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3D printing technologies have expanded the possibilities of fabricating new composite materials with tailored properties, which depend on both the materials selected and the structural design at multiple length scales. Here, a catalyst-free CVD method has been used to produce hybrid materials based on 3D printed cellular alpha-Al2O3 substrates decorated by either nanocrystalline graphene or nanocrystalline graphitic films of tunable number of layers. Graphene-based coatings of variable thickness and crystallinity have been controlled by the alteration of the parameters of CVD processing, performed under CH4/H2 flux. Transmission electron microscopy has confirmed the effective growth of nanocrystalline graphene layers on the scaffolds due to the penetration of CVD gases into the open pores. The fully-connected and highly conductive 3D pathways have displayed a room temperature electrical conductivity in the range of 101-103 S m-1. Furthermore, the thermal conductivity has also increased by 50% for the specimen decorated with a 20 nm thick graphitic coating as compared to a bare 3D ceramic scaffold. The developed structures open up new possibilities for expanding the field of application of graphene/ceramic composites for conditions requiring dielectric substrates of various shapes coated with conductive films or graphene-based catalytic supports with good structural stability., Funding Agencies|Spanish Government [RTI2018-095052-B-I00, PID2020-120562RJ-I00, EIN2020-112153]; European Union; Estonian Research Council [PRG643]

[EN]The remarkable tunability of 2D carbon structures combined with their non-toxicity renders them interesting candidates for thermoelectric applications. Despite some limitations related to their high thermal conductivity and low Seebeck coefficients, several other unique properties of the graphene-like structures could out-weight these weaknesses in some applications. In this study, hybrid structures of alumina ceramics and graphene encapsulated alumina nanofibers are processed by spark plasma sintering to exploit advantages of thermoelectric properties of graphene and high stiffness of alumina. The paper focuses on thermal and electronic transport properties of the systems with varying content of nanofillers (1–25 wt.%) and demonstrates an increase of the Seebeck coefficient and a reduction of the thermal conductivity with an increase in filler content. As a result, the highest thermoelectric figure of merit is achieved in a sample with 25 wt.% of the fillers corresponding to ~3 wt.% of graphene content. The graphene encapsulated nanofibrous fillers, thus, show promising potential for thermoelectric material designs by tuning their properties via carrier density modification and Fermi engineering through doping.