Green preparation of vanadium carbide through one-step molten salt electrolysis

Vanadium carbide (VC) as excellent ceramic and functional material is usually prepared by carbothermal reduction of V₂O₅ which must be extracted from a typical V slag by complex processes. Pollutants, such as ammonia-nitrogen wastewater, NH₃ and CO₂ are inevitably discharged. A novel and green method for VC preparation was proposed by one-step co-electrolysis of soluble NaVO₃ and CO₂ in molten salt. It was found that VC with high purity was easily obtained by reducing electrolysis temperature and CO₂ flow rate to 600 °C and 10 mL min^?1 at 3.0 V. Besides VC with particles and layered stacking structure in products, a small amount of carbon and oxygen elements existed. The atomic percentage contents of C, V, and O elements in VC were about 50.0%, 44.5% and 3.8%, respectively. During electrolysis, CO₃^2? and VO₃^? was reduced at about ?0.55 V (vs. Ag/AgCl) and ?1.38 V (vs. Ag/AgCl), respectively. CO₃^2? ions were more easily reduced than VO₃^?, and was firstly reduced to CO₂^2? and then converted to C. Then, VC was prepared by two routes from CO₂ and NaVO₃. One route is that VO₃^? ions are firstly electroreduced to VO₂^? ions and then are further electroreduced to VC with C. Another route is that VO₃^? ions are electroreduced to V which in-situ reacted with C to VC. Both VO₃^? and CO₃^2? ions are electroreduced by two-step process. In final, VC is in-situ deposited on cathode. It provides a novel and green way to prepare VC and also achieves the high value-added utilization of vanadium slag and CO₂.