ZIF-67 derived Co nanoparticles on ZIF-Derived carbon for hydrogen spillover and storage

Abstract

Hydrogen spillover involves the dissociation of H2 on transition metal nanoparticles and further atomic hydrogen surface migration on catalyst supports. Hence, the spillover phenomenon has been reported in applications of heterogeneous catalysis in hydrogenation and room-temperature hydrogen storage. However, a proper catalyst design is requisite to initiate hydrogen spillover, considering the transition metal particle dispersion, sorbent surface modification, porosity, etc. In this report, we pyrolyzed the zeolitic imidazolate framework ZIF-67 for residual Co metal nanoparticles and N-dopant on ZIF-derived carbon (ZDC) for hydrogen adsorption via spillover effect. Catalyst optimization by proper ZIF carbonization process regarding manipulated pyrolytic temperatures, atmospheres, and ramping rates, results in different properties in ZDCs. Well-distributed Co nanoparticles can be obtained on N-rich graphitic sorbent ZDCs with retained high specific surface area. The Co on ZDC exhibits improved room-temperature hydrogen capacity of 0.77 wt% than neat ZIF-67 of 0.09 wt% at 30 bar, 300 K. The adsorption sites were examined experimentally by nitrogen hydrogenation, and possible atomic hydrogen diffusion was evaluated theoretically showing energy barrier reduced by over 0.1 eV. It demonstrates that cobalt nanoparticles can successfully initiate hydrogen spillover on ZIF-derived carbon with nitrogen functionality, even without noble metals.