ACCELERATED DISCOVERY AND DEVELOPMENT OF PEROVSKITES FOR SOLAR THERMOCHEMICAL CHEMICAL HYDROGEN PRODUCTION WE PROPOSE TWO TASKS TO DEVELOP NOVEL OXIDE PEROVSKITES FOR WATER SPLITTING MATERIALS THAT MEET DOE TARGETS FOR COST (< $2/KG H2) AND EFFICIENCY (> 25% SOLAR-TO-HYDROGEN EFFICIENCY). TO THIS END, MATERIALS WILL BE DESIGNED WITH LOW THERMAL REDUCTION TEMPERATURES (< 1400°C), HIGH H2 PRODUCTION CAPACITY (> 200 ΜMOL H2/G/CYCLE), MATERIAL STABILITY AND REACTIVITY OVER MANY CYCLES (< 10% LOSS IN H2 PRODUCTION FROM CYCLES 100 TO 200), AND RAPID REDUCTION AND OXIDATION KINETICS (CYCLE TIMES <= 20 MINUTES). OUR PROJECT AIMS TO ACHIEVE THIS GOAL THROUGH A MATERIALS-BY-DESIGN EFFORT COMBINING QUANTUM CHEMICAL DENSITY FUNCTIONAL THEORY (DFT) COMPUTATION, MACHINE LEARNING (ML), EXPERIMENT, AND CHARACTERIZATION TO RELIABLY IDENTIFY NOVEL SOLAR THERMOCHEMICAL (STCH) PEROVSKITE OXIDES BY ACCOUNTING FOR THE EFFECT OF LOCAL DISORDER ON THE ELECTRONIC STRUCTURE AND OTHER STCH-RELEVANT PROPERTIES DURING HIGH-THROUGHPUT SCREENING. THE GOAL OF THE PROPOSED RESEARCH IS TO UTILIZE ML COMBINED WITH DFT COMPUTATION TO RAPIDLY EVALUATE CANDIDATE STABLE OXIDE PEROVSKITES FOR THERMODYNAMIC VIABILITY IN STCH USING ENTHALPY OF FORMATION (¿HF, FOR STABILITY), ELECTRONIC ENTROPY OF REDUCTION (¿SRED, FOR ELECTRONIC CONTRIBUTIONS TO THE REDUCTION FREE ENERGY, ¿GRED), AND OXYGEN VACANCY FORMATION ENTHALPY (¿HVAC, FOR REDUCTION POTENTIAL, WHICH CORRELATES TO HYDROGEN PRODUCTIVITY). IN BUDGET PERIOD 1 (Y1Q1-Y1Q4), WE WILL DEMONSTRATE THE VIABILITY OF OUR ML-BASED APPROACHES FOR SCREENING MATERIALS AND INVESTIGATING THE EFFECTS OF LOCAL DISORDER ON THE STCH-RELEVANT ELECTRONIC PROPERTIES. IN BUDGET PERIODS 2 AND 3 (Y2Q1-Y2Q4 AND Y3Q1-Y3Q4), WE WILL APPLY THESE MODELS TO FIRST SCREEN AA'BB'O6 PEROVSKITES (A AND B REPRESENTING A WIDE RANGE OF ELEMENTS) FOR STABILITY BASED ON THEIR DECOMPOSITION ENTHALPIES (¿HD > 50 MEV/ATOM), REDUCTION ENTHALPY (2 EV/ATOM < ¿HVAC < 4 EV/ATOM), AND H2 PRODUCTIVITY (>100 ΜMOL/G/CYCLE). THE MOST PROMISING COMPOSITIONAL FAMILIES IDENTIFIED FROM THE SET OF AA'BB'O6 COMPOUNDS WILL THEN BE USED TO INVESTIGATE MULTIPLE AYA'1-YBXB'1-XO6 ALLOYS. THROUGHOUT THE SCREENING PROCESS, WE WILL PERFORM EXPERIMENTS TO DEMONSTRATE THE WATER SPLITTING ABILITY OF CANDIDATE MATERIALS BOTH AT CU AND MINES, AS WELL AS AT EMN NODES. IN ALL THREE BUDGET PERIODS, WE HAVE INCLUDED MILESTONES FOR EXPERIMENTAL FEEDBACK AND VALIDATION OF THE COMPUTATIONAL METHODS AND THE CRITERIA USED FOR DOWN-SELECTION CANDIDATE ACTIVE MATERIALS IDENTIFIED IN TASK 1. WE HAVE ALSO INCLUDED DEI MILESTONES IN BUDGET PERIODS 1-3 WHERE WE WILL GIVE AT LEAST ONE RESEARCH SEMINAR AT AN HBCU OR MSI, HOST AT LEAST 1 STUDENT RESEARCHER FROM AN UNDERREPRESENTED BACKGROUND IN OUR LABS, AND RECRUIT STUDENTS FROM UNDERREPRESENTED BACKGROUNDS TO PARTICIPATE IN A SUMMER OUTREACH PROGRAM AIMED AT EDUCATING EARLY CAREER SCIENTISTS.