(145e) Nano- to Macro Scale Morphological Impacts on CO2 electroreduction Product Selectivity over Cu Catalysts

CO₂ electroreduction has recently attracted a great deal of attention as a method to produce highly valuable chemicals and fuels from the waste CO₂. Among the possible products generated in this process, hydrocarbons such as methane and ethylene are of interest owing to their wide applications. Cu is the only metal catalyst which can produce hydrocarbons in significant quantities. However, it needs a high overpotential and also produces other side products which are not as desirable. Among the factors affecting the product selectivity and efficiency of the Cu catalysts, the surface morphology plays a significant role^1-4. Although it has been observed that increasing the roughness, which is a morphological parameter, is frequently associated with ethylene formation enhancement, the reason for this relationship is still under investigation^{1, 4-5}.

In this study, the effect of different nanoscale morphologies on the product selectivity was investigated. The Cu catalysts were synthesis by electropoishing and electrodeposition. We found a trend between electrochemical roughness and the faradaic efficiency (%FE) of methane and ethylene. By increasing the roughness from 1.6 to 7.8, the product selectivity changed from methane formation to ethylene formation. On the Cu/Cu 1.6 catalyst, we obtained 28%FE towards methane and 12%FE towards ethylene at -1.18V vs. RHE. In contrast, on the Cu/Cu 7.8 catalyst, 36%FE towards ethylene and 8%FE towards methane was observed at the same potential. Roughness follows the product selectivity frequently but not all time. We have found that electrochemical roughness can be similar on very different catalyst morphologies (Cu/Cu 1.6 and Cu/Cu 1.5) and result different product selectivities, illustrating more basic underlying effects are in play. We observed high selectivities toward ethylene on Cu rough catalysts that had higher current intensities on the surface of the catalyst. We have also observed that this current effect can be translated across length scale from nano to macro. We have found that by changing the electrode geometry from Cu flag shaped to Cu wire shaped, the product selectivity also can be switched between methane and ethylene. Moreover, it was observed that Cu wire had a higher catalytic activity compared to the Cu flag.

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