Assessment of coal and graphite electrolysis on carbon fiber electrodes

Novel carbon fiber electrodes prepared by plating of noble metals (Pt, Rh, Pt–Rh, Pt–Ir, Pt–Ir–Rh) on carbon fibers were evaluated for the electrolysis of coal and graphite under galvanostatic conditions. Graphite was used as a baseline to compare its performance with coal. The electrodes were tested on a sandwich configuration coal electrolytic cell (CEC) designed to reduce the ohmic resistance of the system. Among Pt, Rh, Pt–Rh, Pt–Ir, and Pt–Ir–Rh electrodes with the same loading (5 mg cm−1 of fiber bundle), Pt and Pt–Ir seemed to produce the highest CO2 Faradaic efficiency. Factorial design was used to determine the effect of loading and composition on the electrooxidation of coal and graphite to CO2. The effect of abrasion on the coating of the electrodes was determined by performing weight change analysis. Most electrodes were not significantly affected by abrasive effect (about 2% weight loss); however, Pt and Pt–Rh electrodes were significantly affected by erosion (above 10% weight loss). The presence of graphite had a positive effect on the electrooxidation of coal to CO2 in a graphite–coal slurry mixture. The energy consumption for the production of hydrogen from the electrolysis of coal was about 22 Wh g−1 of H2 for all the electrodes tested (50% lower than that for hydrogen production by electrolysis of water under similar operating conditions). This fact shows that coal electrolysis is a competitive method for in situ hydrogen generation.