271 which connect the interior 270 of vessel 260 with the electrically conductive carbon fiber gas diffusion cathode 220 whereat the hydrogen gas isgenerated. In one practice, the method further comprises controlling the temperature of the electrically conductive carbon fiber gas diffusion anode 210, electrically conductive the carbon fiber gas diffusion cathode 220, and the graphene oxide membrane and / or the graphdiyne oxide membrane, 230. For example, the temperature at which the electrically conductive carbon fiber gas diffusion anode 210, the electrically conductive carbon fiber gas diffusion cathode 220, and the graphene oxide membrane and / or the graphdiyne oxide membrane, 230, is controlled so as to be at or about the dew point of the humid atmosphere that is in contact with the surface 213 of the electrically conductive carbon fiber gas diffusion anode 210 opposite the graphene oxide membrane or the graphdiyne oxide membrane, 230. Thus, for example, in arid conditions, the temperature can be controlled so that the temperature is at the dew point and controlled so as to condense the water from the air onto surface 213. Temperature control can be achieved by enclosed all or part of the electrically conductive carbon fiber gas diffusion anode 210, the electrically conductive carbon fiber gas diffusion cathode 220, and the graphene oxide membrane and / or the graphdiyne oxide membrane, 230, and controlling the temperature therein by means known in the art.I. Graphene Oxide:

[0038] In one practice, the membrane comprises graphene oxide (GO) which is a nonspecifically oxidized derivative of graphene, and which is composed of macromolecular, one atom-thick sheets of sp2 -hybridized carbon. Thus, a number of carbon sites are sp3 -hybridized with a variety of functional groups such as epoxy, hydroxyl, carbonyl, or carboxyl. GO is also water dispersible, enabling the production of continuous films from GO, which procedures are known in the art. The basal plane and edges of GO platelets are composed of distributed chemical groups containing oxygen, see Figs. 3(a), 3(b), which increases the hydrophilicity of GO and consequently enhance the sensitivity of the sensors to water. Moreover, these chemical groups make GO electronically insulating. The proton conductivity mechanism in GO is initiated by water adsorbed molecules, interacting with hydrophilic functional groups in GO, generating protons (H+). In one aspect, the disclosure is based on the direct current (DC) measurements versus temperature at fixed and well-defined humidity levels, introducing specific values ofprotonic concentrations in GO films, initiated by water molecules adsorbed and dissociated on the GO surface.II. Humidity control: Dew point (TD, °C) vs. Relative Humidity (RH, %). Water adsorption coverage function 0:

[0039] In one practice of the disclosure, moisture content control and reporting is in terms of relative humidity (RH, %). The common range of RH (e.g., from 5% to 95%) corresponds to very narrow concentrations of water molecules in air (from approximately 103to 104ppm or, within the range of dew point (TD) values, approximately from -15°C to +20 °C, as seen in Fig. 3. Additionally, relative humidity depends on temperature and in one practice is determined at a specified temperature only. Typically, controlling humidity in the low moisture concentration range by using RH as a metric is difficult. Thus, in one practice, dew point (TD) (or frost point (TF) at low humidity levels, when TD<0°C), which is a measure of the absolute amount of moisture in the air regardless of temperature, is used for moisture control. Using same as a metric for controlling humidity, rather than relative humidity which varies with temperature, dew point provides an indication of moisture or the latent energy content in air and will remain constant regardless of temperature.

[0040] Dew point temperature is known as the temperature to which air would have to cool (at constant pressure and constant water vapor content) in order to reach saturation. In one practice of the disclosure, measurements of dew point by Chilled Mirror Hygrometers, as known in the art and as used in Standards and Metrology labs as well as in industrial applications, can be employed and are called dew point because this value predicts at what temperature moisture will condense on a cooled mirror surface. In one instance, Chilled Mirrors Hygrometers measure the dew point temperature (or frost point at the temperatures below freezing) directly by controlling a reflective surface to equilibrate dew (frost) formation and evaporation, and precisely measure the temperature of the mirror at this point. The reflection of the light by the surface of the mirror is the measurable physical parameter that is changed at the dew or frost point temperature. The coverage of the surface with the water molecules at dew point is a rather smooth s- shape (ascompared to a sharp, step-like shape) function 0 changing from 0 to 1 depending upon the temperature T with an inflection point which corresponds to dew point TD, sec Fig. 4.III. Model for the Kinetics of Water Molecules Adsorption and the Thermal Adsorption Spectroscopy Method:

