Enhanced H-storage property in Li–Co–N–H system by promoting ion migration
Motivated by the ion migration mechanism proposed by David et al. [J. Am. Chem. Soc. 129 (2007) 1594–1601], we mechanically mill the Li3N/Co powder mixture to obtain defective Li3N-type structure with enhanced Li+ mobility. Compared with Li3N, the hydrogen storage property of such defective phase is markedly improved, presumably due to the ion-migration-enhancing effect from the incorporation of Co and Fe (from milling utensils). During subsequent cycling, however, this effect cannot persist due to the precipitation of Co–Fe alloy upon hydrogenation. The close correlation between Co–Fe incorporation/precipitation and property variation of Li3N hydrogen storage material provides a preliminary evidence to support the ion migration mechanism.
Keywords: Hydrogen absorbing materials; Nitride materials
Fig. 1. XRD patterns of (a) as-milled Li3N sample, (b) as-milled Li3N + Co sample, (c) as-milled Li3N + Co sample with additional milling under H2 atmosphere, and (d) Li3N + Co sample at dehydrogenated state after one hydriding/dehydriding cycle.
Fig. 2. Hydrogen desorption curves of (a) as-milled Li3N + Co sample, (b) as-milled Li3N + Co sample with additional milling under H2 atmosphere, and (c) as-milled Li3N at 255 °C in the first cycle (after hydrogenation under 5 MPa at 160 °C for 10 h).
Fig. 3. Hydrogen desorption curves of (a) Li3N + Co sample, (b) Li3N + Co sample with additional milling under H2 atmosphere, and (c) Li3N sample at 255 °C in the second cycle. The inset shows the hydrogen capacity in the first five cycles.