Preferential outward diffusion of Ni in a CuNi alloy proliferates active sites by an order of magnitude for the OER and MOR.

An effective thermal oxidation strategy was implemented to enhance the electrochemically accessible surface areas (ECSAs) and active sites (ECASs) of CuNi (CN) alloy catalysts. This treatment engenders a Ni-rich Cu-Ni-O heterointerface, substantially increasing both the density and electrochemical accessibility of active sites. The optimized o-CN600 catalyst, comprising a Cu2O/CuO/NiO surface layer, exhibits oxygen evolution reaction (OER) performance comparable to that of benchmark IrO2, unambiguously reflecting the profound augmentation of active sites induced by thermal oxidation. The ECAS-optimized o-CN600 anode was screened for the methanol oxidation reaction (MOR), achieving 198 mV at 10 mA cm-2 and surpassing the performance of state-of-the-art catalysts. When an asymmetric electrolyzer comprising a Pt/C cathode and the ECAS-enhanced o-CN600 anode was deployed for the co-electrolysis of water with methanol, the cell voltage required to achieve -10 mA cm-2 for H2 production was significantly reduced to 1.55 V, compared with 1.75 V for conventional water electrolysis in 1.0 M KOH. The increased MOR activity also revealed that the conversion of OH* into O* is the rate-determining step (RDS) in the OER. This energy-efficient co-electrolysis approach highlights the advantage of the thermally oxidized o-CN600 anode and underscores its potential for hydrogen generation via water-methanol co-electrolysis.