Sodium borohydride for hydrogen generation and storage

Caroline R. Cloutier, Akram Alfantazi, Elod Gyenge

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

Abstract

It is widely acknowledged that hydrogen is one of the best fuel options of the future. The major limitations to its large-scale adoption in transportation are the lack of a practical storage method, and concerns associated with its safe handling. Chemical hydrogen carriers have the potential to address these concerns. Due to its high hydrogen content (10.58 wt%) and energy density (1.4 KWh/l), sodium borohydride (sodium tetrahydroborate, NaBH4), is one of the most attractive chemical hydride for hydrogen generation and storage. It has been demonstrated by Millennium Cell Inc., in conjunction with Daimler-Chrysler, that NaBH4 solutions for on-board hydrogen generation and storage can be efficiently used to feed proton exchange membrane fuel cell (PEMFC) in automotive applications. Nevertheless, the high production cost and difficult recyclability of NaBH4 hinder its acceptance as the H2 carrier of choice for fuel cell vehicles. The current research aims at addressing these barriers. This paper includes a review of the practicality of a NaBH4 based economy. The boron sources were evaluated and the current NaBH4 production process was assessed for sustainability. The need to develop an effective regeneration method to transform the NaBH4 hydrolysis by-product, sodium inelaborate (NaBO2), back to NaBH4 is obvious. A reversible electrochemical regeneration route would represent the ideal recycling solution as it could lead to an emission free and cost-effective energy cycle. A conceptual infrastructure for the distribution and electrochemical regeneration of this fuel is proposed. Electrochemical recycling investigations require the knowledge of the key properties of concentrated NaBO2 alkaline aqueous solutions. Since no information is available in the literature, the physico-chemical properties of NaBO2 alkaline aqueous solutions were experimentally determined. Typically, NaOH is employed as the stabilizer for aqueous solutions of NaBH4. However, KOH or LiOH can also be used. The impact of the different alkaline cations on the solution's properties was investigated. The solubility, pH, density, conductivity and viscosity of aqueous NaBO2 solutions containing different weight percentages (1, 3, 5 and 10 wt %) of alkali hydroxides were evaluated at 25oC. The results demonstrated that NaOH might not be the most suitable alkali additive for this application. The optimum media will be used to investigate the electroreduction of NaBO2 to NaBH4. Electrochemical measurements will be made using diverse electrode materials. Organic compounds will be added to increase the hydrogen evolution reaction overpotential and, thereby, favor the reduction of NaBO2 to NaBH4. The electroreduction of NaBO2 to NaBH4 could lead to an emission free and cost-effective energy cycle.

Original languageBritish English
Title of host publicationProceedings of the 1st European Fuel Cell Technology and Applications Conference 2005, EFC2005 - Book of Abstracts
Pages66
Number of pages1
StatePublished - 2005
Event1st European Fuel Cell Technology and Applications Conference 2005, EFC2005 - Rome, Italy
Duration: 14 Dec 200516 Dec 2005

Publication series

NameProceedings of the 1st European Fuel Cell Technology and Applications Conference 2005 - Book of Abstracts
Volume2005

Conference

Conference1st European Fuel Cell Technology and Applications Conference 2005, EFC2005
Country/TerritoryItaly
CityRome
Period14/12/0516/12/05

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