[0041] Thermal Adsorption Spectroscopy (TAS) is a method applicable to a constant rate of cooling mode, when AT= -aAt (t is time, T is temperature, and a is the rate of the temperature change with time). Key steps in developing the model are outlined below. In the constant rate of cooling mode, the conductance of GO film as the specific physical parameters reflecting polar water molecules condensation (and the coverage function 0(T)) of the surface of CNTs (1-D conducting material) and GO (film of 2-D flakes). The coverage function 0 is defined herein as the ratio of the adsorbed water molecules Nad on the surface to the maximum possible places for adsorption Nad max'

[0042] Applying the constant rate of cooling mode to the TAS experimental method, i.e., dT=-a dt (t is time, T is temperature, and a is an experimental parameter - rate of the temperature change with time), for the 1st order adsorption, the solution for the coverage function is obtained as: ln(0) = -C ( ) exp (-y) or 9 = exp{ -C ( ) exp (- )} • (3)

[0043] This solution shows an explicit behavior of the adsorption via the coverage function 3 in respect to the temperature T: if — > 0 , 9 = 1 , and if T ■x, 9 = 0. Equation 3 obtains S-like descending curve, as seen in Fig. 5(a), with a significant dependence of the position of the inflection point of the coverage function 9 (T) on the parameter To(related to the activation energy of adsorption Ead) at fixed parameter C. This calculated curve is similar to theexperimental shape of the resistance of the GO membrane in the presence of water vapors in atmosphere shown in the Fig. 5(b).

[0044] Examples: Demonstration of Hygroelectricity:

[0045] When GO membrane was subjected to humid atmosphere, an open circuit potential difference between positive and negative electrodes of the membrane was observed, see Figs. 6(a) to 6(d). The potential difference increased gradually until reaching the saturation of approximately 25 mV at humidity of TD= 5°C (see Fig.6(a)) and goes down to zero, when the humidity drops lower than TD= -10°C (see Fig. 5(b)). This behavior was found to be consistent with the hygroelectricity effect, when the water molecules adsorbed on the surface of graphene oxide membrane spontaneously dissociate, and the protons diffuse through the membrane due to the gradient of the protons, creating a potential difference on the opposite sides of the membrane. The total proton current density j due to drift and diffusion components is given:where “e” is the unit electric charge, G. D and 3N / 3x are the conductivity, diffusion coefficient and the concentration gradient of protons, and cU / cx is the potential gradient through the membrane. The open circuit steady-state zero current density (j=0) is a balance of proton transport driven by the concentration gradient and the induced electrical potential gradient, which goes from (la): n fdN\ (du\ .De l — 1 = 0- 1 — I (2a) dx / dxj

[0046] According to the mechanism interpreted above and Equation (2a), the generated potential gradient and is a result the hygroelectric signal of the potential difference AU across the membrane thickness 1:will exist as long as the proton concentration gradient due to water molecules adsorption and dissociation is present. Such a conclusion is supported by the results shown in Figs. 7(a) to 7(d) with the potential difference (hygroelectric voltage AU) signals consist of positive pulses only. To identify the factors that influence the induced potential difference and to determine themechanism of proton conductivity, the effects of the humidity level at fixed temperature and the membrane temperature in a wide temperature range that water vapor condensation and adsorption occurs and proton current at fixed small voltage applied to the membrane was observed. Information on the nature of the proton transport can be obtained by measuring the conductivity.

[0047] Effect of the humidity level on proton conductivity at fixed temperature:

[0048] Observations of the proton current through GO film when a small potential difference was applied between the upper and the lower surfaces with humidity variation at room temperature were made. Fig. 7(a) shows typical behavior of the proton current versus time with the step-like variation of the humidity TD increasing from -15°C to +15°C. This proton current increase was plotted versus TD in Fig. 7(b). This dependence was exponential and appeared to be linear in semi-log scale, which explained the exponential dependence of the proton current versus humidity measured in dew points. The linear dependence of the proton current versus the absolute concentration of water molecules measured in ppm according to the plot shown in Fig. 3. This observation indicated the proportionality of the proton conductivity to the concentration of the water molecules being adsorbed, dissociated on the surface of GO layer and, as a result, determined the concentration of the protons participating in the current flow. Fig. 7(c) is a graph showing the linear dependence of the proton current vs. humidity in TD in semi-log scale. Fig. 8(a) is a graph showing a double potential step and the current response, and Fig. 8(b) is a graph showing a current response in linear coordinates and in insert: the current response Cottrell coordinates (see equation 6 herein) is linear.

