I'm just back from the 2011 US DOE Hydrogen and Vehicle Technologies Program Annual Merit Review and Peer Evaluation Meeting in Crystal City, across the river from Washington DC. It was well attended; I heard there were 1,700 people at the two hotels where it was held.
My favorite presentation was by Avālence LLC CTO Paul Dunn, presenting his project "High-Capacity, High Pressure Electrolysis System with Renewable Power Sources." He mentioned how they had a problem in the lab last year with 6,500 psig alkaline electrolysis of hydrogen and oxygen: they produced oxygen gas with only a 96% purity (or 4% H2 in O2.) There's a big problem with operating this way: the lower flammability limit of hydrogen in air, or oxygen, is 4%! It's a wonder that they didn't blow themselves up!
The best part is where he described their plan to reduce the hydrogen content of the oxygen by recirculating their electrolyte on both the anode and cathode sides of the electrolyzer. Guess what - he told us they used a thermosiphon to recirculate electrolyte without a pump, and it reduced their oxygen to 0.3% hydrogen! Guess what my Giner Electrochemical Systems poster presentation discussed last year? A proton exchange membrane (PEM) electrolyzer using a thermosiphon to recirculate the catholyte! Just a coincidence? Who knows! I'm just glad I helped minimize his chances of blowing up!!