Chemical hydrogen storage of carbon material

Abstract

Hydrogen is chemically absorbed into graphite by mechanical ball-milling process under H2, and its hydrogen capacity reaches to about 3.6 mass%. Noteworthy, when iron (Fe) mingles with graphite from steel balls during the milling process, the hydrogen capacity is drastically enhanced. In this work, the hydrogen absorption and desorption properties of the hydrogenated graphite with and without Fe were investigated. The hydrogen capacity of graphite including Fe was about 6 mass% (H/C), suggesting that the excess hydrogen of 2.4 mass% would originate in the Fe related phase. It is clarified by spectroscopic studies that the mingled iron formed a non-stoichiometric iron-carbon (Fe-C) phase as hydrogen absorption site. Assuming that the Fe/C ratio is 1, its hydrogen capacity is estimated to be H/(Fe-C-H) > 10 mass%, which is a larger value than that of the conventional hydrogen storage materials. The hydrogen absorbed in the C-Fe phase is released at 450°C with the transformation of the C-Fe Dhase to well-ordered carbides such as Fe 3C. Therefore, if the C-Fe Dhase could be synthesized independentlv. it should be recocr-fhized as a nrnmisincr hydro