Linking Fast Sodium Conduction with Low‐Temperature Hydrogen Release in Sodium Borohydride

• Published in: Advanced energy and sustainability research 2024-10, Vol.5 (10), p.n/a
• Main Authors: Salman, Muhammad Saad, Srivastava, Kshitij, Muñiz, César Menéndez, Aguey‐Zinsou, Kondo‐Francois
• Format: Article
• Language: English
• Subjects: borohydride; complex anion; hydrogen desorption; ionic conductivity; solid‐state electrolytes
• ISSN: 2699-9412; 2699-9412
• DOI: 10.1002/aesr.202400046

Complex hydrides, such as sodium borohydride (NaBH4), are attractive materials for hydrogen storage because of their high hydrogen capacity. However, practical application of these materials is limited because of their unfavorable hydrogen thermodynamics and poor kinetics. Herein, it is demonstrated that the inclusion of BF4− in NaBH4 results in remarkable Na+ conductivity of 1.5 × 10−3 S cm−1, which is 10 000 times higher compared to pure NaBH4 (7.0 × 10−8 S cm−1) at 115 °C. The ionic conductivity is also comparable to values reported for some of the best borohydride‐based conductors reported to date. More remarkably, this improvement of ionic conductivity is found to be correlated to lower hydrogen release temperatures for BF4−‐modified NaBH4 releasing hydrogen at a temperature of 200 °C instead of 510 °C in the case of pristine NaBH4. Nudged elastic band calculations based on density functional theory reveal that partial substitution of the [BH4]− groups in NaBH4 by BF4− may lead to the formation of distortions within the NaBH4 crystal lattice with favorable channels for Na+ mobility enabling the release of hydrogen at low temperatures. The hydrogen desorption properties of sodium borohydride (NaBH4), a material of high hydrogen storage capacity, are drastically improved by enhancing its intrinsic ionic conductivity. This is achieved through the inclusion of BF4− in NaBH4 resulting in remarkable Na+ conductivity of 1.5 × 10−3 S cm−1, which is 10 000 times higher compared to pure NaBH4.