Thermoelectric Performance of n‐Type Poly(Ni‐tetrathiooxalate) as a Counterpart to Poly(Ni‐ethenetetrathiolate): NiTTO versus NiETT

Abstract The synthesis of the metal‐coordination polymer poly(nickel tetrathiooxalate) (NiTTO) is presented, which represents an alternative route to n‐type thermoelectric materials similar in nature to nickel ethenetetrathiolate (NiETT) polymers. The TTO monomer is synthesized through an electrochemical reduction of carbon disulfide, followed by coordination polymerization with a nickel(II) salt to yield a coordination complex polymer with a neutral repeat unit. An alkali metal counterion exchange and polymerization optimization are performed, and a thermoelectric power factor of 6 µW m⁻¹ K⁻² (electrical conductivity of over 10 S cm⁻¹) is achieved for NiTTO composite films in a polyvinylidene fluoride (PVDF) matrix. This is significantly higher than other reported n‐type polymers (and to within a factor of two of NiETT) and demonstrates the potential of NiTTO as a new thermoelectric material. Elemental analysis indicates a nearly neutral backbone structure in NiTTO with minimal charge balancing alkali ions, indicating that these polymers are more oxidized than NiETTs. X‐ray photoelectron spectroscopy reveals a different coordination environment for NiTTO compared to NiETTs with the same alkali counterion, indicating that—despite their structural similarity in theory—these two materials are indeed different.