Doping and Structure-Promoted Destabilization of NaBH₄ Nanocubes for Hydrogen Storage

Sodium borohydride (NaBH₄) is a potential candidate for hydrogen storage; however, its high thermodynamic stability has hampered its practical use. Doping NaBH₄ with transition metals is an efficient way to improve its hydrogen properties; however, even with the most effective dopants, the temperatures required for hydrogen release are still too high (above 400 °C) for practical use. Herein, we report on vanadium-doped NaBH₄ (V-NaBH₄) nanocubes and the related core–shell like (V-NaBH₄@Ni) structure, which outperforms conventional transition metal (e.g., Co, Cu, Fe, Nb, Ti)-doped NaBH₄ systems and significantly lowers the hydrogen release temperature of V-NaBH₄@Ni to 355 °C. Notably, V-NaBH₄@Ni releases up to 5.3 mass% H₂ below 200 °C, which is a significant improvement compared to unmodified NaBH₄. Detailed structural investigations revealed that the improved hydrogen release is due to the synergistic effects of the unique core–shell structure and the in situ formed V_xB_y and Ni_xB_y at the core–shell interface. The formation of these intermediate borides is believed to enhance the electron transfer from BH₄^– to the boride site and trigger hydrogen release at lower temperatures. This study provides, for the first time, convincing evidence of accelerated decomposition of NaBH₄ in the core–shell structure and paves the way toward tuning the hydrogen properties of transition-metal doped core–shell hydrides.