Promoting hydrogen absorption of liquid organic hydrogen carriers by solid metal hydrides

Abstract

Reversible hydrogen absorption/desorption, the very fundamental property of metal hydrides (MHs), can be utilized to promote the hydrogen absorption of liquid organic hydrogen carriers (LOHCs). The hydrogen absorption of N-ethylcarbazole (NEC) catalyzed by a Ni/Al₂O₃ catalyst was extremely slow, while the process could be significantly enhanced by simply mixing yttrium trihydride (YH₃). The hydrogen absorption performance was similar to that on the noble metal catalyst Ru/Al₂O₃. Using isotope labelling, we demonstrated that the enhanced hydrogen absorption originated from the reversible hydrogen absorption and desorption property of YH₃: the atomic hydrogen in YH₃ can be transferred to the activated NEC molecules on Ni/Al₂O₃; subsequently, the hydrogen vacancy left in YH₃ is replenished by H₂. Inspired by this mechanism, we observed more general MH-promoted hydrogen absorption of LOHCs on transition metal catalysts. The combination of solid MHs and LOHCs with highly complementary merits provides a new strategy to develop high-performance hydrogen storage materials.