Modulation Mechanism of CO₂ Fixation and Tungsten Carbide Deposition during Molten Salt Electrolysis by Li₂O Addition

This study realized the electrolytic preparation of tungsten carbide powders using Li2O to modulate carbon dioxide capture by molten salt. The addition of Li2O to NaCl-KCl-10 wt %Na2WO4 molten salt can effectively modulate the molten salt system to capture CO2 and prepare tungsten carbide products by electrolytic conversion. The electrochemical impedance spectroscopy of the molten salt system reveals that the addition of Li2O changes the electrolysis process from charge transfer control to mixed charge transfer and diffusion control. The test on the carbon content of the molten salt during the electrolysis process revealed that Li2O could increase the carbon content of the molten salt from 0.0076 to 0.0093 wt % and keep it above 0.0078 wt % throughout the electrolysis process. The results of electrochemical tests indicated that the addition of Li2O enabled the cathodic deposition rate to be increased by nearly 10 times. A cathodic deposition potential was shifted about 0.58 V in the positive direction. The cathodic deposition process can be divided into three stages: carbon deposition, tungsten deposition, and tungsten carbide deposition. Prioritized deposition of carbon promotes the tungsten–carbon codeposition reaction. This provides a new green production idea for the preparation of tungsten carbide by capturing CO2 conversion.