The redox cycle of doped CaMnO3−δ has emerged
as an attractive way for cost-effective thermochemical energy storage
(TCES) at high temperatures in concentrating solar power. The role
of dopants is mainly to improve the thermal stability of CaMnO3−δ at high temperatures and the overall TCES
density of the material. Herein, Co-doped CaMnO3−δ (CaCo
x
Mn1–x
O3−δ, x = 0–0.5)
perovskites have been proposed as a promising candidate for TCES materials
for the first time. The phase compositions, redox capacities, TCES
densities, reaction rates, and redox chemistry of the samples have
been explored via experimental analysis and theoretical calculations.
The results demonstrate that CaCo0.05Mn0.95O3−δ showed an enhanced redox capacity (1000 °C
at pO2 = 10–5 bar) without
decomposition and provided the highest TCES density of ∼571
kJ kg–1 reported so far. The effective Co doping
tended to increase the valence states of B-site cations in perovskite
and facilitate the diffusion of the lattice oxygen atoms into the
surface-active oxygen sites. Furthermore, the high cooling rates deteriorated
the microstructure of CaCo0.05Mn0.95O3−δ particles and resulted in incomplete heat release, which is instructive
to the design and operation of the TCES systems.
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