Molecular Design of Mesoporous NiCo2O4 and NiCo2S4 with Sub‐Micrometer‐Polyhedron Architectures for Efficient Pseudocapacitive Energy Storage

Abstract

Spinel‐type NiCo2O4 (NCO) and NiCo2S4 (NCS) polyhedron architectures with sizes of 500–600 nm and rich mesopores with diameters of 1–2 nm are prepared facilely by the molecular design of Ni and Co into polyhedron‐shaped zeolitic imidazolate frameworks as solid precursors. Both as‐prepared NCO and NCS nanostructures exhibit excellent pseudocapacitance and stability as electrodes in supercapacitors. In particular, the exchange of O2− in the lattice of NCO with S2− obviously improves the electrochemical performance. NCS shows a highly attractive capacitance of 1296 F g−1 at a current density of 1 A g−1, ultrahigh rate capability with 93.2% capacitance retention at 10 A g−1, and excellent cycling stability with a capacitance retention of 94.5% after cycling at 1 A g−1 for 6000 times. The asymmetric supercapacitor with an NCS negative electrode and an active carbon positive electrode delivers a very attractive energy density of 44.8 Wh kg−1 at power density 794.5 W kg−1, and a favorable energy density of 37.7 Wh kg−1 is still achieved at a high power density of 7981.1 W kg−1. The specific mesoporous polyhedron architecture contributes significantly to the outstanding electrochemical performances of both NCO and NCS for capacitive energy storage.