Methods and systems for electrocatalytic dual hydrogenation

Abstract

A method of electrocatalytic dual hydrogenation includes loading a first hydrogenation solution and a second hydrogenation solution into a first hydrogenation compartment and a second hydrogenation compartment of an electrocatalytic hydrogenation assembly, in which the first hydrogenation compartment and the second hydrogenation compartment are separated from an electrochemical cell by a hydrogen-permeable anode and a hydrogen-permeable cathode. The method includes applying and maintaining a voltage to the electrochemical cell to reduce a cathode solution and to oxidize an anode solution to provide hydrogen in the cathodic compartment and / or the anodic compartment. The hydrogen may be absorbed through the hydrogen-permeable anode and / or the hydrogen-permeable cathode and hydrogenate an unsaturated substrate in the first hydrogenation solution and / or the second hydrogenation solution. The method includes producing a first hydrogenated product and a second hydrogenated product with a total Faradic efficiency from 150% to 200%.

Description

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to U.S. Provisional Application Ser. No. 63 / 440,044, filed Jan. 19, 2023, the entire contents of which are incorporated herein by reference.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] This invention was made with government support under CHE-1914546 and CHE-2102220 awarded by the National Science Foundation. The government has certain rights in the invention.TECHNICAL FIELD

[0003] The present disclosure relates to methods and systems for electrocatalytic hydrogenation, and in particular, to methods and systems for electrocatalytic hydrogenation utilizing dual hydrogen-permeable electrodes.BACKGROUND

[0004] Hydrogenation plays an important role in the chemical industry. For example, industrial chemical processes such as petroleum refining, chemical feedstock manufacturing, and pharmaceutical synthesis generally comprise at least one hydrogenation step. Currently, the dominating hydrogenation strategy involves energy-intensive thermocatalytic processes conducted at high pressure and elevated temperature using molecular hydrogen (H2) as both the reductant and hydrogen sources.

[0005] Electrocatalytic hydrogenation is regarded as a low-cost, energy-efficient alternative because it can be driven by renewable electricity under ambient conditions and use water as the hydrogen source. Conventional electrocatalytic hydrogenation generally involves the generation of active hydrogen (H*) from proton reduction on the cathode, which subsequently hydrogenates unsaturated substrates. However, for various reasons, the scalability of the conventional method to meet the market need is of great concern.

[0006] In conventional electrocatalytic hydrogenation systems, an oxidation reaction simultaneously takes place at the anode, which may yield a low-value product (for example, O2) and pay a large overpotential penalty due to its sluggish kinetics. For another example, the conventional system typically uses protic electrolytes as hydrogen source to generate H*, which therefore limits the scope of application to unsaturated substrates soluble in the protic electrolytes. While substrate solubility may be improved by adding co-solvents, adding co-solvents may result in an increase in resistance and thus a need for a higher voltage to drive the electrocatalytic hydrogenation.

[0007] Accordingly, a need exists for a method and a system that can electrocatalytically hydrogenate a broader range of unsaturated organic substrates soluble in either protic or non-protic solvents with improved yield and efficiency at a low energy cost.SUMMARY

[0008] Embodiments of the present disclosure are directed to methods of electrocatalytic hydrogenation and producing valuable organic products at both the cathode and anode and corresponding systems, referred to herein as “electrocatalytic dual hydrogenation.” In some embodiments, the electrocatalytic dual hydrogenation is carried out in a system comprising hydrogenation compartments spatially separated from an electrochemical cell by hydrogen-permeable electrodes. The hydrogen-permeable electrodes may absorb active hydrogens generated in the electrochemical cell to hydrogenate an unsaturated substrate in the hydrogenation compartments. The methods described herein enable electrocatalytic hydrogenation with a Faradaic efficiency approaching 200%.

[0009] In accordance with one embodiment of the present disclosure, a method of electrocatalytic dual hydrogenation may comprise loading a first hydrogenation solution into a first hydrogenation compartment of an electrocatalytic hydrogenation assembly, wherein the first hydrogenation compartment is separated from an electrochemical cell by a hydrogen-permeable anode; loading a second hydrogenation solution into a second hydrogenation compartment of the electrocatalytic hydrogenation assembly, wherein the second hydrogenation compartment is separated from the electrochemical cell by a hydrogen-permeable cathode; applying a voltage to the electrochemical cell to reduce a cathode solution in a cathodic compartment of the electrochemical cell to provide hydrogen, whereby the hydrogen is absorbed through the hydrogen-permeable cathode to hydrogenate the second hydrogenation solution; and maintaining the voltage to permit anions to flow from the cathodic compartment to an anodic compartment of the electrochemical cell through a semi-permeable membrane, whereby the anions oxidize an anode solution to provide hydrogen, whereby the hydrogen is absorbed through the hydrogen-permeable anode to hydrogenate the first hydrogenation solution.

[0010] In accordance with another embodiment of the present disclosure, a system for electrocatalytic dual hydrogenation may comprise an electrocatalytic hydrogenation assembly comprising a first hydrogenation compartment and a second hydrogenation compartment connected to an electrochemical cell connected to a voltage supply, a hydrogen-permeable anode separating the first hydrogenation compartment from the electrochemical cell, and a hydrogen-permeable cathode separating the second hydrogenation compartment from the electrochemical cell, wherein the first hydrogenation compartment is configured to hold a first hydrogenation solution; the second hydrogenation compartment is configured to hold a second hydrogenation solution; the voltage supply is configured to apply a voltage to the electrochemical cell to reduce a cathode solution in a cathodic compartment of the electrochemical cell to provide hydrogen, whereby the hydrogen is absorbed through the hydrogen-permeable cathode to hydrogenate the second hydrogenation solution; and the voltage supply is configured to maintain the voltage to permit anions to flow from the cathodic compartment to an anodic compartment of the electrochemical cell through a semi-permeable membrane, whereby the anions oxidize an anode solution to provide hydrogen and the hydrogen is absorbed through the hydrogen-permeable anode to hydrogenate the first hydrogenation solution.

[0011] In accordance with a further embodiment of the present disclosure, a method of improving hydrogenation rate and Faradaic efficiency of a hydrogenation reaction may comprise separating a first hydrogenation compartment of an electrocatalytic hydrogenation assembly from an electrochemical cell by a hydrogen-permeable anode; separating a second hydrogenation compartment of the electrocatalytic hydrogenation assembly from the electrochemical cell by a hydrogen-permeable cathode; loading a hydrogenation solution to the first hydrogenation compartment and the second hydrogenation compartment; loading an electrochemical solution comprising an alkali hydroxide to a cathodic compartment and an anodic compartment of the electrochemical cell, wherein the cathodic compartment and the anodic compartment are fluidly coupled through a semi-permeable membrane, and the electrochemical solution in the anodic compartment further comprises an aldehyde; applying a voltage to the electrochemical cell to reduce the electrochemical solution in the cathodic compartment to provide hydrogen, whereby the hydrogen is absorbed through the hydrogen-permeable cathode to hydrogenate the hydrogenation solution in the second hydrogenation compartment; and maintaining the voltage to permit anions to flow from the cathodic compartment to the anodic compartment through the semi-permeable membrane, whereby the anions oxidize the aldehyde to provide hydrogen, whereby the hydrogen is absorbed through the hydrogen-permeable anode to hydrogenate the hydrogenation solution in the first hydrogenation compartment.

[0012] These and other features, aspects, and advantages will become better understood with reference to the following description and the appended claims.

[0013] Additional features and advantages of the embodiments described herein will be set forth in the detailed description that follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, including the detailed description that follows, the claims, as well as the appended drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The following detailed description of specific embodiments of the present disclosure can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:

[0015] FIG. 1 schematically depicts an embodiment of an electrocatalytic dual hydrogenation system according to one or more embodiments described herein;

[0016] FIG. 2 schematically depicts a palladium membrane according to one or more embodiments described herein;

[0017] FIG. 3A depicts scanning electron microscope (SEM) images of the palladium membrane of FIG. 2;

[0018] FIG. 3B depicts scanning electron microscope (SEM) images of the palladium membrane of FIG. 2;

[0019] FIG. 3C depicts scanning electron microscope (SEM) images of the palladium membrane of FIG. 2; and

[0020] FIG. 4 depicts the experimental setup of the electrocatalytic dual hydrogenation system of FIG. 1, according to one or more embodiments described herein.DETAILED DESCRIPTION

[0021] Reference will now be made in detail to embodiments of systems for electrocatalytic dual hydrogenation. Methods of electrocatalytic dual hydrogenation and methods of improving hydrogenation rate and Faradaic efficiency will be subsequently described.

[0022] Referring initially to FIG. 1, and according to embodiments, a system for electrocatalytic dual hydrogenation may comprise an electrocatalytic hydrogenation assembly 100 comprising a first hydrogenation compartment 130 and a second hydrogenation compartment 140 coupled to an electrochemical cell 120. Optionally, the electrochemical cell is connected to a voltage supply 150. In some embodiments, a hydrogen-permeable anode 132 may separate the first hydrogenation compartment 130 from the electrochemical cell 120. In some embodiments, a hydrogen-permeable cathode 142 may separate the second hydrogenation compartment 140 from the electrochemical cell 120. In some embodiments, the first hydrogenation compartment 130 may be configured to hold a first hydrogenation solution, and / or the second hydrogenation compartment 140 may be configured to hold a second hydrogenation solution. In some embodiments, the voltage supply 150 may be configured to apply a voltage to the electrochemical cell 120 to reduce a cathode solution in a cathodic compartment 124 of the electrochemical cell 120 to provide hydrogen, whereby the hydrogen is absorbed through the hydrogen-permeable cathode 142 to hydrogenate the second hydrogenation solution. In other embodiments, the voltage supply 150 may also be configured to maintain the voltage to permit anions to flow from the cathodic compartment 124 to an anodic compartment 122 of the electrochemical cell 120 through a semi-permeable membrane 126, whereby the anions oxidize an anode solution to provide hydrogen, and the hydrogen is absorbed through the hydrogen-permeable anode 132 to hydrogenate the first hydrogenation solution. In some embodiments, the semi-permeable membrane 126 may be an anion exchange membrane.

[0023] Regarding the electrodes, as used herein, “hydrogen-permeable electrode,”“hydrogen-permeable anode,” or “hydrogen-permeable cathode” refers to an electrode, anode, or cathode made of materials with hydrogen permselectivity to selectively allow hydrogen to pass through the electrode, anode, or cathode while blocking other substances.

[0024] According to embodiments, the hydrogen-permeable anode 132 and / or the hydrogen-permeable cathode 142 may be palladium membranes. Without being bound by any particular theory, the active hydrogens (H*) generated from proton reduction on the palladium membrane cathode may be absorbed by and subsequently permeate through the membrane electrode, as shown in FIG. 1. In conventional electrocatalytic hydrogenation, it is generally considered that such hydrogen permeation is infeasible in palladium when used as an anode, since palladium is generally regarded as an electrocatalyst for the hydrogen oxidation reaction (HOR), negating the possibility of hydrogenation of the substrate by the anode. However, as described herein, the HOR may be avoided when the palladium membrane anode 132 is used to separate the first hydrogenation compartment 130 from the electrochemical cell 120 such that the first hydrogenation compartment 130 is not in fluid contact with the anode solution in the electrochemical cell 120. As explained below, hydrogenation at the anode in the first hydrogenation compartment 130 becomes feasible in the presently disclosed systems.

