Solar thermal hydrogen production from water and carbon monoxide production from CO2 using reducible metal oxides is being approached from transport, kinetic, thermodynamic and system design perspectives.  The bottleneck of these technologies is the thermodynamic stability of oxides, such that oxygen removal via R2 is the rate determining step requiring very high temperatures. The efficiency of the overall system is determined by the oxygen evolution during the regeneration period of the looping material. H2O+Me ? MeOx +H2                                                                (R1)MeOx + heat?O2 + Me                                               (R2)The equilibrium thermodynamics of the Me/MeOx pairs were screened by plotting Ellingham diagrams. Mixed oxides of cobalt and lead were found favorable towards CO2 and H2O reduction. Experimentally, it was demonstrated that CO2 was reduced to CO while oxidizing lead to PbO up to 800 oC. On the other hand H2O could be used as the oxidizer of PbO up to 700oC. PbO thermally decomposes after 900oC. The inherently cyclic and high temperature nature of the aforementioned approach prevents this operation to continuously and economically produce hydrogen gas. Due to this sequential mode of operation, hydrogen can be produced in a sequence of pulses as the reaction chamber switches between hydrogen production and catalyst regeneration requiring temperature differences (> 100�C) between the two reaction steps. We propose to address these shortcomings through the implementation of a network of individual reaction cells, each cell would be operating in its cyclic pattern with a purposefully designed phase shift between the individual cell cycles. Based on an accurate dynamic model of an individual cell, constructed by considering the reaction rate and transport equations, we predict the size and the number of individual cells needed to continuously produce hydrogen gas. The detailed kinetics of each of the cycle steps and their coupling to the waste heat recovery protocols will be discussed.

Using nonstoichiometric Co-Pb mixed metal oxides for solar thermal synthesis of hydrogen and CO

248th National Meeting (2014)

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