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

Abstract

This work presents electronic structural tuning of metal oxides within a CuO/Se@WO₃/Cu(OH)₂ catalyst on Ni foam for efficient and sustainable electrocatalytic overall water splitting, addressing key limitations of scarce noble metal catalysts. A dendritic CuO layer is electrodeposited, followed by Se doping in WO₃ (Se@WO₃), forming a stable p–n junction that enhances the interfacial charge transfer for improved HER and OER activity. Selenium doping optimizes band alignment, enabling a more facile Z-scheme electron transfer pathway with CuO, minimizing electron–hole recombination. An additional Cu(OH)₂ layer acts as a hole extractor, further enhancing process kinetics, achieving Tafel slopes of 35 mV dec⁻¹ (OER) and 45 mV dec⁻¹ (HER). The modified catalyst achieved overpotentials as low as 202 mV for the OER and 55 mV for the HER at a current density of 10 mA cm⁻², surpassing traditional RuO₂ (for the OER) and comparable to Pt/C (for the 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 the presence of the Cu(OH)₂ hole extraction layer. Gibbs free energy calculations for hydrogen adsorption indicate a ΔG_H* of −0.17 eV, representing favorable HER kinetics. From the distribution of relaxation time (DRT) analysis, the time constants associated with various relaxation processes indicate a faster diffusion and charge transfer kinetics across the interfaces. 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.