[0049] Diffusion controlled proton current:

[0050] Proton diffusion is responsible for the hygroelectric voltage built up when water molecules are adsorbed and spontaneously dissociated at the hydrophilic functional groups on the surface of GO layer, generating protons (H+):H20 = 2H++l / 2O2+2e-

[0051] The humidity level determined the concentration of the protons participating in current flow. As a result, according to the equations (2a) and (3a), the potential difference AU across the membrane thickness was determined by the diffusion coefficient and the concentration gradient of protons. If a small potential difference was applied to both sides of the membrane, the proton current through GO membrane was diffusion controlled (diffusion limited current). The diffusion-limited current response ID(1) is known to be determined by the Cottrell equation, when the potential is a step function in time, for the planar electrode and one-dimensional diffusion:where, I( t)= current, in amperes , F - Faraday constant 96485 C / mol, A - area of the (planar) electrode in cm2, Co- initial concentration of protons due to in mol / cm3, D- diffusion coefficient of protons in cnr / s t -time in s.

[0052] This equation can be rewritten for the diffusion controlled current density and expressing the concentration of the protons as:

[0053] This equation describes the current density response when the potential is a step function in time at specified temperature T, as long as D(T) and the carrier concentration No (protons in cm'3). In practice, the Cottrell equation simplifies to jD(t) = k t“1 / 2, (6) where k is the collection of e, D, No. The Cottrell equation describes the change in electric current with respect to time in a controlled potential experiment, such as chronoampcromctry. Specifically, it describes the current response when the potential is a step function in time. It wasderived by Frederick Gardner Cottrell in 1903. The current measured depends on the rate at which the analyte diffuses to the electrode. That is, the current is said to be "diffusion controlled". Figs. 9(a) and 9(b) show the transient current response on a step change of voltage on the membrane. The current response in Cottrell coordinates is linear. This is proof that proton current through the GO membrane is diffusion controlled.

[0054] Mechanism of Proton Transport through a Multilayer of Two-Dimensional Crystals (GO film):

[0055] The measurements of proton transport through two-dimensional (2D) crystals of graphene demonstrated that these crystals pose an energy barrier for incoming protons of about 0.8 eV for graphene, see e.g., S. Hu, M. Lozada-Hidalgo, F. C. Wang, A. Mishchenko, F. Schedin, R. R. Nair, E. W. Hill, D. W. Boukhvalov, M. I. Katsnelson, R. A. W. Dryfe, I. V. Grigorieva, H. A. Wu, A. K. Geim. “Proton transport through one-atoni-thick crystals” Nature, 516, 227 (2014). Critically, the initial energy of incoming protons is not given by thermal excitations (about 25 meV at room temperature) but is instead, about 0.2 eV owing to zero-point oscillations of protons bound to oxygen atoms in the proton-conductive media. This correction lifts the total energy barriers, E, posed by the crystals to about 1.0 eV for graphene. Measurements were made of proton transport through GO film, which presents a multilayer of two-dimensional graphene crystals. A small voltage of 0.1 V was applied to the membrane and the temperature was scanned in the range from +20°C to -60°C at fixed value of the humidity with a constant temperature rate dT=-a dt (t is time, T is temperature, and a is an experimental parameter - rate of the temperature change with time). As observed, well-defined peaks of the proton current signal vs. time (see Fig 9(a) and 9(b)) and versus. T (see Fig. 9(c)) which indicates that the right conditions have been created for proton transport to the negative electrode and for hydrogen evolution. The magnitude of the peak and its position depend strongly on the humidity value TD.

