- Heat (really serious hot) does decompose water partially BUT (1) how do you separate both gases prior to recombination (2) what kind of solids shall resist?
- There are certainly less direct processes that use technological temperatures. Like: produce CO from CO2, use CO in other reactions to get H2. True chemists can tell you more - I'm not one.
- Wiki's article telling hot zirconium decomposes water into H2 and O2 at Fukushima is just false.
- H2 is good for fuel cells (is that your target?) but hydrocarbons or alcohols are better for gasoline engines and are easier to produce by thermal means.
- If you want to produce fuels by concentrated Sunlight, it's definitely a good idea. Storable, easier to use by present engines.
- This task is hard because oil and gas are so dirt-cheap. They get expensive through taxes. Processes like yours will be accepted by governments only if they compete with the cost before taxes, which is very difficult.