Directional oxygen diffusion in Cu1.5Mn1.5O4 crystals for long reversible thermochemistry

JL Deng and CD Gu and HR Xu and G Xiao, SOLAR ENERGY MATERIALS AND SOLAR CELLS, 260, 112474 (2023).

DOI: 10.1016/j.solmat.2023.112474

Redox activity of metal oxides are the key to the development of high- temperature thermochemical energy storage. However, few studies have reported that the reactivity of metal oxides as thermochemical energy storage is significantly affected by the changes of crystal structure and morphology during redox, caused by ion diffusion and vacancy formation and migration. In this study, we find a previously unreported high-performance ther-mochemical energy storage material Cu1.5Mn1.5O4 with special structure. Cu1.5Mn1.5O4 shows high energy densities during reduction and oxidation (-219.852 and 207.618 kJ/kg), and keeps 97.06% and 92.98% reac-tivity after 600 cycles. Voids on specific surfaces are observed after cycling, but not in the fresh sample. We find the voids provide abundant Cu2+, Mn4+ species and lattice oxygen to promote its reaction performance. Cu ions migrate obviously after oxidation and molecular dynamics simulations reveal that DCu (7.4 x 10-14 cm2 s- 1) is higher than DMn (5.1 x 10-14 cm2 s- 1) and DO (1.7 x 10-14 cm2 s- 1). Cu1.5Mn1.5O4 exhibits voids during oxidation due to ion transport described by the Kirkendall effect. In addition, DFT calculations verify that O2-is more easily to adsorb and diffuse on (111) surface, revealing the optimal transport path and directional diffusion mechanism of O2-. These mechanisms can provide ideas for the reasonable design of materials to improve thermochemical reaction performance.

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