Highly active and porous M3S4 (M=Ni, Co) with enriched electroactive edge sites for hybrid supercapacitor with better power and energy delivery performance

Abstract

High electroactive areas, high electrochemical activity and low charge transfer resistance are crucial for high electrochemical performance, but their simultaneous realization is still a great challenge. In this work, porous M3S4 (M = Ni, Co) samples with different Ni to Co ratios have been synthesized by anion-exchange-based precursor conversion method. Wherein, the anions exchange causes outer motion and recombination of transition metal ions with S2−, giving rise to a porous microstructure enriched with electroactive edge sites. The synergy between Ni and Co results in superior electrochemical activity for high specific capacity performance. The M3S4 phase contributes to low charge transfer resistance for better rate performance. As a result, the Ni2CoS4 exhibits the best specific capacity of 768 C g−1 at 1 A g−1 and retains 59% of capacity value at 50 A g−1. In addition, the Ni2CoS4 is also used as the cathode materials to assemble hybrid supercapacitor (HSC) with reduced graphene oxide (RGO), and the resulting HSC device demonstrates both high energy and power densities of 34.3 Wh kg−1 at 0.66 kW kg−1 or 19.8 Wh kg−1 at 18.5 kW kg−1. Our work demonstrates that the electrochemical performance can be maximized by the microstructure designing in terms of edge sites of microstructure and crystal structure.