Progress in Nickel‐Coordinated Polymers as Intrinsically Conducting n‐Type Thermoelectric Materials

Abstract

Organic thermoelectrics have witnessed rapid development in the past decade for low temperature energy harvesting applications. While high performance p-type polymers have been demonstrated, ntype materials have lagged behind due to the limited number of stable n-dopants and low doping efficiencies. Nickel-coordination polymers are a promising class of n-type polymers as they are conducting without extrinsic doping, thus overcoming a major challenge. However, advantages in thermoelectric properties are outweighed by a complicated synthesis and a poorly understood reaction mechanism that has resulted in a large variation in literature for the same material. This progress report provides a comprehensive and critical overview of syntheses and thermoelectric property optimization approaches for two coordination polymers, namely Ni-ethenetetrathiolate (NiETT) and Nitetrathiooxalate (NiTTO). In particular, material characterization and thin film fabrication techniques are discussed, and the importance of reporting statistically relevant thermoelectric properties is highlighted to ensure reproducibility among different groups. A short discussion on prototype devices based on NiETT is presented, and finally, directions for future development of these and other n-type metal-coordinated polymers are suggested.

Dichlorinated Dithienylethene‐Based Copolymers for Air‐Stable n‐Type Conductivity and Thermoelectricity

“…Recently, several effective strategies for enhancing PF by improving S or σ have been demonstrated, including the electrochemical synthesis of nickel-coordination polymers which do not require extrinsic doping and can overcome the restriction of limited numbers of stable n-type dopants, and the introduction of ions to improve S and PF. [12,13] Sun et al developed very low band gap poly(Ni-ett) continuous large area thin films by using electrochemical deposition for n-type TE materials with high electrical conductivity of 220 S cm −1 and remarkable PF of 453 µW m −1 K −2 . [14] By introducing Cl − into PEDOT:PSS films, high negative S values of −18200 µV K −1 and a significant PF of 1700 µW m −1 K −2 were obtained by Kim et al [2] The Pei group developed a series of donor-acceptor (D-A) BDOPV-based conjugated polymers for high-performance n-type TE materials.…”

The effect of metalation processes on polymer morphology and conductivity properties

“…The diminishment of conductivity can be depending on the low coordination numbers. 5,12,[14][15][16]40,71 According to the experimental results, the amount of metal is lower than the theoretical calculation, which can be because the metals have a low coordination number on the polymeric structure. [72][73][74] The ICP, FT-IR and the conductivity results match perfectly because the number of the donated electrons change depending on the valance electron configuration of Co(d 7 ), Ni(d 8 ) and Cu(d 9 ).…”

“…8,10,11 Conductive polymers are one of the best potential materials for protection of the Li battery surfaces. [12][13][14][15][16][17] The morphological features of the polymers and their production methods, the number of donor atoms and centres, the kind of metals and their ionic charge, the hydrogen bond and the π-π stacking in the polymer and the steric hindrance are crucial for designing well-tuned and stable electrodes. 14,[18][19][20][21][22] More specifically, the type of organic linker in the polymer is also one of the most significant points to achieve a targeted, efficient porous morphology because linker ligands, having a single C-C bond (sp 3 ) and donor group, have the ability to give flexibility to each of the polymeric units.…”

Synthesis and Characterization of the Thermoelectric Nickel Tetrathiooxalate Polymer as Nanoparticles

“…Among OTE materials, M(ett) and M(tto) (M = Co, Ni, Cu) are currently taken into consideration, as evidenced by several recent experimental [8]- [14] and theoritical [15] [16] [17] articles (and ref. therein), after a long period of lack of interest in this kind of material.…”