One of the many projects I’ve made many prototypes for over my years of making has been electrolytic cells. The concept of a clean-burning fuel, producing only water vapour1 and burning many times the heat of more traditional carbon-based fuels is really cool.
Although really when you think about it fossil fuels are still burn in power plants. My ideal plan would be to power it off solar cells, however this as well requires many many prototypes. ↩