Additive manufacturing of highly conductive carbon nanotube architectures towards carbon-based flexible thermoelectric generators

Moving the fabrication of electronics from the conventional 2D orientation to 3D space, necessitates the use of sophisticated additive manufacturing processes which are capable to deliver multifunctional materials and devices with exceptional spatial resolution. In this study, it is reported the nozzle-guided 3D-printing of highly conductive, epoxy-dispersed, single-walled carbon nanotube (SWCNT) architectures with embedded thermoelectric (TE) properties, capable to exploit significant waste thermal energy from the environment. In order to achieve high-resolution and continuous printing with the SWCNT-based paste through a confined nozzle geometry, i.e. without agglomeration and nozzle clogging, a homogeneous epoxy resin-dispersed SWCNT paste was produced. As a result, various 3D-printed structures with high SWCNT concentration (10 wt%) were obtained via shear-mixing processes. The 3D printed p- and n-type epoxy-dispersed SWCNT-based thermoelements exhibit high power factors of 102 and 75 μW mK⁻², respectively. The manufactured 3D carbon-based thermoelectric generator (3D-CTEG) has the ability to stably operate at temperatures up to 180 °C in ambient conditions (1 atm, relative humidity: 50 ± 5% RH), obtaining TE values of an open-circuit voltage V_OC = 13.6 mV, short-circuit current I_SC = 1204 μA, internal resistance R_TEG = 11.3 Ohm, and a generated power output P_max = 4.1 μW at ΔT = 100 K (with T_Cold = 70 °C). The approach and methodology described in this study aims to increase the flexibility of integration and additive manufacturing processes for advanced 3D-printed conceptual devices and the development of multifunctional materials.