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 AGH* 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.