Enhancing the thermoelectric performance of Cu–Ni alloys by introducing carbon nanotubes

High power factor and low thermal conductivity are imperative to maximize the energy conversion efficiency of thermoelectric materials. Constantan (Cu–Ni alloy), a widely-used material for thermocouples, has higher power factor (∼12000 μW m⁻¹ K⁻² at 950 K) [Mao et al. 2015] than the classic Bi₂Te₃-based thermoelectric materials (∼4500 μW m⁻¹ K⁻² at 300 K) [Poudel et al. 2008]. However, the high thermal conductivity restricts its thermoelectric performance. In this work, we demonstrate that, the thermal conductivity of Cu–Ni alloy can be effectively reduced from 48.1 to 9.6 W m⁻¹ K⁻¹ at 873 K by introducing carbon nanotubes (CNTs), and the thermoelectric performance is remarkably improved with the figure of merit (zT) being up to 0.41, an enhancement of about 141% over the pristine Cu–Ni alloy. Negative correlation between the total thermal conductivity of hybrid composite and the specific surface area of CNTs is further identified. The thermal conductivity suppression mechanism is ascribed to the introduction of both porous structures and carbon-nanotube-metal interfaces. Our studies provide a promising and general strategy to enhance the thermoelectric properties of materials with high thermal conductivity.