Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/40—Carbon monoxide
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B3/00—Electrolytic production of organic compounds
  • C25B3/20—Processes
  • C25B3/25—Reduction
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
  • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
  • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms

Definitions

• This invention relates generally to the reduction of CO 2 .
• Sustainable production of C-based fuel requires using renewable energy to power the reductive fixation of CO 2 .
• Coupling renewable electricity to an electrolytic device is an attractive strategy for this goal because it enables the use of multiple renewable energy sources and independent optimization of catalysis.
• Solid oxide electrolytic cells reduce CO 2 to CO efficiently at high current densities, but require operating temperatures of 750-900 °C and cannot access other products.
• a method for electrochemically reducing CO or CO 2 is provided.
• a cathode is provided, wherein the cathode comprises a conductive substrate with a catalyst of a metal and a metal oxide based coating on a side of the cathode.
• An anode is spaced apart from the cathode.
• An ionic transport is provided between the anode and cathode.
• the cathode is exposed to CO or CO 2 and 3 ⁇ 40.
• the anode is exposed to H 2 0.
• a voltage is provided between the cathode and anode.
• a method for electrochemically reducing CO or CO 2 is provided.
• a coating is formed on a cathode by heating a metal layer of the cathode in air, electrochemically oxidizing the metal layer of the cathode, or by a metal oxide deposition to form a metal and metal oxide interface.
• An anode is spaced apart from the cathode.
• An ionic transport is provided between the anode and cathode.
• the coating is exposed to CO or CO 2 and H 2 O.
• the anode is exposed to H 2 O.
• a voltage is provided between the cathode and anode.
• an apparatus for electrochemically reducing CO or CO 2 is provided.
• An anode is provided.
• An oxidized cathode is spaced apart from the anode.
• a chamber for exposing the anode and oxidized cathode to at least one electrolyte is adjacent to the anode and oxidized cathode.
• a gas chamber for exposing the oxidized cathode to CO or CO 2 is adjacent to the oxidized cathode.
• a CO or CO 2 source for providing CO or CO 2 to the gas chamber is connected to the gas chamber.
• FIG. 1 A shows the XPS spectra of untreated Sn foil before and after electrolysis and Sn foil after etching in HBr.
• FIG. IB is a plot of total current density vs time, CO faradaic efficiency vs time, and overall HCO 2 H faradaic efficiency at -0.7 V vs RHE in C0 2 -saturated 0.5 M NaHC0 3 for unetched Sn.
• FIG. 1C is a plot of total current density vs time, CO faradaic efficiency vs time, and overall HCO 2 H faradaic efficiency for untreated Sn at -0.7 V vs RHE in CO 2 - saturated 0.5 M NaHC0 3 for etched Sn.
• FIG. 2A depicts the bulk electrolysis trace at -0.7 V in NaHC0 3 /C0 2 electrolyte for a Ti cathode before and after the addition of 1 mM SnCi 2 to the electrolyte.
• FIG. 2B shows SEM images of a Ti electrode before and after deposition showing the formation of a porous, particulate film with -100 nm-diameter pieces atop a more uniform layer.
• FIG. 2C is a high resolution Sn 3d 5/2 XPS of a Sn/SnO x catalyst removed 30 min or 12 h after the addition of Sn 2+ .
• FIG. 2D provides graphs of XRD patterns showing Sn°, SnC> 2 , and Ti peaks after 30 min or 12 h.
• FIGS. 3A-C shows the comparison of CO 2 reduction catalysis for unexcited Sn foil and in situ deposited Sn/SnO ⁇ thin film electrodes.
• FIGS. 4A-E shows the total geometric current density (j tot ) vs time, the faradaic efficiency (FE) for CO vs time and the overall FE for HCO 2 H for the polycrystalline Cu electrode and several of the annealed electrodes with progressively thicker initial C3 ⁇ 40 layers at -0.5 V vs the reversible hydrogen electrode.
• FIG. 4F shows the average FE for CO vs the amount of charge required to reduce the C3 ⁇ 40 layer per electrode area.
• FIGS. 5A-F show the scanning electron microscopy (SEM) images, X-ray diffraction (XRD) patterns, and high-resolution Cu 2p X-ray photoelectron spectroscopy (XPS) spectra for a Cu electrode after annealing procedure and after subsequent CO 2 reduction electrolysis.
