Strategies to dope 3D graphene for flexible thermoelectric applications

• Novel doping strategies for 3D graphene sheets (3DGS) enable flexible thermoelectric devices. • PEI-A, N-DMBI, and TBD dopants significantly enhance n-type conductivity and Seebeck coefficient. • Sulfuric and nitric acid treatments improve p-type behavior via oxygen functionalization. • A flexible TE device with doped 3DGS achieved 9.7 µW power output at ∼18 K ΔT. • Device performance remains stable across a wide range of relative humidity levels. This study presents a systematic investigation of doping strategies for three-dimensional graphene sheets (3DGS) possessing distinctive architecture to enhance their thermoelectric (TE) properties for flexible energy harvesting applications. Both n-type and p-type doping were achieved using polymeric and chemical dopants, including Polyethyleneimine (PEI), Annealed PEI (PEI-A), (4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl) dimethylamine (N-DMBI), TBD (1,5,7-triazabicyclo[4.4.0]dec-5-ene), urea, PVP (polyvinylpyrrolidone), sulfuric acid, and nitric acid. Structural and electronic modifications were confirmed through X-ray photoelectron spectroscopy (XPS) and Kelvin Probe Force Spectroscopy (KPFS), while electrical performance was evaluated via Seebeck coefficient (SC) and electrical conductivity (EC) measurements. Among the n-type dopants, PEI-A exhibited the highest performance with a SC of approximately −44 µV K -1 , EC of ∼57 S cm -1 , and a power factor (PF) of ∼11.2 µW m -1 K -2 . This superior performance is attributed to the deprotonation of amine groups during thermal annealing, which restores lone-pair electrons on nitrogen and enhances electron donation to the graphene lattice. The sulfuric acid treatment yielded strong p-type behavior with a SC of +34.8 µV K -1 . A flexible TE device fabricated using optimized doped 3DGS demonstrated a power output of 9.7 µW at a ΔT of ∼18 K, with minimal performance degradation under ∼82% relative humidity and after 20 days of exposure. Subject: Thermoelectric Energy Generation and Harvesting, Chemical Vapor Deposition (CVD), Characterization techniques (Seebeck, conductivity, XPS, KPFS), Sustainable energy solutions.