Through combining predictive theory and experiment new functional materials for thermochemical cycles and reactions such as the oxygen evolution reaction. Many of these materials include metastable polymorphs of the groundstate materials and necessitate careful optimization of the inherent defect structure for that polymorph. The often exhibit multifunctional behavior. Barium nickelate, BaNiO₃, and its sub-oxides have shown potential as oxygen evolution reaction catalysts. Initial results indicate performance comparable to precious metal catalysts. We have synthesized highly phase pure materials and evaluated it in a thermochemical redox cycle. In this work we examine the structural and phase changes that occur during the redox cycling of BaNiO₃ at high temperature. Thermogravimetric analysis (TGA) on sol-gel synthesized powders under reducing and oxidizing conditions indicates a reversible cycling through multiple oxidation states. The structure of the BaNiO₃powder as determined by synchrotron x-ray diffraction is measured prior to and after TGA analysis to track the phase changes associated with redox cycling. Transimission electron microscopy is used to track changes in the powder surface, crystal structure and morphology. The stability of this structure over a wide range of oxidation states gives this material applicability in a number of energy applications such as electrochemical water splitting, multiferroics, and solid oxide fuel cells, all of which are discussed.

This work was funded by the Center for the Next Generation of Materials by Design, an U.S. Department of Energy, Office of Science EFRC under Contract No. DE-AC36-08GO28308 to NREL.