Tin-doped NiFe₂O₄ nanoblocks grown on an iron foil for efficient and stable water splitting at large current...

Developing low-cost and self-supported bifunctional catalysts for highly efficient water splitting devices is of great significance. Herein, different from previously reported NiFe₂O₄-based electrocatalysts, we have grown nano-NiFe₂O₄ directly onto the iron foil (IF) surface and in situ introduced Sn⁴⁺ into NiFe₂O₄. The resulting experimental phenomena confirmed that the as-synthesized Sn-NiFe₂O₄/IF can deliver large-current densities (>1000 mA cm^-2) during oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) processes at a low overpotential. The needed overpotentials at the current density of 10 and 1000 mA cm^-2 are 231 and 368 mV for OER and 57 and 439 mV for HER, respectively. Additionally, when applied for the two-electrode water splitting, the corresponding needed voltage for Sn-NiFe₂O₄/IF at the current density of 10 mA cm^-2 was only 1.56 V, which was comparable to the commercial Pt/C-RuO₂/IF electrode. Thus, the introduced Sn⁴⁺ greatly enhanced the electrocatalytic property of Sn-NiFe₂O₄/IF, resulting in a superior bifunctional catalyst that can be applied for large-scale hydrogen production.