Since thermoelectric generators make electricity through thermal flux, could a device that mixes NaOH and HCl on one side (heat) and Ba(OH)2•8H2O and NH4SCN (cold) be efficient? Could it produce more energy than it consumes?
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1$\begingroup$ Thermoelectric generators are in general not efficient at all. Generally 5% or less. They are used because they are simple and reliable. "Could it produce more energy than it consumes?" No. The energy used to form the fuel compounds counts as part of the input energy. Unless you dig up or extract all those chemicals straight up from nature like with oil and coal. And doing that needs to take less energy than what you get out of it which it won't because <5% efficiency. But in that case you're better off just digging oil and coal out of the ground because burning it as much more efficient. $\endgroup$– DKNguyenCommented May 2, 2022 at 21:56
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Could it work? Yes. Is it practical for any scale? No.
As @DKNguyen says in their comment, if you had a free source of these components you could generate this heat and use it to do things. But it is extremely unlikely you have a free source of these materials. So the input energy includes the production of your components. Fossil fuels work because we let the earth spend a million years producing the fuel we use; the original energy source was organic growth powered by the sun.
Thermoelectric generators are only practical where you have a free source of heat and no other way to use it, so the inefficiency of converting heat to electricity this way isn't a concern.
And there are exactly zero cases of where you can produce more energy in total than you put in.
