Large-scale synthesis of LiNi0.75Fe0.25PO4 covalently anchored on graphene nanosheets for remarkable electrochemical water oxidation

Abstract

The exploration of earth-abundant and efficient oxygen evolution reaction (OER) catalysts is significant for a sustainable economy. Herein, a novel olivine structured lithium mixed transition-metal phosphate material anchored on graphene sheets (LiNi_0.75Fe_0.25PO₄/rGO) is reported as a highly effective OER catalyst. The synergy between the catalytic activity of the olivine-structured LiNi_0.75Fe_0.25PO₄ and the enhanced conducting, buffering and confining effects arising from in situ introduced graphene nanosheets resulted in superior electrocatalytic properties. It exhibits an extremely low overpotential of 295 mV to reach a current density of 10 mA cm⁻², fast kinetics with a small Tafel slope of 47 mV per decade in an aqueous alkaline electrolyte and maintains its high catalytic activity after consecutive 2000 cycles, which are superior to those of the benchmark RuO₂ and IrO₂ catalysts under identical experimental conditions and comparable to those of the best noble metal-free OER electrocatalysts reported so far. This achievement provides a straightforward route to design cost-effective and efficient catalysts from commercially available materials to replace the state-of-the-art noble-metal electrocatalysts for large-scale water splitting.