Molybdenum-Induced Pore Expansion in CoFe-Nanomesh for Efficient Oxygen Evolution Reaction

We report a pore modification approach to transform ink-bottle type mesopores into slit-type hierarchical mesopores by Mo-doping into CoFe20-nanomesh. MoO₄ ^2- exhibited dual roles as intercalating and surface-coordination agents, promoting the formation of 3D mesoporous nanoflowers, exfoliation, and pore opening through electrostatic repulsion and anion exchange, corroborated by FTIR, SEM, TEM, AFM, and BET analyses. Among all materials, CoFe20Mo5 exhibited remarkable OER performance, achieving an overpotential of 318 mV, mass activity of 429 A/g, and TOF of 3.10 s^-1. CoFe20Mo5 had a substantial roughness factor of 1238, implying 1238 times ion accessibility enhancement. The excellent activity was due to (a) the hierarchical mesopores with enhanced surface area that facilitated the electrolyte accessibility inside nanomaterial, (b) the high electrical conductivity improved ion accessibility, lowered charge transfer resistance at electrode-electrolyte interface and reduced pseudoresistance for intermediate formation, (c) the leaching of MoO₄ ^2-/Mo⁶⁺ further improved the accessible active sites, (d) Mo⁶⁺ doping tuned the oxidation states and electronic environment, generating Co³⁺ active sites and oxygen vacancies, while Fe³⁺ ions increased the conductivity and stability through mutual interaction. Thus, this work highlights the efficiency of molybdenum-induced surface and pore restructuring and electrical modulation for enhancing OER activity and the stability of the catalyst.