Reversible hydrogen desorption from LiBH4 catalyzed by graphene supported Pt nanoparticles

Abstract

The thermally induced de-/rehydrogenation performance of the graphene supported Pt nanoparticles (Pt/G) doped LiBH₄ was greatly improved even at very low catalyst content due to a synergetic effect of Pt addition and nanoconfinement in graphene. For the 5 wt% Pt/G doped LiBH₄ sample, the onset hydrogen desorption temperature is about 140 °C lower than that of the pure LiBH₄. With increasing loading of the Pt/G catalysts in LiBH₄ samples, the onset dehydrogenation temperature and the two main desorption peaks from LiBH₄ were found to decrease while the hydrogen release amount increased. About 17.8 wt% can be released from the 50 wt% Pt/G doped LiBH₄ sample below 500 °C. Moreover, variation of the equilibrium pressure (350–450 °C) indicates that the dehydrogenation enthalpy is reduced from 74 kJ mol⁻¹ H₂ for the pure LiBH₄ to ca. 48 kJ mol⁻¹ H₂ for the 10 wt% Pt/G doped LiBH₄, showing improved thermodynamic properties. More importantly, a reversible capacity of ca. 8.1 wt% in the 30th de-/rehydrogenation cycle was achieved under 3 MPa H₂ at 400 °C for 10 h, indicating that the Pt/G catalysts play a crucial role in the improvement of the hydrogen uptake reversibility of LiBH₄ at lower temperature and pressure conditions. Especially, LiBH₄ was reformed and a new product, Li₂B₁₀H₁₀, was detected after the rehydrogenation process.