A new nickel coordination polymer electrode material for hybrid supercapacitors

Battery-type electrode materials store charge through chemical reactions, leading to low power densities and rendering it difficult to reach the performance levels associated with capacitors. This study introduces a coordination polymer electrode material for hybrid supercapacitors, specifically, poly[[tri-μ-ethanolato-di-μ₃-sulfido-hexakis(μ₄-2-sulfidobenzoato)dinickel(II)tetranickel(III)dipotassium(I)[potassium(I)/sodium(I)(0.60/0.40)]] quaterhydrate], {[Ni^III₄Ni^II₂K_2.60Na_0.40(C₂H₅O)₃(C₇H₄O₂S)₆S₂]·0.25H₂O}_n or Ni-mba-K(Na), where H₂mba is 2-mercaptobenzoic acid, (1). As a hybrid capacitor electrode material, Ni-mba-K(Na) exhibits the characteristics of battery-type electrode materials but demonstrates a capacitor-level power density and cycling stability. The microstructure, element composition, phase structure and thermodynamic stability of Ni-mba-K(Na) are characterized through techniques such as crystal structure determination and X-ray photoelectron spectroscopy. Single-crystal X-ray diffraction shows that compound (1) consists of a hexanuclear nickel cluster, two mononuclear K nodes and a mononuclear K_0.60/Na_0.40 shared node, resulting in the formation of a complex covalent three-dimensional network. Due to this novel structure, Ni-mba-K(Na) exhibits supercapacitor performance that combines high energy density and high power density.