Au Dendrite Electrocatalysts for CO2 Electrolysis

By Nesbitt, Nathan T.; Ma, Ming; Trze?niewski, Bartek J.; Jaszewski, Samantha; Tafti, Fazel; Burns, Michael J.; Smith, Wilson A.; Naughton, Michael J.
Published in The Journal of Physical Chemistry C 2018

Abstract

Electrochemical CO2 reduction can convert CO2 into fuels and valuable chemicals using renewable electricity, which provides a prospective path toward large-scale energy storage. Au nanostructured electrodes have demonstrated the best catalytic performance for CO2 conversion: high catalytic selectivity for CO formation at low overpotentials, high current density, and long-term durability. Here, we report selective electrocatalytic CO2 reduction to CO on nanostructured Au with various morphologies, prepared via electrocrystallization with a megahertz potential oscillation. X-ray diffraction showed that the proportion of 100 and 110 to 111 surfaces increased at more negative deposition potentials. Cyclic voltammetry showed the potential of zero charge on an Au film was approximately 0.35 V vs standard hydrogen electrode (SHE) and that the surface energy decreased by ?1 eV/nm2 at ?0.5 V vs SHE, tending to 0 within several volts in either direction. Scanning electron micrograms showed that the Au crystals grow primarily in the ?110? directions. From these data, a model for crystallization from melts was adapted to calculate the roughening temperature of the 111, 100, and 110 Miller indices as 7000, 4000, and 1000 K, decreasing for more negative deposition potentials. This offers a framework for exposed facet control in electrocrystallization. In CO2 electrocatalysis, ?0.35 V vs reversible hydrogen electrode was observed to be a turn-on potential for improved CO2 reduction activity; dendrites showed 50% Faradaic efficiency for CO production at more cathodic potentials. The Tafel slope was measured to be 40 mV/decade for 100 and 110-rich Au dendrites and 110 mV/decade for 111-dominated Au plates, suggesting the higher surface energy crystal facets may stabilize all of the CO2 reduction reaction intermediates.

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