[0025] In one or more embodiments, the palladium membrane 300 may have a thickness of from about 500 nm to about 5 μm, such as from about 500 nm to about 800 nm, from about 500 nm to 1 μm, from about 500 nm to about 1.2 μm, from about 500 nm to about 1.8 μm, from about 500 nm to about 2 μm, from about 500 nm to about 2.4 μm, from about 500 nm to about 3 μm, from about 500 nm to about 3.5 μm, from about 500 nm to about 4 μm, from about 1 μm to about 1.8 μm, from about 1 μm to about 2.4 μm, from about 1 μm to about 3.5 μm, from about 1 μm to about 4 μm, from about 1 μm to about 5 μm, from about 1.8 μm to about 3 μm, from about 1.8 μm to about 3.5 μm, from about 1.8 μm to about 5 μm, from about 2.4 μm to about 3 μm, from about 2.4 μm to about 4 μm, from about 3.5 μm to about 4 μm, from about 3.5 μm to about 5 μm, or from about 4 μm to about 5 μm.

[0026] Referring to FIGS. 1 and 2 together, in one or more embodiments, the palladium membrane 300 may comprise a hydrogenation face 320 in fluid contact with the first hydrogenation compartment 130 and / or the second hydrogenation compartment 140, an electrochemical face 360 in fluid contact with the electrochemical cell 120, and a membrane material 340, disposed between the hydrogenation face 320 and the electrochemical face 360. In some embodiments, the hydrogenation face 320 may comprise palladium, porous materials, conductive materials, or combinations thereof. In other embodiments, the electrochemical face 360 may comprise palladium, porous materials, conductive materials, or combinations thereof. In another embodiments, the membrane material 340 may comprise palladium, porous materials, conductive materials, or combinations thereof. As used herein, “porous materials” may include, for example, porous aromatic frameworks (PAFs), thioamide incorporated polymer of intrinsic microporosity (TPIMs), polyvinylidene fluoride membranes, polyimide films, or combinations thereof. As used herein, “conductive materials” may include, for example, polyelectrolyte-based conductive hydrogels, carbon nanotubes, graphene, conducting polymers, or combinations thereof. Conducting polymers, as used herein, may include polyanilines, polypyrroles, polythiophenes, polyacetylenes, poly(para-phenylene) s, poly(phenylenevinylene) s, polyfurans, or combinations thereof. In further embodiments, the hydrogenation face 320 and the electrochemical face 360 are palladium.

[0027] Referring to FIG. 2, to increase the number of active sites, in one or more embodiments, the palladium membrane 300 may comprise particles 200. In particular, to increase the number of active hydrogenation sites, in some embodiments, the particles 200 may be disposed on the hydrogenation face 320 of the palladium membrane 300. As used herein, the particles 200 may be disposed by wet or dry deposition methods including, but not limited to, electrodeposition, physical vapor deposition, chemical vapor deposition, atomic layer deposition, successive ionic layer adsorption and reaction, and the like.

[0028] Referring to FIGS. 3A, 3B, and 3C together, in one or more embodiments, the particles 200 may have a diameter of from about 50 nm to about 1000 nm, such as from about 50 nm to about 500 nm, from about 50 nm to about 75 nm, from about 50 nm to about 250 nm, from about 75 nm to about 150 nm, from about 75 nm to about 350 nm, from about 100 nm to about 350 nm, from about 100 nm to about 600 nm, from about 250 nm to about 750 nm, from about 500 nm to about 1000 nm, from about 500 nm to about 750 nm, or from about 750 nm to about 1000 nm. As used herein, “particles” means nanoparticles, clusters comprising nanoparticles, or micro-particles. For example, and in embodiments, the particles 200 may be nanoparticles comprising a diameter of from about 50 nm to about 200 nm, such as from about 50 nm to about 100 nm, from about 50 nm to about 75 nm, or from about 75 nm to 150 nm. In some embodiments, the particles may be clusters of nanoparticles, and the cluster may comprise a diameter of from about 50 nm to about 1000 nm, such as from about 50 nm to about 500 nm, from about 50 nm to about 75 nm, from about 50 nm to about 250 nm, from about 75 nm to about 150 nm, from about 75 nm to about 350 nm, from about 100 nm to about 350 nm, from about 100 nm to about 600 nm, from about 250 nm to about 750 nm, from about 500 nm to about 1000 nm, from about 500 nm to about 750 nm, or from about 750 nm to about 1000 nm. In other embodiments, the particles may be micro-particles comprising a diameter of from about 150 nm to about 1000 nm, such as from about 150 nm to about 350 nm, from about 150 nm to about 600 nm, from about 350 nm to about 1000 nm, from about 350 nm to about 600 nm, from about 500 nm to about 1000 nm, from about 500 nm to about 750 nm, or from about 750 nm to about 1000 nm.

[0029] In one or more embodiments, the particles 200 may comprise a crystal facet, such that the crystalline lattice may expand following the absorption of hydrogen atoms. In some embodiments, the particles 200 may comprise palladium, platinum, gold, silver, copper, or combinations thereof. In further embodiments, the particles200 comprising palladium may have a (111) crystal facet.

[0030] Regarding the anode solution, according to embodiments, the hydrogen sources for hydrogenation on the anode may be aldehydes. Without being bound by any particular theory, palladium is electrocatalytically active in the oxidation of organics, for example, formaldehyde. Under alkaline conditions, palladium may electrocatalytically oxidize formaldehyde (formaldehyde oxidation reaction, FOR) following either a one-electron transfer (equation (1)) or a two-electron transfer (equation (2)) process to generate H*:

[0031] The oxidation potential may vary, depending on the alkalinity. Therefore, in one or more embodiments, the anode solution may comprise an aldehyde and an alkali hydroxide. In some embodiments, the aldehyde in the anode solution is oxidized. In further embodiments, the anode solution may have an oxidation potential of from about −0.1 V to about −1 V, such as from about −0.2 V to −0.6 V, or from −0.2 V to −0.4 V.

[0032] In one or more embodiments, the aldehyde may be selected from formaldehyde, paraformaldehyde, or combinations thereof.

[0033] It is also contemplated that, aromatic aldehydes and aliphatic aldehydes shown in Table A and Table B may also be selected as the hydrogen source. In some embodiments, the aldehyde may be furanics, such as furfural, hydroxylmethylfurfural, and their derivatives.

[0034] In some embodiments, the aldehyde may be formaldehyde. In further embodiments, the formaldehyde may be present in a concentration of from about 100 mM to about 2000 mM, such as from about 100 mM to about 1800 mM, from about 100 mM to about 1600 mM, from about 100 mM to about 1400 mM, from about 100 mM to about 1200 mM, from about 100 mM to about 1000 mM, from about 100 mM to about 800 mM, from about 100 mM to about 600 mM, from about 100 mM to about 400 mM, from about 100 mM to about 200 mM, from about 200 mM to about 2000 mM, from about 200 mM to about 1800 mM, from about 200 mM to about 1600 mM, from about 200 mM to about 1400 mM, from about 200 mM to about 1200 mM, from about 200 mM to about 1000 mM, from about 200 mM to about 800 mM, from about 200 mM to about 600 mM, from about 200 mM to about 400 mM, from about 400 mM to about 2000 mM, from about 400 mM to about 1800 mM, from about 400 mM to about 1600 mM, from about 400 mM to about 1400 mM, from about 400 mM to about 1200 mM, from about 400 mM to about 1000 mM, from about 400 mM to about 800 mM, from about 400 mM to about 600 mM, from about 600 mM to about 2000 mM, from about 600 mM to about 1800 mM, from about 600 mM to about 1600 mM, from about 600 mM to about 1400 mM, from about 600 mM to about 1200 mM, from about 600 mM to about 1000 mM, from about 600 mM to about 800 mM, from about 800 mM to about 2000 mM, from about 800 mM to about 1800 mM, from about 800 mM to about 1600 mM, from about 800 mM to about 1400 mM, from about 800 mM to about 1200 mM, from about 800 mM to about 1000 mM, from about 1000 mM to about 2000 mM, from about 1000 mM to about 1800 mM, from about 1000 mM to about 1600 mM, from about 1000 mM to about 1400 mM, from about 1000 mM to about 1200 mM, from about 1200 mM to about 2000 mM, from about 1200 mM to about 1800 mM, from about 1200 mM to about 1600 mM, from about 1200 mM to about 1400 mM, from about 1400 mM to about 2000 mM, from about 1400 mM to about 1800 mM, from about 1400 mM to about 1600 mM, from about 1600 mM to about 2000 mM, from about 1600 mM to about 1800 mM, or from 1800 mM to 2000 mM.

[0035] In one or more embodiments, the aldehyde may be paraformaldehyde. In further embodiments, the paraformaldehyde may be present in a concentration of from about 1 g L−1 to less than or equal to 60 g L−1, such as from about 5 g L−1 to less than or equal to 50 g L−1, from about 7 g L−1 to less than or equal to 30 g L−1, from about 10 g L−1 to less than or equal to 40 g L−1, from about 10 g L−1 to less than or equal to 30 g L−1, or from about 15 g L−1 to less than or equal to 30 g L−1.

[0036] Regarding the cathode solution, according to embodiments, the hydrogen sources for hydrogenation on the cathode may be water. In order to maintain electrical neutrality in the cell, in one or more embodiments, the cathode solution may comprise an alkali hydroxide. In some embodiments, both the anode solution and the cathode solution may comprise an alkali hydroxide.

[0037] In one or more embodiments, the alkali hydroxide may be selected from LiOH, NaOH, KOH, RbOH, CsOH, or combinations thereof. In some embodiments, the alkali hydroxide may be NaOH, KOH, or combinations thereof. In some embodiments, the alkali hydroxide may be present in a concentration of from about 100 mM to about 1500 mM, such as from about 600 mM to about 1200 mM, from about 600 mM to about 1000 mM, from about 800 mM to about 1200 mM, or from about 900 mM to about 1100 mM.

[0038] Optionally, the anode solution and / or the cathode solution may be argon-saturated, thereby reducing the hydrogen oxidation reaction.

[0039] Regarding the hydrogenation solutions, according to embodiments, the first hydrogenation solution and / or the second hydrogenation solution may comprise one or more molecules having an unsaturated substrate, wherein the unsaturated substrate may comprise at least one carbon-carbon double bond or at least one carbon-carbon triple bond. For example, in embodiments, the unsaturated substrate may be selected from dicarboxylic acids, dicarboxylic anhydrides, carboxylic acids, aldehydes, dicarbaldehydes, aromatic alkenes, aliphatic alkenes, aromatic alkynes, aliphatic alkynes, or combinations thereof. Exemplary unsaturated substrates are shown in Tables A to F.

