The Dopamine Assisted Synthesis of MoO₃/Carbon Electrodes With Enhanced Capacitance in Aqueous Electrolyte

A capacitance increase phenomenon is observed for MoO₃ electrodes synthesized via a sol-gel process in the presence of dopamine hydrochloride (Dopa HCl) as compared to α-MoO₃ electrodes in 5M ZnCl₂ aqueous electrolyte. The synthesis approach is based on a hydrogen peroxide-initiated sol-gel reaction to which the Dopa HCl is added. The powder precursor (Dopa)_xMoO_y, is isolated from the metastable gel using freeze-drying. Hydrothermal treatment (HT) of the precursor results in the formation of MoO₃ accompanied by carbonization of the organic molecules; designated as HT-MoO₃/C. HT of the precipitate formed in the absence of dopamine in the reaction produced α-MoO₃, which was used as a reference material in this study (α-MoO₃-ref). Scanning electron microscopy (SEM) images show a nanobelt morphology for both HT-MoO₃/C and α-MoO₃-ref powders, but with distinct differences in the shape of the nanobelts. The presence of carbonaceous content in the structure of HT-MoO₃/C is confirmed by FTIR and Raman spectroscopy measurements. X-ray diffraction (XRD) and Rietveld refinement analysis demonstrate the presence of α-MoO₃ and h-MoO₃ phases in the structure of HT-MoO₃/C. The increased specific capacitance delivered by the HT-MoO₃/C electrode as compared to the α-MoO₃-ref electrode in 5M ZnCl₂ electrolyte in a -0.25-0.70 V vs. Ag/AgCl potential window triggered a more detailed study in an expanded potential window. In the 5M ZnCl₂ electrolyte at a scan rate of 2 mV s^-1, the HT-MoO₃/C electrode shows a second cycle capacitance of 347.6 F g^-1. The higher electrochemical performance of the HT-MoO₃/C electrode can be attributed to the presence of carbon in its structure, which can facilitate electron transport. Our study provides a new route for further development of metal oxides for energy storage applications.