Computational and Experimental Study of Fluorine Doped (Mn_1–<i>x</i>Nb_<i>x</i>)O₂ Nanorod Electrocatalysts for Acid-Mediated Oxygen Evolution Reaction

Abstract

Identification, development, and engineering of high-performance, earth-abundant, and cost-effective precious group metal (PGM)-free electrocatalysts for catalyzing oxygen evolution reaction (OER) in acidic electrolytes are vital for the commercialization of proton exchange membrane based water electrolysis (PEMWE) technology. Utilizing the density functional theory (DFT) calculations to rationalize the thermodynamics and kinetics of adsorption of OER, juxtaposed with cohesive energy and electronic structure, we report the generation of 10 wt % fluorine (F)-doped (Mn1–xNbx)O2:10F nanorods (NRs) as active and durable PGM-free solid solution electrocatalysts for acid-mediated OER. The DFT calculations reveal an optimal solid solution composition of (Mn0.8Nb0.2)O2:10F containing Nb and F in α-MnO2 structure, exhibiting the optimized surface electronic structure (ΔG for the OER rate-determining step ∼ 1.72 eV) and cohesive energy (Ecoh ∼ −16.30 eV/(formula unit)) for OER, contributing to its higher catalytic performance in comparison to α-MnO2. Consequently, (Mn1–xNbx)O2:10F compositions with well-defined one-dimensional (1D) nanorod architectures are synthesized with the optimal composition of (Mn0.8Nb0.2)O2:10F, demonstrating improved electrocatalytic performance for acidic OER in good agreement with the DFT calculations. The superior electrochemical performance of (Mn0.8Nb0.2)O2:10F NRs includes significantly lower charge transfer resistance (∼11.8 Ω cm2), lower Tafel slope (∼371.17 mV dec–1), lower overpotential to deliver a current density of 10 mA cm–2geo (∼0.68 V), higher mass activity (∼29 A g–1), large electrochemically active surface area (ECSA ∼ 26.28 m2g–1), and turnover frequency (TOF ∼ 0.0065 s–1) with higher BET and ECSA normalized activity (∼0.5 mA cm–2BET and 0.11 mA cm–2ECSA) contrasted with (Mn1–xNbx)O2:10F (x = 0, 0.1, and 0.3) compositions, at an overpotential of 0.67 mV. Further, (Mn0.8Nb0.2)O2:10F NRs exhibit good electrochemical stability in acidic OER regimes, with no substantial catalytic activity degradation, validating its structural robustness for prolonged OER and making it a promising PGM-free OER electrocatalyst for acid-mediated PEMWE.