Open-Air Pulsed Laser-Deposited NiCoCuFeMoMnOx High-Entropy Oxide Thin Films for Efficient Electrocatalytic Oxygen Evolution Reaction

High-entropy materials have garnered significant attention as possible non-noble metal-based electrocatalysts for the production of hydrogen via water electrolysis. High-entropy oxides demonstrate high activity and stability at relatively low costs. This study presents the synthesis and characterization of NiCoCuFeMoMnO_x high-entropy oxide thin films deposited on graphite substrates via open-air pulsed laser deposition for electrocatalytic oxygen evolution reaction. The pulsed laser deposition process facilitates the oxidation of high-entropy alloy targets, forming a stable oxide phase. X-ray diffraction patterns reveal a mixture of amorphous (28.3%) and face-centered cubic crystalline (71.7%) phases. Morphological analysis using scanning electron microscopy and transmission electron microscopy shows a porous, flower-like structure, enhancing surface area and active site availability. Electrochemical measurements demonstrate significant improvements in oxygen evolution reaction performance with reduced overpotentials down to 180 ± 7 mV to reach 10 mA·cm^–2 and enhanced reaction kinetics. The high-entropy oxide films maintain stability over 100 h, showing improved catalytic efficiency after long-term stability measurements. Electrochemically active surface area and electrochemical impedance spectroscopy analyses indicate increased active surface area and reduced charge transfer resistance. These results highlight NiCoCuFeMoMnO_x high-entropy oxide films as promising robust electrocatalysts for efficient water splitting.