rexresearch.com
rexresearch1.com
Karl WESTENDORFF, et al.
Electro-Catalysis
https://news.mit.edu/2024/mit-researchers-boost-common-catalytic-reactions-with-electricity-0215
With just a little electricity, MIT researchers boost common catalytic reactions
Applying a small voltage to a catalyst can increase the rates of reactions used in petrochemical processing, pharmaceutical manufacture, and many other processes.
David L. Chandler | MIT News
A simple technique that uses small amounts of energy could boost the efficiency of some key chemical processing reactions, by up to a factor of 100,000, MIT researchers report. These reactions are at the heart of petrochemical processing, pharmaceutical manufacturing, and many other industrial chemical processes.
The surprising findings are reported today in the journal Science, in a paper by MIT graduate student Karl Westendorff, professors Yogesh Surendranath and Yuriy Roman-Leshkov, and two others.
“The results are really striking,” says Surendranath, a professor of chemistry and chemical engineering. Rate increases of that magnitude have been seen before but in a different class of catalytic reactions known as redox half-reactions, which involve the gain or loss of an electron. The dramatically increased rates reported in the new study “have never been observed for reactions that don’t involve oxidation or reduction,” he says.
The non-redox chemical reactions studied by the MIT team are catalyzed by acids. “If you’re a first-year chemistry student, probably the first type of catalyst you learn about is an acid catalyst,” Surendranath says. There are many hundreds of such acid-catalyzed reactions, “and they’re super important in everything from processing petrochemical feedstocks to making commodity chemicals to doing transformations in pharmaceutical products. The list goes on and on.”
“These reactions are key to making many products we use daily,” adds Roman-Leshkov, a professor of chemical engineering and chemistry.
But the people who study redox half-reactions, also known as electrochemical reactions, are part of an entirely different research community than those studying non-redox chemical reactions, known as thermochemical reactions. As a result, even though the technique used in the new study, which involves applying a small external voltage, was well-known in the electrochemical research community, it had not been systematically applied to acid-catalyzed thermochemical reactions.
People working on thermochemical catalysis, Surendranath says, “usually don’t consider” the role of the electrochemical potential at the catalyst surface, “and they often don’t have good ways of measuring it. And what this study tells us is that relatively small changes, on the order of a few hundred millivolts, can have huge impacts — orders of magnitude changes in the rates of catalyzed reactions at those surfaces.”
“This overlooked parameter of surface potential is something we should pay a lot of attention to because it can have a really, really outsized effect,” he says. “It changes the paradigm of how we think about catalysis.”
Chemists traditionally think about surface catalysis based on the chemical binding energy of molecules to active sites on the surface, which influences the amount of energy needed for the reaction, he says. But the new findings show that the electrostatic environment is “equally important in defining the rate of the reaction.”
The team has already filed a provisional patent application on parts of the process and is working on ways to apply the findings to specific chemical processes. Westendorff says their findings suggest that “we should design and develop different types of reactors to take advantage of this sort of strategy. And we’re working right now on scaling up these systems.”
While their experiments so far were done with a two-dimensional planar electrode, most industrial reactions are run in three-dimensional vessels filled with powders. Catalysts are distributed through those powders, providing a lot more surface area for the reactions to take place. “We’re looking at how catalysis is currently done in industry and how we can design systems that take advantage of the already existing infrastructure,” Westendorff says.
Surendranath adds that these new findings “raise tantalizing possibilities: Is this a more general phenomenon? Does electrochemical potential play a key role in other reaction classes as well? In our mind, this reshapes how we think about designing catalysts and promoting their reactivity.”
Roman-Leshkov adds that “traditionally people who work in thermochemical catalysis would not associate these reactions with electrochemical processes at all. However, introducing this perspective to the community will redefine how we can integrate electrochemical characteristics into thermochemical catalysis. It will have a big impact on the community in general.”
While there has typically been little interaction between electrochemical and thermochemical catalysis researchers, Surendranath says, “this study shows the community that there’s really a blurring of the line between the two, and that there is a huge opportunity in cross-fertilization between these two communities.”
Westerndorff adds that to make it work, “you have to design a system that’s pretty unconventional to either community to isolate this effect.” And that helps explain why such a dramatic effect had never been seen before. He notes that even their paper’s editor asked them why this effect hadn’t been reported before. The answer has to do with “how disparate those two ideologies were before this,” he says. “It’s not just that people don’t really talk to each other. There are deep methodological differences between how the two communities conduct experiments. And this work is really, we think, a great step toward bridging the two.”
In practice, the findings could lead to far more efficient production of a wide variety of chemical materials, the team says. “You get orders of magnitude changes in rate with very little energy input,” Surendranath says. “That’s what’s amazing about it.”
The findings, he says, “build a more holistic picture of how catalytic reactions at interfaces work, irrespective of whether you’re going to bin them into the category of electrochemical reactions or thermochemical reactions.” He adds that “it’s rare that you find something that could really revise our foundational understanding of surface catalytic reactions in general. We’re very excited.”
“This research is of the highest quality,” says Costas Vayenas, a professor of engineering at the university of Patras, in Greece, who was not associated with the study. The work “is very promising for practical applications, particularly since it extends previous related work in redox catalytic systems,” he says.
The team included MIT postdoc Max Hulsey PhD ’22 and graduate student Thejas Wesley PhD ’23, and was supported by the Air Force Office of Scientific Research and the U.S. Department of Energy Basic Energy Sciences.
http://dx.doi.org/10.1126/science.adk4902
Science 15 Feb 2024 Vol 383, Issue 6684 pp. 757-763
Electrically driven proton transfer promotes Br nsted acid catalysis by orders of magnitude
Karl S. Westendorff, et al.
...Westendorff et al. report that the application of an electrochemical potential can tilt protonation pre-equilibria and thereby accelerate an acid-catalyzed alcohol dehydration by up to 100,000-fold. The strategy was also effective in accelerating a Friedel-Crafts acylation...
Abstract -- Electric fields play a key role in enzymatic catalysis and can enhance reaction rates by 100,000-fold, but the same rate enhancements have yet to be achieved in thermochemical heterogeneous catalysis. In this work, we probe the influence of catalyst potential and interfacial electric fields on heterogeneous Br nsted acid catalysis. We observed that variations in applied potential of ~380 mV led to a 100,000-fold rate enhancement for 1-methylcyclopentanol dehydration, which was catalyzed by carbon-supported phosphotungstic acid. Mechanistic studies support a model in which the interfacial electrostatic potential drop drives quasi-equilibrated proton transfer to the adsorbed substrate prior to rate-limiting C O bond cleavage. Large increases in rate with potential were also observed for the same reaction catalyzed by Ti/TiOyHx and for the Friedel Crafts acylation of anisole with acetic anhydride by carbon-supported phosphotungstic acid...
US2020067106BACKGROUND
DRIVING HETEROGENEOUS CATALYSIS VIA ELECTROCHEMICAL PROTON PUMPING IN PROTON-ELECTRON CONDUCTING FILMS
[ PDF ]
[0003] Many industrially important commodity conversions involve the transfer of hydrogen atoms. For example, hydrogen oxidation, methanol oxidation and formic acid oxidation, all of which are anode reactions for fuel cells; alkane dehydrogenation, generating alkenes that are precursors for higher order industrial products; and carbon dioxide and carbon monoxide reduction to useful chemicals. However, many of these conversions require harsh conditions, for example, strong acids and bases, fragile catalysts, high temperatures, and pressures (e.g., the Haber-Bosch process). Thus, there exists a need for robust catalysts that can catalyze these vital chemical conversions under mild conditions.