• SEM scanning electron microscopy
• XRD X-ray diffraction
• XPS high-resolution Cu 2p X-ray photoelectron spectroscopy
• FIGS. 6A-C show the total current densities and faradaic efficiencies for the major products for a Cu electrode annealed at 500 °C for 12 h and for polycrystalline Cu.
• FIG. 7 shows Tafel data for a Cu electrode annealed at 500 °C for 12 h and Tafel data for polycrystalline Cu.
• FIG. 8 is a high level flow chart of an embodiment of the invention.
• FIGS. 9A-B are enlarged cross-sectional views of part of a conductive substrate with a metal coating, forming part of a cathode.
• FIG. 10 is a schematic view of an electrolyzer that may be used in an embodiment of the invention.
• FIG. 11 is a high level flow chart of another embodiment of the invention.
• FIG. 12 is a schematic view of an electrolyzer that may be used in another embodiment of the invention.
• SnO ⁇ is essential to CO 2 reduction catalysis on Sn. This may be shown by demonstrating that removal of SnO ⁇ from a Sn electrode results in nearly exclusive 3 ⁇ 4 evolution activity. This insight is subsequently applied to prepare a composite Sn/SnO ⁇ thin film catalyst that exhibits greatly enhanced CO 2 reduction activity relative to a typical Sn electrode.
• FIG. 1A shows the XPS spectra of untreated Sn foil before and after electrolysis (left) and Sn foil after etching in HBr (right). The curves are combinations of two Gaussian/Lorentzian curves at 486.5 eV and 484.7 eV.
• IB is a plot of total current density vs time (indicated by the line), CO faradaic efficiency vs time (indicated by the ⁇ points) and overall HCO 2 H faradaic efficiency for untreated Sn at -0.7 V vs RHE in C0 2 -saturated 0.5 M NaHC0 3 for unetched Sn.
• FIG. 1C is a plot of total current density vs time (indicated by the line), CO faradaic efficiency vs time (indicated by the ⁇ points) and overall HCO 2 H faradaic efficiency for untreated Sn at -0.7 V vs RHE in C0 2 -saturated 0.5 M NaHC0 3 for etched Sn.
• Etched electrodes were prepared by immersing the Sn foil in 24% HBr at 90° C for 10 min.
• An XPS spectrum of the etched electrode taken immediately after removal from the HBr solution exhibited a SnO x :Sn° ratio of 17:83 (FIG. 1A).
• the residual oxide observed on this electrode is likely due to oxide regrowth in the brief exposure to air upon transferring to the XPS chamber, as assessed by independent XPS experiments with a sputtered electrode.
• etched electrodes were rinsed with deionized water at the conclusion of the etching procedure and used immediately to minimize oxide regrowth.
• FIG. IB shows the total geometric current density (j tot ) vs time and the faradaic efficiency for CO production at various time points for an untreated Sn electrode.
• the electrode exhibits a current density of 0.4-0.6 mA/cm 2 and a steady-state faradaic efficiency for CO of 5-10%. NMR analysis of the electrolyte at the conclusion of the experiment indicates 19% faradaic efficiency for HCO 2 H; the remainder of the current is accounted for by 3 ⁇ 4 formation. This CO 2 reduction activity is consistent with the best reported activity for Sn at -1.06 V, taking into account the difference in overpotential.
• An electrode examined by XPS after a 12 h electrolysis at -0.7 V exhibited a SnO x :Sn° ratio of 89: 11, indicating that the native SnO x layer is stable to the reduction conditions (FIG. 1A).
• an etched Sn electrode exhibits a much higher j tot of 3-4 mA/cm 2 , but very low faradaic efficiency for CO (0.5%) and HC0 2 H production (0.3%) (FIG. 1C).
• the higher j tot likely reflects a larger electrochemical surface area due to etching.
• the geometric partial current density for CO 2 reduction is lower for the etched Sn electrode (24-32 ⁇ /cm 2 ) than the untreated Sn electrode (92- 140 ⁇ /cm 2 ) due to the much lower faradaic efficiency.
• the XPS and electrolysis results indicate that removal of the native SnO x layer from a Sn electrode suppresses C0 2 reduction activity such that H 2 evolution accounts for > 99% of the current density.
