Partial crystallization of Co–Fe oxyhydroxides towards enhanced oxygen evolution activity.

Developing high-performance noble-metal-free electrocatalysts for the oxygen evolution reaction (OER) is of great significance for the large-scale implement of electrochemical water splitting. Here, we demonstrate that cobalt-iron oxyhydroxide (CoFe 0.8 (OH) x) with appropriate crystallization exhibits excellent OER activity with a low overpotential of only 246 mV, which is much lower than that achieved on amorphous one. Kinetic experiments indicate that the OER active sites should be di-μ-oxo bridged Fe–Co, on which lower energy barrier is attained than that on Fe–O and Co–O sites. Partial crystallization is beneficial to the lattice contraction, the formation of Co–O–Fe sites, and the decrease of charge transfer resistance, thus accelerating OER process. Compared with amorphous Co-Fe oxyhydroxides, partially crystallized ones show higher OER activity due to faster charge transfer and lower reaction barrier. [Display omitted] • Partially crystallized CoFe 0.8 (OH) x shows higher OER activity than amorphous one. • CoFe 0.8 (OH) x exhibits an overpotential of only 246 mV at 10 mA cm−2. • Bimetallic CoFe 0.8 (OH) x shows lower OER barrier than monometallic counterpart. • The charge transfer ability can be enhanced by partial crystallization. • The OER active sites should be di-μ-oxo bridged Fe–Co. [ABSTRACT FROM AUTHOR]