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 (15× improvement) and a suppression of the hydrogen evolution reaction up to 20×. Furthermore, the local pH within the catalyst microenvironment indicates that local speciation of the bicarbonate electrolyte influences the selectivity between H2 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.

Duke Scholars

Author Benjamin J. Wiley Chemistry