Also I couldn't find about Carbon Nitride when I searched about hydrogen storage methods. It seems to work very well (10% w.t. H2).
Another thing that wasn't so clear. Metal-air batteries can work as flow batteries, so its capacity can be increased by having a bigger tank storing metal slurry:https://en.wikipedia.org/wiki/Zinc%E2%80%93air_battery#Alternative_configurations
In this configuration there is only one anode catalyst, oxygen membrane and other expensive component, chosen proportionally to the required power output and not total storage capacity.
Also filters made for separating oxygen from the air have improved a lot and were tested on combustion engines, using a separate component releasing pre-filtered oxygen into the porous catalyst at the cathode may be better than the current approach of mixing all functions into one component (the cathode and the oxygen capture).>>1718613
It got down into levels that passed some requirements (still loud). But the whole series of events that led to it being cancelled looked very suspicious and african.