Enhanced Hydrogen Evolution Reaction Performance of NiCo₂P by Filling Oxygen Vacancies by Phosphorus in Thin-Coating CeO₂

A series of NiCo 2 P-based electrocatalysts, which were wrapped by CeO 2 whose oxygen vacancies (V O ) are partially filled with phosphorus atoms (named as NiCo 2 P x /P x FVo-CeO 2, where x refers to the consumption of NaH 2 PO 2 ·H 2 O), have been fabricated to improve the electrocatalytic reactivity of NiCo 2 P toward hydrogen evolution in alkaline solution. In the novel catalysts, the P atoms fill the oxygen vacancies, elevate the chemical valence state of Ni 2+ and Co 3+, and increase the hydride acceptors, which reinforcing the promoting effect of CeO 2 in the hydrogen evolution reaction (HER). Moreover, the negatively charged P atoms capture the positively charged protons more easily, benefiting the Volmer step during HER. Furthermore, the synergistic effect between oxygen vacancies and the filled P atoms accelerates the migration rate of electrons/ions and increases the electrochemical active area. All of the above are advantageous to the hydrogen evolution of NiCo 2 P x /P x FVo-CeO 2 in alkaline electrolyte. As a result, the overpotential as low as 33.6 mV is achieved for NiCo 2 P 0.3 /P 0.3 FVo-CeO 2 in alkaline media to drive a current density of 10 mA cm –2 . The reactivity is superior to that of Pt/C at a large current density along with a Tafel slope of 61.24 mV dec –1 and long-term durability, which giving a new technology for efficient transition-metal catalyst candidates toward HER in alkaline solution.