International Journal of Hydrogen Energy 33 (2008) 417 – 422 www.elsevier.com/locate/ijhydene Glass micro-container based hydrogen storage scheme D.K. Kohli, R.K. Khardekar ∗ , Rashmi Singh, P.K. Gupta Target Laboratory, LMD & D Division, Raja Ramanna Centre for Advanced Technology, Indore 452013, India Received 28 June 2007; accepted 9 July 2007 Available online 19 September 2007 Abstract Glass is the material of choice for inertial confinement fusion (ICF) targets due to its high strength [Bartenev GM, Sanditov DS. The strength and some mechanical and thermal characteristics of high-strength glasses. J Cryst Solids 1982;48:405]. There exist many technologies for producing fusion grade glass microballoons (GMBs) also known as hollow glass microspheres (HGMS) and filling techniques up to 1000 bars. These glass micro-containers offer a novel scheme of hydrogen storage [Rambach GD, Hendricks C. Hydrogen transport and storage in engineered glass microspheres. In: Proceedings of the 1996 USDOE hydrogen program review meeting, Miami, National Renewable Energy Laboratory; 1996. p. 765]. A comparative evaluation of hydrogen storage efficiency has been done for high tensile strength GMBs at different radius to wall thickness ratio termed as aspect ratio. By experimental and theoretical calculations, we propose the use of high aspect ratio GMBs with storage efficiency from 15% to 25% w/w for GMBs at pressures below 500bars. Such efficiencies are unique, being greater than large cryostat (∼ 14% w/w), and safe compared to large pressure vessels, etc. For the pressure range 150–300 bars a prototype hydrogen filling system has been developed in our laboratory. We have experimentally attained gravimetric efficiency  = M H /(M H + M S ) as 15–17% for the GMBs. The advantages and also some shortcomings of this technique are compared with other hydrogen storage methods such as metal hydrides, physisorption and chemisorption, etc.  2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. Keywords: Glass microballoons; GMBs; Glass micro-containers; Hallow glass microspheres; HGMS; Drop tower furnace 1. Introduction Energy security and global warming are twin factors mak- ing hydrogen economy attractive currently. For hydrogen to replace fossil fuels, safe and efficient storage techniques with high gravimetric and volumetric efficiencies are required. The hydrogen economy issue is broad and basically addresses three challenging areas of hydrogen production, its storage, and uti- lization mechanisms for the desired applications. An elegant solution to the storage problem of H 2 is one of the most impor- tant issues. There are mainly six storage methods viz. (1) gas storage, (2) liquid hydrogen, (3) physisorption, (4) metal hy- drides, (5) complex hydrides, (6) chemical reactions [1]. There are many criterions for deciding upon the storage scheme but the important ones are: safety, gravimetric and volumetric ef- ficiencies, cost, reversibility of uptake and release, etc. Every ∗ Corresponding author. Tel.: +91 731 2442393; fax: +91 731 2488250. E-mail address: khardekr@cat.ernet.in (R.K. Khardekar). 0360-3199/$ - see front matter  2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2007.07.044 technique listed above has one or the other limitations along with its advantages. The pressure vessel gas storage has limi- tation on volumetric efficiency but the gravimetric efficiency is considerably higher. The liquid hydrogen system suffers from the drawback of large energy required for liquefaction of liquid hydrogen. The physisorption suffers from the drawback of low efficiency. The metal hydrides show promise as good storage medium with high volumetric efficiency but the counter part, gravimetric efficiencies are very low. The complex hydride sys- tems and chemical systems though have reasonably good effi- ciency suffer with the problem of reversibility. The scheme of pressurized glass micro-containers for hydro- gen storage is a type of high-pressure storage system with the distinction that it uses high strength glasses of density much lower than steel. Using the sol–gel route high strength glasses with specific compositions are being investigated for high fill- ing and release rates. The present study is also useful to the glass microballoons (GMBs) developed for these studies with transition metal doping for the photo-enhanced diffusion [2].