Coupling amino acid L-Val with THF for superior hydrogen hydrate kinetics: Implication for hydrate-based hydrogen storage

Hydrogen (H2) emerges as a promising future clean energy for the low-carbon and sustainable future due to its high energy density and no pollutant or greenhouse gas emissions after combustion. The advantage of H2 storage in solid-hydrate form is the requirement of only moderate pressure and temperature compared to compressed H2 storage and the relatively lower energy consumption compared to liquid H2 storage. However, the slow kinetics of H2 hydrate formation is one major challenge to breakthrough for the large-scale development of hydrate-based H2 storage. In this study, we introduced an environmental-benign kinetic promoter (L-valine, L-Val) and coupled it with a thermodynamic promoter tetrahydrofuran (THF) using stoichiometric concentration (5.56 mol%) to enhance H2 hydrate formation kinetics. 0.3 wt% L-Val coupled with 5.56 mol% THF yields the optimal kinetic enhancement, and the maximum volumetric H2 uptake (VH2) is 29.83 +/- 1.22 volume of H2/volume of H2-THF hydrate (v /v). The reusability of L-Val is proved in five consecutive cycles of H2-THF hydrate formation and dissociation with consistently superior H2 uptake. Furthermore, it was identified that cooling rate (Rc) was an important factor determining the H2-THF hydrate formation kinetics. Lower Rc (0.05 K/min) shows an optimal promoting effect of VH2, which was 105.29% higher than that at higher Rc (0.3 K/min). A mechanism is proposed to explain the effect of Rc on H2-THF hydrate formation kinetics. The maximum gravimetric H2 (GH2) reported in our study reaches 0.26 +/- 0.01 wt%, which was superior in current literature below 15.0 MPa. The results provide insights into speeding up H2 uptake in solid-hydrate form and have potential applications in hydrate-based hydrogen storage.