Anisotropically conductive Mg(NO3)2·6H2O/g-C3N4-graphite sheet phase change material for enhanced photo-thermal storage

Abstract

The use of phase change materials (PCMs) for solar thermal collection can solve the mismatch problem of energy supply and demand caused by intermittent solar radiation. Traditionally, photo-thermal storage performance has been limited by the low thermal conductivity of PCMs and the massive heat transfer loss between PCMs and their external environment. Herein, we demonstrate that embedding a highly oriented graphite sheet (GS) network in a PCM results in an anisotropic thermal conduction structure, endowing the material with rapid internal thermal conduction and reduced heat loss to the external environment, thereby enhancing photo-thermal storage performance. We imitate the structure of layer cake to create a multilayered composite phase change material (CPCM), Mg(NO3)2∙6H2O/g-C3N4-GS (MNH/CN-GS), which has a highly oriented anisotropic thermal conductivity. The through-plane and in-plane thermal conductivities of MNH/CN-GS reach 0.55 and 15.70 W/(m·K), respectively, at 40 wt% GS loading in the CN-GS matrix. This corresponds to a high anisotropic degree of thermal conduction of 28.56, which results in a high average photo-thermal storage efficiency of 88.4%. The photo-thermal storage efficiency remains above 80% even at a high temperature of approximately 94 ℃. The proposed anisotropic thermal conduction structure eliminates the trade-off between high photo-thermal conversion rate and high energy efficiency in solar thermal storage.