A ferromagnetic composite of PEDOT:PSS and nitrogen-graphene decorated with copper oxide nanoparticles with high anisotropic thermoelectric properties

Abstract

Although the PEDOT:PSS/graphene (PP/GR) thermoelectric (TE) system has a high electrical conductivity (σ), it faces great issues regarding its high thermal conductivity (k) and its relatively low Seebeck coefficient (S) which restrict its TE applications. Therefore, a new composite of PEDOT:PSS and copper oxide (CuO) nanoparticle decorated nitrogen doped graphene (PP/^CuONG) has been introduced in this work with a good anisotropic TE performance in order to solve these limitations. Doping of graphene with nitrogen plays a dual role in improving the Seebeck coefficient (S) by creating interfacial energy barriers and decreasing the k value by scattering the phonons. Besides, the adornment of CuO on the NG surface reduces the stacking nature of NG layers and hence decreasing the k value. Moreover, the ferro-magnetic performance of CuO nanoparticles provides a high spin Seebeck coefficient which improves the S value of the composite systems. For CuO < 20 wt%, an increasing trend in anisotropic TE functions is obtained, whereas a great drop in anisotropic TE functions is observed at R.T for CuO > 20 wt%. Interestingly, the anisotropic TE functions are significantly improved by the CuO addition, with the anisotropic power factors PF of the composite with 20 wt% CuO (PF_‖ ∼ 180.62 ± 3 μW m⁻¹ K⁻² and PF_⊥ ∼ 106.52 ± 4 μW m⁻¹ K⁻²) showing a ∼550% improvement over PP/GR (PF_‖ ∼ 32.35 ± 2 μW m⁻¹ K⁻², PF_⊥ ∼ ¹8^.23 ± 3 μW m⁻¹ K⁻²). Furthermore, the composite displays k_‖ ∼ 0.31 ± 0.045 W m⁻¹ K⁻¹ and k_⊥ ∼ 0.27 ± 0.060 W m⁻¹ K⁻¹ at RT for 20 wt% CuO which is >2.8 times smaller than that of PP/GR (k_‖ ∼ 0.87 ± 0.04 W m⁻¹ K⁻¹ and k_⊥ ∼ 0.606 ± 0.07 W m⁻¹ K⁻¹). Accordingly, the optimized film displays a large anisotropic figure of merit zT (zT_‖ ∼ 0.175 ± 0.004 and zT_⊥ ∼ 0.118 ± 0.003) at R.T, which is >13 times larger than that of PP/GR (zT_‖ ∼ 0.011 ± 0.003 and zT_⊥ ∼ 0.009 ± 0.005). This study presents simple, safe, economic, and effective TE composites with promising TE performance which can be potentially applied in TE generators, temperature sensors and spintronics.