Hybrid thermoelectric (TE) nanocomposites containing conducting polymers and nanocarbon materials have been extensively studied in recent years due to their unique advantages over single-phase organic/inorganic TE materials. Nanocarbon materials have been developed as conductive nanofillers to improve the electrical conductivity of the polymer matrix, and to create a strong π–π interfacial interaction with the matrix to enhance the TE performance. However, previous designs of the hybrid TE nanocomposites tend to cause aggregation of nanocarbon materials, which is detrimental to the TE performance. Also, they are limited in their fabrication to thin film technologies with submicron thicknesses, which prevents these composites from being used in practical TE devices. Herein, we present the synthesis and thermoelectric properties of free-standing, three-dimensional graphene (3DG)–polyaniline (PANI) composites with greater than 100 μm thicknesses for high performance flexible p-type thermoelectrics. Our 3DG matrix has been synthesized by Chemical Vapor Deposition (CVD) with particulate nickel catalysts, and used as a scaffold for the polymer composites. This material provides an excellent electrical conductivity and a reasonable Seebeck coefficient along with very good mechanical integrity preserved when bending, thus making it a promising candidate for flexible TE. PANI polymer was electrochemically grown on the 3DG scaffold as a filler to further tune the TE properties. The proposed 3DG–PANI composites showed a maximum power factor of 81.9 μW m⁻¹ K⁻² with a PANI loading of 80 wt% and highly reproducible TE performance after repeated mechanical bending tests. This novel material provides a different strategy for simple and scalable fabrication of flexible thermoelectrics with high performance TE energy harvesting and improved mechanical properties.

Graphene foam (GF) is a three-dimensional (3D) graphene structure that has been intensively studied as an electrode material for energy storage applications. The porous structure and seamlessly connected graphene flakes make GF a promising electrode material for supercapacitors and batteries. However, the electrical conductivity of GF is still unsatisfactory due to the lack of macropore size (∼300 μm) control that hinders its applications. Previously we reported a new seamless 3D graphene structure – graphene pellets (GPs) – with well-controlled mesopore size (∼2 nm), high electrical conductivity (148 S cm⁻¹) and good electromechanical properties that differ substantially from the known GF. Here we demonstrate that the obtained 3D graphene structure is an ideal scaffold electrode for pseudocapacitive materials and redox additive electrolyte systems. For example, after electrochemical coating with MnO₂, the GP/MnO₂ electrode showed specific and volumetric capacitance up to 395 F g⁻¹ and 230 F cm⁻³ at 1 A g⁻¹, respectively. When combined with a hydroquinone and benzoquinone redox additive electrolyte, the GPs showed a specific capacitance of 7813 F g⁻¹ at 10 A g⁻¹. Moreover, when the GP/MnO₂ electrode was assembled with a GP/polypyrrole electrode, the obtained full cell showed good electrochemical performance with a maximum energy density of 26.7 W h kg⁻¹ and a maximum power density of 32.7 kW kg⁻¹, and a reasonable cycle life for practical application. The ease in material processing combined with the excellent electrical and electromechanical properties makes GPs promising for a variety of energy storage applications.