"Perhaps even more attractive is the idea to use the sun's heat for splitting water into hydrogen and oxygen and storing them in two separate vessels. The high temperature produced by recombining oxygen and hydrogen is known to be the most intense heat available to mankind. Moreover, one could use the hydrogen for lighting, and inexpensively produced oxygen would also close a longstanding gap. But how can one use the sun's energy to split water? In my opinion, thermopiles, which have already accomplished excellent performance, could solve this problem ...
Quotation Augustin Mouchot (1825 - 1912) in his book: "The solar heat and its industrial application", 1879