[0040] In one or more embodiments, the unsaturated substrate may be present at a concentration of from about 1 mM to about 500 mM, such as from about 1 mM to about 400 mM, from about 1 mM to about 300 mM, from about 1 mM to about 200 mM, from about 1 mM to about 100 mM, from about 1 mM to about 80 mM, from about 1 mM to about 60 mM, from about 1 mM to about 40 mM, from about 1 mM to about 20 mM, from about 1 mM to about 10 mM, from about 10 mM to about 500 mM, from about 10 mM to about 400 mM, from about 10 mM to about 300 mM, from about 10 mM to about 200 mM, from about 10 mM to about 100 mM, from about 10 mM to about 80 mM, from about 10 mM to about 60 mM, from about 10 mM to about 40 mM, from about 10 mM to about 20 mM, from about 20 mM to about 500 mM, from about 20 mM to about 400 mM, from about 20 mM to about 300 mM, from about 20 mM to about 200 mM, from about 20 mM to about 100 mM, from about 20 mM to about 80 mM, from about 20 mM to about 60 mM, from about 20 mM to about 40 mM, from about 40 mM to about 500 mM, from about 40 mM to about 400 mM, from about 40 mM to about 300 mM, from about 40 mM to about 200 mM, from about 40 mM to about 100 mM, from about 40 mM to about 80 mM, from about 40 mM to about 60 mM, from about 60 mM to about 500 mM, from about 60 mM to about 400 mM, from about 60 mM to about 300 mM, from about 60 mM to about 200 mM, from about 60 mM to about 100 mM, from about 60 mM to about 80 mM, from about 80 mM to about 500 mM, from about 80 mM to about 400 mM, from about 80 mM to about 300 mM, from about 80 mM to about 200 mM, from about 80 mM to about 100 mM, from about 100 mM to about 500 mM, from about 100 mM to about 400 mM, from about 100 mM to about 300 mM, from about 100 mM to about 200 mM, from about 200 mM to about 500 mM, from about 200 mM to about 400 mM, from about 200 mM to about 300 mM, from about 300 mM to about 500 mM, from about 300 mM to about 400 mM, or from about 400 mM to about 500 mM.

[0041] In one or more embodiments, the unsaturated substrate may be present at a concentration of from about 1 mM to a neat liquid. A neat liquid of hydrogenation solution may consist essentially unsaturated substrates, which herein means the unsaturated substrates are present as a neat liquid or substantially free of solvent or additives, such as less than 1 vol. % solvent or additives, less than 0.5 vol. % solvent or additives, less than 0.1 vol. % solvent or additives, less than 0.05 vol. % solvent or additives, or less than 0.01 vo. % solvent or additives. For example, and in embodiments, a neat liquid of the unsaturated substrate may be present at a concentration of from about 2 M to about 28 M, such as from about 2 M to about 25 M, from about 2 M to about 20 M, from about 2 M to about 15 M, from about 2 M to about 10 M, from about 2 M to about 5 M, from about 5 M to about 28 M, from about 5 M to about 25 M, from about 5 M to about 20 M, from about 5 M to about 15 M, from about 5 M to about 10 M, from about 10 M to about 28 M, from about 10 M to about 25 M, from about 10 M to about 20 M, from about 10 M to about 15 M, from about 15 M to about 28 M, from about 15 M to about 25 M, from about 15 M to about 20 M, from about 20 M to about 28 M, from about 20 M to about 25 M, or from about 25 M to about 28 M.

[0042] Therefore, in some embodiments, the unsaturated substrate may be present at a concentration of from about 1 mM to about 28 M, such as from about 1 mM to about 20 M, from about 1 mM to about 15 M, from 1 mM to about 10 M, from 1 mM to about 5 M, from 1 mM to about 1 M, from 1 mM to about 800 mM, from 1 mM to about 500 mM, from about 1 mM to about 200 mM, from about 1 mM to about 100 mM, from about 1 mM to about 60 mM, from about 1 mM to about 20 mM, from about 1 mM to about 10 mM, from about 10 mM to about 28 M, from about 10 mM to about 20 M, from about 10 mM to about 15 M, from 10 mM to about 10 M, from 10 mM to about 5 M, from 10 mM to about 1 M, from 10 mM to about 800 mM, from 10 mM to about 500 mM, from about 10 mM to about 200 mM, from about 10 mM to about 100 mM, from about 10 mM to about 60 mM, from about 10 mM to about 20 mM, from about 20 mM to about 28 M, from about 20 mM to about 20 M, from about 20 mM to about 15 M, from 20 mM to about 10 M, from 20 mM to about 5 M, from 20 mM to about 1 M, from 20 mM to about 800 mM, from 20 mM to about 500 mM, from about 20 mM to about 200 mM, from about 20 mM to about 100 mM, from about 20 mM to about 60 mM, from about 60 mM to about 28 M, from about 60 mM to about 20 M, from about 60 mM to about 15 M, from 60 mM to about 10 M, from 60 mM to about 5 M, from 60 mM to about 1 M, from 60 mM to about 800 mM, from 60 mM to about 500 mM, from about 60 mM to about 200 mM, from about 60 mM to about 100 mM, from about 100 mM to about 28 M, from about 100 mM to about 20 M, from about 100 mM to about 15 M, from 100 mM to about 10 M, from 100 mM to about 5 M, from 100 mM to about 1 M, from 100 mM to about 800 mM, from 100 mM to about 500 mM, from about 100 mM to about 200 mM, from about 200 mM to about 28 M, from about 200 mM to about 20 M, from about 200 mM to about 15 M, from 200 mM to about 10 M, from 200 mM to about 5 M, from 200 mM to about 1 M, from 200 mM to about 800 mM, from 200 mM to about 500 mM, from about 500 mM to about 28 M, from about 500 mM to about 20 M, from about 500 mM to about 15 M, from 500 mM to about 10 M, from 500 mM to about 5 M, from 500 mM to about 1 M, from 500 mM to about 800 mM, from about 800 mM to about 28 M, from about 800 mM to about 20 M, from about 800 mM to about 15 M, from 800 mM to about 10 M, from 800 mM to about 5 M, from 800 mM to about 1 M, from about 1 M to about 28 M, from about 1 M to about 20 M, from about 1 M to about 15 M, from 1 M to about 10 M, from 1 M to about 5 M, from about 5 M to about 28 M, from about 5 M to about 20 M, from about 5 M to about 15 M, from 5 M to about 10 M, from about 10 M to about 28 M, from about 10 M to about 20 M, from about 10 M to about 15 M, from about 15 M to about 28 M, from about 15 M to about 20 M, or from about 20 M to about 28 M.

[0043] In one or more embodiments, the first hydrogenation solution and / or the second hydrogenation solution may comprise protic solvent, non-protic solvent, or combinations thereof. As used herein, protic solvents refers to solvents that have a hydrogen atom bound to an electronegative atom, such as oxygen or nitrogen, and can donate a hydrogen bond. For example, protic solvents may include water, methanol, ethanol, isopropyl alcohol, acetic acid, formic acid, butanols, amines, and the like. As used herein, non-protic solvents refer to solvents that cannot donate a hydrogen bond. For example, non-protic solvents may include acetone, ethyl acetate, dichloromethane, tetrahydrofuran, dimethylformamide, dimethyl sulfoxide, acetonitrile, hexamethylphosphoric triamide, benzene, chloroform, and the like.

[0044] Reference will now be made in detail to embodiments of methods of electrocatalytic dual hydrogenation. Methods of improving hydrogenation rate and Faradaic efficiency will be subsequently described. The methods of electrocatalytic dual hydrogenation and the methods of improving hydrogenation rate and Faradaic efficiency may utilize any of the systems and / or electrocatalytic hydrogenation assemblies 100 previously described.

