Coordination compound-derived La-doped FeS2/N-doped carbon (NC) as an efficient electrocatalyst for the oxygen evolution reaction

Abstract

By annealing/sulfuring of coordination compound (CC) precursors, [La_xFe_1−x(H₂O)₈Fe(CN)₆]·2hmt (x = 0, 0.33 and 0.5) (hmt = hexamethylenetetramine), FeS₂/N-doped carbon (NC), La-doped FeS₂/NC-0.33 and La-doped FeS₂/NC-0.5 were synthesized. All of them can electrolyze the oxygen evolution reaction (OER). Among them, the optimum sample La-doped FeS₂/NC-0.33 shows a low overpotential (η) of 217/239 mV at 30/50 mA cm⁻², which is comparable and even superior to commercial RuO₂ and many iron sulfide-based catalysts reported previously. Furthermore, La-doped FeS₂/NC-0.33 exhibits long-term OER activity with the transformation of FeS₂ → FeOOH over 60 h electrolysis at 20 mA cm⁻². In addition, density functional theory (DFT) simulations reveal that the rate-determining steps on La-doped FeS₂ and FeS₂ (200) surfaces are the formation of O₂ and Fe*–OH, respectively, and La-doped FeS₂ exhibits a less ΔG_max value of 1.585 eV with a smaller η value of 0.355 V, which is attributed to their different d-band centers before and after La-doping.