• the small residual CO 2 reduction activity observed on etched Sn likely reflects the growth of a small amount of SnO x on the etched electrode before the start of electrolysis.
• FIG. 2A depicts the bulk electrolysis trace at -0.7 V in NaHC0 3 /C0 2 electrolyte for a Ti cathode before and after the addition of 1 mM SnCl 2 to the electrolyte.
• the Ti electrode Prior to the addition of Sn 2+ , the Ti electrode exhibits a current density of -10 ⁇ /cm 2 with very little detectable CO 2 reduction. Addition of Sn 2+ results in a sharp rise in the current density to a steady-state value of -1.8 mA/cm 2 and the formation of a grey deposit on the electrode surface.
• the current density is stable for > 10 h and corresponds to > 85% CO 2 reduction with the remainder accounted for by 3 ⁇ 4 evolution. Nearly identical results are obtained if Sn(OTf) 2 is used instead of SnCl 2 , indicating that Cr is not necessary for catalyst formation.
• composition and structure of the electrodeposited catalyst were characterized by a combination of scanning electron microscopy (SEM), XPS and powder x-ray diffraction (XRD).
• a catalyst was prepared via in situ deposition as described above and removed from the electrolyte 30 min after the addition of Sn 2+ .
• FIG. 2B shows SEM images of a Ti electrode before (left) and after (right) deposition showing the formation of a porous, particulate film with -100 nm-diameter pieces atop a more uniform layer.
• FIG. 2C is a high resolution Sn 3d 5 2 XPS of a Sn/SnO x catalyst removed 30 min (left) or 12 h (right) after the addition of Sn 2+ .
• FIG. 2D provides graphs of XRD patterns showing Sn° ( ⁇ ), SnC> 2 (*) and Ti ( ⁇ ) peaks after 30 min or 12 h.
• Sn° peaks are observed along with small peaks that correspond to SnC> 2 .
• the latter are absent for a Sn foil electrode with a native SnO x .
• a separate catalyst film was prepared and removed for analysis 12 h after the addition of Sn 2+ .
• the XPS spectrum, shown in FIG. 2C, and XRD pattern for this electrode are very similar to those of the sample removed after 30 min. Together, these results indicate that a composite Sn/SnO x material is formed under the deposition conditions.
• the electrodeposited catalyst (hereafter referred to as "Sn/SnO x ”) exhibits greatly enhanced CO 2 reduction catalysis compared to a typical Sn foil electrode with a native SnO x layer.
• CO, HCO 2 H and 3 ⁇ 4 together account for > 99% of the reduction products in NaHC0 3 /C0 2 electrolyte.
• To compare the activities of Sn foil and Sn/SnO x we measured their partial current densities for CO and HCO 2 H at selected potentials between -0.5 and -0.7 V. Comparison of CO 2 reduction catalysis for Sn foil and in situ deposited Sn/SnO ⁇ thin film electrodes are illustrated in FIGS. 3A-C.
• FIG. 3A-C Comparison of CO 2 reduction catalysis for Sn foil and in situ deposited Sn/SnO ⁇ thin film electrodes are illustrated in FIGS. 3A-C.
• FIG. 3A shows Tafel plots for HC0 2 H production.
• FIG. 3B shows Tafel plots for CO production.
• FIG. 3C is a bar graph showing Faradaic efficiencies for HCO 2 H and CO at various potentials. These data were obtained by performing stepped-potential electrolyses with periodic quantification of the gaseous products by GC and removal of aliquots after each step for NMR analysis.
• the observed slopes are instead much closer to 59 mV/dec, which supports mechanisms in which there is a reversible 1 e ⁇ transfer to CO 2 to form CO 2 ' prior to a chemical rate- determining step.
• Possibilities for the chemical rate-determining step include protonation of CO 2 ' or migration to an alternative site on the electrode surface.
• Competing rate-determining steps such as protonation at C vs O of CO 2 ' , may determine the HCO 2 H vs CO selectivity.
