Clean preparation of mixed trivalent and quadrivalent vanadium electrolyte for vanadium redox flow batteries by catalytic reduction with hydrogen

The vanadium redox flow battery (VRFB) is a promising technology for large-scale stationary energy storage systems. However, the high preparation cost of mixed valent vanadium electrolyte hinders the large-scale commercial application of VRFB. In this work, a simple, green and low-cost method is proposed to prepare the mixed valent vanadium electrolyte for VRFB. The clean hydrogen is chosen as the reducing agent to obtain trivalent vanadium ions from quadrivalent vanadium ions. The Pt/C material is used as the catalyst to accelerate the reduction rate at atmospheric pressure. The impurity-free mixed valent vanadium electrolyte, with a mean valence number of 3.5, prepared by the catalytic reduction process exhibits excellent battery performance with CE of 93% and EE of 85%. Furthermore, a catalytic reactor using Pt/C decorated graphite felt is designed and used to continuously produce the mixed valent vanadium electrolyte. According to the result of simple cost analysis, the proposed catalytic hydrogen reduction process can reduce theoretically the manufacturing cost by approximately 22.6% compared with the present industrial electrolytic process. As a consequence, the simple, clean and low-cost manufacture method of the mixed valent vanadium electrolyte exhibits remarkable competitiveness and promising potential for the practical production application of VRFB.