SUMMARY
[0004] The present disclosure provides devices capable of catalyzing a range of industrially important chemical transformations.
[0005] In one aspect, the device comprises a porous support substrate, and a film in contact with the porous support substrate, wherein the film comprises:
[0006] a first oxide layer; and
[0007] an ionic conductor layer; wherein
the oxide is selected from the group consisting of WO3, WO2, MoO3, MoO2, TiO2, TiO, ZnO, ZrO2, ZrO, CeO2, CeO, TiCeO2, YCeO2, carbon, V2O5, MoS2, WS2, NiOOH, MnO2, SnO2, Fe2O3, and CrOx, wherein x is a number from 0.1 to 3; and
the ionic conductor is selected from the group consisting of an electrolyte, a polymer membrane, and an inorganic compound.
[0010] In another aspect, the device comprises a porous support substrate, and a film in contact with the porous support substrate, wherein the film comprises:
[0011] a first catalyst layer;
[0012] a first oxide layer; and
[0013] an ionic conductor layer; wherein the catalyst is selected from the group consisting of a metal, a metal nitride, a metal oxide, a metal sulfide, a metal carbide, Pt, Pd, Ru, Re, Co, Cu, Rh, CoMo, NiMo, NiW sulfide, Ni, Fe, and Au; the oxide is selected from the group consisting of WO3, WO2, MoO3, MoO2, TiO2, TiO, ZnO, ZrO2, ZrO, CeO2, CeO, TiCeO2, YCeO2, carbon, V2O5, MoS2, WS2, NiOOH, MnO2, SnO2, Fe2O3, and CrOx, wherein x is a number from 0.1 to 3; and the ionic conductor is selected from the group consisting of an electrolyte, a polymer membrane, and an inorganic compound.
[0017] In yet another aspect, the device comprises a porous support substrate, and a film in contact with the porous support substrate, wherein the film comprises:
[0018] a first catalyst layer;
[0019] a first oxide layer;
[0020] an ionic conductor layer;
[0021] a second oxide layer; and
[0022] a second catalyst layer; wherein
each catalyst is independently selected from the group consisting of a metal, a metal nitride, a metal oxide, a metal sulfide, a metal carbide, Pt, Pd, Ru, Re, Co, Cu, Rh, Pt sulfide, Pd sulfide, Rh sulfide, CoMo sulfide, NiMo sulfide, NiW sulfide, Ni, Fe, and Au; the oxide is selected from the group consisting of WO3, WO2, MoO3, MoO2, TiO2, TiO, ZnO, ZrO2, ZrO, CeO2, CeO, TiCeO2, YCeO2, carbon, V2O5, MoS2, WS2, NiOOH, MnO2, SnO2, Fe2O3, and CrOx, wherein x is a number from 0.1 to 3; and the ionic conductor is selected from the group consisting of an electrolyte, a polymer membrane, and an inorganic compound.
[0026] In certain aspects, the present disclosure provides methods of using the aforementioned devices to perform chemical transformations.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1A depicts a cross-section SEM image of a magnetron sputter deposited Pt/WO3 film, supported on a porous polycarbonate membrane.
[0028] FIG. 1B depicts a top-down SEM image of a Pt/WO3 film.
[0029] FIG. 1C depicts a transmission electron microscopy (TEM) image of Pt particles supported on WO3, both of which were magnetron sputter deposited on a Cu/lacey carbon TEM grid. The white circles were drawn to guide the eyes to the Pt particles.
[0030] FIG. 1D depicts X-ray photoelectron spectroscopy (XPS) of the W 4f region on the surface (black), and after one cycle of Ar<+> sputter (red) for the Pt/WO3 surface.
[0031] FIG. 1E depicts the XPS of Pt 4f region on the Pt/WO3 film surface.
[0032] FIG. 1F depicts an exemplary schematic of the WO3 and Pt fabrication process, and the assembly into a working electrode.
[0033] FIG. 1G depicts X-ray photoelectron spectroscopy (XPS) of the W 4f region for the Pt/WO3 surface.
[0034] FIG. 1H depicts an transmission electron microscopy (TEM) image of Pt particles supported on WO3, both of which were magnetron sputter deposited on a Cu/lacey carbon TEM grid. The white circles were drawn to guide the eyes to the Pt particles.
[0035] FIG. 2A depicts cyclic voltammetry plots for the Pt/WO3 working electrode with N2 (red) and H2 (black) being supplied.
[0036] FIG. 2B depicts the steady-state H2 oxidation current density versus potential for Ar-saturated (black squares), O2-saturated (grey squares) and CO-saturated (triangles) electrolyte.
[0037] FIG. 2C depicts cyclic voltammetry plots for the Pt/WO3 working electrode with N2 (red) and H2 (black) being supplied.
[0038] FIG. 2D depicts the steady-state H2 oxidation current density versus potential for Ar-saturated (squares), O2-saturated (squares) and CO-saturated (triangles) electrolyte.
[0039] FIG. 3 depicts the H2 oxidation current density at 0.50 V polarization when 10 mM Cu<2+> was added to the electrolyte.
[0040] FIG. 4 depicts the adsorption of hydrogen onto an exemplary catalyst surface (i.e., palladium).
[0041] FIG. 5A depicts the partial reduction of WO3.
[0042] FIG. 5B depict the mobility of electrons in WO3.
[0043] FIG. 5C depicts the mobility of protons in WO3.
[0044] FIG. 6 depicts a schematic of an exemplary device of the disclosure.
[0045] FIG. 7A depicts the correlation between HOR current and the thickness of the catalyst (e.g., platinum).
[0046] FIG. 7B depicts the correlation between HOR current and the thickness of the catalyst (e.g., platinum).
[0047] FIG. 8A depicts the correlation between HOR current and the thickness of the metal oxide (e.g., WO3).
[0048] FIG. 8B depicts the correlation between HOR current and the thickness of the metal oxide (e.g., WO3).
[0049] FIG. 9 depicts the correlation between HOR current and acidity.
[0050] FIG. 10 depicts the pathway of H2 to proton conversion of an exemplary catalyst/oxide pairing (e.g., platinum and WO3).
[0051] FIG. 11 depicts the selectivity of exemplary devices of the disclosure.
DETAILED DESCRIPTION
[0052] Transition metal oxides, including but not limited to tungsten oxide, molybdenum oxide and titanium oxide, exhibit mixed electron and ion conductivity at room temperature. Importantly, when in contact with an electrolyte, these materials allow for the electrically driven intercalation and deintercalation of cations, protons in particular, from or into the electrolyte. This property allows for the electrochemical control of the proton concentration within the material. Simultaneously, proton-electron pairs (i.e., hydrogen atoms) can flow between the metal oxide and a contacting catalyst, such as platinum or palladium. These two noble metals have, for example, been widely adopted as heterogeneous catalysts for a great number of important reactions such as oxygen reduction, hydrogen oxidation, methanol oxidation, carbon dioxide and carbon monoxide hydrogenation, alkane dehydrogenation, hydrogenation reactions, to name but a few. By exploiting the spillover of hydrogen between the metal oxide to the catalyst, the electrochemical control of heterogeneous catalytic processes becomes possible.
