Remarkable enhancement of the alkaline oxygen evolution reaction activity of NiCo2O4 by an amorphous borate shell

It is highly desirable but still a challenging task to find a simple, fast and straightforward method to greatly improve the alkaline oxygen evolution reaction (OER) performance of a NiCo2O4 catalyst. In this communication, we demonstrate that developing an amorphous borate shell on a NiCo2O4 surface can boost its OER activity in alkaline media. As a 3D catalyst electrode, a NiCo2O4@Ni-Co-B nanoarray on carbon cloth needs an overpotential of only 270 mV to achieve a geometrical catalytic current density of 10 mA cm(-2) in 1.0 M KOH, which is 100 mV less than that for a NiCo2O4 nanoarray. Notably, this electrode also demonstrates strong electrochemical durability, maintaining its activity for at least 100 h. The superior activity of NiCo2O4@Ni-Co-B is attributed to the amorphous Ni-Co-B shell on NiCo2O4 favoring the in situ electrochemical generation of more active species during water oxidation.