On the role of dihydrogen in the co-intercalation reactions into graphite of potassium and chalcogen

Abstract The influence of dihydrogen gas on the reactions between graphite and liquid potassium containing a very small amount of a chalcogen (O, S, Se, Te) was studied. The reactions were carried out under a pure argon atmosphere in a stainless steel reactor, between 400 and 600°C. Controlled amounts of dihydrogen gas can be added in this reactor. When dihydrogen is strictly absent, the co-intercalation of potassium and chalcogen does not take place at 400°C: only potassium intercalates, leading to the KC8 binary compound. The same experiments carried out with controlled amounts of dihydrogen at the same temperature lead to various ternary compounds with oxygen, sulphur, selenium and tellurium. However, at 600°C, and strictly without dihydrogen, co-intercalation occurs, but only for S, Se and Te, allowing the preparation of new well-defined ternary graphite intercalation compounds. The co-intercalation of potassium and oxygen is possible only in the presence of dihydrogen, at any temperature.