Effects of heteroatom-doped hierarchical porous carbon on hydrogen storage properties of MgH2

Abstract

In this paper, the nitrogen doped (N-HPC), nitrogen and phosphorus co-doped hierarchical porous carbon (NP-HPC) are prepared by cross-linking phytic acid and poly pyrrole/aniline precursor, respectively. They are mixed with MgH2 by high-energy ball milling, and then their effects and mechanisms on the hydrogen absorption and desorption properties of MgH2 are investigated. Meanwhile, the hydrogen storage properties of MgH2 added with graphite (G) are also compared. The results show that the additions of NP-HPC, N-HPC, and G all exhibit the catalytic effect on the hydrogen absorption and desorption of MgH2. As for the hydrogen desorption, the catalytic effect is enhanced in the order of N-HPC, G and NP-HPC. Compared with pure MgH2, the hydrogen desorption temperature is reduced by 65.3 °C, 79.6 °C and 91.1 °C, respectively. Among them, the MgH2 + NP-HPC system can release 5.17 wt% hydrogen at 300 °C within 30 min. First-principles calculations reveal that the P-doped and vacancy-containing carbon materials significantly reduce the H2 recombination barrier from the surface of MgH2 and distort the atomic structure of near-surface layer of MgH2, which in turn weakens the Mg-H bond strength. This may be the intrinsic reason for the excellent catalytic effect of NP-HPC and vacancy-containing G on the hydrogen desorption performance of MgH2.