Owing to their excellent thermal and electrical properties combined with pronounced porosity, carbon nanotube forests are promising as support materials for catalysts in smart reactors. In order to maximise the catalytic turnover, the available surface has to be increased while precise control over the flow of the reactants and over the distribution of heat is maintained.
In this work, multiwalled carbon nanotubes are grown on substrates in three dimensions that are based on triply periodic minimal surfaces. These structures offer superior mechanical properties alongside controlled flow dynamics and enhanced rates of heat transfer. The substrates are fabricated by laser powder bed fusion and are subsequently coated by injection chemical vapour deposition.
In order to evaluate the limitations of the design, the impact of a decreasing permeability on the morphology of the coating is investigated. The permeability decreases with the size of the unit cell of the minimal surfaces and with the introduction of an external wall, and the characteristic structure of the nanotube forest gradually transforms. Provided that the permeability and the accessibility of the precursor to the internal surfaces remain sufficiently high, the morphology and the composition of the forests closely resemble those grown on flat substrates.
Introducing the wall leads to a transition from vertically aligned forests to horizontally oriented networks, because the flow becomes more laminar. These networks are less dense, but the quality of the nanotubes is higher. Below a critical minimal permeability, carbon nanostructures with numerous defects form. The successful coating and the control of its morphology enable the use of carbon nanotubes for the further smart tailoring of the reactor.
The study is a collaboration between Hamburg University of Technology, the University of Hamburg and the Fraunhofer Research Institution for Additive Manufacturing Technologies IAPT, carried out within the Collaborative Research Centre CRC 1615 (SMART Reactors).
Fabian Riebesehl, Serhan Acikgöz, Timo Merbach, Christiane Roller, Dominique Lumpp, Dirk Herzog, Jakob Albert, Ingomar Kelbassa, Michael Schlüter, Bodo Fiedler (2026). Impact of Permeability of Triply Periodic Minimal Surface-Based Substrates on Multiwalled Carbon Nanotube Growth. Ind. Eng. Chem. Res. 65 (30), 16002-16013.
