Surface-tuning nanoporous AuCu3 engineering syngas proportion by electrochemical conversion of CO2

Abstract

The direct electrochemical conversion of CO2 to syngas with controllable composition remains challenging. In this work, driven by concentration gradient, a simple air-heating aided strategy has been developed to adjust surface composition of the self-supporting nanoporous AuCu3 alloy. According to Fick First Law, the interior Cu atoms of the AuCu3 alloy with Au-rich surface gradually segregated outwards during heating, realizing Cu-rich surface eventually. Correspondingly, the competing electrocatalytic CO2 reduction (ECR) to CO and hydrogen evolution reactions (HER) were tactfully balanced on these alloy surfaces, thus achieving proportion-tunable syngas (CO/H2). Density functional theory (DFT) calculations on the Gibbs free energy change of the COOH* and H* (ΔGCOOH*, ΔGH*) on the alloy surfaces were conducted, which are generally considered as the selectivity descriptors for CO and H2 products, respectively. It shows ΔGCOOH* gradually increases in contrast to the decreased ΔGH* with more Cu on the surface, suggesting H2 is more favored over Cu sites, which is consistent with the declining CO/H2 ratio observed in the experiments. This study reveals that the surface composition controls ECR activity of nanoporous AuCu3 alloy, providing an alternative way to the syngas production with desirable proportion.