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

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 mu W 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.