MoO2 nanocrystals interconnected on mesocellular carbon foam as a powerful catalyst for vanadium redox flow battery

Abstract

To increase the performance of vanadium redox flow battery (VRFB), the rate of the reaction of the VO2+/VO2+ redox couple, known as the rate determining reaction, should be increased. To increase the rate of this reaction, molybdenum dioxide nanocrystals interconnected on mesocellular carbon foam (MoO2/MSU-F-C) are suggested as a new catalyst. Initially, the optimal amount of MoO2 embedded on MSU-FC is determined, whereas its activity, reversibility and charge-discharge behavior are investigated. The specific surface area, crystal structure, surface morphology and component analysis of the composite are also measured using BET, XRD, TEM, TGA, EELS and XPS. As a result, the MoO2/MSU-F-C results in a high peak current, small peak potential difference and high electron transfer rate constant, confirming that the composite is an excellent catalyst for the VO2+/VO2+ redox reaction. In terms of multiple charge-discharge tests, a VRFB single cell, including MoO2/MSU-F-C, induces high voltage and energy efficiencies with high specific capacity and a low capacity loss rate. These results are attributed to the intercalation of MoO2 by metal cations such as VO2+ and VO2+ and the existence of hydrophilic functional groups on the surface of MoO2/MSU-F-C. The intercalated MoO2 plays an excellent conductor role in promoting fast ionic and electron transfer and reducing overpotential, whereas the hydrophilic functional groups improve the VO2+/VO2+ redox reaction by lowering its activation energy.