Structural diversity and hydrogen storage properties in the system K-Si-H.

KSiH 3 exhibits 4.1 wt% experimental hydrogen storage capacity and shows reversibility under moderate conditions, which provides fresh impetus to the search for other complex hydrides in the K-Si-H system. Here, we reproduce the stable Fm 3̄ m phase of K 2 SiH 6 and uncover two denser phases, space groups P 3̄ m 1 and P 6 3 mc at ambient pressure, by means of first-principles structure searches. We note that P 3̄ m 1-K 2 SiH 6 has a high hydrogen content of 5.4 wt% and a volumetric density of 88.3 g L -1 . Further calculations suggest a favorable dehydrogenation temperature T des of -20.1/55.8 °C with decomposition into KSi + K + H 2 . The higher hydrogen density and appropriate dehydrogenation temperature indicate that K 2 SiH 6 is a promising hydrogen storage material, and our results provide helpful and clear guidance for further experimental studies. We found three further potential hydrogen storage materials stable at high pressure: K 2 SiH 8 , KSiH 7 and KSiH 8 . These results suggest the need for further investigations into hydrogen storage materials among such ternary hydrides at high pressure.