During electrodeposition at high current values, the size and residence time of H2 bubbles vary based on the substrate and on the in-situ deposited Cu, leading to significantly different catalyst morphologies. Consequently, well-defined dendritic structures with large pores are observed (inset of Fig. 1) for Cu deposited on Cu substrate (CuCat/Cu) as compared to Cu deposited on Pt substrate (CuCat/Pt). Interestingly, product quantification by gas chromatography during electrochemical measurements showed that the product selectivity observed for all variations of the catalysts deposited on a particular substrate does not depend significantly on the differences in pore size and film thickness of the material. However there is a difference in product selectivity for the respective catalysts deposited on different substrates as represented in Fig. 1, where ethylene and carbon-monoxide selectivities are shown at two different potentials. The formation of methane is significantly suppressed (<1%) on both substrates in the potential range where the catalysts show high selectivity for ethylene. From X-ray absorption measurements it is observed that the catalysts are composed of metallic Cu and CuI2O species with no evidence of CuIIO species. The morphological changes, atomic state and composition of the catalyst may have a dialectic role in deciding the selectivity. In the follow-up work, the selectivity of various Cu films electrodeposited on both the substrates will be correlated with respect to surface area and CuI2O content after comprehensive quantification of the gaseous and liquid reaction products by gas chromatography, liquid gas chromatography and HPLC. These studies are expected to reveal strategies by which catalysts can be designed for higher selectivity towards a specific hydrocarbon product.
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