Boosting electrocatalytic activity toward overall water electrolysis via constructing core-shell structured NiCo@NiCoP nanorod on nickel foam

초록

core-shell structured nickel cobalt alloy@nickel cobalt phosphide (NiCo@NiCoP) nanorod was directly constructed on nickel foam (NF) and used as bifunctional electrocatalyst for OER and HER. The NiCo@NiCoP/NF electrocatalyst was synthesized through four-step synthetic procedure. First, 1D-structured nickel cobalt carbonate hydroxide (NiCo-CH) nanorod was directly grown on NF by hydrothermal method using metal precursors and urea. Second, the obtained NiCo-CH/NF was annealed at 440 °C for 2 h under hydrogen flow to form NiCo alloy nanorod (NiCo/NF). After that, the NiCo/NF was electrochemically oxidized using chronopotentiometry at current density of 300 mA cm-2 for 60 min in 1.0 M KOH solution to generate nickel cobalt oxyhydroxide (NiCo-OH) shell on NiCo alloy. Finally, the NiCo@NiCo-OH/NF was annealed with NaH2PO2 at 350 °C for 2 h under Ar atmosphere to obtain core-shell structured NiCo@NiCoP nanorod on NF. The NiCo alloy core serve as electron highway during the electrochemical water splitting, while the NiCoP shell provide efficient active sites for OER and HER owing to its rich redox property. Furthermore, it is easy for hierarchical 1D structure of NiCo@NiCoP to absorb a liquid-phase electrolyte onto the electrode surface, which is mainly ascribed to the strong capillary force. The efficient infiltration of electrolytes can reduce the gas-solid interface friction and promote the release of generated oxygen gas bubbles. As a result, the core-shell structured NiCo@NiCoP/NF exhibited the outstanding activity with low overpotentials of 340 mV and 146 mV at a current density of 100 mA cm-2 for OER and HER, respectively, and long-term durability under continuous operation over 100 h in alkaline solution