3D-Printed Hierarchically Micro–Nano-structured NiFe Catalysts for the Stable and Efficient Oxygen Evolution Reaction

The high overpotential of the oxygen evolution reaction (OER) is the main obstacle to water electrolysis for green hydrogen production. NiFe-based materials are the potential non-precious metal electrocatalysts for the OER, but their poor stability and limited activity have been of concern. Herein, a three-dimensional self-supporting NiFe electrode is prepared by direct writing 3D printing using spherical powders of Ni and Fe metals followed by hydrothermal treatment at 130 °C in urea and NH4F mixed solution. The fabricated 3D micro–nano-structured NiFe electrode presents an excellent OER activity of 220 mV overpotential to reach 100 mA cm–2 with a Tafel slope of 49.1 mV dec–1 and stability up to 100 h in continuous or intermittent power supply. The hydrothermal treatment produces in situ growth of flower-like clusters of NiFe2O4 nanoneedles wrapped with FeOOH nanosheets on the surface of the 3D NiFe bimetal microsphere network, and the outstanding OER activity is attributed to a wide variety of interfaces and heterojunctions among metal microspheres, metal oxides, and hydroxides. This study provides an approach for preparing high-performance self-supporting electrodes for electrochemical processes.