Preferential Outward Diffusion of Ni in CuNi Alloy Proliferates Active Sites by An Order of Magnitude for OER and MOR

Abstract

An effective thermal-oxidation strategy was implemented to enhance the electrochemically accessible surface area (ECSA) and active sites (ECAS) 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 benchmark IrO2, unambiguously reflecting the profound augmentation of active sites induced by thermal oxidation. The ECAS optimized o-CN600 anode was screened for methanol oxidation (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 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.