Crystal phase-dependent optical properties of CoMn-based spinel oxides for solar thermal conversion†
Abstract
Spinel materials are promising solar absorbing candidates in concentrating solar power (CSP) due to their excellent high-temperature stability and adjustable light-absorbing properties. However, it is still unclear how the crystal structure of spinels affects their solar absorption properties and further solar-to-heat conversion efficiency. In this work, we found that both the absorption coefficient and skin depth of cubic phase Co2MnO4 are higher than those of tetragonal phase CoMn2O4. The difference in light absorption properties between Co2MnO4 and CoMn2O4 is attributed to the different excitation modes and d–d transitions of the materials. The cubic Co2MnO4 allows a direct electronic transition process and multiple allowed d–d transitions, which is responsible for the improved absorption properties of Co2MnO4. Therefore, the cubic Co2MnO4 spinel exhibits higher macroscopic absorption than its tetragonal counterpart in the UV-vis-IR diffuse reflectance spectra, especially at around 1400 nm. As a result, Co2MnO4 displays an internal photothermal conversion efficiency of 94.0%, which is higher than that of CoMn2O4 (69.4%). This work reveals the intrinsic correlation of the crystal phase of CoMnO-based spinel materials with its optical properties and solar thermal conversion efficiency.
- This article is part of the themed collection: Journal of Materials Chemistry A HOT Papers