In our recent article about Greenwashing, we referenced the use of hydrogen as the ‘Silver Bullet’ for cutting aircraft emissions, and just recently Rolls Royce and EasyJet have joined forces to develop a commercially viable aero engine for the future: https://www.rolls-royce.com/media/press-releases/2022/28-11-2022-rr-and-easyjet-set-new-aviation-world-first-with-successful-hydrogen-engine-run.aspx
This is good news looking forward to reducing all harmful emissions aircraft operations, for as the article states, the only by-product after combustion is water vapour.
Rolls Royce have also conducted tests on smaller jet engines in partnership with the German Aerospace Centre (DLR), https://www.hydrogeninsight.com/transport/-world-first-rolls-royce-and-easyjet-tests-show-100-hydrogen-combustion-can-power-aircraft-take-off/2-1-1523925
Further research is needed to investigate how the gas can be stored at low pressure, and chilled below -250 centigrade, then pressured for delivery to the engines. As the second article states, hydrogen burns hotter and faster than current fuels, which brings another set of issues to be solved.
The hydrogen for the UK test was produced in the Orkneys using tidal and wind energy. Whilst of course the UK as an island has coastlines a plenty, the economies of scale to produce enough hydrogen for the whole UK airline industry is not really realistic.
The concept of how to produce a sustainable supply for the world’s aviation industry must run concurrently with any engine developments, or the whole race to zero emissions from aviation will achieve little.