• Achieving efficient Cu-catalyzed CO2 reduction requires preparing Cu particles whose surfaces have active sites that are different from those on the surface of a polycrystalline Cu electrode. Electrochemical reduction of metal oxides provides one possible route to metal particles with altered surface structures. researchers have previously used electrochemical methods including potential cycling and anodic pulses to form and subsequently reduce oxides on Cu electrodes. These treatments have resulted in increased hydrogen evolution activity in alkaline electrolytes and altered product selectivity at high overpotential in CO2 reduction electrolyses. While these studies provide evidence of altered electrocatalytic properties, substantial improvements to the energetic efficiency of CO2 reduction have not been observed. researchers have also used copper oxide electrodes in CO2 reduction electrolyses.
• Electrodes were prepared by electropolishing pieces of polycrystalline Cu foil (99.9999%) in 85% phosphoric acid and subsequently annealing the electrodes in air at selected temperatures for variable amounts of time. The activities of these electrodes were compared to that of a polycrystalline Cu electrode in controlled potential electrolyses performed in C0 2 -saturated 0.5 M NaHC0 3 electrolyte ("NaHC0 3 /C0 2 ") in a two- compartment electrolysis cell. The headspace of the cathodic chamber was continuously purged with CO2 into the sampling loop of a gas chromatograph (GC) to enable periodic quantification of the gas-phase products. The solution-phase products were quantified by NMR analysis of the electrolyte at the conclusion of the electrolyses.
• GC gas chromatograph
• FIGS. 4A-E shows the total geometric current density (j tot ) vs time, the faradaic efficiency (FE) for CO vs time and the overall FE for HCO 2 H for the
• polycrystalline Cu electrode (FIG. 4A) and several of the annealed electrodes (FIG. 4B-E) with progressively thicker initial C3 ⁇ 40 layers at -0.5 V vs the reversible hydrogen electrode (RHE; all potentials are referenced to this electrode).
• the polycrystalline Cu electrode exhibited aj ' to t of -100 ⁇ /cm 2 , a FE for CO that declined from 10% at the start of the electrolysis to ⁇ 2% over the course of 7 h and a FE for HCO 2 H of 3%. The majority of the current, > 90%, was due to 3 ⁇ 4 evolution. These values are consistent with the previously measured activity for Cu in KHCO 3 electrolytes.
• the electrodes annealed at higher temperatures exhibited larger j tot values and improved CO 2 reduction FEs upon reduction of the C3 ⁇ 40 layer.
• the electrode annealed at 300 °C for 30 min exhibited an initial j ' tot of 10 mA/cm 2 for 2 min as the C3 ⁇ 40 was reduced and subsequently a stable j tot of 1.0 mA/cm 2 .
• the FE for CO was 25% during the first hour of electrolysis before declining to 10% over 7 h; the FE for HCO 2 H on the reduced electrode was 5%. Further improvements were obtained by starting with a thicker Cu 2 0 layer.
• FIG. 4F A plot of the average CO FEs for the annealed electrodes vs the amount of charge passed per electrode area (Q) in the Cu 2 0 reduction is shown in FIG. 4F.
• the FEs increased with the amount of charge passed until reaching a plateau at 30-40% for Q > -5 C/cm 2 .
• FIGS. 5A-F show the scanning electron microscopy (SEM) images (FIGS. 5A, D), X-ray diffraction (XRD) patterns (FIGS. 5B, E), and high-resolution Cu 2p X-ray photoelectron spectroscopy (XPS) spectra (FIGS. 5C, F) for a Cu electrode after this annealing procedure (FIGS. 5A- C) and after subsequent CO 2 reduction electrolysis (FIGS. 5D-F). After annealing, the SEM showed a dense array of rods with 100-1000 nm diameters on the electrode surface.
• the electrochemically active surface area of a reduced electrode that had been annealed at 500 °C for 12 h was determined by measuring the double layer capacitance in 0.1 M HCIO 4 after CO 2 reduction electrolysis.
• the capacitance was 13.9 mF/cm 2 , which is 475x larger than the capacitance of 29 ⁇ /cm 2 measured for a polycrystalline Cu electrode.
• This roughness factor is considerably larger than the difference inj ' to t between the two electrodes ( ⁇ 30x), consistent with the difference in FEs between the two electrodes.
• FIGS. 6A-C which provides comparisons of electrocatalytic activities of polycrystalline Cu and Cu annealed at 500 °C for 12 h.
• FIG. 6A is a graph of total current density vs. potential.
