Nanoporous Gold as a Highly Selective and Active Carbon Dioxide Reduction Catalyst

Abstract

Electrochemical conversion of CO_2 into useful chemicals is a promising approach for transforming CO_2 into sustainably produced fuels and/or chemical feedstocks for industrial synthesis. We report that nanoporous gold (np-Au) films, with pore sizes ranging from 10 to 30 nm, represent promising electrocatalytic architectures for the CO_2 reduction reaction (CO_2RR) due to their large electrochemically active surface area, relative abundance of grain boundaries, and ability to support pH gradients inside the nanoporous network. Electrochemical studies show that np-Au films support partial current densities for the conversion of CO_2 to CO in excess of 6 mA cm^(–2) at a Faradaic efficiency of ∼99% in aqueous electrolytes (50 mM K_2CO_3 saturated with CO_2). Moreover, np-Au films are able to maintain Faradaic efficiency greater than 80% for CO production over prolonged periods of continuous operation (110 h). Electrocatalytic experiments at different electrolyte concentrations demonstrate that the pore diameter of nanoporous cathodes represents a critical parameter for creating and controlling local pH gradients inside the porous network of metal ligaments. These results demonstrate the merits of nanoporous metal films for the CO_2RR and offer an interesting architecture for highly selective electrocatalysis capable of sustaining high catalytic currents over prolonged periods.