Carbon deposit growth on the electrodes of a plasma converter in the generation of hydrogen from methane

This paper investigated the carbon deposit growth on the electrodes of a pulsed plasma converter due to spark discharging. The experimental parameters included the O/C ratio (molar ratio of O2/CH4) and the system operating time. An scanning electron microscope (SEM) and a micro Raman & micro PL spectroscope were used for analysing the microstructure of the carbon deposit, and a gas chromatographer was used for the analysis of produced gases.The experiments showed that carbon deposit was found to accumulate fast under a low O/C ratio of 0.2. From the SEM photographs of both the anode and cathode, the carbon deposit comprised snow-like white carbon layers for the O/C ratios tested, and translucent diamond shaped particles appeared on the cathode at an O/C ratio of 0.5. From the analysis with the micro Raman & micro PL spectroscopy, the snow-like white layers were classified as either D-band disordered graphite or G-band graphite structures while the diamond-like particles could be G-band microcrystalline graphite or even diamond. It was shown that from the analysis of gas chromatographer, the case with an O/C ratio of 0.2 resulted in a high hydrogen concentration, the electrodes were more prone to carbon deposition, causing the hydrogen concentration to rapidly decrease. While with an O/C ratio of 0.5, the hydrogen concentration was almost independent of the system operating time.