• FIG. 6B is a graph of faradaic efficiencies for CO and
• FIG. 6C is a graph of faradaic efficiencies for CH4, C2H4 and C2H6 vs potential. Attempts to collect the corresponding data under identical conditions with polycrystalline Cu were unsuccessful due to the rapid degradation of catalytic activity. Instead, optimal data from previous studies with polycrystalline Cu at several potentials in 0.1 M KHCO 3 are included for comparison.
• the annealed Cu electrode exhibits a high efficiency for CO2 reduction at remarkably low overpotentials.
• a peak faradaic efficiency of -45% for CO production is obtained at potentials ranging from -0.3 V to -0.5 V, corresponding to 0.19 V to 0.39 V of overpotential for this product (FIG. 6B).
• annealed Cu catalyzes the reduction of CO2 to ethylene and ethane (FIG. 6C).
• polycrystalline Cu produces only ethylene and methane at high overpotential.
• Previous work on Cu single crystals has shown that the ratio of ethylene to methane can be boosted by introducing (111) steps in the (100) basal plane, i.e. by using single crystal Cu electrodes with a high index face exposed to the solution.
• methane was never fully suppressed and no ethane was observed in these studies.
• These results indicate that the surface structures of the Cu particles produced by C3 ⁇ 40 reduction are distinct from the structures of the high index faces of Cu.
• no methanol was detected among the reduction products for annealed Cu at any potential examined here, in contrast to what has been reported for CO 2 reduction catalysis with Cu electrodes annealed at lower temperatures.
• FIG. 8 is a high level flow chart of an embodiment of the invention.
• a cathode with a catalyst metal is provided (step 804).
• a metal oxide coating is formed on the catalyst metal (step 808).
• the metal oxide coating and the catalyst metal form a metal and metal oxide coating, which may comprise a metal oxide coating over a metal coating or a single coating with both metal oxide particles and metal particles.
• An anode is spaced apart from the cathode (step 812).
• An ionic transport is provided between the anode and cathode (step 816).
• the cathode is exposed to CO 2 and H 2 O (step 820).
• the anode is exposed to H 2 O (step 824).
• a voltage is provided between the cathode and anode (step 828). The voltage causes CO 2 and H 2 O to be reduced to CO, 3 ⁇ 4 , and (3 ⁇ 4.
• the CO and 3 ⁇ 4 may be converted to hydrocarbon or alcohol products.
• the cathode is formed by providing a conductive substrate (step 804) with a catalyst metal coating (step 808).
• FIG. 9A is an enlarged cross-sectional view of part of a conductive substrate 904 with a metal coating 908, forming part of a cathode 912.
• the conductive substrate 904 is steel.
• the metal coating 908 is copper.
• the conductive substrate may be in the form of a net over which the metal coating is applied.
• the conductive substrate and metal coating may be a single piece of the same material, such as a copper wire. In such a case, the metal coating may be considered an outer layer of the metal substrate.
• a metal oxide coating is formed on the catalyst metal (step 808).
• FIG. 9B shows the part of the cathode 912 after the metal oxide coating 916 is formed.
• part of the copper catalyst metal coating 908 is formed into copper oxide by heating the cathode to at least 300 °C for at least 15 minutes.
• the metal oxide coating is thicker than a native oxide layer.
• the metal oxide coating has a thickness of at least twice the thickness of a native metal oxide layer. More preferably, the metal oxide coating is at least 50 nm thick.
• the metal oxide coating 916 may be provided by a deposition process to deposit the metal oxide coating on the catalyst metal coating.
• the copper catalyst metal coating 908 and the metal oxide coating 916 form a metal and metal oxide coating.
• metal particles and metal oxide particles may form a single layer to form the metal and metal oxide coating.
• the native metal oxide layer may be reduced before or during usage as a cathode.
• the term "oxidized cathode" will apply to a cathode on which an oxide layer is formed on the cathode by a process that increases the thickness of the metal oxide beyond that of a native metal oxide, whether the metal oxide coating remains or is subsequently reduced. Therefore the oxidized cathode is a cathode with an oxidized cathode layer, which is a metal and metal oxide coating where the metal oxide either remains or is reduced back to metal, and wherein the metal oxide is at least twice as thick as native metal oxide.
• FIG. 10 is a schematic view of an electrolyzer 1000 that may be used in an embodiment of the invention.
• An anode is formed by a conductive anode substrate 1004 covered with an anode material 1008.
