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

A series of NiCo₂P-based electrocatalysts, which were wrapped by CeO₂ whose oxygen vacancies (V_O) are partially filled with phosphorus atoms (named as NiCo₂P/PFVo-CeO₂, where x refers to the consumption of NaH₂PO₂·H₂O), have been fabricated to improve the electrocatalytic reactivity of NiCo₂P toward hydrogen evolution in alkaline solution. In the novel catalysts, the P atoms fill the oxygen vacancies, elevate the chemical valence state of Ni²⁺ and Co³⁺, and increase the hydride acceptors, which reinforcing the promoting effect of CeO₂ 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 NiCo₂P/PFVo-CeO₂ in alkaline electrolyte. As a result, the overpotential as low as 33.6 mV is achieved for NiCo₂P^0.3/P^0.3FVo-CeO₂ 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.