Abstract
Although the synthesis of borohydride nanostructures is sufficiently established for advancement of hydrogen storage, obtaining ultrasmall (sub-10 nm) metal borohydride nanocrystals with excellent dispersibility is extremely challenging because of their high surface energy, exceedingly strong reducibility/hydrophilicity and complicated composition. Here, we demonstrate a mechanical-force-driven self-printing process that enables monodispersed (~6 nm) NaBH4 nanodots to uniformly anchor onto freshly-exfoliated graphitic nanosheets (GNs). Both mechanical-forces and borohydride interaction with GNs stimulate NaBH4 clusters intercalation/absorption into the graphite interlayers acting as a ‘pen’ for writing, which is accomplished by exfoliating GNs with the ‘printed’ borohydrides. These nano-NaBH4@GNs exhibit favorable thermodynamics (decrease in ∆H of ~45%), rapid kinetics (a greater than six-fold increase) and stable de-/re-hydrogenation that retains a high capacity (up to ~5 wt% for NaBH4) compared with those of micro-NaBH4. Our results are helpful in the scalable fabrication of zero-dimensional complex hydrides on two-dimensional supports with enhanced hydrogen storage for potential applications.
Highlights
The solution to the first challenge is to decrease the thermodynamic stability of NaBH4; the solution to the second challenge is to improve the de-/re-hydrogenation kinetics and reversibility[16]
We present a simple and facile solvent-free, mechanical force-induced self-printing (MFSP) method for the synthesis of ultrasmall (~6 nm) NaBH4 nanodots with excellent dispersibility that can self-assemble on multi-layered graphitic nanosheets
To the best of our knowledge, such a low Ea for hydrogen desorption from NaBH4 has not been previously reported. These results clearly indicate that improvements in both the thermodynamics and kinetics are achieved in the nano-NaBH4@graphitic nanosheets (GNs) composites
Summary
The solution to the first challenge is to decrease the thermodynamic stability of NaBH4; the solution to the second challenge is to improve the de-/re-hydrogenation kinetics and reversibility[16]. Ngene et al.[26] impregnated NaBH4 into nanoporous carbon to decrease the nanoparticles aggregation for obtaining much faster desorption kinetics; the unacceptable dead mass contributed by the nanosupports reduced the storage efficiency To address this issue, Meganne et al.[27] adopted a core-shell strategy for restricting the NaBH4 particles to a size between 10 and 200 nm using a nanothick Ni-shell coating. Developing a novel method to synthesize ultrasmall NaBH4 nanoparticle with excellent dispersibility to establish the essential nanoscale effects is imperative but challenging Achievement of this goal may open a door to the nanostructured material designs required to transform the performance of hydrogen storage materials to levels at which they are practical for the thermodynamics and kinetics events
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