Improving Seebeck coefficient of thermoelectrochemical cells by controlling ligand complexation at metal redox centers

Practical conversion of waste heat into electricity via thermoelectrochemical cells requires high Seebeck coefficient (α) to increase cycle efficiency. The complexation of Cu²⁺ species with dissolved multidentate ligands, such as ethylenediaminetetraacetic acid, and the control of dimerization equilibria with bridging ligands, such as 1,6-diaminohexane or 1,2-diaminoethane, dramatically improve, by up to ∼185%, the magnitude of the α of Cu/Cu²⁺ thermoelectrochemical cells. This results in the highest α for any Cu/Cu²⁺ redox system yet reported. The coefficient α is directly proportional to the change in entropy (ΔS). It was experimentally measured and correlated with ΔS obtained from quantum-chemical methods. This offers a deeper insight about a molecule-based interpretation of the macroscopic response. The agreement between the theoretically estimated and experimentally observed α is remarkable. Hence, we believe that this synergistic approach allows us to systematically scan different systems to obtain efficient thermoelectrochemical cells with enhanced Seebeck coefficient.