Porous carbon membrane embedded with high-loading NiCoP nanoparticles as bifunctional electrodes for supercapacitors and electrocatalytic water splitting

Porous carbon membrane-based bifunctional electrodes (NixCoyP@CSA) are developed by direct carbonization followed by vapor-phase phosphidation of Ni2+/Co2+-crosslinked starch aerogel. During the carbonization and phosphidation processes, the crosslinked starch framework is transformed into a hierarchically porous, conductive, and mechancially strong carbon membrane while the Ni2+/Co2+ species are concurrently converted into embedded carbon-coated NixCoyP nanoparticles with a loading exceeding 40 wt%. Benefitting from hierarchically porous structure, excellent wettability, abundant active sites, the best NiCo2P@CSA electrode exhibits a high areal specific capacitance (Ca) of 9.41 F cm-2 at 2 mA cm-2, a volumetric capacitance (CV) of 115.0 F cm-3 at 20 mA cm-3, and a NiCo2P loading-based mass capacitance (Cm) of 1108.9 F g-1 at 0.2 A g-1, in a three-electrode system. In addition, an asymmetrical supercapacitror (SC) assembled by paring NiCo2P@CSA and activated carbon/Ni foam (AC/NF) exhibits a high Ca of 2.46 F cm-2 at 2 mA cm-2, an energy density of 0.41 mWh cm−2 at the power density of 1.1 mW cm−2, and a 75 % capacitance retention with a unit coulombic efficiency after 10000 cycles. In addition, the NiCo2P@CSA can also be directly used as a binder-free bifunctional electrode for electrocatalytic water splitting, requiring low overpotentials of 192.4 and 418.5 mV to achieve a current density of 100 mA cm-2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, and it exhibits superior durability in both HER (>100 h at 20 mA cm-2) and OER (>40 h at 20 mA cm-2).