Tuning of a CuAl2O4:NiO hybrid semiconductor with a Eu cocatalyst: state-of-the-art design and sustainable approach for H2 generation from water splitting.

There is growing and accelerating interest among both the scientific community and the public in reducing global dependence on fossil fuels. In this context, hydrogen (H2) produced via electrochemical water splitting represents a promising approach for achieving this objective. Herein, we present the synthesis and characterization of europium-doped copper aluminate spinel as a bifunctional catalyst for water electrolysis. The spinel materials were synthesized by a hydrothermal method, followed by a thermal treatment procedure to obtain well-crystallized spinel. XRD analysis confirmed the formation of pure CuAl2O4 with successful incorporation of Eu. SEM analysis shows uniform morphology with small-sized particles. XPS analysis also found that Eu doping modifies the electronic structures of copper sites and increases the density of active copper cations (Cu2+) and oxygen vacancies in the spinel system. The electrochemical performance of the synthesized nanomaterials was systematically investigated for the oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and overall water splitting to assess their multifunctional capabilities. Their behavior was evaluated using electroanalytical techniques, including cyclic voltammetry (CV), double-layer capacitance (C dl), and electrochemical impedance spectroscopy (EIS). From electrochemical evaluation studies in an alkaline environment (1.0 M KOH), it was observed that the 3% Eu-doped CuAl2O4:NiO catalyst is more efficient than its undoped counterpart for the OER and HER processes. In particular, the optimal 3% Eu-doped CuAl2O4:NiO catalyst exhibits excellent activity with an overpotential of 270 mV for the OER, while the Tafel slope is 69.2 mV dec-1. For the HER, the catalyst exhibits an overpotential of 250 mV and a Tafel slope of 51 mV dec-1, comparable to that of pristine copper aluminate. The improved catalytic efficiency is due to the synergistic effect of Eu doping, which enables surface reconstruction and enhances charge-transfer dynamics. The current study reports a facile approach for rationally designing rare-earth-doped spinel oxides as promising electrocatalysts for advanced water-splitting applications.