So, in the style of the original remit of "Ignition!", here's a list of the desirable properties for electrochemical long term storage solutions which have not yet been met.<p>- The process must take a liquid electrolyte with two electrodes in it and a current applied, and emit some substances (I'm going to say "products") at anode and cathode which can be stored<p>- The process must be reversible with reasonable efficiency<p>- The electrodes must have a reasonable capital cost (i.e. not platinum) and lifetime (problem for exotic materials)<p>- same for any required proton exchange membrane (these are expensive and have finite lifetime)<p>- The products must be storeable, that is shelf-stable in tanks. This also means they must be fluids at room temperature; processes which emit solids are used in battery cells instead<p>- The products must be capable of being handled with standard plumbing, nothing weirder than stainless steel and rubber seals (may be a problem for hydrogen)<p>- Gas products must not be toxic (this is a big objection to using ammonia)<p>- Liquid products must be within the range of normally handle-able toxic substances which can be dealt with by dilution (e.g. conc sodium hydroxide is used in households, but some substance which can poison an aquifer if it leaks would be unacceptable)<p>- products should not be too explosive (risk for hydrogen) or react too violently on contact with air or, ideally, water<p>That is, it should be possible to build a system of electrolysers and tanks which is not significantly more expensive than a brewery or petrol station and, crucially, doesn't require spending too much on safety or trained personnel or insurance, doesn't require exceptional planning permission, which can be run <i>intermittently</i> (i.e. cheap enough that amortized capital costs are less then operating income) to store and release electricity.<p>Design one of those and you could be a global hero.