Low-cost composite electrodes by active Fe₃O₄ (111) of fly ash magnetic-sphere for efficient electrochemical overall water splitting

Developing highly efficient and low-cost composite electrode is a crucial step to achieve hydrogen and oxygen evolution reaction from overall water splitting. Herein, a ternary composite electrode derived from coating fly ash magnetic spheres and Graphite nanosheet on the carbon cloth surface, could greatly boost hydrogen and oxygen evolution reaction. Meanwhile, the efficiencies of overall water splitting were highly enhanced. The microstructure characterizations of composite material revealed that abundant magnetite crystals were existed on the fly ash magnetic spheres surface, and the main exposed crystal plane was active Fe₃O₄ (111). Moreover, the composite electrode exhibited remarkable catalytic activities for hydrogen and oxygen evolution reaction, with lower overpotential of 175.6 mV and 328 mV at 10 mA·cm⁻², small Tafel slope of 45.5 mV·dec⁻¹ and 77.9 mV·dec⁻¹, respectively, accompanied by prominent cycle stability. The overpotentials of hydrogen and oxygen evolution reaction were increased merely after 3000 CV cycles. Moreover, the electrocatalysis reaction mechanisms conducted by Density Functional Theory calculation illustrated that the combination of both advantages of Graphite nanosheet displaying superior electron transmission capacity, and the crystal plane of Fe₃O₄ (111) gaining excellent electrocatalytic activity, gave ternary composite noticeably improved performances toward hydrogen and oxygen evolution reactions. Specifically, it required merely 1.73 V of potential difference to onset the overall water splitting reaction. This work opens a strategy to develop low-cost, efficient and earth-abundant catalysts for water splitting, and broaden the comprehensive utilization way of coal fired fly ash.