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.