[0045] Referring again to FIG. 1, according to embodiments, methods of electrocatalytic dual hydrogenation may comprise loading the first hydrogenation solution into the first hydrogenation compartment 130 of the electrocatalytic hydrogenation assembly 100, wherein the first hydrogenation compartment 130 is separated from the electrochemical cell 120 by the hydrogen-permeable anode 132; loading the second hydrogenation solution into the second hydrogenation compartment 140 of the electrocatalytic hydrogenation assembly 100, wherein the second hydrogenation compartment 140 is separated from the electrochemical cell 120 by the hydrogen-permeable cathode 142; applying the voltage to the electrochemical cell 120 to reduce the cathode solution in a cathodic compartment 124 of the electrochemical cell 120 to provide hydrogen, whereby the hydrogen is absorbed through the hydrogen-permeable cathode 142 to hydrogenate the second hydrogenation solution; and maintaining the voltage to permit anions to flow from the cathodic compartment 124 to the anodic compartment 122 of the electrochemical cell 120 through the semi-permeable membrane 126, whereby the anions oxidize an anode solution to provide hydrogen, whereby the hydrogen is absorbed through the hydrogen-permeable anode 132 to hydrogenate the first hydrogenation solution.TABLE AAromatic aldehydesName (CAS)StructureBenzaldehyde (100-52-7)4-Chlorobenzaldehyde (104-88-1)4-cyanobenzaldehyde (105-07-7)Methyl 4- formylbenzoate (1057-08-0)p-Tolualdehyde (104-87-0)1-Formyl-4- trifluoromethylbenzene (455-19-6)4-Fluorobenzaldehyde (459-47-4)4-Nitrobenzaldehyde (555-16-8)4-Bromobenzaldehyde (1122-91-4)4- Methoxybenzaldehyde (123-11-5)4-(Dimethylamino) benzaldehyde (100-10-7)2,6-Dimethyl- benzaldehyde (1123-56-4)2,4,6-trimethyl- benzaldehyde (487-68-3)3,5-Dimethyl- benzaldehyde (5779-95-3)TABLE BAliphatic AldehydesName (CAS)Structure5-Bromofuran-2- carbaldehyde (1899-24-7)Furan-2,5- dicarbaldehyde (823-82-5)5-Ethyl-2- furaldehyde (23074-10-4)Furfural (98-01-1)5-Hydroxymethyl furfural (67-47-0)Butyraldehyde (123-72-8)Hydrocinnamaldehyde (104-53-0)Phenylacetaldehyde (122-78-1)Cyclopropanecarbaldehyde (1498-69-6)3-Methylcrotonaldehyde (107-86-8)1,3-Benzothiazole-2- carbaldehyde (6639-57-2)FormaldehydeHCHO(50-00-0)TABLE CAromatic AlkenesName (CAS)StructureStyrene (100-42-5)1-Chloro-4- vinylbenzene (1073-67-2)4-tert-Butylstyrene (1476-23-2)1-Fluoro-4-vinylbenzene (405-99-2)α-Methylstyrene (98-83-9)4-Acetoxystyrene (2628-16-2)4-Vinylbenzoic acid (1075-49-6)4- (Trifluoromethyl)styrene (402-50-6)Methyl 4-vinylbenzoate (1076-96-6)2-Bromostyrene (2039-88-5)N,N-Dimethyl-4- vinylaniline (2039-80-7)Chloromethylstyrene (57458-41-0)(E)-1-Methoxy-4-(prop- I-en-1-yl)benzene (4180-23-8)Indene (95-13-6)1-Nitro-4- vinylbenzene (100-13-0)1-Bromo-4- vinylbenzene (2039-82-9)trans-Cinnamic acid (140-10-3)1-Methoxy-4- vinylbenzene (637-69-4)Cinnamyl alcohol (104-54-1)Cinnamyl bromide (4392-24-9)trans-Stilbene (103-30-0)2-Vinylnaphthalene (827-54-3)9-Vinylanthracene (2444-68-0)4-Vinylbiphenyl (2350-89-2)(1E,3E)-1,4- Diphenylbuta-1,3- diene (538-81-8)ethene-1,1′- diyldibenzene (530-48-3)cis-Stilbene (645-49-8)1-Vinylnaphthalene (826-74-4)TABLE DAliphatic AlkenesName (CAS)StructureAllylbenzene (300-57-2)Vinylbenzyl chloride (30030-28-2)4-Phenyl-1-butene (768-56-9)2-Cyclohexen-1-ol (822-67-3)1-Isopropyl-4- methylcyclohexa- 1,3-diene (99-86-5)3- Methylcrotonaldehyde (107-86-8)Cyclooctene (931- 88-4)Cyclohexene (110-83-8)3-Bromocyclohexene (1521-51-3)3-Methyl-1- cyclohexene (591-48-0)Allyl chloroformate (2937-50-0)1-Hexene (592-41-6)Allyl bromide (106-95-6)Allyl acetate (591-87-7)3-Chloro-2- methyl-1-propene (563-47-3)Maleic acid (110- 16-7)tert-Butyl allylcarbamate (78888-18-3)1-Octadecene (112-88-9)6-Bromo-1- hexene (2695-47-8)Allylamine (107-11-9)5-Bromo-1-pentene (1119-51-3)1-Octene (111-66-0)3-Methylbut-3-en- 1-o1 (763-32-6)Pent-4-en-1-ol (821-09-0)Ally alcohol (107- 18-6)Allyl chloride (107-05-1)11-Bromo-1-undecene (7766-50-9)Arachidonic acid (506-32-1)TABLE EAromatic AlkynesName (CAS)Structure Phenylacetylene (536-74-3)4-Ethynylanisole (768-60-5)4-Ethynylaniline (14235-81-5)1-Ethyl-4- ethynylbenzene (40307-11-7)2-Ethynyl- naphthalene (2949-26-0)4-Ethynyl-1,1′- biphenyl (29079-00-3)1-Ethynyl-4- nitrobenzene (937-31-5)1-Butyl-4- ethynylbenzene (79887-09-5)TABLE FAliphatic AlkynesName (CAS)Structure2-Ethynylthiophene (4298-52-6)1-Ethynylcyclohexene (931-49-7)1-Octyne (629-05-0)3-Phenyl-1-propyne (10147-11-2)1-Hexyne (693-02-7)In one or more embodiments, the voltage may be from about 0.35 V to about 1 V, such as from about 0.35 V to about 0.5 V, from 0.35 V to about 0.65 V, from 0.35 V to about 0.8 V, from 0.35 V from 0.95 V, from about 0.5 V to about 0.65 V, from 0.5 V to about 0.8 V, from 0.5 V to about 0.95 V, from about 0.5 V to about 1 V, from about 0.65 V to about 0.8 V, from about 0.65 V to about 0.95 V, from about 0.65 V to about 1 V, or from about 0.8 V to about 1 V.In some embodiments, applying the voltage to the electrochemical cell 120 may reduce water in the cathode solution. In other embodiments, the aldehyde in the anode solution may be oxidized.In one or more embodiments, applying the voltage generates a current density of from about 5 mA cm−2 to about 100 mA cm−2, such as from about 5 mA cm−2 to about 50 mA cm−2, from about 5 mA cm−2 to about 30 mA cm−2, or from about 7 mA cm−2 to about 30 mA cm−2.According to embodiments, the methods disclosed herein may further comprise producing a first hydrogenated product in the first hydrogenation compartment 130. In one or more embodiments, producing the first hydrogenated product has a Faradic efficiency of from about 75% to about 100%, such as from about 85% to about 97%, from about 85% to about 95%, from about 85% to about 92%, from about 75% to about 95%, from about 80% to about 90%, or from about 90% to about 95%. In some embodiments, the methods disclosed herein may further comprise separating the first hydrogenated product from the first hydrogenation solution.Similarly, according to embodiments, the methods disclosed herein may further comprise producing a second hydrogenated product in the second hydrogenation compartment 140. In one or more embodiments, producing the second hydrogenated product has a Faradic efficiency of from about 75% to about 100%, such as from about 85% to about 97%, from about 85% to about 95%, from about 85% to about 92%, from about 75% to about 95%, from about 80% to about 90%, or from about 90% to about 95%. In some embodiments, the methods disclosed herein may further comprise separating the second hydrogenated product from the second hydrogenation solution.

[0051] Further, any absorbed hydrogen remaining in the hydrogen-permeable membrane after electrolysis may continue to diffuse out of the electrode via the hydrogenation face to drive the hydrogenation. Therefore, according to embodiments, the methods disclosed herein may further comprise ceasing application of the voltage and stirring the first hydrogenation solution and / or the second hydrogenation solution. In some embodiments, the first hydrogenation solution and / or the second hydrogenation solution may be stirred for about 4 hours, such as about 2 hours, about 1.5 hours, about 1 hour, or about 0.5 hour.

[0052] As demonstrated in the Examples, palladium membrane cathodes may achieve a Faradaic efficiency (FE) of about 100% for the hydrogen evolution reaction and succinic acid production. Surprisingly and unexpectedly, when palladium membrane 300 is used as the anode in any of the systems and / or electrocatalytic hydrogenation assemblies 100 previously described, it may maintain a Faradaic efficiency (FE) approaching 100%.

[0053] Therefore, according to embodiments, methods of improving hydrogenation rate and Faradaic efficiency may comprise separating the first hydrogenation compartment 130 of the electrocatalytic hydrogenation assembly from the electrochemical cell 120 by the hydrogen-permeable anode 132; separating the second hydrogenation compartment 140 of the electrocatalytic hydrogenation assembly from the electrochemical cell 120 by the hydrogen-permeable cathode 142; loading the hydrogenation solution to the first hydrogenation compartment 130 and the second hydrogenation compartment 140; loading the electrochemical solution comprising the alkali hydroxide to the cathodic compartment 124 and the anodic compartment 122 of the electrochemical cell 120, wherein the cathodic compartment 124 and the anodic compartment 122 are fluidly coupled through the semi-permeable membrane 126, and the electrochemical solution in the anodic compartment 122 further comprises the aldehyde; applying the voltage to the electrochemical cell 120 to reduce the electrochemical solution in the cathodic compartment 124 to provide hydrogen, whereby the hydrogen is absorbed through the hydrogen-permeable cathode 142 to hydrogenate the hydrogenation solution in the second hydrogenation compartment 140; and maintaining the voltage to permit anions to flow from the cathodic compartment 124 to the anodic compartment 122 through the semi-permeable membrane 126, whereby the anions oxidize the aldehyde to provide hydrogen, whereby the hydrogen is absorbed through the hydrogen-permeable anode 132 to hydrogenate the hydrogenation solution in the first hydrogenation compartment 130.

[0054] In one or more embodiments, the hydrogen-permeable anode 132 and the hydrogen-permeable cathode 142 may be substantially identical. As used herein, “substantially identical” means the hydrogen-permeable anode 132 and the hydrogen-permeable cathode 142 are made of identical materials with an inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, manufacture process. For example, and in embodiments, the hydrogen-permeable anode 132 and the hydrogen-permeable cathode 142 may be palladium membranes with an inherent degree of variation in its thickness. For example, and in embodiments, the hydrogen-permeable anode 132 and the hydrogen-permeable cathode 142 may be palladium membranes comprising particles with an inherent degree of variation in the dimension of the particles.

[0055] As demonstrated in the Examples, and in embodiments, producing the hydrogenated product in the first hydrogenation compartment 130 and the second hydrogenation compartment 140 may have a total Faradic efficiency of from about 150% to about 200%, such as from 170% to about 190%, from 150% to about 180%, from about 180% to about 190%, from about 180% to about 200%, or from about 190% to about 200%.EXAMPLES

[0056] Embodiments will now be further clarified by the following examples. The following Examples are offered by way of illustration and are presented in a manner such that one skilled in the art should recognize. The following Examples are not meant to be limiting to the present disclosure as a whole or to the appended claims.I. Materials

[0057] Palladium foil (99.9%) was purchased from Alfa Aesar. Palladium chloride (≥99.9%), potassium hydroxide (≥85%), formaldehyde (37 wt. % in H2O), methanol (>99.9%), dichloromethane (≥99.9%), acetylacetone (>99%), D2O (99 atom % D), DMSO-d6 (99.9 atom % D), potassium deuteroxide solution (40 wt. % in D2O, 98 atom % D), and hydrochloric acid (37 wt. % in H2O) were purchased from Sigma-Aldrich. Maleic acid (99%), succinic acid (99%), and formic acid (99%) were purchased from Acros Organics. Ammonium acetate (99%) and glacial acetic acid (99.9%) were purchased from Fisher Scientific. Maleic anhydride (>99%) was purchased from TCI. Fumaric acid (99%) was purchased from Ambeed. Paraformaldehyde was purchased from Bio Basic. Anion exchange membrane (Fumasep FAA-3-50) was purchased from FuelCellStore.

[0058] The PdNP / Pd membrane electrodes were prepared via an electrodeposition method using PdCl2 (15.9 mM) and HCl (1.0 M) as the electrolyte. Specifically, a Pd membrane as the working electrode was clamped between an electrochemical chamber and a chemical chamber, while a Pt mesh and a Ag / AgCl (sat. KCl) electrode were used as the counter and reference electrodes, respectively, in the electrochemical chamber. The electrodeposition was performed at a constant potential of −0.2 V vs Ag / AgCl till 16.75 C was passed.II. Characterization

[0059] Scanning electron microscopy (FEI XL30, 15 kV) was used to characterize electrocatalyst samples. X-ray diffraction (XRD) patterns were collected on a Philips X'Pert Pro PW3040 / 00 (PAN 2 analytical) instrument. The scan range was set from 20° to 90° (in 2θ) with a Cu-tube operated at 45 kV and 40 mA. Post-electrolysis XRD of Pd membrane anode (PdA) and Pd membrane cathode (PdC) were measured within 30 min after the electrolysis of passing 400 C at 50 mA. UVvis absorption spectra were collected on an Agilent 8453 UV-visible spectrophotometer. 1HNMR spectra were recorded in the designated solvents on a Bruker AV 400 MHz spectrometer. High resolution mass spectra were collected on a Thermo Scientific LTQ-FT mass spectrometer.

[0060] All electrochemical measurements were conducted on a VMP-3 potentiostat (Biologic Science Instruments). All reported potentials are referenced to the RHE by calibration using Pt as the working electrode in H2-saturated 1.0 M KOH.III. Electrocatalytic H2 Production on the Pd Membrane AnodeExample 1: Pd Membrane as Anode

[0061] Now the use of Pd membrane as anode is illustrated.

