Sub-100 mA/cm(2) CO2-to-CO Reduction Current Densities in Hierarchical Porous Gold Electrocatalysts Made by Direct Ink Writing and Dealloying

While most research efforts on CO2-to-CO reductionelectrocatalystsfocus on boosting their selectivity, the reduction rate, directlyproportional to the reduction current density, is another criticalparameter to be considered in practical applications. This is becausemass transport associated with the diffusion of reactant/product speciesbecomes a major concern at a high reduction rate. Nanostructured Auis a promising CO2-to-CO reduction electrocatalyst forits very high selectivity. However, the CO2-to-CO reductioncurrent density commonly achieved in conventional nanostructured Auelectrocatalysts is relatively low (in the range of 1-10 mA/cm(2)) for practical applications. In this work, we combine directink writing-based additive manufacturing and dealloying to designa robust hierarchical porous Au electrocatalyst to improve the masstransport and achieve high CO2-to-CO reduction currentdensities on the order of 64.9 mA/cm(2) with CO partial currentdensity of 33.8 mA/cm(2) at 0.55 V overpotential using anH-cell configuration. Although the current density achieved in ourrobust hierarchical porous Au electrocatalyst is one order of magnitudehigher than the one achieved in conventional nanostructured electrocatalysts,we found that the selectivity of our system is relatively low, namely52%, which suggests that mass transport remains a critical issue despitethe hierarchical porous architecture. We further show that the bulkdimension of our electrocatalyst is a critical parameter governingthe interplay between selectivity and reduction rate. The insightsgained in this work shed new light on the design of electrocatalyststoward scale-up CO2 reduction and beyond.