(165e) Design and Fabrication of Conductive 3D Printed Carbon Lattices Via Gel Infusion and Polymerization of Acrylonitrile and Subsequent Pyrolysis

High-temperature pyrolysis of 3D printed polymers to produce conductive pyrolytic carbon is gaining prominence in sustainable energy storage, carbon capture, and electrification applications. Pyrolysis necessitates structures with high surface-to-volume ratios to maintain mechanical integrity, as thinner features allow for the efficient escape of volatile components during heating, thereby preventing deformation. However, traditional molding methods are not able to fabricate large objects with microscale features, such as beam-based lattice structures. High resolution vat photopolymerization (VP) 3D-printing of non-moldable structures with high surface area to volume ratios, such as via the state-of-the-art continuous liquid interface production (CLIP) method, therefore adds significant value to pyrolysis. One of the most widely used materials in pyrolysis is polyacrylonitrile (PAN), which is a precursor for generating conductive high-strength carbon fibers that are commonly used in lightweight structural applications and have been incorporated into battery systems for sustainable energy storage. However, limited literature exists that demonstrates generation of high-resolution structures (< 100 µm features) composed of PAN by a scalable VP 3D-printing method, such CLIP. During VP 3D-printing, the formation of a crosslinked network, which is crucial for preserving high-resolution architectures during photo-initiated polymerization, is hindered by the linear polymer nature of PAN which leads to precipitation reactions and subsequent powder formation.

To overcome the challenges faced by VP 3D-printing high-resolution PAN structures for pyrolysis, we have developed a novel method for producing 3D carbon structures from PAN. This process involves: (1) 3D printing a microscale crosslinked acrylate gel lattice sacrificial scaffold via CLIP, (2) infusing the gel scaffold structure with acrylonitrile monomer and a thermal initiator, (3) polymerizing the AN monomer to PAN linear chains inside the gel scaffold structure forming a semi-interpenetrating polymer network, and then (4) subjecting the PAN-infused gel lattice structure to thermal treatment processes (e.g. an oxidative pre-treatment, isothermal holds, and pyrolysis) that converts the PAN to 3D pyrolytic carbon (Figure 1). This method is inspired by previous work by Saccone, M. and Greer, J. et al. investigating metal hydrogel infusion.

We have investigated the impact of pyrolysis conditions on the char yield of these PAN-swelled gel scaffolds over a wide range of temperatures and excipient gas (air, nitrogen) flow rates. With optimized conditions, we demonstrate > 40% char yield by mass, which is comparable to industry values of char yield for conventionally electrospun PAN fibers. Characterization of the resulting pyrolytic carbon structures has demonstrated that they exhibit evidence of graphitization, they are electrically conductive, and they exhibit promising voltage potential ranges for energy storage. This method additionally shows promise for incorporation of other high char yield linear polymers beyond PAN into high-resolution lattice structures to tailor pyrolytic carbon properties. PAN-based pyrolytic carbon lattice structures developed via our novel gel infusion method hold significant promise for use in commercial applications including electrodes for battery energy storage, susceptors for electrifying thermochemical reactors, and substrates for carbon capture electrocatalysis.