Electronic structure tuning to facilitate charge transfers in Z- Scheme mediated CuO/Se@WO3 aided by synchronized Cu (OH)2 for efficient overall water splitting

Abstract

This work presents electronic structure tuning of metal oxide with CuO/Se@WO₃/Cu(OH)2 catalyst on Ni foam designed for efficient and sustainable electrocatalytic overall water splitting, addressing key limitations of scarce noble metal catalysts. A dendritic CuO layer is electrodeposited followed by selenium-doping in WO₃ (Se@WO₃), to form a stable p-n junction that facilitates rapid interfacial charge transfer, enhancing both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities. Selenium doping alters the electronic structure to facilitate the alignment of the valence and conduction bands more favorably there by enabling a facile Z-scheme electron transfer pathway between Se@WO₃ and CuO, reducing the electron-hole recombination. An additional Cu(OH)₂ layer was electrodeposited as a hole extractor to further enhance the kinetics of the process, achieving a Tafel slope values of 35 mV/dec for OER and 45 mV/dec for HER. The modified catalyst achieved overpotentials as low as 202 mV for OER and 55 mV for HER at a current density of 10 mA/cm², surpassing traditional RuO₂ (for OER) and comparable to Pt/C (for HER) benchmarks. Density functional theory (DFT) calculations confirmed that Se doping increases the electron density at W sites and reduces the band gap, enhancing the OER through a Z-scheme aided electron-hole separation in presence of Cu(OH)₂ hole extraction layer. Gibbs free energy calculations for hydrogen adsorption indicate ΔGH* of −0.17 eV, representing a favorable HER kinetics as well. From the distribution of relaxation time (DRT) analysis where we have determined the time constants associated with different relaxation processes and supported the fact that the Se doped CuO/Se@WO₃/Cu(OH)₂ has both the enhanced diffusion and charge transfer kinetics. These findings highlight the potential of CuO/Se@WO₃/Cu(OH)₂ as a low-cost, high-performance catalyst for durable hydrogen and oxygen production from water splitting.