• the anode material 1008 is nickel.
• An anode electrolyte compartment 1012 is adjacent to the anode and holds an anode electrolyte.
• the anode electrolyte is provided from an anode electrolyte source 1016, which may continuously circulate anode electrolyte through the anode electrolyte compartment 1012.
• a cathode electrolyte compartment 1020 holds a cathode electrolyte.
• the cathode electrolyte is provided from a cathode electrolyte source 1024, which may continuously circulate cathode electrolyte through the cathode electrolyte compartment 1020. Alternatively, the cathode electrolyte may flow to a tank where the solution-phase products are collected.
• a separator 1028 is placed between the anode electrolyte compartment 1012 and the cathode electrolyte compartment 1020.
• the separator 1028 may be a porous frit or membrane that may allow certain ions to pass through the separator 1028.
• a cathode comprising a conductive substrate 904 with an oxidized cathode layer 1032 forms a cathode adjacent to the cathode electrolyte compartment 1020.
• a gas chamber 1036 is placed on the backside of the cathode.
• a CO 2 source 1040 provides a flow of CO 2 into the gas chamber 1036.
• a product collector 1044 collects gas-phase products and unused CO 2 from the gas chamber 1036. Product in the product collector 1044 may be isolated and the remaining CO 2 may be recycled back to the CO 2 source 1040.
• a voltage source 1048 such as a battery, provides a voltage between the anode and cathode.
• the anode electrolyte source 1016 flows electrolyte through the anode electrolyte compartment 1012.
• the cathode electrolyte source 1024 flows electrolyte through the cathode electrolyte compartment 1020.
• CO 2 is flowed from the CO 2 source 1040 into the gas chamber 1036.
• the voltage source 1048 applies a positive voltage to the anode substrate 1004 and a negative voltage to the cathode substrate 904 with the anode connected to a positive terminal and the cathode connected to a negative terminal.
• the process provides electrolysis of the C(3 ⁇ 4.
• Various chemical reactions may occur during the electrolysis of CO 2 , depending on the metal cathode and other factors.
• One chemical reaction is C0 2 +H 2 0 ⁇ CO+H 2 +0 2 .
• Other chemical reactions provide products of HCO 2 H, CH 3 OH or C2H4.
• the product collector 1044 provides the product to another system that converts CO, O 2 , and 3 ⁇ 4 and possibly other products to methanol or some other fuel or usable chemical.
• the metal oxide layer on a cathode that is thicker than the native oxide layer and subsequently reducing the metal oxide layer, the reduction of CO 2 is improved. Without being bound by theory, it is believed that the reduction of the thick metal oxide layer results in metal particles that have unique structures that result in improved CO 2 reduction, however, the reason for the improvement is currently unknown. It has also been unexpectedly found that for some cathodes having a metal and metal oxide interface improves CO 2 reduction.
• the metal and metal oxide use the same metal material.
• the metal is something other than cerium such as tin or copper. Since cerium would turn to cerium oxide during electrolysis, tin is used to provide a native metal for an enhanced metal oxide metal interface, which provides improved CO 2 reduction.
• a square wave potential routine is preferred to obtain the metal oxide layer.
• a thick, hydrous ⁇ 3 ⁇ 4(3 ⁇ 4 layer can be formed on the Au electrode by applying a square wave potential alternating between 2.7 V and 0.45 V vs Hg/HgS0 4 at a frequency of 1 kHz for 30-60 min. Subsequent reduction of this ⁇ 3 ⁇ 4(3 ⁇ 4 layer results in a Au electrode with greatly improved CO 2 reduction activity and resistance to catalyst deactivation. Similarly, growth of a silver oxide on silver electrodes by application of a square wave potential routine, followed by electrochemical reduction, results in an Ag electrode with greatly improved C(3 ⁇ 4 reduction activity and resistance to catalyst deactivation.
• FIG. 11 is a high level flow chart of another embodiment of the invention.
• a cathode with a catalyst metal is provided (step 1104).
• a metal oxide coating is formed on the catalyst metal (step 1108).
• the metal oxide coating and the catalyst metal form a metal and metal oxide coating, which may comprise a metal oxide coating over a metal coating or a single coating with both metal oxide particles and metal particles.
• An anode is spaced apart from the cathode (step 1112).
• An ionic transport is provided between the anode and cathode (step 1116).
