Revealing operando reconstruction effect of Ni–Co dual-cation in black phosphorus for promoting oxygen evolution reaction

Abstract

Sluggish reaction kinetic and large overpotential of the oxygen evolution reaction (OER) result in low energy efficiencies of different OER related devices. To solve these challenges, an OER electrocatalyst is constructed by coupling black phosphorus with Co/Ni nanosheets during a facile electrolysis-solvothermal process, where the bulky BP is successfully exfoliated into BP sheets (BP NSs) and the Co or Ni precursors are generated via anodic oxidation. Then, BP sheets are combined with Co–Ni species and finally formed into Co–Ni/BP composite via subsequent solvothermal process. The OER tests on this composite show the overpotential is 292 mV at 10 mA cm−2, much lower than that (341 mV) on a RuO2 catalyst. The TOF value of this composite is 0.71 s−1 at 1.8 V (vs. RHE), 14.2 times higher than that of Co/BP (0.05 s−1) and 23.7 times higher than Ni/BP (0.03 s−1). Operando structure characterizations of this composite reveal that Co2+-Ni2+ dual-sites are formed on Co–Ni/BP and electrons are transferred from Ni to Co via a P bridge. These Co2+-Ni2+ dual-sites evolve into Co3+-Ni3+ dual-sites during the OER, where Ni2P is formed into NiOOH and CoP turns into Co3O4. The Ni-Px-Co bridge is finally transformed into a heterogeneous Co3O4/NiOOH structure. This heterostructure efficiently regulates electronic structure of Co and Ni sites, resulting in the favorable adsorption of OH*, conversion of rate-determining step, reduced activation energy of the whole reaction, and eventually enhanced intrinsic activity toward the OER. This work provides a guidance to explore operando reconstruction mechanism of black phosphorus based electrocatalysts during electrocatalytic reactions.