How to turn seawater (or Martian air) into jet fuel New Scientist

Faced with global warming and potential oil shortages, the US navy is experimenting with making jet fuel from seawater.
Navy chemists have processed seawater into unsaturated short-chain hydrocarbons that with further refining could be made into kerosene-based jet fuel. But they will have to find a clean energy source to power the reactions if the end product is to be carbon neutral.
The process involves extracting carbon dioxide dissolved in the water and combining it with hydrogen – obtained by splitting water molecules using electricity – to make a hydrocarbon fuel.