[0053] This process is illustrated, for example, by the simple oxidation of hydrogen using a Pt/WO3 interface. Therein, H2 dissociatively adsorbs on platinum as hydrogen atoms at the transition metal oxide/platinum/gas interface. Subsequently, hydrogen migrates across the Pt/WO3 interface to WO3. Intercalation of hydrogen into the oxide material reduces tungsten(VI) to tungsten(V), converting the semi-conducting tungsten trioxide to metallic conducting tungsten bronze. Under applied anodic potentials and in contact with an electrolyte, electrons are driven through the external circuit while protons migrate into the electrolyte. As an overall result, hydrogen gas is oxidized to protons. Similarly, the reverse process is possible, wherein protons are electrochemically transported from the solution into WO3, followed by the spillover onto Pt and evolution of hydrogen at the WO3/Pt catalyst interface.
[0054] The herein described technology reduces the commonly used electrochemical interface from a 3-phase boundary comprising electrolyte, substrate-phase and conducting phase to a 2-phase boundary comprising a mixed electron-proton conductor in contact with the substrate phase, thereby leading to substantially improved mass transport in electrochemically driven processes near room temperature. Importantly, the substrate-phase at the metal oxide/metal interface can either be a gas or a liquid phase. Furthermore, this technology allows for full control of the proton-electron migration direction and rate and proton-electron concentration in the intercalation material. Thus, allowing for active control of dehydrogenation and hydrogenation reactions taking place on the solid-substrate interface.
[0055] Furthermore, the devices described herein can be employed as a selective catalytic interface. WO3 is inert towards the electrochemical O2 reduction. Thus, the Pt/WO3 composite can be polarized in presence of dissolved O2 in the electrolyte, while not leading to oxygen reduction current. The sole catalytic process taking place under these circumstances happens at the substrate-solid interface, thus making the device a selective anode catalyst for membrane-free fuel cells.
[0056] Herein the technology is exemplified using WO3 as an example ion intercalation material. However, the same description applies to all other suitable intercalating mixed ion-electron conductors that are described herein.
Hydrogen Spillover From a Metal to WO3
[0057] Substrate molecules, such as those described herein (e.g., hydrogen, alkanes, alkenes and oxygenates, etc.) dissociatively adsorb on metals to form H atoms. When the metal is in contact with WO3, hydrogen atoms migrate across the metal-WO3 interface to intercalate into WO3. The resulting H-intercalated HxWO3 is called tungsten bronze. Unlike WO3 which is in light yellow color and is a wide band-gap semi-conductor, HxWO3 is a metallic conductor due to the partial reduction of W(VI) to W(V). The intervalence charge transfer between W(VI) and W(V) gives rise to the dark blue color of tungsten bronze. Here we utilize the hydrogen spillover phenomenon to activate the substrate molecules as hydrogen atoms are intercalated in WO3. The overall effect results in the dehydrogenation of the substrate.
Charge Separation and H-to-Proton Conversion
[0058] Once partially reduced to tungsten bronze, the material becomes a metallic conductor with high electron mobility. The intercalated H atoms undergo charge separation during which electrons are inserted into the d-band of tungsten while protons bind to coordinate oxygen atoms. The protons can move between neighboring oxygen atoms with a moderate proton mobility. By applying an external anodic potential between the metal/WO3 film and the electrolyte in direct contact with the WO3 side, protons are driven by the electric field into the electrolyte. In the meantime, electrons flow away from the composite film via the external circuit. As a result, hydrogen atoms are oxidized to protons via the metal/WO3 composite.
Selectivity Towards Hydrogen Oxidation in the Presence of O2
[0059] During hydrogen oxidation catalysis metal sites face towards the substrates and WO3 towards the electrolyte in an exemplary configuration described here. Because the metal is separated from the electrolyte by WO3, and WO3 is inert for catalytic reactions (e.g., oxygen reduction), even if the electrolyte is saturated by O2, it does not affect hydrogen activation on the metal sites. Thus, we can realize selective anode catalysis with the metal/WO3 composite to facilitate the membrane-free fuel cell.
Charge Separation and H-to-Proton Conversion
[0060] The metal/WO3 configuration provides a platform to use electrochemistry to control the rate of catalysis. By altering the applied potential or current, we are able to modulate the rate of H-atom removal from the WO3 membrane and the H-atom concentration intercalated in the WO3. The H-atom concentration is proportional to the rate of hydrogen spillover, which is the rate-limiting step in hydrogen oxidation catalysis. Accordingly, we can modulate the rate of catalysis using electrochemistry.
Utilizing Reversal of Hydrogen Spillover for Reductive Hydrogen Spillover
[0061] Upon applying a reductive potential across the metal/WO3 composite, we can convert electrolyte protons to hydrogen atoms which are intercalated into WO3. At the interface between metal and WO3, hydrogen atoms migrate from WO3 to the metal. When substrates such as alkenes, alkynes, oxygenates, carbonyls or CO2, CO, etc. are supplied to the metal, the adsorbed hydrogen atoms reduce these substrates, thus realizing hydrogenation catalysis.
[0062] Metal oxides display proton and electron conductivity at room temperature and allow for electrochemically controlled cation intercalation—specifically proton intercalation. By combining such materials with metal catalysts (e.g., Pt, Pd) spillover of hydrogen atoms between the oxide and the metal catalyst can be exploited to electrochemically drive heterogeneous catalytic transformations.
[0063] Compared to the traditional heterogeneous catalysis, this configuration possesses a number of novel and surprising advantages. First, this design separates the metal sites from the electrolyte. It is well-documented that Pt and Pd are readily poisoned by electrolyte ions such as phosphate, and electrolyte-dissolved species such as O2 and CO. The separation of metal active sites from the electrolyte eliminates this pathway to catalyst poisoning, thus improving the stability of the catalysts.
[0064] Additionally, in traditional electrocatalysis, especially for gaseous substrates, a gas-catalyst-electrolyte 3-phase boundary is required. Here, this 3-phase boundary is reduced to a 2-phase boundary by using a low-temperature mixed electronic-ionic conductor, leading to substantial improvements in catalyst accessibility and mass transport. Moreover, our technology allows for precise control of catalytic activity by modulating the transport of hydrogen atoms. For example, the applied electrochemical potential exclusively determines whether hydrogen atoms spill over from metal to oxides or vice versa, which drives the dehydrogenation or hydrogenation of substrate molecules. A benefit of eliminating the presence of pure dihydrogen in these reactions is the reduction of common side-reactions such as over-hydrogenation, hydrogenolysis, or back-hydrogenation in dehydrogenation processes.
[0065] The devices disclosed herein can catalyze a number of industrially important commodity conversions involving the transfer of hydrogen atoms. This includes hydrogen oxidation, methanol oxidation and formic acid oxidation which are anode reactions for fuel cells; alkane dehydrogenation generating alkenes which are precursors for higher order industrial products; carbon dioxide and carbon monoxide reduction to useful chemicals which have the potential to complete the renewable energy cycle. Further applications include the electrochemically-driven selective hydrogenation of petrochemicals and biofuel intermediates. These chemical conversions catalyzed by our composite heterogeneous catalyst at low temperature are attractive to the fuel cell industry, the fuel and petrochemical industries, and companies working on carbon capture and conversion.
