A Molecular Dynamics Simulation Study on the Diffusion Coefficients of the ^•OH, ^•H, and ^•HO₂ Free Radicals Related in the Hydrogen Production Process in Supercritical Water

Supercritical water (SCW) gasification is a clean and efficient utilization method of coal or biomass for hydrogen generation. However, the intrinsic mechanisms in this complex process are still unclear, in which radical diffusion studies are essential. For a severe SCW environment, relevant experiments are difficult. From this perspective, molecular dynamics (MD) simulations have become an efficient and convenient approach to investigate the process in SCW. Therefore, free radical diffusion in a SCW environment was studied by means of MD simulations in this study. And, the effects of temperature and pressure on the free radical diffusion coefficients were investigated in this work. The results illustrated that a higher temperature in a SCW environment can enhance the diffusion of free radicals in this study, especially for the ^•H radical, therefore facilitating and promoting reactions for hydrogen production. Lower pressure could promote the diffusion coefficients of free radicals. This work is expected to help understand the diffusion properties of free radicals in SCW better and may provide theoretical support for accomplishing efficient complete coal gasification for hydrogen production.