Adjusting grain boundary within NiCo 2 O 4 rod arrays by phosphating reaction for efficient hydrogen production.

In this work, the density and electronic structures of the metal active sites in NiCo 2 O 4 nanorod arrays were concurrently tuned by controlling the sample's exposure time in a phosphorization process. The results showed that both the density and electronic structure of the active adsorption sites played a key role towards the catalytic activity for water splitting to produce hydrogen. The optimal catalyst exhibited 81 mV overpotential for hydrogen evolution reaction (HER) at 10 mA cm -2 and 313 mV overpotential towards oxygen evolution reaction at 50 mA cm -2 . The assembled electrode delivered a current density of 50 mA cm -2 at 1.694 V in a fully functional water electrolyzer. The further results of theoretical density functional theory calculations revealed the doping of P elements lowered down the H adsorption energies involved in the water splitting process on the various active sites of P-NiCo 2 O 4 -10 catalyst, and thus enhanced its HER catalytic activities.