THE GOAL OF THE PROPOSED EFFORT IS TO DEVELOP NOVEL NONSTOICHIOMETRIC PEROVSKITE OXIDES WITH HIGH STABILITY AND FAVORABLE THERMODYNAMIC AND KINETIC PROPERTIES, TO OPTIMIZE MICROSTRUCTURE FOR MAXIMIZING THE FUEL PRODUCTIVITY, AND TO BUILD A PROTOTYPE REACTOR TRAIN SYSTEM (RTS) COMPRISING AT LEAST ONE REACTOR TO MEET SPECIFIC PERFORMANCE TARGETS: (1) CAPABLE OF AN IN-HOUSE SOLAR THERMOCHEMICAL HYDROGEN (STCH) PRODUCTIVITY = 12 ML G-1 FOR STABLE CONTINUOUS OPERATION = 20 CYCLES; AND (2) DEMONSTRATION OF SCALABLE SOLAR FUELS PRODUCTION AT PRACTICAL SOLAR REACTOR LEVEL IN AN INDUSTRIAL-SCALE CONCENTRATED SOLAR TOWER (CST) USING DEVELOPED PEROVSKITES TO ACHIEVE A HYDROGEN PRODUCTION RATE = 1 G H-1. SPECIFIC OBJECTIVES ARE TO RATIONALLY IDENTIFY AND OPTIMIZE PEROVSKITE OXIDES AND TO DEMONSTRATE THEIR CAPABILITY IN PRACTICAL REACTORS FOR SCALABLE SOLAR FUELS PRODUCTION BY STCH TECHNOLOGY.