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

Abstract

A series of NiCo2P-based electrocatalysts, which were wrapped by CeO2 whose oxygen vacancies (VO) are partially filled with phosphorus atoms (named as NiCo2Px/PxFVo-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, whichreinforcing 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 NiCo2Px/PxFVo-CeO2 in alkaline electrolyte. As a result, the overpotential as low as 33.6 mV is achieved for NiCo2P0.3/P0.3FVo-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.