I’m somewhat surprised they haven’t gone straight to optimizing for methanol combustion and buying a startup producing methanol from solar and atmospheric CO2. Solar methanol production is not terribly novel now, and is easier to store and transport than hydrogen.

https://www.honeywell.com/us/en/insights/articles/how-astm-a...

https://arena.gov.au/knowledge-bank/vast-renewables-port-aug...

(Biodiesel isn’t an option, won’t scale without causing potential rainforest and other land conservation loss)