[0062] In this example, a two-compartment electrochemical cell with an anodic compartment and a cathodic compartment separated by an anion exchange membrane was used. Pd foil, Pt mesh and Hg / HgO (1.0 M KOH) were used as the working, counter and reference electrodes, respectively. The Pd foil working electrode and Hg / HgO (1.0 M KOH) reference electrode were placed in the anodic compartment, while the Pt mesh counter electrode was placed in the cathodic compartment. All linear sweep voltammetry (LSV) experiments were conducted using a three-electrode configuration at a scan rate of 10 mV s−1 without iR correction. The electrochemical double-layer capacitance (Ca) was determined by collecting cyclic voltammograms over a narrow range (±60 mV) centered around the open circuit potential (OCP) of each working electrode of interest at scan rates varying from 10 mV s−1 to 80 mV s−1. The Cal values were then estimated by plotting the difference (j) between the anodic (ja) and cathodic (jc) current densities (j=ja−jc) at the OCP versus the scan rate. The resulting linear slopes are equivalent to 2Cdl.

[0063] It was observed that, when a commercial Pd foil (Alfa Aesar) was used as the anode, the LSV experiments revealed that a rapid positive current rise was observed in 1.0 M KOH upon the addition of 0.6 M HCHO when the scanning potential was more positive than 0.25 V versus RHE. Further positive scanning resulted in the observation of gas bubbles emerging on the Pd surface. H2 was detected by gas chromatography. In contrast, in the absence of HCHO, no current rise was observed until a scanning potential about +1.5 V versus RHE was applied. Similarly, chronoamperometry curves of HCHO oxidation showed that, upon the addition of 0.6 M HCHO, an immediate current rise was observed due to HCHO oxidation. In contrast, in the absence of HCHO, an extremely small capacitance current was observed. The LSV experiments further revealed that, with a HCHO concentration of from about 0.2 M to about 1.5 M, a current density of from about 20 mA cm−2 to about 28 mA cm−2 was produced upon applying a voltage as low as 0.5 V versus RHE.

[0064] Additionally, it was observed that increasing the hydroxide concentration may lead to a steady rise in the anodic current when the electrolyte ionic strength remained constant. For example, using a cathode solution comprising LiOH(aq) and an anode solution comprising 0.6 M HCHO, the LSV experiments using the two-compartment electrochemical cell described showed that increasing the concentration of LiOH(aq) from 0.1 M to 1.0 M increased the anodic current density from about 0.95 mA cm−2 to about 4.8 mA cm−2 at 0.5 V versus RHE. Under the similar conditions, the cation effect of the supporting electrolyte including alkali ions Li+, Na+, K+, or Cs+ was probed. With 1.0 M Na+ or K+ and 0.6 M HCHO, applying 0.5 V versus RHE generates a current density of from about 15 mA cm−2 to about 25 mA cm−2.Example 2: Electrocatalytic H2 Production in a Two-Compartment Electrochemical Cell

[0065] Now the H2 production on the Pd membrane anode in the two-compartment electrochemical cell described in Example 1 is discussed.

[0066] In this case, two Pd foils were used as the anode and cathode, respectively. The cathode solution was 1.0 M KOH(aq) (40 ml), while the anode solution contained 0.6 M HCHO in 1.0 M KOH (50 ml). Chronopotentiometry experiments were conducted at 20, 50 and 100 mA. The produced H2 was analyzed via gas chromatography (GC, SRI 8610C) equipped with a Molecular Sieve 13 packed column, a HayesSep D packed column, and a thermal conductivity detector. The oven is kept at 80° C. using Ar as the carrier gas. The quantity of H2 production in the anodic and cathodic compartments was determined via a water displacement method and compared to standard hydrogen gas with known concentrations.

[0067] It was observed that when the same Pd foil was used as an anode under the same conditions described in Example 1, the amounts of H2 produced were far less than the theoretical values based on passed charge, as shown in Table 1. The calculated FEs of H2 production were all less than 30% on a Pd anode. Such a drastic difference in H2 production efficiency implies that effective hydrogen oxidation (H*→H++e−) occurs on Pd when it acts as an anode, which is in agreement with Pd being an active HOR electrocatalyst. No CO2 was detected in the anodic compartment, indicating that HCHO was not completely oxidized to CO2 under these conditions. The two-compartment electrochemical cell resembled a conventional electrocatalytic hydrogenation system, in which the Pd anode was completely immersed in the electrolyte. When the Pd anode was complete immersed in the electrolyte, the HOR was inevitable.TABLE 1Faradaic efficiency of H2 production in a two-compartment electrochemical cellSampleExample 2Example 2Example 4ElectrodePdCPdAPdAApplied currentFaradaic Efficiency 20 mA100%12%92% 50 mA100%26%68%100 mA100%22%60%IV. Improving Electrocatalytic H2 Production via H-atom Diffusion

[0068] The following examples illustrate that HOR observed in Example 2 was avoided when the H atom was separated from the electrochemical cell by coupling the Pd anode to a spatially-separated chemical compartment.Example 3: H-atom Absorption and Diffusion Through the Pd Membrane Anode

[0069] In this case, a three-compartment assembly with a chemical compartment connected to the anodic compartment of the two-compartment electrochemical cell described in Example 1 was used. In this three-compartment assembly, the chemical compartment and the anodic compartment were spatially separated by a PdNP / Pd membrane anode (area: 2.27 cm2), and a Pd foil (area: 2 cm2) was used as a cathode. The Pd nanoparticle-deposited face of the PdNP / Pd membrane was in fluid contact with the chemical compartment. The fluid in the chemical compartment was water. The cathode solution was 1.0 M KOH(aq) (40 ml), and the anode solution contained 0.6 M HCHO in 1.0 M KOH (50 ml). Chronopotentiometry experiments were conducted at 20, 50 and 100 mA.

[0070] Using the three-compartment assembly, the absorption of H atoms at the Pd membrane anode was observed. It is known that the crystalline lattice of Pd will expand following the absorption of hydrogen atoms. Before water-reduction electrolysis, the power X-ray diffraction (XRD) patterns of Pd membrane cathode showed characteristic XRD peaks at 40.1°, 46.5°, 68.0°, and 82.0°, corresponding to the (111), (200), (220) and (311) facets of its face-centered cubic (fcc) phase crystal structure (JCPDS card no. 46-1043), respectively. After electrolysis, the H-saturated Pd membrane cathode showed a 4% increase in the lattice parameter of its face-centered cubic (fcc) phase crystal structure. By spatially separating the chemical compartment from the anodic compartment, similar XRD patterns and lattice expansion was observed in Pd membrane anode, suggesting hydrogen was absorbed into the Pd membrane anode. In addition, it was observed that, utilizing the scanning electron microscopy, the Pd surface became rougher after serving as either cathode or anode. These results indicate that the absorbed hydrogen might diffuse through the Pd membrane anode to the chemical compartment where hydrogen recombination to release H2 (HER) may occur.

[0071] To increase the number of active sites for the HER, Pd nanoparticles were electrodeposited on the hydrogenation face of the Pd membrane anode as described in Example 1. XRD analysis confirmed that this PdNP / Pd membrane electrode retained the same fcc phase structure as pristine Pd membrane discussed in Example 1 but with more pronounced (111) crystalline facet at 2θ of 40.1°. Scanning electron microscopy (SEM) was conducted on the side of the PdNP / Pd membrane covered by electrodeposits and revealed a uniform coverage of the Pd surface by porous Pd nanoparticles and nanosheets, as shown in FIGS. 3A, 3B, and 3C.

[0072] The cyclic voltammograms were used to compare electrochemical double-layer capacitance of the PdNP / Pd membrane and the pristine Pd membrane electrode. Using the two-compartment electrochemical cell described in Example 1, the PdNP / Pd membrane showed an about 80-fold increase in electrochemical double-layer capacitance (11.0 mF cm−2) compared with the pristine Pd membrane electrode (0.134 mF cm−2).Example 4: H2 Production in the Spatially-Separated Chemical Compartment

[0073] To test the hypothesis that the absorbed hydrogen generated from HCHO oxidation can diffuse through the Pd membrane anode to a hydrogenation compartment, chronopotentiometry experiments were conducted at currents of 20 mA, 50 mA, and 100 mA in the three-compartment assembly described in Example 3. The amounts of H2 generated in both the anodic compartment and the chemical compartment were recorded separately. In all cases, H2 was the sole gaseous product detected by the gas chromatography and the amount of H2 produced in the chemical compartment was greater than that produced in the anodic compartment, as shown in Table 2. For example, at an applied current of 20 mA and after passing 400 C, about 1.6 mmol of H2 was produced in the chemical compartment, and about 0.28 mmol of H2 was produced in the anodic compartment.

[0074] It was observed that the total FE of H2 generation on the Pd membrane anode may be dependent on the applied current and the applied voltage. As shown in Table 2, varying on the applied current from 20 mA to 100 mA, the total FE of H2 generation on the Pd membrane anode ranged from 92% (20 mA) to 60% (100 mA), substantially higher than the results described in Example 2. These surprising results show that the generated H* can diffuse through the Pd membrane anode and migrate to the chemical compartment separated from the anodic compartment.TABLE 2Faradaic efficiency of H2 production in a three-compartment assembly at different applied currentApplied Current 20 mA 50 mA100 mACharge Passed400 C400 C400 CH2 production (mmol)Chemical compartment1.611.160.92Anodic compartment0.280.260.33Total1.891.421.25Faradaic Efficiency92% 68%60%

[0075] As shown in Table 3, using the three-compartment assembly, but with Pt mesh as the cathode, the observed Faradaic efficiency of H2 generation at the Pd membrane anode was from about 65% to approaching 100% after passing 100 C at an applied potential of from about 0.6 V to 1.0 V versus RHE.TABLE 3Faradaic efficiency of H2 production in a three-compartment assembly at different applied voltageApplied Voltage0.6 V0.8V1.0 VCharge Passed97 C100 C110 CH2 production (mmol)0.460.420.37Faradaic Efficiency90%79%64%V. Electrocatalytic Dual Hydrogenation of Unsaturated Substrates

[0076] After the unexpected observation of H* diffusing through a Pd membrane anode, the following examples will now illustrate the electrocatalytic hydrogenation at the Pd membrane anode and, further, electrocatalytic dual hydrogenation.Example 5: Electrocatalytic Dual Hydrogenation Assembly

[0077] In this and following examples, a four-compartment assembly similar to the electrocatalytic hydrogenation assembly 100 was used, as shown in FIG. 4. In the four-compartment assembly, the two-compartment electrochemical cell described in Example 1 was connected with two hydrogenation compartments. The two hydrogenation compartments were individually coupled to the anodic compartment and the cathodic compartment via a PdNP / Pd membrane electrode (area: 2.27 cm2). The PdNP / Pd membrane electrode spatially separated the two hydrogenation compartments from the anodic compartment and the cathodic compartment. The Pd nanoparticle-deposited face (the hydrogenation face) of the PdNP / Pd membrane was in fluid contact with the hydrogenation compartment. The hydrogenation solution in each hydrogenation compartment was 50 mM maleic acid in water (36 ml). The cathode solution was 1.0 M KOH(aq) (40 ml), and the anode solution was 0.6 M HCHO in 1.0 M KOH (50 ml). The linear sweep voltammograms (LSV) were collected at a scan rate of 10 mV s−1 with 90% iR correction, and chronoamperometry experiments were performed at 10, 20 and 50 mA. The final product was obtained as a white solid after the evaporation of water.

