Finetuning hierarchical energy material microstructure via high temperature material synthesis route

Abstract

Hierarchical energy materials such as graphite are a backbone of various scientifically and commercially important emerging technologies including high-energy density energy storage systems with fast charging capability, multifunctional catalyst systems, selective membrane separation systems, and next-generation nuclear material systems. Consequently, it is extremely crucial to develop an efficient and cost-effective route of bulk hierarchical material synthesis (e.g., carbonaceous materials with a well-controlled fraction of the graphitic content) to cater the extraordinary operational and energy material requirements in a very complex coupled thermophysicochemical environment. Here we present a fabrication of Polyacrylonitrile (PAN) derived carbon films and fibers (~with linear dimension ~100 nm) via electrospinning and spin coating methods ensued by a heat-treatment in the range of 1000–3000 °C under inert atmospheric conditions. Intriguingly, we observed at least a two orders of magnitude enhancement (~134%) in length of graphitic plane accompanied by 36% more graphitization when the carbonization temperature increased from 1000 °C to 3000 °C. Such significant enhancements were attributed to the differences in the fundamental nanomorphology of initial carbonaceous materials and their subsequent kinetic evolution as it was more favorable for underlying graphene layers in films to stack and bond to the adjacent ones without strong rotations as compared to fibers, which were further evident from fewer voids and cracks in the films. The covalent cross-links, substrate effect and physical entanglements of carbon domains in PAN-derived carbon films contributed to a higher graphitic length owing to more shear stress between the graphene layers, compared to fibers and undergoes an enormous transformation from turbostratic structures to ordered state along with nitrogen removing over high temperature heating. This morphology dependent graphitization was also investigated from computational approach and concluded in the similar thoughts. The outcomes from this systematic study can be beneficial to the carbon research community focusing in the morphology dependent applications, for instance catalysis, energy storage, sensors etc.