FeNiS 2 /reduced graphene oxide electrocatalysis with reconstruction to generate FeNi oxo/hydroxide as a highly‐efficient water oxidation electrocatalyst

Abstract It is critical to developing electrocatalysts with highly active and cost‐effective for oxygen evolution to resolve environmental pollution and energy issues, in which FeNi‐based nanomaterials hold a great promise. Herein, (Fe 0.33 Ni 0.67 )S 2 and (Fe 0.33 Ni 0.67 )S 2 /reduced graphene oxide (rGO)‐ x % ( x = 10, 20) composites, which exhibited highly efficient oxygen evolution reaction (OER) electrocatalytic activity under alkaline conditions, were synthesized via a hydrothermal approach and following thermal treatment with sulfur powders. Benefiting from the integrated structure of (Fe 0.33 Ni 0.67 )S 2 and support of conductive graphene backbones, (Fe 0.33 Ni 0.67 )S 2 /rGO‐20% electrocatalyst showed the best OER activity with an overpotential of 172 mV at 10 mA·cm −2 and Tafel slopes of 45 mV·decade −1 . The composition, phase, and surface structure of the catalyst were characterized before and after OER reaction. The results indicated that crystal phase of the catalyst was reconstructed to the amorphous crystalline features after OER, with oxidation of iron‐nickel sulfide and appearance of Ni–Fe oxo/hydroxide species, which may play a crucial role in the high OER performance as the catalytic‐active. Moreover, in a two‐electrode system towards overall water splitting with (Fe 0.33 Ni 0.67 )S 2 /rGO‐20%/NF and Pt/C/NF as the anode and cathode, respectively, the catalysts exhibited excellent catalytic performance with the voltage of only 1.42 V at 10 mA·cm −2 .