A facile approach to deposit high performance electrocatalyst high entropy oxide coatings using a novel plasma spray route for efficient water splitting in an alkaline medium†

Electrocatalytic water splitting is a promising technique for producing sustainable hydrogen, but its effectiveness depends on the development of cost-effective and high-performance electrodes. In this work, phase-pure high entropy oxide (HEO) (Ni, Fe, Co, Cu, Mn)₃O₄ nanostructured coating electrodes were fabricated using a solution precursor plasma spray coating technique under optimized conditions with two different molar concentrations (1 M and 2 M) of solution precursors. This process enables precise deposition of a porous catalyst coating on stainless steel substrates, with an average thickness of 30 micrometers. The as-deposited coating shows a spinel structure, and its degree of crystallinity increases with higher molar concentrations of the solution precursors. The HEO coating electrodes demonstrate excellent activity in alkaline media for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), with low overpotentials of 129 mV and 220 mV, respectively, at a current density of 10 mA cm⁻². A two-electrode device was fabricated, and the results reveal that the required overall potential to achieve a current density of 10 mA cm⁻² is 1.47 V only. This work highlights the potential of solution precursor plasma spray coating as a versatile and scalable approach for producing phase-pure HEO-based water-splitting electrodes, paving the way for large-scale hydrogen generation in sustainable energy systems.