In response to the global demand for sustainable energy, water electrolysis powered by renewable sources has become a cornerstone technology for green hydrogen production. This work introduces a rapid, scalable, and substrate-integrated strategy for fabricating high-entropy alloy (HEA) catalyst layers for water splitting. HEAs comprising five or more principal elements in near-equimolar ratios offer unique characteristics such as lattice distortion, entropy stabilization, and multiple oxidation states, which enable the formation of highly active and stable catalytic centers.1–3