Experimental study on correlation between volatile matter of low-rank coal and hydrogen production performance of coal water slurry electrolysis

Although low-rank coal is abundant, its quality is poor, and traditional utilization methods such as combustion, gasification, and pyrolysis have low thermal efficiency, significant environmental pollution, and severe resource waste, making it difficult to meet the “dual carbon” goals. The coal water slurry electrolysis technology not only reduces the energy consumption for hydrogen production from water electrolysis but also enables multi-level energy conversion of coal, making it a highly promising new approach for efficient and green coal utilization. This study focuses on three typical low-rank coals, systematically comparing their hydrogen production performance through electrochemical experiments combined with a series of characterization methods, including FTIR, BET, and SEM. The results indicate that higher volatile matter content in coal corresponds to better electrolysis performance, closely related to the reactivity of the structures associated with the volatiles. Further analysis reveals that the main chemical and porous structures contributing to volatile matter significantly influence electrolysis performance. Specifically, the chemical structures include aromatic structures, aliphatic structures, and oxygen-containing functional groups. Lower aromatic ring condensation leads to reduced structural stability of coal, facilitating electrolysis, higher relative content of aliphatic hydrogen enhances the hydrophilicity of coal, promoting its participation in the electrolyte, the oxygen-containing functional groups increase to varying degrees after electrolysis; and a looser porous structure enables easier contact between Fe³⁺ and the internal surfaces of coal particles, resulting in increased current density and enhanced reactivity. Additionally, after electrolysis, the coal shows increased porosity, larger average pore size, greater surface roughness, and more surface debris. Finally, the effects of temperature and stirring speed on the electrolysis performance of coal water slurry were investigated, showing that increasing temperature and stirring speed lead to higher current density, with limited increases beyond a stirring speed of 400 r/min. This research aims to provide theoretical support and technical guidance for developing efficient and clean coal utilization technologies and low-cost hydrogen production via water electrolysis.