Heterostructured NiSe2/CoSe2 hollow microspheres as battery-type cathode for hybrid supercapacitors: Electrochemical kinetics and energy storage mechanism

Constructing heterostructures can adjust the electronic structure and cause the interfacial charge redistribution to promote the reaction kinetics. Besides, metal selenides as emerging battery-type cathode materials for hybrid supercapacitors (HSCs) have recently attracted increasing interests. However, the reasonable design and fabrication of heterostructured bimetallic selenides hollow microspheres, especially the theoretical explanation of their electrochemical reaction processes and energy storage mechanisms, are scarcely explored. Herein, the heterostructured NiSe2/CoSe2 hollow microspheres are prepared via one-pot hydrothermal treatment and their energy storage mechanisms are proved with experimental and theoretical analyses. Meanwhile, the charge redistribution at the heterogeneous phase boundaries is authenticated by density functional theory (DFT) calculations. Benefiting from the abundant heterogeneous phase interfaces, unique hollow heterostructure and synergistic effect, the heterostructured NiSe2/CoSe2 hollow microspheres exhibit expected electrochemical properties, particularly admirable rate capability. Moreover, a HSC device is assembled based on the hetero-structured NiSe2/CoSe2 hollow microspheres cathode, displaying a superior energy density (53.7 Wh kg(-1)), an extremely high power density (26.1 kW kg(-1)) and a preeminent cycle stability. This work reveals the energy storage mechanisms of selenide and the charge redistribution of heterojunctions, which can provide a meaningful reference for constructing high-rate heterobimetallic selenide hollow microspheres with abundant phase boundaries.