[0056] The dependence of the conduction of protons through graphene oxide (GO) membrane versus temperature at fixed humidity levels was determined to depend on temperature as it is seen in Figs. 10(a), 10(b). Initial increases of the conduction while the temperature dropped corresponded to the protonic concentration increase due to water molecules adsorption atcondensation and with dissociation. In the condensation process, dew point temperature was determined, as the temperature of the fastest adsorption rate of water molecules (and the proton conduction fastest increase). At some temperatures, either close to 0°C, or at lower temperatures, the proton conductivity started strong exponential decreases via the Arrhenius-type dependence with the activation energy close to 1.0 eV (see Figs. 10(a) and 10(b)). The dependence of proton conductivity through GO films on temperature at fixed and relatively low humidity levels (for example, with the frost point set to Tf = -12 °C), possesses a peak-like behavior, as shown in the Figs. 9(a) to 9(c). An analysis of these types of the curves in the semi-log scale showed the asymmetric shape behavior with 2-3 orders of magnitude conductance change on each side of the peak. This meant that a competition of totally opposite processes in the vicinity of dew Td(Tf) point was present.

[0057] A plot of the lower temperature- side pail of the conductance dependence on temperature (see Fig. 10(a)) in Arrhenius coordinates showed the straight line (see Fig. 10(b)). The activation energy EA is calculated from this Arrhenius plot, described by the equationwhere o is the conductivity of GO film exposed to the water vapor, ku is the Boltzmann constant and T is the absolute temperature.

[0058] The value of the activation energy EA of proton conductivity through GO films was determined to be about leV. One- atom- thick crystals are impermeable to atoms and molecules, but hydrogen ions (thermal protons) penetrate through them. During proton transport through two-dimensional (2D) graphene crystals in the external electric field, the protons penetrate through the hexagonal lattice rings covered with dense electron clouds (see Figure 12). The electron cloud density in the lattice rings greatly affects the proton transport barrier. It was demonstrated that these crystals posed an energy bander for incoming protons of about 0.8 eV for graphene.

[0059] The initial energy of incoming “free” protons was expected to be equal to zero, or to the thennal excitations I<BT( about 25 meV at room temperature). Instead, the charged protons werenot isolated and not free. They strongly interacted with their surroundings. It is known that (i) oxygen groups present on GO arc mainly present in forms of epoxy, OH, carbonyl and carboxyl groups; and that (ii) most epoxy and OH groups lie on the basal plane of the graphene sheet and carbonyl and carboxyl groups can only sit at the edge or vacancy sites (see Figs. 13(a) and 13(b)). Another GO model proposed the functional groups are at the edges are mainly double- interactive carboxyls and double-adjacent phenolic hydroxyls, while the groups on the plane are mainly collocated epoxies and hydroxyls on both sides of the plane with meta-positional hydrogen bond interaction. The epoxide functional groups are a major contributor to efficient proton transport proton bonding to oxygen atoms of epoxide functional groups in GO it is about 0.2eV below to zero-point oscillations of protons. This correction lifts the total energy barriers, EA, posed by the crystals to about l.OeV for graphene (see Fig. 11).

[0060] When the electron cloud density in the lattice rings affected the proton transport bander, proton conductivity and the rate of hydrogen production needed to be increased and the activation energy of proton transport in the membrane substrate needed to be reduced.

[0061] Graphdiyne oxide (GDYO) is the oxidized form of Graphdiyne (GDY). GDY is a 2D carbon allotrope composed of sp and sp2 hybridized carbon atoms (see Figs. 15(a) and 15(b)). The sp hybridization provided GDYO with greater electron-withdrawing properties as compared to GO, thereby enabling faster humidity response. GDYO nanosheets exhibit the highest proton conductivity among the reported oxidized carbon allotropes. The 2D structure of GDYO provides a platform of introducing hydrophilic sites for the formation of proton conduction channels. Thus, with GDYO films, cells of the disclosure demonstrate significantly improved rates of hydrogen production in our prototype.

