Copper-modulated nickel nanoparticles embedded in nitrogen-doped carbon nanotubes for efficient electrocatalytic saline water splitting

Modulating the electronic structure of catalysts to enhance the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is critical for advancing efficient and durable water electrolysis. In this study, we synthesize Cu-doped Ni nanoparticles (NPs) encapsulated in nitrogen-doped carbon nanotubes (NCNT) supported on carbon cloth (CuNi@NCNT/CC) as a high-performance bifunctional electrocatalyst. Experimental characterization and density functional theory (DFT) calculations demonstrate that the CuNi synergy in CuNi@NCNT/CC optimizes the electronic structure and d-band center, balances the adsorption/desorption free energies of reaction intermediates, and significantly lowers the energy barriers for the rate-determining steps of HER and OER, thereby accelerating reaction kinetics. As a result, the assembled water electrolyzer achieves a low cell voltage of 1.50 V at 10 mA cm⁻² in 1.0 M KOH. Furthermore, even in 1 M KOH +0.5 M NaCl, the CuNi@NCNT/CC only requires 1.52 V to deliver 10 mA cm⁻². Additionally, the NCNT encapsulation endows the catalyst with exceptional stability, maintaining efficient overall water splitting performance for over 200 h even in 1 M KOH +0.5 M NaCl for 100 and 500 mA cm⁻². This work provides a rational design strategy for developing robust bifunctional electrocatalysts through electronic structure modulation.