Morphological considerations in templated porous Ag catalysts for electrochemical CO2 reduction

Abstract

Electrochemical reduction of CO2 using renewable electricity is a promising strategy to produce fuels and chemical feedstocks while simultaneously decreasing greenhouse gas emissions. Porous Ag catalysts are reported to have a high CO selectivity and activity, but the complex combination of porosity and morphology makes it hard to gain a full understanding of CO2 reduction in porous metals. In order to study the effect of morphology variations in porous Ag, a template-based electrodeposition route was developed. In addition, the effect of porosity was established by comparing porous Ag to non-porous Ag. Electrodeposition parameters were varied to control the morphology of porous and non-porous Ag. Porous Ag consistently reached higher CO partial current density values, 3.45 - 4.25 mA/cm2, compared to non-porous Ag, 2.21 - 2.97 mA/cm2, at -1.4 V vs RHE. We demonstrated that only for certain Ag morphologies, porous samples reached higher CO and lower H2 faradaic efficiencies compared to their non-porous counterpart. In combination with the absence of porosity-induced suppression of the hydrogen evolution reaction in coral-like porous structures, this indicated that the morphology surrounding porosity contributes significantly to the catalytic performance. Therefore, this study establishes that porosity enhances CO2 to CO conversion, while simultaneously highlighting the importance of additional morphological considerations.