Tin-doped NiFe 2 O 4 nanoblocks grown on an iron foil for efficient and stable water splitting at large current densities.

Developing low-cost and self-supported bifunctional catalysts for highly efficient water splitting devices is of great significance. Herein, different from previously reported NiFe 2 O 4 -based electrocatalysts, we have grown nano-NiFe 2 O 4 directly onto the iron foil (IF) surface and in situ introduced Sn 4+ into NiFe 2 O 4 . The resulting experimental phenomena confirmed that the as-synthesized Sn-NiFe 2 O 4 /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-NiFe 2 O 4 /IF at the current density of 10 mA cm -2 was only 1.56 V, which was comparable to the commercial Pt/C-RuO 2 /IF electrode. Thus, the introduced Sn 4+ greatly enhanced the electrocatalytic property of Sn-NiFe 2 O 4 /IF, resulting in a superior bifunctional catalyst that can be applied for large-scale hydrogen production.