Adjusting grain boundary within NiCo₂O₄rod arrays by phosphating reaction for efficient hydrogen production

In this work, the density and electronic structures of the metal active sites in NiCo2O4 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-NiCo2O4-10 catalyst, and thus enhanced its HER catalytic activities.