Optimization of Thermoelectric Properties of Single-Walled Carbon Nanotubes by Transition Metal Ion Doping and Application to Waste Heat Power Generation

Single-walled carbon nanotubes (SWCNTs) are considered promising materials for future flexible thermoelectric applications due to their high electrical conductivity and tunable thermoelectric properties. However, the mutual constraints between their Seebeck coefficients and electrical conductivity severely limit further improvements for thermoelectric performance. In this study, we propose a doping strategy based on transition metal ions (TMIs) to break through the bottleneck of SWCNT-based materials by synergistically regulating the carrier concentration and mobility. Five low-cost metal ions (Fe3+, Co2+, Ni2+, Cu2+, and Zn2+) were employed as dopants to systematically investigate the thermoelectric properties of TMI/SWCNT films. The Cu2+-doped SWCNT exhibited optimal performance, achieving an electrical conductivity of 4051.84 S·cm–1, 10.66 times higher than that of pristine SWCNTs, and a power factor (PF) of 153.76 μW·m–1·K–2. Through X-ray photoelectron spectroscopy (XPS) and Raman spectra, the performance enhancement originates from a dual synergistic mechanism: (1) charge transfer between Cu2+ and SWCNTs effectively increases the hole concentration; (2) formation of a d–π conjugation system between d-orbitals of transition metal and the tubular π-electron cloud of SWCNTs constructs highly efficient charge-transport channels and reduces carrier migration resistance. A nine-pair thermoelectric module fabricated with the optimized material demonstrated an output power of 1.18 μW under a 60 K temperature gradient. This study provides both theoretical insights and a technical pathway for developing highly efficient, flexible, and low-cost SWCNT-based thermoelectric devices.