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

Abstract

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, graphene nanotube (GNT) 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 GNT-based paste through a confined nozzle geometry, i.e. without agglomeration and nozzle clogging, a homogeneous epoxy resin-dispersed GNT paste was produced. As a result, various 3D-printed structures with high GNT concentration (10 wt %) were obtained via shear-mixing processes. The 3D printed p- and n-type epoxy-dispersed GNT-based thermoelements exhibit high power factors of 102 and 75 μW/mK2, 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 VOC = 13.6 mV, short-circuit current ISC = 1204 μA, internal resistance RTEG = 11.3 Ohm, and a generated power output PMAX = 4.1 μW at ΔΤ = 100 K (with TCold=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.