(228e) Understanding the Fundamentals of the “Hercynite Cycle” and It Operational Behavior Under Pseudo-Isothermal Water Splitting Conditions

Muhich, C. L., University of Colorado at Boulder
Ehrhart, B. D., University of Colorado at Boulder
Weston, K., University of Colorado at Boulder
Alshankiti, I., University of Colorado at Boulder
Musgrave, C. B., University of Colorado
Weimer, A. W., University of Colorado at Boulder

economically, efficiently and cleanly. Two-step, metal oxide based STWS cycles generate H2 by a metal oxide undergoing sequential high temperature reduction and water re-oxidation.  The “hercynite cycle”, which is based on iron reduction in a spinel structure, relies on intimate contact between CoFe2O4 and Al2O3 phases though the exact mechanism was not well understood. In this work we study both the mechanism of the “hercynite cycle” and its operation under pseudo-isothermal conditions. Through a combination of computational and experimental studies using periodic boundary condition density functional theory, high temperature XRD and EDS we have determined that the hercynite cycle operates via an O-vacancy mechanism rather than the displacement reaction mechanism as previously suggested.  When operating under PITWS conditions we were able to produce H2 in excess of 200 μmol/g, which enables the Hercynite cycle to maintain the high production rates of isothermal water splitting but with higher production rates.