Aluminium or silicon contains more energy per volume and per mass, but when they are burned their oxides are very small: nanoparticles. This is difficult to capture and is also bad for the environment and your health. The oxides of iron are larger: microparticles. Also, iron is very cheap.
What are you working on now?
Currently, we are working on a proof-of-concept. With that, we want to show the feasibility of burning iron powder.
Does the burning of iron release CO2?
No, by burning iron, oxygen is used, so iron oxide (rust) is created. No CO2 is released.