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

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 Delta GH* 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.