Population growth and continued industrialization of developing countries may double global energy consumption by 2035. If such energy demands are largely met by fossil fuels, the deleterious effects of climate change induced by anthropogenic carbon loading of the earth’s ecosystems will greatly intensify. Therefore, developing technologies that capture and store solar energy has become a social imperative. This talk will describe efforts to directly convert highly-concentrated thermal energy from the sun into hydrogen fuel via a thermochemical process; so-called solar thermochemical hydrogen production (STC). Our implementation of  STC is predicated on a simple two-step metal oxide redox cycle that utilizes the entire solar spectrum as high-temperature process heat to produce hydrogen by water splitting (WS). In step one, the oxide is defected by driving oxygen from the lattice at high temperature. In step two, and upon exposure to steam at a lower temperature, oxygen is stripped from the water molecule and transferred back into the oxide. This completes the cycle and results in the net production of hydrogen. A principle advantage of STC over other WS-techniques like photo-driven electrolysis (e.g. integrated as in PEC or disintegrated as in PV-electrolysis) is that STC does not require precious metal catalysts nor engineering of complex multi-layered functionalized structures.<br/> <br/>Here we focus on the use of non-stoichiometric perovskite oxides to accomplish the redox cycle chemistry, and describe our efforts to explore the fundamental underpinnings of important relationships between oxide composition, electronic structure, and functionality. Specifically, we are interested in formulating atomistic design rules that enable tuning of the redox material’s thermodynamic properties important to this application, namely the trade-off between decreasing the perovskite thermal stability (i.e., lowering the energy required to form an oxygen vacancy) while maintaining high favorability to the water-splitting re-oxidation reaction (which occurs at extremely low oxygen chemical potential). We will also review challenges and opportunities for discovering new redox cycle chemistries within the context of achieving high solar-to-hydrogen conversion efficiency in a STC reactor design.

Hydrogen production by solar thermochemical water splitting: Searching for optimal nonstoichiometric perovskite oxides

255th National Meeting (2018)

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