Design Strategy\nfor an Efficient Bifunctional Electrocatalyst\n(IS-NiFeNC) for Overall and Solar-Cell Water Splitting

Herein, we demonstrated an interconnected nanospherical\ninterconnected\nspherical (IS) NiFe-impregnated N-doped carbon (IS-NiFeNC) electrocatalyst\nprepared successfully by simple flame pyrolysis followed by a solvothermal\nmethod. IS-Ni<sub>6</sub>Fe<sub>4</sub>NC has a good morphology to\nhave intimate contact with the electrolyte which significantly boosts\nthe bifunctional activity in a harsh alkaline electrolyte (1.0 M KOH).\nThe well-designed IS-Ni<sub>6</sub>Fe<sub>4</sub>NC/nickel foam (NF)\nnanosphere achieves a 10 mA/cm<sup>2</sup> geometrical current density\nfor the OER and HER with very low overpotentials (η) of 241\nand 95 mV and small Tafel slopes of 83 and 95 mV dec<sup>–1</sup>, respectively. The higher electrochemical surface area (110 m<sup>2</sup> g<sup>–1</sup>) and lower resistivity (2.8 Ω)\nof IS-Ni<sub>6</sub>Fe<sub>4</sub>NC easily exhibited kinetically\nsluggish electrode reactions. In a full-cell experiment, a nonprecious\nelectrode couple of IS-Ni<sub>6</sub>Fe<sub>4</sub>NC/NF//IS-Ni<sub>6</sub>Fe<sub>4</sub>NC/NF required a lower cell voltage of 1.62\nV to drive 10 mA cm<sup>–2</sup> than the voltage required\nfor bare NF//NF (1.87 V). The synergistic chemical coupling of NiFe\nwith N-doped carbon improved the stability and assisted in generating\nactive phases during the OER and HER processes, thus resulting in\noutstanding durability even after 200 h with an ∼3.4% potential\nloss. The solar-driven water electrolysis established the practical\nuse of IS-Ni<sub>6</sub>Fe<sub>4</sub>NC/NF for eco-benign industrial\nH<sub>2</sub> production. This work lays valuable experimental and\npostcharacterization foundations for the structure and properties\nof cost-effective bifunctional catalysts.