A Review of Electrochemical Reduction of Sodium Metaborate

The recycling of sodium borohydride poses a huge challenge to the drive towards a hydrogen economy. Currently, mechano-chemical, thermo-chemical and electrochemical are the only reported methods of recycling sodium metaborate into sodium borohydride. Much attention has been devoted to the mechano-chemical and thermo-chemical methods of reduction, but little focus has been devoted to electrochemical methods. This review describes the electrochemical behaviour of borohydride (BH4-) and metaborate (BO2-) anions in alkaline solutions. The BH4- is stabilized in highly concentrated alkaline solutions, while the electro-oxidation of BH4- is dependent on the type of electrode material. The attempts to electro-reduce the BO2- into BH4- is reviewed and the challenges, suggestions and future outlook of electro-reduction for the recycling of BO2- into BH4- is highlighted.

Automated summary

The recycling of sodium borohydride is a major challenge for the hydrogen economy. Mechano-chemical, thermo-chemical, and electrochemical methods are reported for recycling sodium metaborate into sodium borohydride. Electrochemical behavior of borohydride and metaborate in alkaline solutions is described. Challenges, suggestions, and future outlook of electro-reduction for the recycling of metaborate into borohydride are highlighted.