Multi-step thermochemical

Funk, J. E., Conger, W. L., Carty, R. H., Evaluation of Multi-step Thermochemical Processes for the Production of Hydrogen from Water, The Hydrogen Economy Miami Energy (THEME) Conference, Miami Beach, 457, March 18-20,1974. 

Hydrogen production by a 2-step water splitting thermochemical cycle can be based on metal oxides redox pairs. A two-step, water-split-ting cycle, based on metal oxides redox pairs bypasses the separation hurdle. Multi-step thermochemical cycles can allow the use of more moderate operating temperatures, but their efficiency is still limited by the irreversibility associated with heat transfer and product separation. 

The first multi-step process having a theoretical efficiency above 50% was proposed by Marchetti and Beni in 1970 [2]. This process became the Mark-1 process of the European Commission s Joint Research Center (JRC), Ispra, Italy. A large number of cycles with reasonably high efficiencies were designed after this Abanades and co-workers have recently made a compilation of the available thermochemical cycles that yielded about 280 cycles [67]. A large number of cycles are listed in references [2,4,67,95,97]. However only a few of these processes have exhibited potential for high overall efficiencies and technical feasibility. We discuss a few cycles that are presently under study and promising for practical implementation. 

Table 3. Summary of multi-step chemical cycles for indirect thermochemical hydrogen generation, from Ref. 4.

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