ِAbdulla.... WOW!!!! 6500 psi i.e. about 450 bar???? This is a very high pressure. The future solution for hydrogen storage is to change it into magnesium hydride, MgH2. This is a solid from Hydrogen may be released under control.  Good luck.

I served as a principal investigator for hydrogen storage research for many years and there are two only  pressures that have been considered for compressed hydrogen gas, namely: 350 bars (5000 psi) and 700 bar (10,000 psi). In any case, there are so many publications and most recent research on hydrogen storage that you could download at no cost from the following URL:

www.doe.gov/amr

Where AMR stands for the DOE annual merit review meetings.

Also, you can down load papers from my published work at:

www.researchgate.net/profile/yehia_khalil3

Hope this helps answer your question.

Professor Yehia Khalil, Yale University, USA

Fellow of the University of Oxford, United Kingdom

This may (or may not) be helpful H2 storage in a cavern a 200 bar

https://en.wikipedia.org/wiki/Underground_hydrogen_storage

I have consulted for the refinery (Phillips - Sweeny Texas)  that uses this storage facility and it worked very well for them.. 

Here is another Cavern H2 storage site at 800-2200 PSIG:

http://www.slideshare.net/chojsm1/hydrogen-reliability-cavern-storage

Chapter An Overview of Hydrogen Storage Methods

https://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/bestpractices_h2_storage_materials.pdf

https://ec.europa.eu/jrc/sites/jrcsh/files/jrc_20090224_infosheet_hydrogensafety_en.pdf

https://www.intechopen.com/books/howtoreference/hydrogen-storage/hydrogen-storage-for-energy-application

https://www.nist.gov/programs-projects/measurements-hydrogen-storage-materials