Abstract
Sodium alanate (NaAlH4) with 5.6 wt% of hydrogen capacity suffers seriously from the sluggish kinetics for reversible hydrogen storage. Ti-based dopants such as TiCl4, TiCl3, TiF3, and TiO2 are prominent in enhancing the dehydrogenation kinetics and hence reducing the operation temperature. The tradeoff, however, is a considerable decrease of the reversible hydrogen capacity, which largely lowers the practical value of NaAlH4. Here, we successfully synthesized a new Ti-dopant, i.e., TiH2 as nanoplates with ~50 nm in lateral size and ~15 nm in thickness by an ultrasound-driven metathesis reaction between TiCl4 and LiH in THF with graphene as supports (denoted as NP-TiH2@G). Doping of 7 wt% NP-TiH2@G enables a full dehydrogenation of NaAlH4 at 80°C and rehydrogenation at 30°C under 100 atm H2 with a reversible hydrogen capacity of 5 wt%, superior to all literature results reported so far. This indicates that nanostructured TiH2 is much more effective than Ti-dopants in improving the hydrogen storage performance of NaAlH4. Our finding not only pushes the practical application of NaAlH4 forward greatly but also opens up new opportunities to tailor the kinetics with the minimal capacity loss.
Highlights
Hydrogen storage, bridging hydrogen generation and hydrogen application, plays a crucial role in a future hydrogen energy society [1,2,3,4]
Ta itHem2@pGer-actounrteaiansinlogwsaams p2l5e°Cst,aratnedd to absorb hydrogen at more than 90% of the rehydrogenation can be completed below 90°C, which is close to the working temperature of proton exchange membrane fuel cell (PEMFC)
Two-dimensional TiH2 nanoplates with a lateral size of 50 nm and a thickness of 15 nm were successfully synthesized by using graphene as support, based on a novel facile sonochemical process
Summary
Hydrogen storage, bridging hydrogen generation and hydrogen application, plays a crucial role in a future hydrogen energy society [1,2,3,4]. Catalyst doping has been proved a feasible approach to help reducing the kinetic barriers of hydrogen storage reactions in metal hydrides Transition metals and their compounds, especially Ti-based dopants, were found to have the ability to promote fast dissociation and recombination of hydrogen molecules [12,13,14]. To the best of our knowledge, this is the first example that NaAlH4 can reversibly store hydrogen in the working temperature range of proton exchange membrane fuel cell (PEMFC) with the highest capacity (Figure 1). Such outstanding hydrogen storage performance of NaAlH4 meets the requirement for on-board hydrogen storage application
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