Synergetic CuO/CeO₂ anchored functionalized multi-walled carbon nanotubes as a bifunctional electrocatalyst for alkaline overall water splitting

Water electrolysis is a promising approach for sustainable hydrogen production to address the increasing global energy demand. In this study, a nanohybrid catalyst, FMCC (FMWCNTs/CuO/CeO₂ composite), was synthesized by integrating functionalized multi-walled carbon nanotubes with CuO/CeO₂ on a glassy carbon electrode. Structural and electrochemical analyses in 1.0 M KOH demonstrated enhanced bifunctional catalytic activity toward both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). X-ray photoelectron spectroscopy confirmed that the coexistence of multiple oxidation states and strong interfacial electronic interactions contributed to the superior catalytic performance. The FMCC catalyst achieved low overpotentials of 158 mV for OER and 274 mV for HER at 10 mA cm−2, outperforming the individual oxide counterparts. It also exhibited a high electrochemically active surface area (6.67 ± 0.31 cm2) and double-layer capacitance (0.267 ± 0.012 mF), indicating abundant active sites and improved charge transfer. The electrode maintained stable operation for 50 h at a cell voltage of 1.54 V. Density functional theory calculations revealed that oxygen vacancy engineering in the CeO₂/CuO heterostructure optimized charge redistribution, facilitating HER at Cu sites and OER at Ce sites, thereby enhancing overall water-splitting efficiency.