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Electrochemical Synthesis and Thermal Properties of Graphite Bisulfate

机译：硫酸氢石墨的电化学合成及热性能

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The electrochemical synthesis of graphite bisulfate in 94% H_2SO_4 is studied in galvanostatic (I = 10 μA) and potentiostatic modes. The formation potentials and detailed chemical formulas of stage Ⅰ-Ⅴ graphite bisulfate are determined. It is found that, within the stability range of a given stage, the molar ratio of intercalated H_2SO_4 to HSO_4~- varies slightly. This variation is more significant at larger stage indices. In a potentiostatic mode, ordered stage Ⅰ-Ⅴ graphite bisulfate can be synthesized, with reproducible chemical and phase compositions. It is shown based on rough estimates of the diffusion coefficient D of sulfuric acid in the graphite host that the intercalate layer is indeed in a "quasi-liquid" state: the estimated D is substantially lower than typical diffusivities in solids. The thermal properties of stage Ⅰ-Ⅴ graphite bisulfate are studied systematically for the first time. It is found that, independent of the stage index, graphite bisulfate decomposition results in an unresolved endothermic doublet in the range 170-340℃. Heating to 170℃ leads to partial decomposition of the graphite intercalation compounds, accompanied by an increase in stage index by unity. As a result, sulfuric acid is present in two states: free (deintercalated) and bound (in graphite bisulfate). The lower temperature endotherm in the unresolved doublet is due to the vaporization of free H_2SO_4, and the higher temperature endot-herm is due to the deintercalation and vaporization of bound sulfuric acid. The estimated heat of deintercalation from stage Ⅰ-Ⅴ graphite bisulfate (2.9-0.5 kJ/mol C) decreases steadily with increasing stage index.
机译：以恒电流（I = 10μA）和恒电位模式研究了在94％H_2SO_4中电化学合成硫酸氢石墨。确定了Ⅰ-Ⅴ级硫酸氢石墨的形成势和详细的化学式。发现在给定阶段的稳定性范围内，插入的H_2SO_4与HSO_4〜-的摩尔比略有变化。在较大的阶段索引处，此变化更为明显。在恒电位模式下，可以合成有序的Ⅰ-Ⅴ级硫酸氢石墨，具有可重复的化学和相组成。根据对石墨主体中硫酸扩散系数D的粗略估计，可以看出，插层确实处于“准液体”状态：估计的D明显低于典型的固体扩散率。首次系统地研究了Ⅰ-Ⅴ级硫酸氢石墨的热性能。结果发现，与阶段指数无关，硫酸氢根石墨的分解会导致170-340℃范围内未解析的吸热双峰。加热到170℃会导致石墨插层化合物的部分分解，并伴随着阶段指数的整体增加。结果，硫酸以两种状态存在：游离（脱嵌）和结合（在硫酸氢石墨中）。未分解的双峰中较低的吸热是由于游离H_2SO_4的汽化，而较高的吸热层是由于结合的硫酸的脱嵌和汽化。 Ⅰ-Ⅴ级硫酸氢石墨脱嵌的估计热量（2.9-0.5 kJ / mol C）随着阶段指数的增加而稳定降低。

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