Au Dendrite Electrocatalysts for CO2 Electrolysis

• Published in: Journal of physical chemistry. C 2018-05, Vol.122 (18), p.10006-10016
• Main Authors: Nesbitt, Nathan T, Ma, Ming, Trześniewski, Bartek J, Jaszewski, Samantha, Tafti, Fazel, Burns, Michael J, Smith, Wilson A, Naughton, Michael J
• Format: Article
• Language: English
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.8b01831

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.