[0066] In one aspect, the device comprises a porous support substrate, and a film in contact with the porous support substrate, wherein the film comprises:
[0067] a first oxide layer; and
[0068] an ionic conductor layer; wherein
the oxide is selected from the group consisting of WO3, WO2, MoO3, MoO2, TiO2, TiO, ZnO, ZrO2, ZrO, CeO2, CeO, TiCeO2, YCeO2, carbon, V2O5, MoS2, WS2, NiOOH, MnO2, SnO2, Fe2O3, and CrOx, wherein x is a number from 0.1 to 3; and
[0070] the ionic conductor is selected from the group consisting of an electrolyte, a polymer membrane, and an inorganic compound.
[0071] In another aspect, the device comprises a porous support substrate, and a film in contact with the porous support substrate, wherein the film comprises:
[0072] a first catalyst layer;
[0073] a first oxide layer; and
[0074] an ionic conductor layer; wherein
the catalyst is selected from the group consisting of a metal, a metal nitride, a metal oxide, a metal sulfide, a metal carbide, Pt, Pd, Ru, Re, Co, Cu, Rh, CoMo, NiMo, NiW sulfide, Ni, Fe, and Au;
the oxide is selected from the group consisting of WO3, WO2, MoO3, MoO2, TiO2, TiO, ZnO, ZrO2, ZrO, CeO2, CeO, TiCeO2, YCeO2, carbon, V2O5, MoS2, WS2, NiOOH, MnO2, SnO2, Fe2O3, and CrOx, wherein x is a number from 0.1 to 3; and
the ionic conductor is selected from the group consisting of an electrolyte, a polymer membrane, and an inorganic compound.
[0078] In yet another aspect, the device comprises a porous support substrate, and a film in contact with the porous support substrate, wherein the film comprises:
[0079] a first catalyst layer;
[0080] a first oxide layer;
[0081] an ionic conductor layer;
[0082] a second oxide layer; and
[0083] a second catalyst layer; wherein
each catalyst is independently selected from the group consisting of a metal, a metal nitride, a metal oxide, a metal sulfide, a metal carbide, Pt, Pd, Ru, Re, Co, Cu, Rh, Pt sulfide, Pd sulfide, Rh sulfide, CoMo sulfide, NiMo sulfide, NiW sulfide, Ni, Fe, and Au;
the oxide is selected from the group consisting of WO3, WO2, MoO3, MoO2, TiO2, TiO, ZnO, ZrO2, ZrO, CeO2, CeO, TiCeO2, YCeO2, carbon, V2O5, MoS2, WS2, NiOOH, MnO2, SnO2, Fe2O3, and CrOx, wherein x is a number from 0.1 to 3; and
the ionic conductor is selected from the group consisting of an electrolyte, a polymer membrane, and an inorganic compound.
[0087] In certain embodiments, x is 1. In other embodiments, x is 2. In yet other embodiments, x is 3.
[0088] In one aspect, the device comprises a porous support substrate, and a film in contact with the porous support substrate, wherein the film comprises:
[0089] a first oxide layer; and
[0090] an ionic conductor layer; wherein
the oxide is selected from the group consisting of WO3, MoO3, TiO2, ZnO, ZrO2, CeO2, TiCeO2, YCeO2, carbon, V2O5, MoS2, WS2, NiOOH, MnO2, SnO2, Fe2O3, and CrOx, wherein x is a number from 0.1 to 3; and
the ionic conductor is selected from the group consisting of an electrolyte, a polymer membrane, and an inorganic compound.
[0093] In another aspect, the device comprises a porous support substrate, and a film in contact with the porous support substrate, wherein the film comprises:
[0094] a first catalyst layer;
[0095] a first oxide layer; and
[0096] an ionic conductor layer; wherein
the catalyst is selected from the group consisting of a metal, a metal nitride, a metal oxide, a metal sulfide, a metal carbide, Pt, Pd, Ru, Re, Co, Cu, Rh, CoMo, NiMo, NiW sulfide, Ni, Fe, and Au;
the oxide is selected from the group consisting of WO3, MoO3, TiO2, ZnO, ZrO2, CeO2, TiCeO2, YCeO2, carbon, V2O5, MoS2, WS2, NiOOH, MnO2, SnO2, Fe2O3, and CrOx, wherein x is a number from 0.1 to 3; and
the ionic conductor is selected from the group consisting of an electrolyte, a polymer membrane, and an inorganic compound.
[0100] In yet another aspect, the device comprises a porous support substrate, and a film in contact with the porous support substrate, wherein the film comprises:
[0101] a first catalyst layer;
[0102] a first oxide layer;
[0103] an ionic conductor layer;
[0104] a second oxide layer; and
[0105] a second catalyst layer; wherein
each catalyst is independently selected from the group consisting of a metal, a metal nitride, a metal oxide, a metal sulfide, a metal carbide, Pt, Pd, Ru, Re, Co, Cu, Rh, Pt sulfide, Pd sulfide, Rh sulfide, CoMo sulfide, NiMo sulfide, NiW sulfide, Ni, Fe, and Au;
each oxide is independently selected from the group consisting of WO3, MoO3, TiO2, ZnO, ZrO2, CeO2, TiCeO2, YCeO2, carbon, V2O5, MoS2, WS2, NiOOH, MnO2, SnO2, Fe2O3, and CrOx, wherein x is a number from 0.1 to 3; and the ionic conductor is selected from the group consisting of an electrolyte, a polymer membrane, and an inorganic compound.
[0108] In certain embodiments, the porous support substrate has a thickness of about 10 μm, about 11 μm, about 12 μm, about 13 μm, about 14 μm, about 15 μm, about 16 μm, about 17 μm, about 18 μm, about 19 μm, about 20 μm, about 22 μm, about 24 μm, about 26 μm, about 28 μm, about 30 μm, about 32 μm, about 34 μm, about 36 μm, about 38 μm, about 40 μm, about 42 μm, about 44 μm, about 46 μm, about 48 μm, or about 50 μm. In certain embodiments, the porous support substrate has a thickness of about 15 μm.
[0109] In certain embodiments, the pores of the porous support substrate have an average diameter of about 50 nm, about 100 nm, about 150 nm, about 200 nm, about 250 nm, about 300 nm, about 350 nm, about 400 nm, about 450 nm, about 500 nm, about 550 nm, about 600 nm, about 650 nm, about 700 nm, about 750 nm, about 800 nm, about 850 nm, about 900 nm, about 950 nm, or about 1,000 nm. In certain embodiments, the pores of the porous support substrate have an average diameter of about 50 nm, about 100 nm, about 150 nm, about 200 nm, about 250 nm, about 300 nm, about 350 nm, about 400 nm, about 450 nm, or about 500 nm. In certain embodiments, the pores of the porous support substrate have an average diameter of about 200 nm.
[0110] In certain embodiments, the porous support substrate is hydrophilic. In certain embodiments, the porous support substrate is a polymer, a ceramic, a metal salt, a metal, or a non-metal. In certain embodiments, the polymer is a polycarbonate, polybenzimidazole, a polystyrene, a polyurethane, cellulose, a polyvinyl chloride, or latex. In certain embodiments, polymer is a polycarbonate membrane. In certain embodiments, the ceramic is Al2O3, TiO2, ZrO2, or yttria-stabilized zirconia. In certain embodiments, the metal salt is calcium phosphate. In certain embodiments, the metal is stainless steel, titanium, or silicon. In certain embodiments, the non-metal is carbon.
