Biopolymers as three-dimensional structural binders for nickel-cobalt sulfide supercapacitor electrodes

Ion diffusion and electron transfer are hindered by commonly used hydrophobic binders, which directly affect the electrochemical performance of the electrodes. Hydrophilic binders are selected to efficaciously solve the problem of relatively low actual specific capacitance and rate performance in the field of nickel cobalt sulfide electrode materials. In the paper, RuCoNiS electrodes were prepared using polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), xanthan gum (XG), and chitosan (CS) as binders. The surface wettability, morphological structure, specific surface area, and electrochemical performance of electrodes with different binders were analyzed by XRD, SEM, BET, CV, GCD, and EIS, etc. It's shown that the synthesis of CoNi₂S is confirmed by XRD. The XPS results verify the existence of RuO₂ and Ni²⁺/Ni³⁺ and Co²⁺/Co³⁺ redox couples. A cross-linked network structure is formed on the surface of the RuCoNiS by CS. The CS-RuCoNiS electrode has the largest specific surface area and microporosity. Ion migration in the electrolyte is facilitated by the excellent wettability of the CS-RuCoNiS electrode. The CS-RuCoNiS electrode reachs 1193.52 F g^-1, which is 1.74 times higher than that of the PTFE-RuCoNiS electrode at 1 A g^-1. The CS binder with its three-dimensional structure has the highest ionic conductivity of 2.29 × 10^-4 S cm^-1, a lower R_ct, good cycling stability with a capacity retention of 84.3 % after 5000 cycles at 200 mV s^-1, and excellent rate performance of 85.6 %. It can provide a practical application in supercapacitors.