[0078] It was observed that, in the presence of 0.6 M HCHO, both the PdNP / Pd membrane cathode and anode showed a rapid anodic current rise at about 0.4 V and a current density of over 15 mA cm−2 for a voltage input of 1.0 V by linear sweep voltammetry. On the other hand, in the absence of HCHO, more than 2.5 V was required to reach the same current density using the same PdNP / Pd membrane electrodes for water splitting. If a competent electrocatalyst such as nickel foam was used in place of the Pd membrane anode, more than 2.0 V was still required to deliver a current density of 15 mA cm−2.

[0079] Further, it was also observed that the Pd membrane anode possesses excellent selectivity for the electrochemical oxidation of HCHO with low voltage input. Specifically, commercial HCHO solutions generally contain methanol as a stabilizer and its partial oxidation product formate, which can also be oxidized. Chronoamperometry curve obtained from the above four-compartment assembly at a cell voltage of 1.0 V on sequential addition of 0.6 M CH3OH, 0.6 M HCOOH and 0.6 M HCHO to the anodic compartment showed that the addition of 0.6 M methanol and 0.6 M formic acid resulted in a negligible current increase, whereas the addition of 0.6 M HCHO led to an immediate anodic current rise. These results showed that the selectivity of Pd membrane anode towards formaldehyde oxidation reaction was not affected by the presence of either methanol or formate.Example 6: Electrocatalytic Dual Hydrogenation of Maleic Acid

[0080] The hydrogenation of maleic acid to succinic acid was selected as a model reaction to demonstrate the disclosed electrocatalytic dual hydrogenation.

[0081] Using the four-compartment assembly described in Example 5, chronopotentiometry was carried out with 50 mM maleic acid in the hydrogenation compartments on both sides of the four-compartment assembly. Comparative studies were carried out using a three-compartment assembly, wherein a hydrogenation compartment was coupled to the cathodic compartment. In the comparative studies, an Ni foam (1 cm×2.27 cm) or a PdNP / Pd membrane was used as the anode for water oxidation in the absence of HCHO in the anodic compartment, with a PdNP / Pd membrane electrode as the cathode for one-side hydrogenation of maleic acid.

[0082] During electrolysis, 1H NMR was used to identify and quantify maleic acid, succinic acid, fumaric acid, and maleic anhydride. For the reaction from maleic acid to succinic acid, yield change over passed charge was recorded by 1H NMR using a water suppression method that 500 μL D2O was added to 100 μL of the hydrogenation solution taken from the hydrogenation compartment every 50 C. The quantities of the maleic acid and succinic acid were calculated based on the calibration curves using t-butanol as an internal standard.

[0083] After electrolysis, H2O was removed from the hydrogenation solution and the obtained product was dried under vacuum overnight. The final product from the hydrogenation of maleic acid was analyzed using 1H NMR in D2O. The final products from the hydrogenation of fumaric acid and maleic anhydride were anylzied using 1H NMR in DMSO-d6.

[0084] The yields (%) of hydrogenated products were calculated based on equation (3):Yield⁢ (%)=mole⁢ of⁢ product⁢ formedmole⁢ of⁢ initial⁢ substrate ×100⁢%(3)The Faradaic efficiency (FE) of product formation was calculated based on equation (4):FE⁢ (%)=mole⁢ of⁢ product⁢ formedtotal⁢ charge⁢ passed / (n×F) ×100⁢%(4)where n is the number of electron transfer for each product formation and Fis the Faraday constant (96485° C. mol−1).It was observed that, to generate a current of 10 mA, the electrocatalytic dual hydrogenation as disclosed saved around 1.7 V voltage input (compared to the one-side hydrogenation using a PdNP / Pd membrane anode) and 1.0 V voltage input (compared to the one-side hydrogenation using a Ni foam anode).Table 4 summarizes the yield and Faradaic efficiency of succinic acid production. As shown in Table 4, yield of the succinic acid produced in the hydrogenation showed a nearly linear increase in concentration with charge consumed. At the end of the electrolysis, an 88% (3.11 mmol) yield of succinic acid was achieved at the cathode. It was observed that further stirring the hydrogenation solution for an additional 2 hours resulted in an increased yield of 95% (3.31 mmol). The 1HNMR spectra generally showed that, at both the anode and cathode, the peak area of maleic acid at about 6.286 ppm decreased during electrolysis. After electrolysis stopped, the peak area of maleic acid remained constant. On the other hand, the peak area of succinic acid at about 2.671 ppm increased during electrolysis and continued increasing after the electrolysis had stopped. This again confirmed that any absorbed hydrogen remaining in the PdNP / Pd cathode after electrolysis can continue to diffuse out of the cathode to drive the hydrogenation of maleic acid. Accordingly, the calculated FE increased from 88% to almost 100%, highlighting the preference for hydrogenation over the HER.A similar amount of succinic acid was produced in the hydrogenation compartment connected to the PdNP / Pd membrane anode. This observation is consistent with Examples 3 and 4 that the generated H* could diffuse through the Pd membrane anode and undergo hydrogenation reactions. Furthermore, stirring for an additional 2 hours after ceasing the electrolysis led to a slight increase in the succinic acid yield and FE. Overall, as shown in Table 4, this electrocatalytic dual hydrogenation strategy not only saved substantial voltage input, but also doubled the succinic acid yield and total FE (total FE=184%) compared with the one-side hydrogenation (FE=90%) coupled with water oxidation on a PdNP / Pd membrane or nickel foam anode after passing the same amount of charge.

[0088] It was further observed that the production of succinic acid may be dependent on the applied current. Varying the applied current (10, 20 and 50 mA) in the chronopotentiometry experiments showed that the yield and Faradic efficiency of succinic acid production were dependent on the applied current. Table 5 listed yields of succinic acid production at different applied current. The calculated Faradaic efficiency of succinic acid generation at the anode was from about 60% to approaching 100%, and the Faradaic efficiency of succinic acid generation at the anode was from about 67% to approaching 100%. The yields at the anode and the cathode as well as the total Faradaic efficiency of succinic acid production after passing about 347 C are shown in Table 6.TABLE 4Total Faradaic efficiency of succinic acid productionExample 6Example 6Example 6ElectrodesPdC|PdAPdC|PdANi Foam|PdAAnode solution1.0 M KOH0.6 M HCHO1.0 M KOH1.0 M KOHProducing ElectrodePdCPdATotalPdCNi FoamChargeFEFEYieldYieldYield(C)(%)(%)FE (%)(mmol)FE (%)(mmol)FE (%)(mmol) 50100% 102% 202%0.52105%0.2798%0.26100101% 101% 202%1.05108%0.5695%0.4915098%101% 199%1.54105%0.8193%0.320096%99%195%2.02105%1.0891%0.9425095%96%192%2.48100%1.3088%1.1430092%88%180%2.79 93%1.4580%1.24347.488%85%173%3.11 87%1.5773%1.32347.4*95%89%185%3.31 92%1.6689%1.60*The results were obtained after stirring for an additional 2 hours after the electrolysis had ceased.TABLE 5Yield of succinic acid production applying various current.ElectrodesPdC|PdAAnode solution1.0 M KOH 0.6 M HCHOCharge (C)10 mA20 mA50 mAYield (mmol)500.520.560.261001.051.050.541501.541.570.782002.022.021.052502.482.471.313002.792.781.50347.43.113.041.64TABLE 6Production of succinic acid from different unsaturated substrates.Con-H Cur-SubstratecentrationsourcerentYieldAYieldCFES50 mM 50 mM 50 mMHCHO HCHO HCHO10 mA 20 mA 50 mA89 82 6095 95 66184 177 12620 mMHCHO10 mA666413050 mM 50 mMHCHO PFA10 mA 10 mA87 8997 91184 180YieldA: Yield on anode side.YieldC: Yield on cathode side.FES: Total Faradaic efficiency of succinic acid production.TABLE 7Yield and Faradaic efficiency of succinic acid production with varying maleicacid (MA) and formaldehyde (HCHO) concentrations.[MA] [HCHO]50 mM0.4 M0.6 M0.8 M10 mM100 mMHCHOHCHOHCHO0.6 M0.6 MPdAPdCPdAPdCPdAPdCPdAPdCPdAPdCCharge347 C347 C347 C347 C347 C347 C70 C70 C695 C695 CYield %42%49%45%46%44%51%13%10%53%55%Yield %*62%67%60%69%59%66%60%63%60%66%FEAnode % 62% 60% 59% 60% 60%FETotal %128%126%128%123%126%*The results were obtained after stirring for an additional 2 hours after the electrolysis had ceased.On the other hand, it was observed that when the concentration of HCHO in the anode solution was increased from 0.4 to 0.8 M, there was no appreciable difference in the production rate and yield of succinic acid when the electrolysis was carried out at 50 mA, as shown in Table 7. Particularly, as shown in Table 7, when the maleic acid concentration in the hydrogenation compartment was reduced to 10 mM, after passing the theoretical amount of charge, the yield of succinic acid was only 13%, which was much lower than the yields obtained with higher concentrations (45% and 53% for 50 and 100 mM maleic acid, respectively. However, simply continuing to stir the hydrogenation solution for an extra 2 hours after ending the electrolysis led to an increase in the yield of succinic acid to nearly 60% in all cases. Similar phenomena were observed for hydrogenation on the Pd membrane cathode. Nonetheless, the anodic and total FEs remained nearly constant, approaching 200%, when different concentrations of HCHO and maleic acid were used.Example 7: Comparative Electrocatalytic Dual Hydrogenation of Fumaric AcidFumaric acid is the E isomer of maleic acid and was selected as a comparative study to the hydrogenation of maleic acid. The electrocatalytic dual hydrogenation of fumaric acid was carried out under the similar conditions described in Example 6. In this case, the concentration of fumaric acid was 20 mM. Chronopotentiometry experiments were carried out at 10 mA. As shown in Table 6, the electrocatalytic dual hydrogenation of fumaric acid resulted in a lower total FE of 130%, likely due to the steric hindrance of its trans configuration.Example 8: Comparative Electrocatalytic Dual Hydrogenation of Maleic AnhydrideMaleic anhydride is the acid anhydride of maleic acid and was selected as a comparative study to the hydrogenation of maleic acid. The electrocatalytic hydrogenation of maleic anhydride was carried out under the similar conditions described in Example 6. Chronopotentiometry experiments were carried out at 10 mA. In this case, 0.6 M HCHO was used in the anodic compartment, and the hydrogenation solution in each hydrogenation compartment was 50 mM maleic anhydride in water. As shown in Table 6, excellent hydrogenation was achieved with maleic anhydride (total FE=184%) because of its ready hydrolysis to maleic acid in aqueous media.Example 9: Paraformaldehyde as an Alternative Hydrogen Source for Electrocatalytic Dual Hydrogenation

[0092] Paraformaldehyde (PFA) is the polymeric form of formaldehyde and is more stable than formaldehyde. This example shows that paraformaldehyde (PFA) can also be used for hydrogen production.

