Influences of Background Temperature on Methane Cracking Process in a Low-Pressure RF-ICP Plasma System

This work presents an experimental study on the role of substrate background temperature on the methane cracking process in a low-pressure RF-ICP plasma system. By varying the substrate background temperature from 23 °C to 263 °C, the effects on methane conversion efficiency, hydrogen production, and the structural evolution of carbon deposits are evaluated. Plasma properties and reaction dynamics are characterized using Optical Emission Spectroscopy (OES), Residual Gas Analyzer (RGA) or mass spectrometry, and X-ray Photoelectron Spectroscopy (XPS) measurement techniques. Notably, experiments are performed using high-purity methane to specifically isolate substrate-temperature effects. The results obtained show that electron density increases with background temperature up to about 80 °C, after which it saturates. Besides, methane conversion rate improves modestly with rising temperature. However, both the hydrogen and ethylene concentrations in the plasma decrease significantly. This indicates a temperature-induced shift in selectivity toward carbon-rich products. Furthermore, XPS analysis shows a clear structural transition in the carbon films which from hydrogenated amorphous carbon at low temperatures to increasingly graphitic and less oxidized carbon at higher temperatures. Thus, these findings confirm that while higher substrate background temperatures can enhance CH₄ activation and promote graphitic carbon formation, they simultaneously reduce the hydrogen yield. Hence, the temperature control alone in this low-pressure RF-ICP reactor is an ineffective strategy for optimizing hydrogen production under the studied conditions, though it may benefit applications focused on carbon material synthesis.