[0111] In certain embodiments, the first catalyst layer is Pt or Pd and the first oxide layer is WO3. In certain embodiments, the first catalyst layer is Pt or Pd and the first oxide layer is WO2. In certain embodiments, the first catalyst layer is Pt or Pd and the first oxide layer is MoO3. In certain embodiments, the first catalyst layer is Pt or Pd and the first oxide layer is MoO2. In certain embodiments, the first catalyst layer is Rh and the first oxide layer is TiO2. In certain embodiments, the first catalyst layer is Rh and the first oxide layer is TiO.In certain embodiments, the first catalyst layer is Cu and the first oxide layer is ZnO. In certain embodiments, the first catalyst layer is Pt or Rh and the first oxide layer is CeO2. In certain embodiments, the first catalyst layer is Pt or Rh and the first oxide layer is CeO. In certain embodiments, the first catalyst layer is Pd and the first oxide layer is TiCeO2. In certain embodiments, the first catalyst layer is Fe, Co, Ni, or Cu, and the first oxide layer is TiCeO2. In certain embodiments, the first catalyst layer is Fe, Ru or Re, and the first oxide layer is TiCeO2. In certain embodiments, the first catalyst layer is Ni and the first oxide layer is TiCeO2. In certain embodiments, the first catalyst layer is Pd and the first oxide layer is YCeO2. In certain embodiments, the first catalyst layer is Fe, Co, Ni, or Cu, and the first oxide layer is YCeO2. In certain embodiments, the first catalyst layer is Fe, Ru or Re, and the first oxide layer is YCeO2. In certain embodiments, the first catalyst layer is Pt and the first oxide layer is carbon. In certain embodiments, the first catalyst layer is Pt or Pd and the first oxide layer is V205. In certain embodiments, the first catalyst layer is Pt sulfide, Pd sulfide, Rh sulfide, CoMo sulfide, NiMo sulfide, or NiW sulfide, and the first oxide layer is MoS2. In certain embodiments, the first catalyst layer is Pt sulfide, Pd sulfide, Rh sulfide, CoMo sulfide, NiMo sulfide, or NiW sulfide, and the first oxide layer is WS2. In certain embodiments, the first catalyst layer is Pd, and the first oxide layer is NiOOH. In certain embodiments, the first catalyst layer is Pd or Pt, and the first oxide layer is MnO2. In certain embodiments, the first catalyst layer is Pd or Pt, and the first oxide layer is SnO2. In certain embodiments, the first catalyst layer is Sn, and the first oxide layer is SnO2. In certain embodiments, the first catalyst layer is Fe, Co, Ni, or Cu, and the first oxide layer is SnO2. In certain embodiments, the first catalyst layer is Fe, Ru, or Re, and the first oxide layer is SnO2. In certain embodiments, the first catalyst layer is Pt, and the first oxide layer is Fe2O3. In certain embodiments, the first catalyst layer is Au, and the first oxide layer is Fe2O3. In certain embodiments, the first catalyst layer is Pt, and the first oxide layer is CrOx. In certain embodiments, the first oxide layer is CrOx or Fe2O3. In certain embodiments, the first catalyst layer is Rh and the first oxide layer is ZrO2. In certain embodiments, the first catalyst layer is Rh and the first oxide layer is ZrO.
[0112] In certain embodiments, the second catalyst layer is Pt or Pd and the second oxide layer is WO3. In certain embodiments, the second catalyst layer is Pt or Pd and the second oxide layer is WO2. In certain embodiments, the second catalyst layer is Pt or Pd and the second oxide layer is MoO3. In certain embodiments, the second catalyst layer is Pt or Pd and the second oxide layer is MoO2. In certain embodiments, the second catalyst layer is Rh and the second oxide layer is TiO2. In certain embodiments, the second catalyst layer is Rh and the second oxide layer is TiO. In certain embodiments, the second catalyst layer is Cu and the second oxide layer is ZnO. In certain embodiments, the second catalyst layer is Pt or Rh and the second oxide layer is CeO2. In certain embodiments, the second catalyst layer is Pt or Rh and the second oxide layer is CeO. In certain embodiments, the second catalyst layer is Pd and the second oxide layer is TiCeO2. In certain embodiments, the second catalyst layer is Fe, Ru or Re, and the second oxide layer is TiCeO2. In certain embodiments, the second catalyst layer is Ni and the second oxide layer is TiCeO2. In certain embodiments, the second catalyst layer is Pd and the second oxide layer is YCeO2. In certain embodiments, the second catalyst layer is Fe, Co, Ni, or Cu, and the second oxide layer is YCeO2. In certain embodiments, the second catalyst layer is Fe, Ru or Re, and the second oxide layer is YCeO2. In certain embodiments, the second catalyst layer is Pt and the second oxide layer is carbon. In certain embodiments, the second catalyst layer is Pt or Pd and the second oxide layer is V2O5. In certain embodiments, the second catalyst layer is Pt sulfide, Pd sulfide, Rh sulfide, CoMo sulfide, NiMo sulfide, or NiW sulfide, and the second oxide layer is MoS2. In certain embodiments, the second catalyst layer is Pt sulfide, Pd sulfide, Rh sulfide, CoMo sulfide, NiMo sulfide, or NiW sulfide, and the second oxide layer is WS2. In certain embodiments, the second catalyst layer is Pd, and the second oxide layer is NiOOH. In certain embodiments, the second catalyst layer is Pd or Pt, and the second oxide layer is MnO2. In certain embodiments, the second catalyst layer is Pd or Pt, and the second oxide layer is SnO2. In certain embodiments, the second catalyst layer is Sn, and the second oxide layer is Sn2. In certain embodiments, the second catalyst layer is Fe, Co, Ni, or Cu, and the second oxide layer is SnO2. In certain embodiments, the second catalyst layer is Fe, Ru, or Re, and the second oxide layer is SnO2. In certain embodiments, the second catalyst layer is Pt, and the second oxide layer is Fe2O3. In certain embodiments, the second catalyst layer is Au, and the second oxide layer is Fe2O3. In certain embodiments, the second catalyst layer is Pt, and the second oxide layer is CrOx. In certain embodiments, the second catalyst layer is Rh and the second oxide layer is ZrO2. In certain embodiments, the second catalyst layer is Rh and the second oxide layer is ZrO.
[0113] In certain embodiments, x is an integer from 0.1-3 (e.g., 1, 2, or 3). In other embodiments, x is non-integer number from 0.1-3 (e.g., 0.5, 1.25, 1.5, 2.3, 2.7).
[0114] In certain embodiments, the first catalyst layer has a thickness of about 1 nm, about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, or about 10 nm, about 25 nm, about 50 nm, about 75 nm, about 100 nm, about 125 nm, about 150 nm, about 175 nm, about 200 nm, about 225 nm, about 250 nm, about 275 nm, about 300 nm, about 325 nm, about 350 nm, about 375 nm, about 400 nm, about 425 nm, about 450 nm, about 475 nm, or about 500 nm. In certain embodiments, the first catalyst layer has a thickness of about 1 nm, about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, or about 10 nm. In certain embodiments, the first catalyst layer has a thickness of about 5 nm.