[0062] Cost:

[0063] Estimated cost of 1 kg of hydrogen produced by the practice of the disclosure as compared with the target of the Energy Hydrogen Program Plan, promulgated by the USDepartment of Energy, Feb. 2020, Hydrogen and Fuel Cells Program Record 19009, “Hydrogen Production Cost from PEM Electrolysis- 2019:

[0064] The cost of hydrogen produced from low temperature electrolysis depends on the electricity cost, which currently ranges from $5-$6 / kg-H2 for electricity pricing in the $0.05- $0.07 / kWh range. The availability of lower-cost electricity — for example, in the $0.02- $0.03 / kWh range from emerging wind and solar assets — coupled with ongoing advancements in electrolyzer technologies offers a pathway to cost-competitive hydrogen, at less than $2 / kg, which is the Energy Hydrogen Program target cost.

[0065] The current cost of H2 produced by the method of the disclosure:

[0066] As soon as the applied potential difference = 1.2V and the current density is 0.12 A / cm2, the power needed to run the catalyst-free electrolysis cell of the disclosure of 1 cm2area is:P=V*j = 1.2 V * 0.12 A / cm2= 0.144 W / cm2.The amount of H2 produced per 1 Joule of energy in the catalyst-free electrolysis cell of the disclosure is:RE= R / P= 1.2*10"9kg sec"1cm"2 / 0.144 W cm"2= 8.3* 10"9kg / JouleThe lowest Energy Hydrogen Program price = $0.02 / kWh corresponds to the price- 5.5* 10"9$ / Joule. As a result, the estimated cost of 1 kg of hydrogen produced by the practice of the disclosure is:Cost= price / RE = 5.5*10"9$*Joule-l / 8.3*10"9kg*Joule-l = 0.7 $ / kg

[0067] Given an H2 production rate of 1.2*10"8kg sec"1cm"2and taking into account two variables for scaling up: total current in one cell and Number of Cells, due to the increasingsurface area of the cell from 1 cm2 to 100 cm2, and utilizing 100 cells, during a full day (24 hours) will allow to produce 12kg of H2 ( or 0.5 kg / h). This is advantageous given that 1 kg of hydrogen can produce 33kWh of energy. The estimated cost of 1 kg of hydrogen produced by our method (0.7 $ / kg) is expected to be approx. 3 times less expensive than the lowest cost target ($2 / kg) of the Department of Energy Hydrogen Program Plan.

Claims

CLAIMSWhat is claimed is:

1. An electrolysis cell for catalyst-free electrolysis of water vapor from a humid atmosphere to produce hydrogen gas comprising:(i) an electrically conductive carbon fiber gas diffusion anode and an electrically conductive carbon fiber gas diffusion cathode; and(ii) a graphene oxide membrane or a graphdiyne oxide membrane disposed between the electrically conductive carbon fiber gas diffusion anode and electrically conductive carbon fiber gas diffusion cathode.

2. The electrolysis cell of Claim 1 wherein the graphene oxide membrane or the graphdiyne oxide membrane comprises oxygen-containing functional groups selected from one or more of the following: epoxy, hydroxyl, carbonyl, and carboxyl.

3. The electrolysis cell of Claim 2 wherein the graphene oxide membrane or the graphdiyne oxide membrane comprises flakes; and wherein the majority of the epoxy and hydroxyl groups are located on the basal plane of the flakes; and the majority of the carbonyl and carboxyl groups are located at the edge of the flakes or vacancy sites of the flakes.

4. The electrolysis cell of Claim 1 further comprising a power source to apply a voltage between the electrically conductive carbon fiber gas diffusion anode and the electrically conductive carbon fiber gas diffusion cathode.

5. The electrolysis cell of Claim 4 wherein the power source is configured to supply a voltage less than the voltage of electrolysis threshold.

6. The electrolysis cell of Claim 5 wherein the voltage is less than about 1.23V.

7. The electrolysis cell of Claim 1 wherein the graphene oxide membrane or the graphdiyne oxide membrane comprises a first surface in contact with the electrically conductive carbon fiber gas diffusion cathode, and a second surface in contact with the electrically conductive carbon fiber gas diffusion anode.

8. The electrolysis cell of Claim 7 wherein a surface of the electrically conductive carbon fiber gas diffusion anode opposite the graphene oxide membrane or the graphdiyne oxide membrane is at the dew point or about slightly lower than the dew point temperature of the humid atmosphere to obtain a maximum rate of water molecule adsorption from the water vapor.

