Highly selective plasma-activated copper catalysts for carbon dioxide reduction to ethylene

Abstract

There is an urgent need to develop technologies that use renewable energy to convert waste products such as carbon dioxide into hydrocarbon fuels. Carbon dioxide can be electrochemically reduced to hydrocarbons over copper catalysts, although higher efficiency is required. We have developed oxidized copper catalysts displaying lower overpotentials for carbon dioxide electroreduction and record selectivity towards ethylene (60%) through facile and tunable plasma treatments. Herein we provide insight into the improved performance of these catalysts by combining electrochemical measurements with microscopic and spectroscopic characterization techniques. Operando X-ray absorption spectroscopy and cross-sectional scanning transmission electron microscopy show that copper oxides are surprisingly resistant to reduction and copper+ species remain on the surface during the reaction. Our results demonstrate that the roughness of oxide-derived copper catalysts plays only a partial role in determining the catalytic performance, while the presence of copper+ is key for lowering the onset potential and enhancing ethylene selectivity.

CO2 Reduction: From the Electrochemical to Photochemical Approach

“…In a follow‐up study, the same research group revealed that the roughening process generated a high density of grain boundaries which could support surface active sites normally unstable on individual nanoparticles 58. Cuenya and co‐workers employed facile and tunable plasma treatments to roughen Cu surfaces, and found that the optimal sample demonstrated a lower overpotential (−0.5 V vs RHE) and record selectivity (60% at −0.9 V) toward ethylene 59. Besides larger surface area and the increasing number of low‐coordinated sites, the authors suggested that the stable oxide layer formed during plasma treatment played a key role for enhancing the reaction activity and ethylene selectivity.…”

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

“…23,24 However, the additional (green) peak at 531.7 eV in the O 1s spectrum cannot be caused by It is a reasonable hypothesis that subsurface oxygen contributes to the additional (green) spectral component in Figure 1c, overlapping with the aforementioned electrolyte contribution.…”

“…The precipitate contains K, C and O ( Figure S9) and could be related to K 2 CO 3 precipitation; more details can be found in the Supporting information, section 'Appearance of electrolyte in the APXPS spectra'. Both spectra (b) and (c) in Figure 3 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 Recently, Lee et al 23 and Mistry et al 24 proposed residual Cu 2 O after reduction that would explain the enhanced selectivity of oxide-derived Cu. Their in situ XANES data are consistent with a similar study by Eilert et al 9 and an in situ Raman spectroscopy study by Ren et al, 11 that showed a pure metallic phase after holding the sample at reductive potentials, but their ex situ TEM work that occurred after long exposure to air and post mortem sample preparation showed the presence of an oxide phase (a reference sample reduced with H 2 indicated that the oxide phase was not solely caused by exposure to air).…”

“…[8][9][10][11][12][13][14][15][16] It has been hypothesized that this could be related for instance to an increase of local pH, [17][18][19] grain boundaries, 20 undercoordinated sites, 21 or residual oxides. [22][23][24] Several groups have shown the existence of sites with higher CO binding energy in oxidederived copper. 23,25 However, if the increased binding energy is caused by a simple shift of the dband in the catalyst (such as if we had nickel instead of copper), scaling relations would actually predict a higher overpotential for CO-CO-coupling on Cu(100).…”

Cu metal embedded in oxidized matrix catalyst to promote CO 2 activation and CO dimerization for electrochemical reduction of CO 2

“…We examine here the mechanism by which Cu2O-based electrodes are observed to improve both efficiency and selectivity for C2 products (12)(13)(14)(15), which also suppresses HERs by severalfold. Because Cu2O is subject to reduction (back to Cu metal) under CO2RR conditions, the improved performance was initially attributed to Cu metal surface morphology (8,16).…”