[0115] In certain embodiments, the second catalyst layer has a thickness of about 1 nm, about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10 nm, about 25 nm, about 50 nm, about 75 nm, about 100 nm, about 125 nm, about 150 nm, about 175 nm, about 200 nm, about 225 nm, about 250 nm, about 275 nm, about 300 nm, about 325 nm, about 350 nm, about 375 nm, about 400 nm, about 425 nm, about 450 nm, about 475 nm, or about 500 nm. In certain embodiments, the second catalyst layer has a thickness of about 1 nm, about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, or about 10 nm. In certain embodiments, the second catalyst layer has a thickness of about 5 nm.
[0116] In certain embodiments, the first oxide layer has a thickness of about 0.5 μm, about 1μm, about 1.5 μm, about 2.0 μm, about 2.5 μm, about 5μm, about 7.5 μm, about 10 μm, about 12.5 μm, or about 15 μm. In certain embodiments, the first oxide layer has a thickness of about 1μm.
[0117] In certain embodiments, the second oxide layer has a thickness of about 0.5 μm, about 1 μm, about 1.5 μm, about 2.0 μm, about 2.5 μm, about 5μm, about 7.5 μm, about 10 μm, about 12.5 μm, or about 15 μm. In certain embodiments, the second oxide layer has a thickness of about 1 μm.
[0118] In certain embodiments, the film is deposited upon the porous support substrate by magnetron sputtering, thermal evaporation, e-beam evaporation, spray pyrolysis, doctor blade deposition, atomic-layer deposition, or electrodeposition. In certain embodiments, the film is deposited upon the porous support substrate by magnetron sputtering.
[0119] In certain embodiments, the electrolyte is an aqueous electrolyte. In certain embodiments, the aqueous electrolyte is an acidic solution, a neutral solution, or a basic solution. In certain embodiments, the aqueous electrolyte comprises NaClO4. In certain embodiments, the aqueous electrolyte is an acidic solution. In certain embodiments, the aqueous electrolyte comprises HClO4.
[0120] In other embodiments, the electrolyte is a non-aqueous electrolyte. In certain embodiments, the non-aqueous electrolyte is protic or aprotic. In certain embodiments, the non-aqueous electrolyte is an alcohol, an ether, an acetate, a carboxylic acid, a nitrile, a formamide, an acetamide, a sulfoxide, a halogenated hydrocarbon, a ketone, or a non-aqueous acid. In certain embodiments, the non-aqueous electrolyte is N-methylpyrrolidone, dimethylcarbonate, ethyl methyl carbonate, propylene carbonate, phosphoric acid, ethylene carbonate, acetonitrile, methanol, ethanol, propanol, butanol, isopropanol, acetic acid, trifluoroactic acid, butanoic acid, propanoic acid, dimethyl formamide, dimethylacetatemide, dimethyl sulfoxide, tetrahydrofuran, methyltetrahydrofuran, dichloromethane, trichloroethane, tetrachloromethane, dichloroethane, ethyl acetate, methyl acetate, propyl acetate, or acetone.
[0121] In certain embodiments, the inorganic compound is cesium hydrogen sulfate, cesium dihydrogen phosphate, aluminum oxide, or a cerate perovskite (e.g., strontium cerate perovskite).
[0122] In certain embodiments, the polymer membrane is a sulfonated tetrafluoroethylene based fluoropolymer-copolymer (e.g., Nafion). In certain embodiments, the polymer is tetrafluoroethylene-perfluoro-3,6-dioxa-4-methyl-7-octenesulfonic acid copolymer
Exemplary Methods of Use
[0123] Generally, the described transformations can be performed by any of the devices disclosed herein. For example, in certain embodiments, the transformation(s) can be performed by a device comprising one or more oxide layer(s) and one or more catalyst layer(s). In other embodiments, the transformation(s) can be performed by device comprising one or more oxide layer(s) and one or more ionic conductor layer(s) (e.g., in certain embodiments, the ionic conductor layer is both an ionic conductor and a catalyst, or in certain embodiments, the oxide is the catalyst).
[0124] In certain aspects, the present disclosure provides methods of using the aforementioned devices to perform chemical transformations.
[0125] In certain embodiments, the present disclosure provides a method of hydrogen oxidation, comprising the steps of:
[0126] contacting a device disclosed herein with a source of hydrogen, thereby forming a reaction mixture; and
[0127] applying an electrical potential to the reaction mixture.
[0128] In certain embodiments, the present disclosure provides a method of hydrogen pumping, comprising the steps of:
[0129] contacting a device disclosed herein with a source of hydrogen, thereby forming a
[0130] reaction mixture; and
[0131] applying an electrical potential to the reaction mixture.
[0132] In certain embodiments, the present disclosure provides a method of formic acid dehydrogenation, comprising the steps of:
[0133] contacting a device disclosed herein with a source of formic acid, thereby forming a reaction mixture; and
[0134] applying an electrical potential to the reaction mixture.
[0135] In certain embodiments, the present disclosure provides a method of methanol dehydrogenation, comprising the steps of:
[0136] contacting a device disclosed herein with a source of methanol, thereby forming a reaction mixture; and
[0137] applying an electrical potential to the reaction mixture.
[0138] In certain embodiments, the present disclosure provides a method of alkene hydrogenation, comprising the steps of:
[0139] contacting a device disclosed herein with an alkene and a source of hydrogen, thereby forming a reaction mixture; and
[0140] applying an electrical potential to the reaction mixture.
[0141] In certain embodiments, the present disclosure provides a method of forming a carbon-carbon bond, comprising the steps of:
[0142] contacting a device disclosed herein with a first carbon substrate and a second carbon substrate, thereby forming a reaction mixture; and
[0143] applying an electrical potential to the reaction mixture.
[0144] In certain embodiments, the present disclosure provides a method of silane coupling, comprising the steps of:
[0145] contacting a device disclosed herein with a first silane substrate and a second silane substrate, thereby forming a reaction mixture; and
[0146] applying an electrical potential to the reaction mixture.
[0147] In certain embodiments, the present disclosure provides a method of producing a hydrocarbon, comprising the steps of:
[0148] contacting a device disclosed herein with a source of carbon monoxide and a source of hydrogen, thereby forming a reaction mixture; and
[0149] applying an electrical potential to the reaction mixture.
[0150] In certain embodiments, the present disclosure provides a method of reducing diatomic nitrogen, comprising the steps of:
[0151] contacting a device disclosed herein with a source of diatomic nitrogen and a source of hydrogen, thereby forming a reaction mixture; and
[0152] applying an electrical potential to the reaction mixture.
[0153] In certain embodiments, the present disclosure provides a method of producing hydrogen and carbon monoxide, comprising the steps of
[0154] contacting a device disclosed herein with a source of methane and a source of water, thereby forming a reaction mixture; and
[0155] applying an electrical potential to the reaction mixture.
[0156] In certain embodiments, the present disclosure provides a method of carbon dioxide hydrogenation, comprising the steps of
[0157] contacting a device disclosed herein with a source of carbon dioxide and a source of hydrogen, thereby forming a reaction mixture; and
[0158] applying an electrical potential to the reaction mixture.
