Authors: Qian, X; He, JG; Mastronardo, E; Baldassarri, B; Yuan, WZ; Wolverton, C; Haile, SM

Article.
Matter. vol: 4. page: 2590-2393.
Date: feb-03. 2021.
Doi: 10.1016/j.matt.2020.11.016.

Abstract:
Variable valence oxides of the perovskite crystal structure have emerged as promising candidates for solar hydrogen production via two-step thermochemical cycling. Here, we report the exceptional efficacy of the perovskite CaTi0.5Mn0.5O3-delta (CTM55) for this process. The combination of intermediate enthalpy, ranging between 200 and 280 kJ (mol-O)(-1), and large entropy, ranging between 120 and 180 J (mol-O) (-1) K (-1), of CTM55 create favorable conditions for water splitting. The oxidation state changes are dominated by Mn, with Ti stabilizing the cubic phase and increasing its reduction enthalpy. A hydrogen yield of 10.0 +/- 0.2 mL g (-1) is achieved in a cycle between 1,350 degrees C (reduction) and 1,150 degrees C (water splitting) and a total cycle time of 1.5 h, exceeding all previous fuel production reports. The gas evolution rate suggests rapid material kinetics, and, at 1,150 degrees C and higher, a process primarily limited by the magnitude of the thermodynamic driving force..