Sulfiding and phosphating the layered double hydroxide/metal-organic-framework subsequently to synthesize novel CoMnOxSyPz nanosheets with high-rate and high-areal supercapacitor performance

Abstract

Metal-organic frameworks (MOFs) derived porous nanosheets have sparked widespread interest due to their porosity structure and component tunability, making them promising candidates for energy-storage applications. However, the poor charge-transfer capability limits their supercapacitor capability. Here, we successfully synthesize CoMnO_xS_yP_z porous nanosheet electrodes enriched with oxygen vacancies on the nickel-foam substrate using MOFs as self-sacrificial templates by sulfiding and phosphating. The resulting P-doping and abundant oxygen-vacancy-induced active sites enhance the charge-transfer capability significantly, as indicated by the low charge-transfer impedance ∼0.11 Ω, much lower than that of CoMn-ZIF and CoMnO_xS_y. Consequently, CoMnO_xS_yP_z electrode exhibits a high areal capacitance (9.83 F cm⁻² at 8 mA cm⁻²), 5.85 and 1.48 times that in CoMn-ZIF and CoMnO_xS_y, respectively, with a satisfactory rate of 71.7 % at 50 mA cm⁻². Notably, the asymmetric supercapacitor (ASC) achieves the highest energy density (0.95 mWh) with a power density of 3.2 mW cm⁻², and the maximum power density (40 mW cm⁻²) with an energy density of 0.57 mWh⋅cm⁻². Furthermore, excellent stability is realized in ASC, up to 90 % during 7000 cycles at 16 mA cm⁻². Our results reveal that introducing P, S, and O vacancies by sulfiding and phosphatizing could be an effective strategy to improve the supercapacitor performance of the MOF-derived nanosheet.