Ionic liquid-assisted synthesis of nickel cobalt phosphide embedded in N, P codoped-carbon with hollow and folded structures for efficient hydrogen evolution reaction and supercapacitor

Herein, bimetallic nickel cobalt phosphide and N, P-doped carbon composite (NiCoP/NPC) with folded and hollow spherical structures were first synthesized using a facile ionic liquid-assisted approach. The abundant folds increased the specific surface area by five times compared to the sample without adding ionic liquid. The carbon composites doped with N and P atoms lead to faster electron transfer and more active sites, as verified by density functional theory (DFT). When used as a catalyst, the overpotentials for HER at a current density of 10 mA cm⁻² were 108, 128 and 106 mV in acidic, alkaline and neutral media, respectively. Moreover, the optimally structured also showed superior electrochemical performance in an asymmetric supercapacitor with an energy density as high as 26.8 Wh kg⁻¹ at the power density of 7973.0 W kg⁻¹. This study offers a valuable reference for the rational design and synthesis to improved composite surface area and element-doping.