Polypyrrole/Tin Sulfide Hybrid Nanocomposites as Promising Thermoelectric Materials: A Combined Experimental and DFT Study

Abstract

Conducting polymer-based inorganic/organic nanocomposites has become a popular candidate as eco-friendly thermoelectric (TE) materials in the past few years. This work reports a comprehensive study of the TE properties of tin sulfide (SnS)/polypyrrole (PPy) nanocomposites for the first time. The nanocomposites are prepared via two, low-cost steps: a chemical reaction to synthesize the SnS nanoparticles, followed by an in situ polymerization reaction. The TE properties of these SnS/PPy composites in a temperature interval of 303–373 K are investigated by tuning the content of SnS nanoparticles in the polymer matrix. The observations are discussed based on the results from structure analysis (X-ray diffraction), optical properties (UV–vis), surface morphology analysis (field emission scanning electron microscopy and high-resolution transmission electron microscopy), and chemical composition analysis (Fourier transform infrared spectroscopy, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy). In order to analyze the orbital contribution and the carrier transport mechanism in the SnS/PPy composites, first-principles density functional theory (DFT) calculations are employed. The electronic band structure and density of states spectra clearly dictate that the formation of nanocomposite results in a decrement in the band gap, which might be a reason for the enhanced TE response of the nanocomposites. TE parameters, such as Seebeck coefficient (S), electrical conductivity (σ), and power factor (PF), are enhanced in the composites than in the pure PPy. The study reports maximum S (∼50.67 μV K–1), σ (∼32.26 S cm–1), and PF (∼6 μW m–1 K–2) values for composites containing 20, 10, and 20 wt % of SnS nanoparticles. Among the synthesized samples, the maximum ZT of ∼0.86 × 10–2 is achieved for PPy/20 wt % SnS at 373 K. This work concludes that the inclusion of SnS nanoparticle fillers in the conductive PPy matrix is an efficient route to enhance the TE performance of PPy. The newly fabricated nanocomposite is a novel, low-cost, nontoxic TE material relevant to green energy generation and environmental remediation.