Controllable Integration of Binary Functional Species Endows Directionally Optimized Kinetics for CoNiSe2-Based High-Performance Supercapacitors

Side reactions of water decomposition and capacitive reactions occur concomitantly in aqueous supercapacitors. To improve the energy density, integrated design modifications to address the impact of these two aspects on the reaction kinetics are theoretically effective. Herein, a two-step modification strategy for introducing binary functional species is designed to regulate the chemical environment and electronic structure of the metal active sites and further optimize the electrochemical kinetics comprehensively. For promoting the capacitive reactions, Ag nanoparticles were loaded to decrease the corresponding energy barriers. For suppressing the oxygen evolution side reaction, preintercalation of K+ ions was realized to increase the corresponding energy barriers. The assembled supercapacitor device shows an ultrahigh energy density of 143.2 Wh kg–1. Uniquely, in situ techniques, DFT calculations, and overpotential tests are combined to verify the suppression mechanism. This work provides valuable guidance for coordinating designs and studies on the electrochemical kinetics of transition-metal-based electrode materials.