Carbon composite support improving catalytic effect of NbC nanoparticles on the low-temperature hydrogen storage performance of MgH2

Abstract

Ultrafine carbon-based transition metal compounds have been widely investigated as efficient catalysts for enhancing the hydrogen storage performance of magnesium hydride. In this work, the carbon thermal shock method is applied to synthesize the ultrafine carbon-encapsulated NbC nanoparticles with an average grain size of 17.3 nm. The MgH2–10 wt% NbC/C composites show excellent low-temperature hydrogen storage performance with the onset dehydrogenation temperature of 196.1 °C, which is 92.2 °C and 98 °C lower than that of MgH2–10 wt% NbC and undoped MgH2, respectively. Specifically, MgH2–10 wt% NbC/C can absorb 6.71 wt% H2 at 100 °C within 30 min around and retain almost 100% reversible hydrogen desorption capacity after 10 cycles. For the catalytic mechanism, the electron transfer process between multi-valence Nb cations of in-situ formed NbHx and Mg, H atoms can greatly improve the cyclic de/rehydrogenation kinetics of MgH2-NbC/C. Besides, the enhancement of dehydrogenation kinetics can also be ascribed to MgH2 particle refinement by NbC nanoparticles, and destabilization of the Mg-H bond caused by carbon substrate. This investigation not only proves that carbon-encapsulated NbC nanoparticles can greatly enhance the hydrogen storage performance of MgH2 but provides an idea of preparing carbon-based transition metal carbides as effective catalysts for magnesium-based hydrogen storage materials.