Hydrogen adsorption properties of in-situ synthesized Pt-decorated porous carbons templated from zeolite EMC-2

Abstract

To increase the interaction between the adsorbed hydrogen and the adsorbent surface to improve the hydrogen storage capacity at ambient temperature, decorating the sorbents with metal nanoparticles, such as Pd, Ni, and Pt has attracted the most attention. In this work, Ptdecorated porous carbons were in-situ synthesized via CVD method using Pt-impregnated zeolite EMC-2 as template and their hydrogen uptake performance up to 20 bar at 77, 87, 298 and 308 K has been investigated with focus on the interaction between the adsorbed H2 and the carbon matrix. It is found that the in-situ generated Pt-decorated porous carbons exhibit Pt nanoparticles with size of 2-4 nm homogenously dispersed in porous carbon, accompanied with observable carbon nanowires on the surface. The calculated H2 adsorption heats at/near 77 K are similar for both the plain carbon (7.8 kJ mol-1) and the Pt-decorated carbon (8.3 kJ mol-1) at H2 coverage of 0.08 wt.%, suggesting physisorption is dominated in both cases. However, the calculated H2 adsorption heat at/near 298 K of Pt-decorated carbon is 72 kJ mol-1 at initial H2 coverage, which decreases dramatically to 20.8 kJ mol-1 at H2 coverage of 0.014 wt.%, levels to 17.9 at 0.073 wt.%, then gradually decreases to 2.6 kJ mol-1 at 0.13 wt.% and closes to that of the plain carbon at H2 coverage above 0.13 wt.%. These results suggest that the introduce of Pt particles significantly enhances the interaction between the adsorbed H2 and the Pt-decorated carbon matrix at lower H2 coverage, resulting in an adsorption process consisting of chemisorption stage, mixed nature of chemisorption and physisorption stage along with the increase of H2 coverage (up to 0.13 wt.%). However, this enhancement in the interaction is outperformed by the added weight of the Pt and the blockage and/or occupation of some pores by the Pt nanoparticles, which results in lower H2 uptake than that of the plain carbon.