My favorite effort is
Cool Planet. They are carbon
negative. I just looked, they had 3 press releases in Feb and Mar, so they're still kicking.
Insofar as hydrogen is concerned; I think it should be used in a composite semirigid airship for lift
and thrust. The core would be a limp bag of hot hydrogen—in vacuum. That would be surrounded by ballonettes of steam. It has lift similar to helium as steam, but remove the (hydrogen-provided) heat and it condenses for dynamic control.
The hydrogen combution engines are the least interesting part to me. Oh—also
Aeromodeller2
Sorry, Frank, it a big 'un. It buffers the hydrogen with nitrogen gas.
How about
search?q=electricity+from+synthetic+photosynthesis. Big developments there in the last year.