Enhancing inward and outward mass transport during chemical vapor deposition of pyrolytic carbon for better synthesis of ZTC

Abstract

Zeolite-templated carbon (ZTC) can be prepared by chemical vapor deposition (CVD), which involves the coupled mass transport and chemical reaction of carbon precursors. Combining theoretical and experimental approaches, this work demonstrated that reducing the particle size of the template enhanced both the inward and outward mass transport during zeolite-templated CVD, which, in turn, improved the structural properties of the resulting ZTC. Specifically, the inward diffusion of the carbon precursor was modelled quantitatively by fitting the deposition mass of pyrolytic carbon measured in zeolite templates of different particle sizes (d = 4, 0.8 and 0.002 mm). This model revealed that the inward diffusion of the carbon precursor was enhanced in smaller zeolite particles, allowing more uniform deposition of pyrolytic carbon inside the zeolite and better replication of the zeolite's pore structure in the resulting ZTC. For the outward mass transport, semi-quantitative analysis was conducted on the intermediate components that were responsible for the external deposition of pyrolytic carbon. In particular, the concentration of the intermediate components was predicted to increase with the particle size of the zeolite. This prediction was confirmed by the experimental characterization results, where ZTC samples prepared with larger zeolite particles showed thicker external layers of quasi-crystalline graphitic carbon.