FeSe and Fe3Se4 encapsulated in mesoporous carbon for flexible solid-state supercapacitor

Metal selenides have been developed as promising alternatives of metal oxides in energy storage field due to their high conductivity and low bandgap. However, the synthesis of selenides usually suffers from the low melting point and strong volatility of selenium at temperatures higher than 217 ℃. Herein, a facile strategy was developed to prepare iron selenides using a template of Se-contained MOF gel, which could in situ immobilize Se powder due to the fast gelation process, resulting a porous, uniform and tight precursor. By adjusting the mole ratio of Fe and Se in the precursor, [email protected] and Fe3Se4@C were controllably synthesized with rich mesopores and excellent carbon-encapsulation structure. The kinetics analysis indicates that these unique structures are beneficial for improving electrode kinetics, charge/ion-transfer resistance and electrochemical stability. [email protected] and Fe3Se4@C exhibit significant capacitances (611.0F g−1 and 569.0F g−1 at 1 A g−1), and excellent cycling properties (94.22% and 93.28% retention after 2000 charge–discharge cycles at 5 A g−1). When estimated in practical application, the flexible solid-state symmetric supercapacitor of [email protected]//Fe3Se4@C delivers a high Csp of 160.1F g−1, the superior energy density of 32.1 W h kg−1 and a high specific power density of 5998 W kg−1 with 89.5% capacitance retention after 5000 cycles, and the outstanding flexibility.