Monomolecular heat engine

Addressing heat waste is of crucial importance, considering the fact that more than 70% of the global energy is wasted as heat, contributing to global warming and equipment malfunction. One approach to this problem is to use thermoelectricity and convert extra heat to useful work. For this, one needs the material that would operate close to Carnot efficiency (η_c) limit that can be written in a way η= η_c((1+ZT)^0.5-1)/((ZT+1)^0.5+1- η_c), where ZT is a dimensionless figure of merit. Current commercialized inorganic devices have ZT of less[1] than 6, though it is predicted that in molecular devices the value can be much higher[2]. In this work, we have explored the thermoelectric properties of bi-radical organic molecule (Sme-2Os) in sub-Kelvin temperatures with the double lock-In technique[3]. By subjecting the molecule to the temperature gradient and connecting it in series to useful load R, we realized a particle exchange heat engine. Our findings highlight the pivotal role of connection of the molecule to the leads. We observe the variation of over tenfold in the device performance between the two extensively investigated coupling configurations. This shows the importance of precise control over the molecular coupling when aiming to harness the potential of single molecular devices for energy harvesting applications.

[1] J. Zhang et al. J. Mater. Chem. C, 4, (2016)

[2] L. Cui et al. J. Chem. Phys. 7, (2017)

[3] P. Gehring et al. Nat. Nanotechnol. 16, (2021)