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