[0159] In certain embodiments, the present disclosure provides a method of producing hydrogen, comprising the steps of
[0160] contacting a device of the disclosure with a source of water, thereby forming a reaction mixture; and
[0161] applying an electrical potential to the reaction mixture.
[0162] In certain embodiments, the present disclosure provides a method of producing methanol, comprising the steps of
[0163] contacting a device disclosed herein with a source of carbon dioxide, thereby forming a reaction mixture; and
[0164] applying an electrical potential to the reaction mixture.
[0165] In certain embodiments, the present disclosure provides a method of isomerizing an alkane, comprising the steps of
[0166] contacting a device disclosed herein with an alkane, thereby forming a reaction mixture; and
[0167] applying an electrical potential to the reaction mixture.
[0168] In certain embodiments, the present disclosure provides a method of oxygen reduction, comprising the steps of
[0169] contacting a device disclosed herein with a source of oxygen, thereby forming a reaction mixture; and
[0170] applying an electrical potential to the reaction mixture.
[0171] In certain embodiments, the present disclosure provides a method of cracking methane, comprising the steps of
[0172] contacting a device disclosed herein with a source of methane, thereby forming a reaction mixture; and
[0173] applying an electrical potential to the reaction mixture.
[0174] In certain embodiments, the present disclosure provides a method of producing carbon dioxide and hydrogen, comprising the steps of
[0175] contacting a device disclosed herein with a source of carbon monoxide and a source of water, thereby forming a reaction mixture; and
[0176] applying an electrical potential to the reaction mixture.
[0177] In certain embodiments, the present disclosure provides a method of hydrodesulfurization, comprising the steps of
[0178] contacting a device disclosed herein with a sulfur containing substrate and a source of hydrogen, thereby forming a reaction mixture; and
[0179] applying an electrical potential to the reaction mixture.
[0180] In certain embodiments, the present disclosure provides a method of hydrodenitrogenation, comprising the steps of
[0181] contacting a device disclosed herein with a nitrogen containing substrate and a source of hydrogen, thereby forming a reaction mixture; and
[0182] applying an electrical potential to the reaction mixture
[0183] In certain embodiments, the present disclosure provides a method of carbon monoxide oxidation, comprising the steps of
[0184] contacting a device disclosed herein with a source of carbon monoxide and a source of oxygen, thereby forming a reaction mixture; and
[0185] applying an electrical potential to the reaction mixture.
[0186] In certain embodiments, the present disclosure provides a method of ketone hydrogenation, comprising the steps of
[0187] contacting a device disclosed herein with a ketone and a source of hydrogen, thereby forming a reaction mixture; and
[0188] applying an electrical potential to the reaction mixture.
[0189] In certain embodiments, the present disclosure provides a method of dehydrogenation, comprising the steps of
[0190] contacting a device disclosed herein with a hydrogen containing substrate, thereby forming a reaction mixture; and
[0191] applying an electrical potential to the reaction mixture.
[0192] In certain embodiments, the present disclosure provides a method of hydrogen, comprising the steps of
[0193] contacting a device disclosed herein with hydrogen and a hydrogen storage medium, thereby forming a reaction mixture; and
[0194] applying an electrical potential to the reaction mixture.
[0195] In certain embodiments, the chemical transformations are carried out using the catalyst and oxide pairings disclosed in Table 1.
TABLE 1
xxx
[0196] In certain embodiments, the electrical potential is applied in a cyclic manner (e.g., cyclic voltammetry), a constant manner (e.g., linear sweep voltammetry, chronoamperometry, or chronogalvanometry). In certain embodiments, the electrical potential is applied in a cyclic manner (i.e., cyclic voltammetry).
[0197] In certain embodiments, the electrical potential is applied in a range from about −2.0 V, about −1.9 V, about −1.8 V, about −1.7 V, about −1.6 V, about −1.5 V, about −1.4 V, about −1.3 V, about −1.2 V, about −1.1 V, about −1.0 V, about −0.9 V, about −0.8 V, about −0.7 V, about −0.6 V, about −0.5 V, about −0.4 V, about −0.3 V, about −0.2 V, about −0.1 V, or about 0 V to about 0.1 V, about 0.2 V, about 0.3 V, about 0.4 V, about 0.5 V, about 0.6 V, about 0.7 V, about 0.8 V, about 0.9 V, about 1.V, about 1.1 V, about 1.2 V, about 1.3 V, about 1.4 V, about 1.5 V, about 1.6 V, about 1.7 V, about 1.8 V, about 1.9 V, or about 2.0 V. In certain embodiments, the electrical potential is applied in a range from about 0 V to about 0.5 V.
[0198] In certain embodiments, the electrical potential is modulated at a rate of about 5 mV s<−1>, about 10 mV s<−1>, about 15 mV s<−1>, about 20 mV s<−1>, about 25 mV s<−1>, about 30 mV s<−1>, about 35 mV s<−1>, about 40 mV s<−1>, about 45 mV s<−1>, about 50 mV s<−1>, about 55 mV s<−1>, about 60 mV s<−1>, about 65 mV s<−1>, about 70 mV s<−1>, about 75 mV s<−1>, about 80 mV s<−1>, about 85 mV s<−1>, about 90 mV s<−1>, about 95 mV s<−1>, or about 100 mV s<−1>. In certain embodiments, the electrical potential is modulated at a rate of about 50 mV s<−1>.
[0199] In certain embodiments, the electrical current is applied in a cyclic manner (e.g., cyclic voltammetry or linear sweep voltammetry). In certain embodiments, the electrical current is applied in a constant manner (e.g., chronoamperometry, or chronogalvanometry).
[0200] In certain embodiments, the methods disclose herein further comprise contacting the reaction mixture with a reference electrode. In certain embodiments, the reference electrode is a Mercury-mercurous sulfate electrode.
[0201] In certain embodiments, the methods disclose herein further comprise contacting the reaction mixture with a counter electrode. In certain embodiments, the counter electrode is a platinum electrode.
[0202] In certain embodiments, the methods disclose herein further comprise increasing or decreasing the temperature of the reaction mixture. In certain embodiments, the methods comprises increasing the temperature of the reaction mixture. In certain embodiments, the methods comprises decreasing the temperature of the reaction mixture.
Definitions
[0203] Unless otherwise defined herein, scientific and technical terms used in this application shall have the meanings that are commonly understood by those of ordinary skill in the art. Generally, nomenclature used in connection with, and techniques of chemistry are those well known and commonly used in the art.
[0204] Chemistry terms used herein, unless otherwise defined herein, are used according to conventional usage in the art, as exemplified by “The McGraw-Hill Dictionary of Chemical Terms”, Parker S., Ed., McGraw-Hill, San Francisco, Calif. (1985).
[0205] As used herein, the terms “optional” or “optionally” mean that the subsequently described event or circumstance may occur or may not occur, and that the description includes instances where the event or circumstance occurs as well as instances in which it does not. For example, “optionally substituted alkyl” refers to the alkyl may be substituted as well as where the alkyl is not substituted.
EXAMPLES
[0206] The invention now being generally described, it will be more readily understood by reference to the following examples which are included merely for purposes of illustration of certain aspects and embodiments of the present invention, and are not intended to limit the invention.
