Synergistic geometric and electronic optimized Mo@Mo-Bo electrocatalyst for enhanced oxygen evolution reaction and value-added electrolysis

Abstract

Metal borates have long-lasting uses due their high electrical conductivity and stability. The exothermic solid-state synthesis (SSS) reaction between ammonium molybdate and (NH₄)₂B₄O₇ produces molybdenum/molybdenum borate (Mo@Mo-6Bo) with a lamellar labyrinth-like morphology. The integration of boron into transition metal (Mo) matrices with borate layers and defect-rich lattices and grain boundaries induced strong interaction between the electrolyte and the catalytic sites; it enhanced the absorption–desorption of intermediates to boost catalytic efficiency. The regulation of electronic structure and fast charge transfer on Mo@Mo-6Bo augmented the kinetics of the oxygen evolution reaction (OER) as evidenced by low overpotential (GC/NF) of 271/221 mV. A small Tafel slope of 63/58 mV dec⁻¹ and high performance were maintained over 24 h/50 h @ 10 mA cm⁻². The Mo@Mo-6Bo-based electrolyzer required 1.56 V in the alkaline electrolyte to reach 100 mA cm⁻², and high performance was maintained over 50 h. This alternative process was used as an anode to produce carbon-negative green H₂ and for value-added electrolysis, thereby exploiting economic benefits and converting waste into renewable resources. This work provides an efficient strategy that can be extended to develop a wide range of electrodes by replacing the sluggish OER for renewable electrochemical energy conversion.