• the cathode is exposed to CO and H 2 O (step 1120).
• the anode is exposed to 3 ⁇ 40 (step 1124).
• a voltage is provided between the cathode and anode (step 1128). The voltage causes CO and 3 ⁇ 40 to be reduced to CH 3 CH 2 OH.
• the cathode is formed by providing a conductive substrate (step 1104) with a catalyst metal coating (step 1108).
• the conductive substrate is steel.
• the metal coating is copper.
• the conductive substrate may be in the form of a net over which the metal coating is applied.
• the conductive substrate and metal coating may be a single piece of the same material, such as a copper wire. In such a case, the metal coating may be considered an outer layer of the metal substrate.
• a metal oxide coating is formed on the catalyst metal (step 1108).
• part of the copper catalyst metal coating is formed into copper oxide by heating the cathode to at least 300 °C for at least 15 minutes.
• the metal oxide coating is thicker than a native oxide layer.
• the metal oxide coating has a thickness of at least twice the thickness of a native metal oxide layer. More preferably, the metal oxide coating is at least 50 nm thick.
• the copper catalyst metal coating and the metal oxide coating form a metal and metal oxide coating.
• An anode is spaced apart from the cathode (step 1112).
• FIG. 12 is a schematic view of an electrolyzer 1200 that may be used in an embodiment of the invention.
• An anode is formed by a conductive anode substrate 1204 covered with an anode material 1208.
• the anode material 1208 is nickel.
• An anode electrolyte compartment 1212 is adjacent to the anode and holds an anode electrolyte.
• the anode electrolyte is provided from an anode electrolyte source 1216, which may continuously circulate anode electrolyte through the anode electrolyte compartment 1212.
• a cathode electrolyte compartment 1220 holds a cathode electrolyte.
• the cathode electrolyte is provided from a cathode electrolyte source 1224, which may continuously circulate cathode electrolyte through the cathode electrolyte compartment 1220.
• the cathode electrolyte flows to a product collector 1244 where the solution- phase products are collected.
• a separator 1228 is placed between the anode electrolyte compartment 1212 and the cathode electrolyte compartment 1220.
• the separator 1228 may be a porous frit or membrane that may allow certain ions to pass through the separator 1228.
• a cathode comprising a conductive substrate 1230 with an oxidized cathode layer 1232 forms a cathode adjacent to the cathode electrolyte compartment 1220.
• a gas chamber 1236 is placed on the backside of the cathode.
• a CO source 1240 provides a flow of CO into the gas chamber 1236.
• the product collector 1244 collects products and unused CO from the gas chamber 1236. Product in the product collector 1244 may be isolated and the remaining CO may be recycled back to the CO source 1240.
• a voltage source 1248 such as a battery, provides a voltage between the anode and cathode.
• the anode electrolyte source 1216 flows electrolyte through the anode electrolyte compartment 1212.
• the cathode electrolyte source 1224 flows electrolyte through the cathode electrolyte compartment 1220.
• the electrolyte is KOH in an aqueous solution.
• CO is flowed from the CO source 1240 into the gas chamber 1236.
• the voltage source 1248 applies a positive voltage to the anode substrate 1204 and a negative voltage to the cathode substrate 1230 with the anode connected to a positive terminal and the cathode connected to a negative terminal.
• the process provides electrolysis of the CO.
• the product collector 1044 for a C0 2 reduction system may provide CO for the CO source 1240 for the CO reduction system.
• another source of CO may be used.
• a source of a mixture of CO and C0 2 may provide both CO and C0 2 to a reduction system.
• the pressure of the CO from the CO source 1240 is provided at a pressure greater than 1 atm. The higher pressure increases the solubility of CO in an aqueous solution. The use of an oxide-derived Cu catalyst in embodiments of the invention proved CO reduction with a high energetic efficiency without requiring H 2 .
• CO is converted to acetate according to the equation 2CO + 4e " + 3H + ⁇ CH 3 C0 2 ⁇ .
• CO is converted to ethylene according to the equation 2CO + 8e " + 8H + ⁇ C 2 H4 + 2H 2 0.
• the electrolytic reduction reduces CO to other hydrocarbons or alcohols. In other embodiments, the electrolytic reduction reduces C0 2 to hydrocarbons or alcohols.

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