Example 1
Preparation of Exemplary Compounds
[0207] A metal/WO3 film can be fabricated in a large variety of ways. For example, WO3 can be deposited on a porous substrate which supports the film. The substrate should be easy to handle with, compatible with the metal and WO3, and stable when in contact with the electrolyte. More importantly, the substrate should be porous so that the electrolyte contacts the WO3 film. The substrate pore size in that the pores should be large enough to allow water to enter, but should not be too large to deposit a pinhole-free film of WO3 (e.g., 50-500 nm). Additionally, the substrate cannot be too thin, or it will be too fragile to work with; it cannot be too thick either, or the transport of protons through the pores will become difficult. Taking all of the factors into consideration, we chose hydrophilic porous polycarbonate membranes with 200 nm-diameter pore and 15 μm-thickness as our substrates.
Fabrication of Metal/WO3 Film
[0208] Magnetron sputtering was adopted as one of many possible methods to deposit metal and WO3 films on polycarbonate substrates. For WO3 deposition, we performed reactive RF sputter with W target in Ar and O2 plasma. The thickness of deposited WO3 is approximately 1.0 μm. As a metal catalyst, for example, approximately 5 nm platinum were deposited on WO3 by DC sputtering. The films were characterized by top-down and cross-section scanning electron micrography (SEM) (FIGS. 1A and 1B). No pinholes or cracks were observed. We also deposited Pt and thin WO3 films on Cu/lacey carbon grids to study the Pt morphology by transmission electron micrography (TEM) (FIG. 1C). X-ray photoelectron spectroscopy (XPS) confirmed the presence of W(VI), W(V) (FIG. 1D) and metallic Pt (FIG. 1E). FIG. 1F illustrates the fabrication process.
[0209] Another exemplary method of preparing WO3 films is thermal evaporation. The rate of thermal evaporation deposition is 1-2 angstrom/s. The WO3 films deposited by thermal evaporation exhibit cracks and defects. Therefore, we sinter the as-prepared films at 500° C. in 5% H2/95% Ar for 3 h to minimize the population of cracks and defects. The resulting WO3 films are rougher than the films prepared by magnetron sputtering. We compared the catalytic activity of the WO3 films of different roughness factors.
Assembly of Working Electrode From Metal/WO3 Composite Films
[0210] The metal/WO3 composite films need to be electrically contacted to enable electrochemical operation. Again, various methods can be used to achieve this. As an example, we applied silver paste around a piece of 1⁄4″-diameter polycarbonate-supported metal/WO3 film on the metal side, and then attached the sample to one end of a 5″-long graphite tube with the metal side facing the interior of the tube. The whole setup was used as the working electrode and the substrate was directly supplied into the graphite tube. By employing a reference and counter electrode in the electrolyte, electrochemical measurements were performed. The configuration is illustrated in FIG. 1F.
Pt/WO3 Catalyzing H2-to-Proton Conversion
[0211] We tested the catalytic activity of the Pt/WO3 electrode for hydrogen oxidation reaction. The electrolyte was 0.1 M HClO4, pH 1.0. We first supplied 1 atm of N2 to the working electrode and continuously purged the electrolyte with Ar. We left the electrode in the electrolyte for 15 min to wet the polycarbonate substrate. The uncompensated resistance was about 30Ω. Then we performed cyclic voltammetry measurement from 0.02 V to 0.52 V at 50 mV s<−1 >sweep rate. We only observed double-layer capacitance current (FIG. 2A, bottom line), characterized by a flat CV trace. We then switched to 1 atm of H2 supply to the working electrode, and observed an anodic current, confirming that the anodic current is due to H2 oxidation (FIG. 2A, top line). We also performed chronoamperometry measurements to collect steady-state current by applying potentials from 0.02 V to 0.52 V at 40 mV intervals. The current density reaches a value in excess of 25 mA cm-2, which is 8-fold higher than the diffusion-limited rate of HOR catalysis if the Pt catalysts were directly exposed to the electrolyte. The steady-state current density versus potential data are plotted in FIG. 2B (squares).
Pt/WO3 Tolerance to Electrolyte Impurities
[0212] We then purged the electrolyte with O2 instead of Ar to check the selectivity of HOR of the Pt/WO3 composite in the presence of O2 in the electrolyte. The chronoamperometry data displayed very similar HOR activity to those under Ar-saturated condition (FIG. 2B, circles), suggesting negligible influence of the dissolved O2 in the electrolyte.
[0213] To further confirm the resistance of the Pt/WO3 electrode to dissolved gases in the electrolyte, we used CO as a more stringent probe due to the strong adsorption of CO to Pt surfaces. If carbon monoxide can pass through pinholes of the WO3 film and reach the Pt side, the HOR activity of the composite would decrease dramatically. Indeed, the chronoamperometry data under potentials from 0.02 V to 0.52 V overlay with the ones collected in Ar-saturated electrolyte (FIG. 2B, triangles), suggesting that the Pt/WO3 is not poisoned by carbon monoxide dissolved in the electrolyte.
[0214] Besides the dissolved gaseous species, the Pt/WO3 electrode also tolerates ions in the electrolyte. For instance, we added 10 mM Cu(ClO4)2 to the electrolyte while applying a potential of 0.50 V. The potential is in the range of Cu underpotential deposition at Pt surfaces. Therefore, if Cu<2+> could pass through the WO3 membrane to reach the Pt catalyst, Cu would deposit at the Pt surfaces and thus poison the hydrogen oxidation activity. In our experiments, we did not observe any degradation of hydrogen oxidation current when we added Cu<2+> to the electrolyte (FIG. 3). The results indicate that the WO3 membrane prevents the transfer of ionic impurities dissolved in the electrolyte to the catalyst surfaces.
Increasing the Pt/WO3 Boundary Improves the Catalytic Activity
[0215] Our mechanistic studies of the Pt/WO3 composite electrode to catalyze the hydrogen oxidation reaction suggest that the rate of the catalysis is controlled by the rate of hydrogen spillover. Furthermore, the rate of hydrogen spillover increases proportionally with increasing PtIWO3 boundary density. Therefore, we managed to increase the PtIWO3 boundary density by roughening the WO3 surfaces and increasing the distribution of Pt catalysts. To roughen the WO3 surfaces, we used thermal evaporation and post-annealing to deposit the WO3 membrane. The roughness factor of the thermal evaporated WO3 membrane is 1.2 times of the sputtered membrane. Accordingly, the current of hydrogen oxidation reaction for the roughened WO3 membrane almost doubles the current of the smooth WO3 membrane. The results suggest that the surface area of WO3 membrane and furthermore, the PtIWO3 boundary density, significantly affects the rate of catalysis.
[0216] We also increased the PtIWO3 boundary density by increasing the distribution of Pt. We deposited different patterns of Pt catalyst by altering the time duration magnetron sputtering from 20 s to 45 s. From 20 s to 35 s, Pt catalyst distributes as isolated islands with a diameter remaining around 5 nm independent of deposition time. The increase of Pt deposition time increases the density of Pt islands and thus the PtIWO3 boundary density. For 40 s and 45 s Pt deposition time durations, Pt patterns overlap with each other, thus leading to a decrease of PtIWO3 boundary density. Accordingly, the hydrogen oxidation current increases with increasing PtIWO3 boundary density. The results again suggest that the PtIWO3 boundary density determines the rate of hydrogen spillover and furthermore, the rate of catalysis. Therefore, we are able to control the rate of catalysis by tuning the structure of the Pt/WO3 composite electrode...