[0093] Using a two-compartment electrochemical cell, it was observed that applying 0.5 V versus RHE generated an anodic current at a loading amount as low as 0.1 g L−1. An anodic current density of from about 44 mA cm−2 to about 49 mA cm 2 was observed with a loading amount of from about 20 g L−1 PFA to about 40 g L−1 PFA at 0.5 V versus RHE, as shown in Table 8.TABLE 8Current density generated using PFALoading Amount Current Density (g L−1)(mA cm−2) 0.1 1.5 0.5 5.4 111 53010372044404850316012

[0094] Electrocatalytic dual hydrogenation of maleic anhydride was carried out using PFA as the hydrogen source. In this case, the anode solution contain 20 g L−1 PFA, and the hydrogenation solution in each hydrogenation compartment was 50 mM maleic anhydride in water. The observed LSV curves of PdNP / Pd membrane electrodes were nearly identical to Example 8, in which the anode solution contained 0.6 M HCHO. In both Examples, the onset of current was about or less than 0.5 V, and at an applied voltage of 1 V, both examples had a current density of about 15 mA cm−2. Further, as shown in Table 6, both examples reached comparable total Faradaic efficiencies (184% in the example with HCHO and 180% in the example with PFA).

[0095] Furthermore, in this example, gram-scale production of succinic acid was achieved. Chronopotentiometry experiments were carried out at 20 mA until 1.5-fold of the theoretical amount of charge for the complete conversion of maleic anhydride to succinic acid was passed. By increasing the concentration of maleic anhydride to 300 mM, 2.4 g succinic acid with high purity was obtained.Example 10: Electrocatalytic Dual Hydrogenation in Non-Protic Solvent

[0096] As discussed hereinabove, and demonstrated here, the presently disclosed methods and systems comprising hydrogenation compartments spatially separated from the electrochemical cell enables electrocatalytic hydrogenation of unsaturated substrates in non-protic solvents.

[0097] In this case, 4-ethynylaniline, which is soluble in non-protic solvents, was investigated as a model substrate.

[0098] The four-compartment assembly described in Example 5 was used. The cathode solution was 1.0 M KOD in D2O (40 ml), while the anode solution contained 20.0 g L−1 PFA and 1.0 M KOD dissolved in D2O (50 ml). The hydrogenation solution in both hydrogenation compartments contained 25 mM 4-ethynylaniline in dichloromethane (36 ml). Chronopotentiometry experiments were carried out at 50 mA.

[0099] Under this setting, the deuterated product would be obtained on the cathode side, and the normal hydrogenation product would be formed on the anode side. Indeed, chronopotentiometry at 50 mA using the PdNP / Pd membrane electrodes resulted in deuterated and normal 4-ethylaniline on the cathode and anode sides, respectively, as confirmed by mass spectrometry and 1H NMR spectroscopy. Specifically, the theoretical mass spectrum of [C8H11N+H]+ showed two peaks at 122.1 m / z and 123.1 m / z. The hydrogenated product obtained from the anodic hydrogenation compartment showed two peaks nearly identical to the theoretical spectrum. On the other hand, the hydrogenated product obtained from the cathodic hydrogenation compartment showed additional four peaks at 124.1 m / z, 125.1 m / z, 126.1 m / z, and 127.1 m / z. Likewise, comparing the 1H NMR spectra of products obtained from the cathodic hydrogenation compartment and anodic hydrogenation compartment, the peaks of ethyl hydrogens were significantly diminished in the hydrogenation products obtained from the cathodic compartment. These results confirmed that the production of deuterated 4-enthylaniline in the cathodic hydrogenation compartment. These results again support the observations discussed above that the hydrogen source for hydrogenation on the cathode side is water, while on the anode side it is PFA (that is, HCHO).Example 11: Carbon Balance of Electrocatalytic Dual Hydrogenation

[0100] The organic species produced in the anode solution during HCHO oxidation were quantified.

[0101] The concentration of formaldehyde in the anode solution during electrolysis was determined through a colorimetric reaction with acetylacetone. Acetylacetone (0.2 mL) and glacial acetic acid (0.3 mL) were added to a solution of ammonium acetate (15.4 g) in H2O (50 mL) under stirring and was subsequently diluted with H2O (49.5 mL). The diluted solution was stored in a refrigerator for up to 3 days. To measure the concentration of formaldehyde, 20.0 μL of the anode solution was acidified with 20 μL 2.0 M HCl, which was subsequently diluted 2500 times by water. 2.0 mL of the diluted anode solution was mixed with the diluted acetylacetone solution (2.0 mL) and heated to 60° C. for 10 min. After cooling to room temperature, the UVV is absorbance of the solution was measured at a wavelength of 414 nm and compared with a calibration curve by applying standard solutions with known concentrations of commercially purchased formaldehyde. Methanol and formic acid were identified and quantified by 1H NMR from the calibration curves by applying standard solutions with known concentrations of commercially purchased compounds with t-butanol (10.0 mM) as an internal standard. 100 μL electrolyte taken from the electrochemical cell was acidified with 20 μL concentrated HCl (37%) followed by the addition of 500 μL D2O. 1H NMR were recorded on a Bruker AV 400 MHz spectrometer using a water suppression method.

[0102] A carbon balance of nearly 100% was confirmed. Besides the products of the Cannizzaro reaction, additional formate was produced from the electrocatalytic oxidation of HCHO with an FE close to 100%, suggesting that the HOR was negligible under these conditions.Aspect Listing

[0103] In a first aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method of electrocatalytic dual hydrogenation comprising loading a first hydrogenation solution into a first hydrogenation compartment of an electrocatalytic hydrogenation assembly, wherein the first hydrogenation compartment is separated from an electrochemical cell by a hydrogen-permeable anode; loading a second hydrogenation solution into a second hydrogenation compartment of the electrocatalytic hydrogenation assembly, wherein the second hydrogenation compartment is separated from the electrochemical cell by a hydrogen-permeable cathode; applying a voltage to the electrochemical cell to reduce a cathode solution in a cathodic compartment of the electrochemical cell to provide hydrogen, whereby the hydrogen is absorbed through the hydrogen-permeable cathode to hydrogenate the second hydrogenation solution; and maintaining the voltage to permit anions to flow from the cathodic compartment to an anodic compartment of the electrochemical cell through a semi-permeable membrane, whereby the anions oxidize an anode solution to provide hydrogen, whereby the hydrogen is absorbed through the hydrogen-permeable anode to hydrogenate the first hydrogenation solution.

[0104] In a second aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a system for electrocatalytic dual hydrogenation comprising an electrocatalytic hydrogenation assembly comprises a first hydrogenation compartment and a second hydrogenation compartment connected to an electrochemical cell connected to a voltage supply, a hydrogen-permeable anode separating the first hydrogenation compartment from the electrochemical cell, and a hydrogen-permeable cathode separating the second hydrogenation compartment from the electrochemical cell, wherein the first hydrogenation compartment is configured to hold a first hydrogenation solution; the second hydrogenation compartment is configured to hold a second hydrogenation solution; the voltage supply is configured to apply a voltage to the electrochemical cell to reduce a cathode solution in a cathodic compartment of the electrochemical cell to provide hydrogen, whereby the hydrogen is absorbed through the hydrogen-permeable cathode to hydrogenate the second hydrogenation solution; and the voltage supply is configured to maintain the voltage to permit anions to flow from the cathodic compartment to an anodic compartment of the electrochemical cell through a semi-permeable membrane, whereby the anions oxidize an anode solution to provide hydrogen and the hydrogen is absorbed through the hydrogen-permeable anode to hydrogenate the first hydrogenation solution.

[0105] In a third aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method of improving hydrogenation rate and Faradaic efficiency of a hydrogenation reaction, comprising separating a first hydrogenation compartment of an electrocatalytic hydrogenation assembly from an electrochemical cell by a hydrogen-permeable anode; separating a second hydrogenation compartment of the electrocatalytic hydrogenation assembly from the electrochemical cell by a hydrogen-permeable cathode; loading a hydrogenation solution to the first hydrogenation compartment and the second hydrogenation compartment; loading an electrochemical solution comprising an alkali hydroxide to a cathodic compartment and an anodic compartment of the electrochemical cell, wherein the cathodic compartment and the anodic compartment are fluidly coupled through a semi-permeable membrane, and the electrochemical solution in the anodic compartment further comprises an aldehyde; applying a voltage to the electrochemical cell to reduce the electrochemical solution in the cathodic compartment to provide hydrogen, whereby the hydrogen is absorbed through the hydrogen-permeable cathode to hydrogenate the hydrogenation solution in the second hydrogenation compartment; and maintaining the voltage to permit anions to flow from the cathodic compartment to the anodic compartment through the semi-permeable membrane, whereby the anions oxidize the aldehyde to provide hydrogen, whereby the hydrogen is absorbed through the hydrogen-permeable anode to hydrogenate the hydrogenation solution in the first hydrogenation compartment.

[0106] In a fourth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the hydrogen-permeable anode and / or the hydrogen-permeable cathode are substantially identical.

[0107] In a fifth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the hydrogen-permeable anode and / or the hydrogen-permeable cathode are palladium membranes.

[0108] In a sixth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the palladium membrane comprises a hydrogenation face in fluid contact with the first hydrogenation and / or the second hydrogenation compartment, an electrochemical face in fluid contact with the electrochemical cell, and a membrane material, disposed between the hydrogenation face and the electrochemical face.

[0109] In a seventh aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the palladium membrane has a thickness of from about 500 nm to about 5 μm.

[0110] In an eighth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the palladium membrane comprises particles.

[0111] In a ninth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the particles are disposed on the hydrogenation face of the palladium membrane.

[0112] In a tenth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the particles comprise palladium, platinum, gold, silver, copper, or combinations thereof.

[0113] In an eleventh aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the particles comprise a crystal facet.

[0114] In a twelfth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the particles have a diameter of from about 50 nm to about 1000 nm.

[0115] In a thirteenth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the membrane material comprises palladium, porous materials, conductive materials, or combinations thereof.

[0116] In a fourteenth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the hydrogenation face comprises palladium, porous materials, conductive materials, or combinations thereof.

[0117] In a fifteenth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the electrochemical face comprises palladium, porous materials, conductive materials, or combinations thereof.

[0118] In a sixteenth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the hydrogenation face and the electrochemical face are palladium.

[0119] In a seventeenth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the anode solution comprises an aldehyde and an alkali hydroxide.

[0120] In an eighteenth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the anode solution has an oxidation potential of from about −0.1 V to about −1 V.

[0121] In a nineteenth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the aldehyde is selected from formaldehyde, paraformaldehyde, or combinations thereof.

[0122] In a twentieth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the aldehyde is formaldehyde.

[0123] In a twenty-first aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the formaldehyde is present in a concentration of from about 100 mM to about 2000 mM.

[0124] In a twenty-second aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the aldehyde is paraformaldehyde.

[0125] In a twenty-third aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the paraformaldehyde is present in a concentration of from about 1 g L−1 to less than or equal to 60 g L−1.

[0126] In a twenty-fourth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the cathode solution comprises an alkali hydroxide.

[0127] In a twenty-fifth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the anode solution and the cathode solution comprise an alkali hydroxide.

[0128] In a twenty-sixth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the alkali hydroxide is selected from LiOH, NaOH, KOH, RbOH, CsOH, or combinations thereof.

