Epitaxial grown self-supporting NiSe/Ni3S2/Ni12P5 vertical nanofiber arrays on Ni foam for high performance supercapacitor: Matched exposed facets and re-distribution of electron density

Abstract

NiSe, Ni3S2 and NiSe/Ni3S2 heterostructures with different Se/S ratios were grown on Ni foam (NF) via one-step solvothermal reaction, and they exhibited different morphologies and electrochemical behaviors. Among them, NiSe/Ni3S2/NF-1:1 heterojunction (Se/S molar ratio = 1:1) showed the best electrochemical performance, which was associated with its unique morphology of self-supporting nanofiber arrays vertically grown on Ni foam. The epitaxial growth mechanism of the free-standing NiSe/Ni3S2 nanofibers was investigated and it is related to their matched d spacings. After further phosphorization treatment, Ni12P5 nanoparticles can grow on the surface of NiSe/Ni3S2 nanofibers due to their matched exposed facets. The obtained NiSe/Ni3S2/Ni12P5/NF-1:1 hierarchical nanostructure with a large mass-loading of 8.5 mg cm−2 can provide an ultrahigh areal capacity of 2.04 mA h cm−2 at 10 mA cm−2 (272 mA h g−1 at 1 A g−1) with excellent cycling stability. In a hybrid supercapacitor (HSC), 86% of capacity was retained after 5000 charge/discharge cycles at 140 mA cm−2. The outstanding electrochemical behavior of NiSe/Ni3S2/Ni12P5/NF-1:1 is probably associated with the re-distribution of electron densities within the heterostructure, and the good electron conductivity of the protective Ni12P5 nanoparticles on the surface of nanofibers. Furthermore, the phosphorization mechanism of the nickel chalcogenide/NF was primarily explored.