9. The electrolysis cell of Claim 8 further comprising an accumulation vessel, and wherein a surface of the electrically conductive carbon fiber gas diffusion cathode opposite the graphene oxide membrane or the graphdiyne oxide membrane is configured to release hydrogen gas generated thereat into the accumulation vessel.

10. The electrolysis cell of Claim 1 further comprising a temperature control device configured to control the temperature of the electrically conductive carbon fiber gas diffusion anode, the electrically conductive carbon fiber gas diffusion cathode, and either the graphene oxide membrane or the graphdiyne oxide membrane.

11. The electrolysis cell of Claim 10 wherein the temperature of at least the surface of the electrically conductive carbon fiber gas diffusion anode, the electrically conductive carbon fiber gas diffusion cathode, and either of the graphene oxide membrane or the graphdiyne oxide membrane is controlled to be at the dew point or about slightly lower than the dew point temperature of the humid atmosphere that is in contact with the electrically conductive carbon fiber gas diffusion anode opposite the graphene oxide membrane or the graphdiyne oxide membrane to obtain a maximum rate of water molecule adsorption from the water vapor.

12. A method for catalyst-free electrolysis of water vapor from a humid atmosphere to produce hydrogen gas comprising:(i) providing an electrolysis cell comprising (a) an electrically conductive carbon fiber gas diffusion anode and an electrically conductive carbon fiber gas diffusion cathode; and (b) a graphene oxide membrane or a graphdiyne oxide membrane disposed between the electrically conductive carbon fiber gas diffusion anode and the electrically conductive carbon fiber gas diffusion cathode;(ii) contacting a surface of the electrically conductive carbon fiber gas diffusion anode opposite the graphene oxide membrane or the graphdiyne oxide membrane with a humid atmosphere under conditions effective to transfer at least a portion of the water molecules in the humid atmosphere from the electrically conductive carbon fiber gas diffusion anode to the graphene oxide membrane or the graphdiyne oxide membrane;(iii) dissociating at least a portion of the water molecules transferred in step (ii) in the graphene oxide membrane or the graphdiyne oxide membrane under conditions effective to conduct protons from the dissociated water to the electrically conductive carbon fiber gas diffusion cathode; and(iv) generating hydrogen gas from the protons at the cathode of the graphene oxide membrane or the graphdiyne membrane and penetrate through the electrically conductive carrion fiber gas diffusion cathode.

13. The method of Claim 12 further comprising collecting the hydrogen gas generated in step (iv) in an accumulation vessel.

14. The method of Claim 12 further comprising applying a voltage between the electrically conductive carbon fiber gas diffusion anode and the electrically conductive carbon fiber gas diffusion cathode.

15. The method of Claim 14 wherein the voltage applied is less than about 1.23 V.

16. The method of Claim 12 wherein the graphene oxide membrane or the graphdiyne oxide membrane comprises oxygen-containing functional groups selected from one or more of the following: epoxy, hydroxyl, carbonyl, or carboxyl.

17. The method of Claim 16 wherein the graphene oxide membrane or the graphdiync oxide membrane comprises flakes; and wherein the majority of the epoxy and hydroxyl groups are located on the basal plane of the flakes; and the majority of the carbonyl and carboxyl groups are located at the edge of the flakes or at vacancy sites.

18. The method of Claim 12 further comprising controlling the temperature of the electrically conductive carbon fiber gas diffusion anode, electrically conductive the carbon fiber gas diffusion cathode, and either the graphene oxide membrane or the graphdiyne oxide membrane.

19. The method of Claim 18 wherein the temperature at which the electrically conductive carbon fiber gas diffusion anode, the electrically conductive carbon fiber gas diffusion cathode, and either the graphene oxide membrane or the graphdiyne oxide membrane is controlled so as to be at or about slightly lower than the dew point temperature of the humid atmosphere that is in contact with the surface of the electrically conductive carbon fiber gas diffusion anode opposite the graphene oxide membrane or the graphdiyne oxide membrane.

20. The method of Claim 19 wherein at least a portion of the water molecules in the humid atmosphere condenses on the surface of the electrically conductive carbon fiber gas diffusion anode and penetrate the electrically conductive carbon fiber gas diffusion anode to be adsorbed and dissociate at the surface of the graphene oxide membrane or the graphdiyne oxide membrane.

Images