NiCoP firmly anchored on Mn-treated carbon cloth enabling enhanced supercapacitor performance

Nickel‑cobalt bimetallic phosphides (NCP) are widely employed as supercapacitor electrodes because of their large electrochemical activity originated from the various valence states of Ni/Co. Here, KMnO4 is used to treat carbon cloth (CC), producing Mn-oxides decorated CC (Mn-CC), and NCP is then in situ grown on Mn-CC to obtain a flexible NCP@Mn-CC electrode with urchin-like NCP loading. Compared to bare CC, Mn-CC demonstrates obviously villous structure with Mn oxides attached on the fiber surface, which offers high hydrophilicity, increased specific surface area and more adsorption sites. Strong chemical bonds are built between NCP and the Mn oxides, which change the valence ratio of Ni3+/Ni2+ and Co3+/Co2+ and lead to active electrochemical reactions. It is revealed by density functional theory (DFT) calculation that the bond between NCP and Mn oxides can lead to moved-down d-band center, increased conductivity and decreased OH− adsorption energy in NCP@Mn-CC. These features contribute to the high specific capacitance of NCP@Mn-CC reaching 1149.6 F g−1 at 20 °C and low-temperature capacitance retention rate of 80.2 % at 0 °C. Also, the asymmetric supercapacitor with the NCP@Mn-CC cathode can offer an energy density of 17.67 Wh kg−1 and a power density of 837 W kg−1. •The CC treatment achieve a larger specific surface area, more mesopores, better hydrophilicity and manganese oxide residue.•The residual manganese oxide on CC forms a heterojunction with NCP, resulting in NCP@Mn-CC provide a larger and more stable specific capacity at 20 °C and 0 °C.•DFT verifies that the hetero-junction brings better conductivity, faster electron transport kinetics, lower d-band center and lower OH- adsorption energy in NCP@Mn-CC.