[0129] In a twenty-seventh aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the alkali hydroxide is present in a concentration of from about 100 mM to about 1500 mM.

[0130] In a twenty-eighth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the anode solution and / or the cathode solution are argon-saturated.

[0131] In a twenty-ninth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the first hydrogenation solution and / or the second hydrogenation solution comprise an unsaturated substrate, wherein the unsaturated substrate comprises at least one carbon-carbon double bond or at least one carbon-carbon triple bond.

[0132] In a thirtieth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the unsaturated substrate is present at a concentration of from about 1 mM to about 500 mM.

[0133] In a thirty-first aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the unsaturated substrate is selected from dicarboxylic acids, dicarboxylic anhydrides, carboxylic acids, aldehydes, dicarbaldehydes, aromatic alkenes, aliphatic alkenes, aromatic alkynes, aliphatic alkenes, or combinations thereof.

[0134] In a thirty-second aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the voltage is from about 0.35 V to about 1 V.

[0135] In a thirty-third aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the voltage generates a current density of from 5 mA cm−2 to about 100 mA cm−2.

[0136] In a thirty-fourth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method wherein applying the voltage to the electrochemical cell reduces water in the cathode solution.

[0137] In a thirty-fifth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a system wherein the voltage applied to the electrochemical cell reduces water in the cathode solution.

[0138] In a thirty-sixth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein an aldehyde in the anode solution is oxidized.

[0139] In a thirty-seventh aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method further comprising producing a first hydrogenated product in the first hydrogenation compartment.

[0140] In a thirty-eighth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a system further comprising a first hydrogenated product produced in the first hydrogenation compartment upon applying the voltage to the electrochemical cell.

[0141] In a thirty-ninth aspect, alone or in combination with any other aspect described herein, the present disclosure relates a method further comprising producing the first hydrogenated product has a Faradic efficiency of from about 75% to about 100%.

[0142] In a fortieth aspect, alone or in combination with any other aspect described herein, the present disclosure relates a system further comprising a Faradic efficiency of producing the first hydrogenated product that is from about 75% to about 100%.

[0143] In a forty-first aspect, alone or in combination with any other aspect described herein, the present disclosure relates a method further comprising separating the first hydrogenated product from the first hydrogenation solution.

[0144] In a forty-second aspect, alone or in combination with any other aspect described herein, the present disclosure relates a system wherein the first hydrogenated product is separable from the first hydrogenation solution.

[0145] In a forty-third aspect, alone or in combination with any other aspect described herein, the present disclosure relates a method further comprising producing a second hydrogenated product in the second hydrogenation compartment.

[0146] In a forty-fourth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a system further comprising a second hydrogenated product produced in the second hydrogenation compartment upon applying the voltage to the electrochemical cell.

[0147] In a forty-fifth aspect, alone or in combination with any other aspect described herein, the present disclosure relates a method wherein producing the second hydrogenated product has a Faradic efficiency of from about 75% to about 100%.

[0148] In a forty-sixth aspect, alone or in combination with any other aspect described herein, the present disclosure relates a system further comprising a Faradic efficiency of producing the second hydrogenated product that is from about 75% to about 100%.

[0149] In a forty-seventh aspect, alone or in combination with any other aspect described herein, the present disclosure relates a system wherein the second hydrogenated product is separable from the second hydrogenation solution.

[0150] In a forty-eighth aspect, alone or in combination with any other aspect described herein, the present disclosure relates a method further comprising producing a first hydrogenated product in the first hydrogenation compartment and a second hydrogenated product in the second hydrogenation compartment.

[0151] In a forty-ninth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method wherein producing the first hydrogenated product and the second hydrogenated product has a total Faradic efficiency of from about 150% to about 200%.

[0152] In a fiftieth aspect, alone or in combination with any other aspect described herein, the present disclosure relates a method further comprising separating the second hydrogenated product from the second hydrogenation solution.

[0153] In a fifty-first aspect, alone or in combination with any other aspect described herein, the present disclosure relates a method further comprising ceasing application of the voltage and stirring the first hydrogenation solution and / or the second hydrogenation solution.

[0154] In a fifty-second aspect, alone or in combination with any other aspect described herein, the present disclosure relates a method wherein the first hydrogenation solution and / or the second hydrogenation solution are stirred for about four hours.

[0155] In a fifty-third aspect, alone or in combination with any other aspect described herein, the present disclosure relates a method or a system wherein the semi-permeable membrane is an anion exchange membrane.

[0156] In a fifty-fourth aspect, alone or in combination with any other aspect described herein, the present disclosure relates to a method or a system wherein the first hydrogenation solution and / or the second hydrogenation solution may comprise protic solvent, non-protic solvent, or combinations thereof.

[0157] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs. The terminology used in the description herein is for describing particular embodiments only and is not intended to be limiting. As used in the specification and appended claims, the singular forms “a,”“an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0158] It is noted that one or more of the following claims utilize the term “wherein” as a transitional phrase. For the purposes of defining the present technology, it is noted that this term is introduced in the claims as an open-ended transitional phrase that is used to introduce a recitation of a series of characteristics of the structure and should be interpreted in like manner as the more commonly used open-ended preamble term “comprising.”

[0159] It should be understood that where a first component is described as “comprising” or “including” a second component, it is contemplated that, in some embodiments, the first component “consists” or “consists essentially of” the second component. Additionally, the term “consisting essentially of” is used in this disclosure to refer to quantitative values that do not materially affect the basic and novel characteristic(s) of the disclosure.

[0160] It should be understood that any two quantitative values assigned to a property or measurement may constitute a range of that property or measurement, and all combinations of ranges formed from all stated quantitative values of a given property or measurement are contemplated in this disclosure.

[0161] As used herein, the term “about,” when referring to a value or to an amount of mass, weight, time, volume, concentration or percentage is meant to encompass variations of in some embodiments±20%, in some embodiments±10%, in some embodiments±5%, in some embodiments±1%, in some embodiments±0.5%, and in some embodiments±0.1% from the specified amount, as such variations are appropriate to perform the disclosed method.

[0162] It should be understood that every maximum numerical limitation given throughout this specification includes every lower numerical limitation, as if such lower numerical limitations were expressly written herein. Every minimum numerical limitation given throughout this specification will include every higher numerical limitation, as if such higher numerical limitations were expressly written herein. Every numerical range given throughout this specification will include every narrower numerical range that falls within such broader numerical range, as if such narrower numerical ranges were all expressly written herein.

[0163] While particular embodiments have been illustrated and described herein, it should be understood that various other changes and modifications may be made without departing from scope of the claimed subject matter. Moreover, although various aspects of the claimed subject matter have been described herein, such aspects need not be utilized in combination. It is therefore intended that the appended claims cover all such changes and modifications that are within the scope of the claimed subject matter.

Claims

1. A method of electrocatalytic dual hydrogenation, comprising:loading a first hydrogenation solution into a first hydrogenation compartment of an electrocatalytic hydrogenation assembly, wherein the first hydrogenation compartment is separated from an electrochemical cell by a hydrogen-permeable anode;loading a second hydrogenation solution into a second hydrogenation compartment of the electrocatalytic hydrogenation assembly, wherein the second hydrogenation compartment is separated from the electrochemical cell by a hydrogen-permeable cathode;applying a voltage to the electrochemical cell to reduce a cathode solution in a cathodic compartment of the electrochemical cell to provide hydrogen, whereby the hydrogen is absorbed through the hydrogen-permeable cathode to hydrogenate the second hydrogenation solution; andmaintaining the voltage to permit anions to flow from the cathodic compartment to an anodic compartment of the electrochemical cell through a semi-permeable membrane, whereby the anions oxidize an anode solution to provide the hydrogen, whereby the hydrogen is absorbed through the hydrogen-permeable anode to hydrogenate the first hydrogenation solution.

2. The method of claim 1, wherein the hydrogen-permeable anode and / or the hydrogen-permeable cathode are palladium membranes.

3. The method of claim 2, wherein the palladium membrane comprises:a hydrogenation face in fluid contact with the first hydrogenation compartment and / or the second hydrogenation compartment,an electrochemical face in fluid contact with the electrochemical cell, anda membrane material, disposed between the hydrogenation face and the electrochemical face.

4. The method of claim 2, wherein the palladium membrane has a thickness of from about 500 nm to about 5 μm.

5. The method of claim 3, wherein the palladium membrane comprises particles.

6. The method of claim 5, wherein the particles are disposed on the hydrogenation face of the palladium membrane.

7. The method of claim 5, wherein the particles comprise palladium, platinum, gold, silver, copper, or combinations thereof.

8. The method of claim 5, wherein the particles comprise a crystal facet.

9. The method of claim 5, wherein the particles have a diameter of from about 50 nm to about 1000 nm.

10. The method of claim 3, wherein the membrane material comprises palladium, porous materials, conductive materials, or combinations thereof.11-40. (canceled)41. A system for electrocatalytic dual hydrogenation, comprising:an electrocatalytic hydrogenation assembly comprises a first hydrogenation compartment and a second hydrogenation compartment connected to an electrochemical cell connected to a voltage supply, a hydrogen-permeable anode separating the first hydrogenation compartment from the electrochemical cell, and a hydrogen-permeable cathode separating the second hydrogenation compartment from the electrochemical cell, wherein:the first hydrogenation compartment is configured to hold a first hydrogenation solution;the second hydrogenation compartment is configured to hold a second hydrogenation solution;the voltage supply is configured to apply a voltage to the electrochemical cell to reduce a cathode solution in a cathodic compartment of the electrochemical cell to provide hydrogen, whereby the hydrogen is absorbed through the hydrogen-permeable cathode to hydrogenate the second hydrogenation solution; andthe voltage supply is configured to maintain the voltage to permit anions to flow from the cathodic compartment to an anodic compartment of the electrochemical cell through a semi-permeable membrane, whereby the anions oxidize an anode solution to provide the hydrogen and the hydrogen is absorbed through the hydrogen-permeable anode to hydrogenate the first hydrogenation solution.

42. The system of claim 41, wherein the hydrogen-permeable anode and / or the hydrogen-permeable cathode are palladium membranes.

43. The system of claim 42, wherein the palladium membrane comprises:a hydrogenation face comprising palladium, porous materials, conductive materials, or combinations thereof,an electrochemical face comprising palladium, porous materials, conductive materials, or combinations thereof, anda membrane material, disposed between the hydrogenation face and the electrochemical face, comprising palladium, porous materials, conductive materials, or combinations thereof.

44. The system of claim 43, wherein the palladium membrane comprises particles deposited on the hydrogenation face of the palladium membrane, and the particles comprise palladium, platinum, gold, silver, copper, or combinations thereof.

45. The system of claim 44, wherein the particles comprise a dimension from about 50 nm to 1000 nm.

46. The system of claim 41, wherein the anode solution comprises an aldehyde and an alkali hydroxide.

47. The system of claim 46, wherein the aldehyde is selected from formaldehyde, paraformaldehyde, or combinations thereof.

48. The system of any of claim 46, wherein the aldehyde is formaldehyde.

49. The system of claim 48, wherein the formaldehyde is present in a concentration of from about 100 mM to about 2000 mM.

50. The system of claim 46, wherein the aldehyde is paraformaldehyde.51-79. (canceled)

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