Hierarchical mesoporous selenium@bimetallic selenide quadrilateral nanosheet arrays for advanced flexible asymmetric supercapacitors

Abstract

Metal selenides are promising candidates as electrode materials for advanced supercapacitors. However, their performance is still limited due to the insufficient utilization of active materials and the low porosity of electrodes. Herein, a facile strategy is reported for in situ growth of hierarchical mesoporous selenium@bimetallic selenide quadrilateral nanosheet arrays on various conductive substrates using two-dimensional bimetal porphyrin paddlewheel framework (MCo–TCPP, TCPP = tetrakis(4-carboxyphenyl)porphyrin; M = Ni, Zn) nanosheets as templates. The as-obtained Se@(NiCo)Se₂ sample provides a suitable electrolyte environment to promote fast faradaic reactions, which endows the carbon cloth-supported electrode with a high specific capacity of 240 mA h g⁻¹ at 2 A g⁻¹, high rate capability, and remarkable cycling stability (83.2% after 5000 cycles at 20 A g⁻¹), superior to those of most well-known CoSe₂-and MOF-based systems. The high availability of electrochemically active sites/interfaces along with the strong intercomponent synergy of (NiCo)Se₂, selenium, and the carbon skeleton enable the fast charge transfer kinetics required for superior charge-storage capabilities. Density functional theory simulations demonstrate that doping Ni in (NiCo)Se₂ could reduce the adsorption free energy of OH− and regulate the electrical properties. A unique Se@(NiCo)Se₂//AC flexible asymmetric supercapacitor device delivers high specific capacitance, negligible capacitance decay, excellent coulombic efficiency, and outstanding energy and power densities (49.4 W h kg⁻¹@787.3 W kg⁻¹ and 13 882.4 W kg⁻¹@23.6 W h kg⁻¹). This study also provides a neoteric perspective on the construction of mesoporous selenium@bimetallic selenide nanoarrays for energy-related applications.