Subsurface Oxygen in Oxide-Derived Copper Electrocatalysts for Carbon Dioxide Reduction

Abstract

Copper electrocatalysts derived from an oxide have shown extraordinary electrochemical properties for the carbon dioxide reduction reaction (CO 2 RR). Using in situ Ambient Pressure Xray Photoelectron Spectroscopy (APXPS) and quasi in situ Electron Energy Loss Spectroscopy (EELS) in a Transmission Electron Microscope (TEM), we show that there is a substantial amount of residual oxygen in nanostructured, oxide-derived copper electrocatalysts, but no residual copper oxide. Based on these findings in combination with Density Functional Theory (DFT) simulations, we propose that residual subsurface oxygen changes the electronic structure of the catalyst and creates sites with higher carbon monoxide binding energy. If such sites are stable under the strongly reducing conditions found in CO 2 RR, these findings would explain the high efficiencies of oxide-derived copper in reducing carbon dioxide to multi-carbon compounds such as ethylene.

Standards and Protocols for Data Acquisition and Reporting for Studies of the Electrochemical Reduction of Carbon Dioxide

“…These studies have stimulated efforts aimed at understanding the origin of the seemingly superior catalytic activity of these oxide-derived catalysts compared to polycrystalline Cu foils. [65][66][67][68][69][70][71][72] However it has not been clearly demonstrated if the enhanced activity is due to an increase in the total surface area of the catalyst or to an enhancement of the intrinsic activity. [61][62][63][64][65][66][67][68] Using the metrics discussed above, we show in Figure 10 an example of an activity comparison 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 between Cu standards (polycrystalline Cu foil and epitaxial Cu thin films) and a plasma treated Cu catalyst for which surface area measurements are available.…”

Catalyst electro-redeposition controls morphology and oxidation state for selective carbon dioxide reduction

“…Selectively producing ethylene over methane circumvents costly paraffin-olefin separation 5 . Developing catalysts that work at ambient conditions to produce C2 selectively over C1 gaseous products will increase the relevance of renewable feedstocks in the chemical sector.Oxide-derived copper is one class of catalyst that has shown enhanced CO 2 RR activity and increased selectivity towards multi-carbon products [6][7][8] . The selectivity of these catalysts is dependent on structural morphology and copper oxidation state 9-17 .…”

“…In situ hard X-ray absorption spectroscopy (hXAS) experiments have suggested stable Cu + species exist at highly negative CO 2 RR potentials of ~− 1.0 versus RHE 9 . However, the presence of Cu + species during CO 2 RR is still the subject of debate; 7,19 and in situ tracking of the copper oxidation state with time resolution during CO 2 RR has remained elusive.Morphological effects of copper nanostructures have a significant effect on the selectivity of CO 2 RR to multi-carbon products [20][21][22][23][24] . Copper catalysts with different morphologies have been synthesized through annealing, chemical treatments on thin films, colloidal synthesis and electrodeposition from solution 6,17,25,26 .…”

“…Oxide-derived copper is one class of catalyst that has shown enhanced CO 2 RR activity and increased selectivity towards multi-carbon products [6][7][8] . The selectivity of these catalysts is dependent on structural morphology and copper oxidation state [9][10][11][12][13][14][15][16][17] .…”

“…Electrochemical reduction of copper oxide catalyst films can lead to grain boundaries, undercoordinated sites and roughened surfaces that are hypothesized to be catalytically active sites 8,18 . Residual oxides, proposed to play a key role in catalysis, may exist after electrochemical reduction 7 . A recent report of oxygen plasma-activated oxide-derived copper catalysts achieved an ethylene FE of 60% at − 0.9 V versus reversible hydrogen electrode (RHE) 9 , with activity attributed to the presence of Cu + species.…”