Thermodynamically favored stable hydrogen storage reversibility of NaBH inside of bimetallic nanoporous carbon nanosheets

Sodium borohydride (NaBH 4 ) has been widely regarded as a potential hydrogen storage material due to its high gravimetric and volumetric capacity. Its practical application, however, is hindered by the high operating temperature of over 500 °C and extremely poor reversibility. Herein, thermodynamically favored reversible hydrogen storage performance of NaBH 4 is developed inside of bimetallic (NiCo) nanoporous carbon nanosheets. Benefiting from the synergetic effect of nanoconfinement and the catalytic role of NiCo alloys, the apparent activation energy for H 2 desorption from NaBH 4 @NiCo-NC is reduced to 36.8 kJ mol −1 with the complete H 2 desorption at only 400 °C, resulting in the simultaneous formation of NiB and CoB as the dehydrogenation products. More interestingly, the reversible transformation between NiB/CoB and Ni 2 B/Co 2 B that are in situ formed during the subsequent re-/dehydrogenation process acts as a B reservoir, leading to a significant decrease of Gibbs free energy change for the reversibility of NaBH 4 to 1.41 eV, 0.62 eV lower than that of pure NaBH 4 . As a result, coupled with the catalytic role of in situ formed Co 2 B/Ni 2 B in promoting the H 2 desorption performance of NaBH 4 , a stable reversible capacity of 9.0 wt% is realized for NaBH 4 at a temperature as low as 400 °C for 5 cycles. Thermodynamically favored reversible hydrogen storage of NaBH 4 is developed via the reversible transformation between NiB/CoB and Ni 2 B/Co 2 B, leading to a significant decrease of Gibbs free energy change for the reversible hydrogen storage of NaBH 4 .