High-Aspect-Ratio Ag Nanowire Mat Electrodes for Electrochemical CO Production from CO2

Economic CO2 conversion to CO or syngas production requires product-selective, high-throughput, and durable electrolyzers. High-surface-area nanocatalysts combined with gas-diffusion layers (GDLs) enable high CO2 flux and conversion but can suffer from ineffective catalyst utilization, premature degradation, and flooding of the GDL that limit electrolyzer operation. Herein, a catalyst layer (CL) composed of a highly conductive catalyst bed of high-aspect-ratio Ag nanowire (Ag NW) electrocatalysts is integrated with a nonconductive porous polytetrafluorethylene (PTFE) GDL to enable more durable and selective electrolyzer performance. This platform enables exploration of CL thickness effects on catalyst utilization efficiency and selectivity. Combined with a 1-D computational model of the Ag NW-PTFE GDL, optimized CL thickness was found to be limited by significant depletion of local aqueous CO2 concentration, resulting in an optimal performance of 250 A/g (15x improvement) and a suppression of the hydrogen evolution reaction up to 20x. Furthermore, the local pH within the catalyst microenvironment indicates that local speciation of the bicarbonate electrolyte influences the selectivity between H-2 and CO. Additional experimental measurements indicate that proton dissociation from bicarbonate contributes significantly to hydrogen evolution at intermediate overpotentials. The combination of a conductive and mechanically stable nanowire catalytic network with a hydrophobic PTFE porous support structure provides an effective platform for tuning the microenvironment of mesoscale catalysts for improved performance and durability during CO2 electroreduction.