Low-valent Mo single atoms stabilized by electronegative oxygen coordination enable efficient water oxidation

Rational design and atomically precise synthesis of efficiently low-valent single atom catalysts, particularly those in which isolated transition-metal centers are directly coordinated to highly electronegative oxygen atoms embedded within layered double hydroxide (LDH) or oxyhydroxide matrices, are pivotal for surmounting the kinetic bottlenecks of the oxygen evolution reaction (OER). In the present work, low-valent molybdenum single atoms (Mo SAs) are successfully anchored onto NiFe LDH (^LSAMo-NiFe LDH) through a low-temperature solution-phase reduction process, resulting in a unique unsaturated and electron-rich Mo-O₃ coordination configuration. Under identical mass loadings, ^LSAMo-NiFe LDH outperforms both pristine NiFe LDH and commercial IrO₂ in alkaline media, delivering substantially higher intrinsic activity. The boost stems from robust electronic interactions between low-valent Mo SAs and the NiFe LDH lattice, which synergistically optimizes the local electronic structure. Remarkably, when architecturally engineered into a 3D monolithic electrode on nickel foam, this electrode achieves an ultra-low overpotential of 158 mV at 10 mA cm^-2, ranking it among the most active single-atom-based OER electrocatalysts yet reported. Post-characterization analyses corroborate that ^LSAMo-NiFe LDH retains its atomic architecture and stoichiometry after prolonged operation. Importantly, operando electrochemical characterization further reveals that the lattice oxygen mechanism pathway serves as the primary redox partner during the OER. Theoretical calculations reveal that the low-valent Mo SAs enhance OER activity and identify the rate-determining steps in the OER process. The present work delivers a universal blueprint for high-performance, low-valent monoatomic catalysts: craft under-coordinated metal centers whose electron density is precisely modulated by adjacent, highly electronegative ligands.