Preparation of Single-Atom Ag-Decorated MnO2 Hollow Microspheres by Redox Etching Method for High-Performance Solid-State Asymmetric Supercapacitors

Single-atom Ag-decorated MnO2 hollow microspheres (Ag-MnO2 HMSs) with oxygen vacancies are successfully fabricated via a self-template strategy and redox etching method. The transmission electron microscopy images and nitrogen-sorption analyses reveal that the as-prepared Ag-MnO2 HMSs exhibit a porous peanut-like hollow structure with a large specific surface area (similar to 240 m(2) g(-1)). High-angle annular dark-field scanning transmission electron microscopy confirms that Ag species exist as isolated single atomic sites. The electrochemical experiments show that the 0.3% Ag-MnO, HMS electrode delivers high specific capacitance (297.5 F g(-1) at 0.3 A g(-1)), 66.3% higher than that of MnO2 HMSs (178.9 F g(-1) at 0.3 A g(-1)), and excellent cycling stability (88.1% capacitance retention after 9000 cycles). Moreover, the assembled Ag-MnO2 HMSs//AC solid-state asymmetric supercapacitor achieves a high operation voltage of 2.0 V and exhibits a high energy density of 15.9 W h kg(-1) at a power density of 250.3 W kg(-1). Besides, the device can successfully light up a light-emitting diode. The experimental results demonstrate that an appropriate amount of single-atom Ag in MnO2 HMSs promotes the formation of oxygen vacancies, which can improve the conductivity of MnO2 HMSs and the charge storage at Mn and O sites, thereby improving the capacitance performance of MnO2 HMSs.