Nanoscale High-Entropy Metal Phosphate Precatalyst for Superior Oxygen Evolution Reaction through a Lattice Oxygen-Mediated Mechanism

The oxygen evolution reaction is recognized as a kinetic bottleneck in the process of water splitting. Activating the lattice oxygen-mediated mechanism (LOM) can surpass the theoretical limitations of the traditional adsorbate evolution mechanism (AEM) and improve the kinetics of the oxygen evolution reaction; however, inadequate stability continues to pose a significant issue for the operation of LOM. In this regard, high-entropy materials with their multicomponent configuration and entropy-stabilized structure can provide a promising solution by simultaneously balancing activity and stability. Herein, we report a nanoscale-range high-entropy metal phosphate (HEMP) precatalyst with Fe, Co, Ni, Mo, and V that undergoes controlled surface reconstruction under alkaline conditions to produce a catalytically active metal (oxy)hydroxide phase for the oxygen evolution reaction. The strategic integration of high-valence metals (Mo, V) with redox-active metals (Fe, Co, Ni) improved active site density, electronic modulation, and oxygen vacancy formation, therefore, transitioning the catalytic mechanism to the LOM. A systematic metal elimination study revealed cobalt as the principal active site within the high-entropy framework. Electrochemical investigations demonstrated a low overpotential of 277 ± 4 mV at 10 mA/cm2, a massive mass activity of 796 ± 7 A/g, and a low Tafel slope of 76 mV/dec, signifying facile OER kinetics over a flat glassy carbon electrode without any use of a high surface area electrode. Mechanistic experiments, encompassing pH-dependent experiments, tetramethylammonium hydroxide (TMAOH) probing, in situ UV–vis studies, and an isotope labeling experiment revealing an inverse kinetic isotope effect, validated the operation of the LOM mechanism. HEMP exhibited 99.4% stability after 100 h of operation at a high current density of 150 mA/cm2. The high mass activity value and excellent stability make this high-entropy material a promising candidate toward large-scale application.