Speaker
Description
Thermoelectrics are poised to become the next generation of sustainable energy materials. However, concerns with rigidity, toxicity and cost associated with traditional materials render many thermoelectrics unsuitable for integration in many applications. Novel thermoelectric materials may resolve these challenges through their intrinsic flexibility, moderate synthetic conditions and low toxicity.
Metal-Organic Frameworks (MOFS) are a class of porous materials comprised of metal centres or clusters coordinated to organic ligands. They benefit from high surface area, tunability and a wide variety of synthetic and deposition strategies. 2D-layered MOFs, analogous to graphene, have come to attention in recent years owing to their semiconducting properties that make them attractive candidates for thermoelectric systems. Moreover, due their intrinsic porous architecture, they exhibit ultra-low thermal conductivity which contributes to a desirable figure of merit, zT.[1]
The Cu-HITP metal-organic framework (MOF) consists of Cu(II) ions coordinated to the catecholate analogue, hexaaminotriphenylene (HITP) in a planar coordination geometry. This structure features hexagonal pores in a proposed eclipsed stacking arrangement, where π-π interactions between the stacked aromatic ligands facilitate charge transport via a through-space mechanism.[2] Moreover, the anisotropy of the framework and nano-structuring promotes Seebeck character through energy filtering mechanisms.[3]
We have prepared the Cu-HITP framework through solvothermal and a layer-by-layer (lbl) protocols to produce both bulk materials and thin films. For the bulk materials, we have recorded electrical conductivities as high as 550 S m-1 and a power factor of 0.758 µW K-2 m-1. As this material’s thermoelectric properties were observed to change rapidly in air, a systematic study was performed by recording HRXANES of Cu-HITP whilst exposed to components of air (O2, H2O,N2), as well as common MOF dopant I2 . This has developed the understanding of the structural and electronic changes to the framework with the introduction of guest species, whilst also identifying the contributions from both the metal centre and ligand. Ultimately, this feeds into understanding the structure-property relationship within this class of materials, which will aid in the rational design of novel thermoelectrics with tunable properties.
References
[1] H. Babaei, M. E. DeCoster, M. Jeong, Z. M. Hassan, T. Islamoglu, H. Baumgart, A. J. H. McGaughey, E. Redel, O. K. Farha, P. E. Hopkins, J. A. Malen and C. E. Wilmer, Nat Commun, 2020, 11:40101, 1-8. [2] Z. Tan, W. Jiang, C. Tang, L. C. Chen, L. Chen, J. Liu, Z. Liu, H. L. Zhang, D. Zhang and W. Hong, CCS Chemistry, 2022, 4, 713–721.
[3] D. Narducci, E. Selezneva, G. Cerofolini, S. Frabboni and G. Ottaviani, Journal of Solid State Chemistry, 2012, vol. 193, pp. 19–25
