Sodium borohydride (NaBH 4 )i sa mong the most studied hydrogen storage materials because it is able to deliver high-purity H 2 at room temperature with controllable kinetics via hydrolysis;h owever,i ts regeneration from the hydrolytic product has been challenging.Now,afacile method is reported to regenerate NaBH 4 with high yield and lowc osts.T he hydrolytic product NaBO 2 in aqueous solution reacts with CO 2 ,forming Na 2 B 4 O 7 ·10 H 2 Oand Na 2 CO 3 ,both of which are ball-milled with Mg under ambient conditions to form NaBH 4 in high yield (close to 80 %). Compared with previous studies, this approach avoids expensive reducing agents such as MgH 2 , bypasses the energy-intensive dehydration procedure to removewater from Na 2 B 4 O 7 ·10 H 2 O, and does not require highpressure H 2 gas,therefore leading to much reduced costs.This method is expected to effectively close the loop of NaBH 4 regeneration and hydrolysis,e nabling aw ide deployment of NaBH 4 for hydrogen storage.

A ZnO encapsulated in a 3D NCNF composite exhibits excellent electrochemical performances both in a half cell and full cell. The improved performances are mainly explained based on the two aspects of structural integrity and kinetics enhancement.

Sodium borohydride (NaBH4) has been identified as one of the most promising hydrogen storage materials; however, it is still challenging to produce NaBH4 with low cost and high efficiency, which are largely determined by the sources of boron and hydrogen and reducing agents used. Herein, we report an economical method to produce NaBH4 by ball milling hydrated borax (Na2B4O7·10H2O and/or Na2B4O7·5H2O) with different reducing agents such as MgH2, Mg, and NaH under ambient conditions. The direct use of natural hydrated borax avoids the dehydration process (at 600 °C) and consequently reduces cost and improves overall energy efficiency. A high yield of 93.1% can be achieved for a short ball mill duration (3.5 h) for Na2B4O7·5H2O-NaH-MgH2 system. In this system, H2 is generated in situ which subsequently reacts with Mg forming MgH2. Low cost Mg is therefore employed to replace the majority of MgH2, leading to an attractive yield of 78.6%. To further reduce the cost of raw materials and improve the utilization of hydrogen source in the hydrated borax, Na2B4O7·10H2O is used to partially substitute for Na2B4O7·5H2O, leading to a complete replacement of MgH2. Compared with literature results, the optimized recipe features low cost and high efficiency since it utilizes hydrogen from the hydrated water in natural borax and avoids high temperatures. Our finding is expected to facilitate applications of NaBH4 for hydrogen storage.

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