Fe3+-mediated coal-assisted water electrolysis for hydrogen production: Roles of mineral matter and oxygen-containing functional groups in coal

Abstract Fe3+-mediated coal-assisted water electrolysis (CAWE) for hydrogen production is an effective way to utilize coal resources. Low-rank coal, which has a high abundance, is rich in mineral matter and oxygen-containing functional groups (OGs). To promote the development of Fe3+-mediated CAWE of low-rank coal, the roles of mineral matter and OGs in Fe3+-mediated CAWE are investigated in this study. Besides, to understand the reaction mechanism of coal electrolysis and provide guidance for the effective use of electrolyzed coal, the microstructural, surface structure, and microcrystalline changes of the coal are analyzed via Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction, respectively. The results show that minerals and OGs have a positive and negative influence on the Fe3+-mediated CAWE, respectively. The hydrogen yields of demineralized coal and oxidized coal are 33.15% and 68.47% lower than that of raw coal owing to the influence of minerals and OGs, respectively. After electrolysis, the degree of aromatic ring condensation increases whereas coal rank decreases; the content of -OH on the coal surface increases and the composition of organic sulfur on the coal surface is altered; and the crystallite diameter of the coal changes.