Vanadium Redox Flow Batteries Fabricated by 3D Printing and Employing Recycled Vanadium Collected from Ammonia Slag

In order to realize sustainable renewable energy supply, large-scale energy storage system is needed to overcome the problem of intermittency of power generation. Vanadium redox flow battery (VRFB) presents the most viable solution but faces the problem of high material cost. In this study, we have established a cost-effective process to prepare vanadium electrolyte for VRFB from an untouched industrial waste, ammonia slag, by pH control under atmospheric condition (< 95°C). The extracted solution changed color during electrolytic reduction as yellow, blue, dark green and purple, matched with the colors of V 5+ , V 4+ , V 3+ , and V 2+ , respectively, indicating accurate change of the valences without forming precipitates. Electrolyte prepared from the recycled vanadium showed almost the same charging/discharging performances as the one prepared from commercial V 2 O 5 reagent battery tests during the first several cycles, but degraded rapidly after 16 cycles, caused by impurities that deactivate the negative electrode for the reduction of V 3+ to V 2+ . The miniature VRFB prototype built by employing 3D printing technique showed a much higher performance than the H-cell, indicating the flow cell configuration could help to push up the diffusion limit of vanadium redox by flowing the electrolyte solution through the electrodes, as well as reducing IR loss and water splitting to increase the efficiency.