Pt Effect on H2 Kinetics Sorption in Mn Oxide-Based Polymeric Material

Abstract

Recent studies have demonstrated how a material based on Mn oxide, supported by a polymeric matrix, shows an interesting H2 absorption capacity in non-drastic temperature and pressure conditions even if the reaction kinetics are particularly slow. In this study, therefore, two different percentages of Pt (5 and 10 wt%) were added to a composite sample, containing 50 wt% of Mn oxide, through a ball milling technique in order to verify the reduction in absorption kinetics of the quantity of added catalyst. The effect of the catalyst quantity on the composite matrix was investigated through morphological analyses of the SEM-EDX and TEM types, with which it was found that the distribution of Pt is more homogeneous compared to the sample containing 5%. XRD studies confirmed the simultaneous presence of the amorphous structure of the polymer and the crystalline structure of Pt, and absorption tests with the Sievert method verified a better kinetic reaction of the 10% Pt sample. In parallel, a modeling study, using the ab initio Density Functional Theory (DFT), was performed. The supercell for this study was Mn22Pt2O48. The number of H atoms gradually increased, starting from 2 (Mn22Pt2O48H2), where the initial desorption energy was 301 kJ/mol, to 211 kJ/mol for 12 H atoms (Mn22Pt2O48H12). From the experimental H2 absorption value (0.22 wt%), the number of respective H atoms was calculated (n = 5), and the corresponding desorption energy was equal to about 273 kJ/mol.