Several metals, including iron and aluminum, can be ground up into fine powders that burn as well as fossil fuels, but without releasing any carbon. What's more, the oxidized remains can then be regenerated back into usable metal powders with the use of renewable energy and electrolysis processes, creating a carbon-free energy cycle for combustion use cases.
US-based Wright Electric has announced a 100-seat electric short-hop aircraft slated to go into service by 2026. It'll either be powered by hydrogen, or it'll use recyclable metal in what the company calls an "aluminum fuel cell."
Yes, iron. Fine iron powder can burn at high temperatures, emitting nothing but rust as a by-product. That rust can be reduced back into iron powder using renewable energy to create a clean, renewable combustion fuel that could have big implications.