The electrochemical performance of MoO2@FeMoO4 composites derived from PMo12@MIL-101(Fe) for supercapacitors

The synergistic coupling of different metal species endows mixed transition metal oxides (MTMOs) as electrode materials for supercapacitors with multiple redox reaction pathways and enhances the electronic conductivity. In this study, three MoO 2 @FeMoO 4 electrode materials were derived from the precursor PMo 12 @MIL-101(Fe) by pyrolysis at 600 °C, 700 °C, and 800 °C under an O 2 atmosphere. The precursor was composed of polyoxomolybdate (H 3 PMo 12 O 40 , PMo 12 ) and Fe-based metal-organic frameworks (MOFs) MIL-101(Fe). The structural characteristics of the three obtained MoO 2 @FeMoO 4 composites were characterized by XRD, XPS, SEM, and N 2 adsorption measurement. Then, the effects of the pyrolysis preparation temperature for the MoO 2 @FeMoO 4 composites on the energy storage performance of the supercapacitor electrode were evaluated by cyclic voltammetry (CV) and galvanostatic charge/discharge tests. Among three electrodes, the specific capacitance of 339.6 F g −1 of the obtained MoO 2 @FeMoO 4 (700 °C) electrode was the highest compared to 291.2 F g −1 of MoO 2 @FeMoO 4 (600 °C) and 209.7 F g −1 of MoO 2 @FeMoO 4 (800 °C) at a current density of 0.5 A g −1 in 1.0 M NaOH electrolyte. As a result, the different pyrolysis preparation temperatures can alter the atomic microelectronic state and geometric configuration of the MoO 2 @FeMoO 4 , which can construct a high-density Fe–Mo bimetallic multicatalytic active site, thus affecting the activity of the composites. The excellent pseudo-supercapacitance response of the MoO 2 @FeMoO 4 (700 °C) electrode can be ascribed to its larger S BET and greater number of voids, which can generate more Fe–Mo bimetallic active sites and facilitate the electrolyte diffusion, indicating high energy conversion efficiency for potential application in supercapacitors.