Nanostructured room-temperature synthesized Cu0.60Ni0.40/PEDOT-derived sulfur-doped carbon composites for enhanced thermoelectric performance via acid-engineered interfaces

Abstract

The integration of sulfur-doped carbon materials into thermoelectric systems presents a promising route for enhancing energy conversion efficiency, yet remains underexplored. In this study, we introduce a tunable strategy for converting poly(3,4-ethylenedioxythiophene) (PEDOT) into sulfur-doped carbon (PEDOT–SC) and incorporating it into nanostructured Cu_0.60Ni_0.40 alloys synthesized at room temperature to achieve enhanced thermoelectric performance. A targeted acid treatment using nitric and sulfuric acids introduces oxygen-containing functional groups across the composite surface, facilitating improved electrical conductivity by enhancing interfacial diffusion at the metal–sulfur-doped carbon junction. Advanced characterization studies reveal the structural and chemical evolution underpinning these improvements. X-ray Photoelectron Spectroscopy (XPS) confirms the successful doping of sulfur and oxygen functionalization, while High-Resolution Transmission Electron Microscopy (HRTEM) reveals a more diffuse interface following acid treatment, suggesting partial removal of the distinct oxide layer observed in untreated samples. Field Emission Scanning Electron Microscopy (FE-SEM) analysis shows that the nanostructured composites exhibit irregular aggregates with distinct granular features and sporadic porosity, which effectively suppress electronic thermal conductivity (κ_e). This structural transformation, combined with lattice defects such as dislocations, promotes enhanced phonon scattering, further reducing thermal conductivity. Conductive Atomic Force Microscopy (C-AFM) and Raman spectroscopy corroborate the acid-induced conductivity enhancement and defect engineering in the composites. As a result, the nitric acid-treated composite achieves a thermoelectric figure of merit (zT) of 0.7 at 720 K, with an electrical conductivity of 6.4 × 10³ S cm⁻¹, a thermopower of −76.7 μV K⁻¹, and a thermal conductivity of 3.85 W m⁻¹ K⁻¹. This study not only establishes sulfur-doped carbon derived from PEDOT as a promising material for thermoelectrics but also unveils a dual strategy of nanostructuring and acid treatment for optimizing interfacial conductivity and thermal transport.