Electrochemically exfoliated nanostructured-graphite nanofluids for heat transfer applications

Abstract

Enhancing the thermal conductivity (TC) of heat-transfer fluids is critical for high-efficiency cooling. This study formulates nanofluids with electrochemically exfoliated graphite (EEG) flakes dispersed in deionized (DI) water and evaluates their thermophysical performance. Two low-hazard exfoliation routes were examined: direct anodic exfoliation in 0.5 M H2SO4 and a two-step NaOH pre-intercalation followed by H2SO4 exfoliation. SEM/EDX, FTIR, UV-visible spectroscopy, and X-ray diffraction reveal the formation of multi-layer exfoliated nanostructured-graphite flakes (average flake thickness approximately 106 nm) bearing 12 to 17 at% surface oxygen, with about 26 crystallite layers. The prominent (002) diffraction peak near two-theta 26.5 degrees (interlayer spacing about 0.34 nm), observed in X-ray diffraction (XRD), confirms graphitic stacking, while an electronic transition band at 267 nm, identified by UV-visible spectroscopy, indicates extended sp2 domains typical of lightly oxidized graphite. Nanofluids containing 0.5 wt% EEG achieved a 25% thermal conductivity enhancement relative to deionized water, while maintaining visual stability for over three months. Thus, electrochemical exfoliation yields partially oxidized exfoliated nanostructured-graphite flakes that are a promising candidate for nanofluids, providing a scalable pathway to energy-efficient cooling fluids.