Catalyzed hydrogen spillover for hydrogen storage.

A crucial bottleneck in developing a hydrogen economy is hydrogen storage. This is particularly true for transportation using hydrogen as the fuel for fuel cells. The U.S. Department of Energy has established specific R&D targets for on-board hydrogen storage. Among the most important targets are system gravimetric/volumetric capacities and charge/discharge rates. New sorbent materials based on hydrogen spillover have shown much promise recently. However, the rates of spillover are low and remain a major concern. Here it is shown that doping with 2 wt % TiCl(3) or VCl(3) can significantly increase the rates of both adsorption and desorption by spillover. Moreover, the small hysteresis loop in the hydrogen isotherms for the spillover system is eliminated upon doping with the metal salt. Both heats of adsorption and activation energies for spillover are decreased by doping with TiCl(3) or VCl(3). This result indicates that the binding energies between the spilled-over hydrogen and the sites on the carbon surface are decreased by doping.