High-entropy materials have attracted extensive attention as emerging electrode materials in various energy applications due to their flexible tunability, unusual outstanding activities, and cost-effectiveness using multiple earth-abundant elements. We introduce a novel high-entropy composite oxide with the five elements of Cu, Ni, Co, Fe, and Cr (HEO-3CNF) for use in the oxygen evolution reaction (OER) in electrocatalytic water splitting. HEO-3CNF is composed of two phases with a non-equimolar, deficient high-entropy spinel oxide of (Cu_0.2−xNi_0.2Co_0.2Fe_0.2Cr_0.2)₃O₄ and monoclinic copper oxide (CuO). Electrochemical impedance spectroscopy (EIS) with distribution of relaxation times (DRT) analysis validates that the HEO-3CNF-based electrode exhibits faster charge transfer than benchmark CuO. It results in improved OER performance with a lower overpotential at 10 mA/cm² and a Tafel slope than CuO (518.1 mV and 119.7 mV/dec versus 615.9 mV and 131.7 mV/dec, respectively) in alkaline conditions. This work may provide a general strategy for preparing novel, cost-effective, high-entropy electrodes for water splitting.

Sustainable and renewable energy technologies have attracted significant attention for reducing greenhouse emissions in the shift from fossil fuels. The production of green hydrogen from water electrolysis is considered an environmentally friendly strategy for a decarbonized economy. We examine the activities of the hydrogen and oxygen evolution reactions (HER and OER) using spin-coated thin-film electrodes with Pt/C and IrO₂ nano-electrocatalysts under acidic conditions. The nano-electrocatalysts are characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and atomic force microscopy (AFM). The electrocatalytic activities of nanoscale Pt/C and IrO₂ are close to those of commercial Pt/C and superior to commercial IrO₂, resulting in improved overall water splitting performance. Furthermore, the OER kinetics analysis using the IrO₂ electrode is conducted using EIS measurements with distribution of relaxation time (DRT) analysis, resulting in a comparable exchange current density to that from the Tafel slope method (6.7 × 10⁻² mA/cm² versus 5.1 × 10⁻² mA/cm²), demonstrating the validity of the kinetics analysis. This work provides a general strategy for preparing novel and highly active OER electrode materials for water electrolysis.