Confined vertical foaming induces graphite crystal orientation: exceptional isotropy of thermal conductivity and anti-leakage properties for phase change systems

Abstract

Phase Change Materials (PCMs) are being increasingly recognized for their pivotal role in thermal regulation but are hindered by low thermal conductivity (TC) and leakage issues. Efforts to improve their thermal performance have typically involved enhancing one-directional TC with highly oriented one-dimensional or layered carbon fillers, leading to high anisotropy. However, the complexities of aligning these materials have prompted a shift toward exploring 3D materials with isotropically high thermal conductivity and anti-leakage properties. Here, we developed a novel 3D graphite fiber-backboned graphitic foam composite (GFBGF) to address these challenges. Our approach involves the infiltration of a graphite fiber matrix, exhibiting a preferred xy-plane orientation, with mesophase pitch. Subsequent confined foaming induces a vertical alignment of graphite crystal structure, significantly enhancing the cross-plane TC in a single, scalable operation. Remarkably, the GFBGF-PCM composite exhibits high TC of 33.05 W m⁻¹ K⁻¹ and 18.76 W m⁻¹ K⁻¹ in the in-plane and cross-plane directions, respectively, and an exceptionally low anisotropy ratio of only 1.75. In addition, the novel interconnected composite architecture encapsulates PCMs to prevent leakage during phase transitions. The simplicity and scalability of the fabrication approach offers a promising solution to unlock the full potential of PCMs across thermal energy storage, solar energy harvesting, and broader renewable technology sectors.