Sulphur-dopant induced breaking of the scaling relation on low-valence Ni sites in nickel ferrite nanocones for water oxidation with industrial-level current density

Abstract

The microstructure of active centers in bimetallic/multimetallic catalysts is under a long-time debate toward oxygen evolution reaction (OER). Here, sulfur doping NiFe2O4 nanocone arrays on iron foams (S-NiFe2O4/IF) is prepared via a scalable hydrothermal method. The favorable 3D nanocone arrays can offer large electrochemical surface area and allow for effective electrolyte access and O2 escape. Physical characterizations confirm low-valence Ni atoms in tetrahedron sites are more actives sites than high-valence Fe atoms in this S-doped bimetallic catalyst. Meanwhile, DFT calculations further verify the S introduction enhances the adsorption and dissociation of water, and optimizes the adsorption of OER intermediates on Ni sites. Therefore, the optimal S-NiFe2O4/IF achieves industrial-level 500 mA cm−2 at an overpotential of only 310 mV and maintains for 100 h in an alkaline medium. In addition, integrating S-NiFe2O4/IF into an anion-exchange membrane water electrolyzer can deliver a current density of 1.0 A cm−2 at 1.79 V.