N-eicosane/expanded graphite as composite phase change materials for electro-driven thermal energy storage

Abstract

• High latent heat composites were obtained by using EG as a support matrix. • The composites has much higher thermal conductivity than pure C20. • The composite with 15 wt.% EG shows excellent electro-to-heat conversion performance. Latent heat storage (LHS) is considered to be a promising technique for thermal energy storage, due to its high energy storage density and nearly constant working temperature. However, the phase change materials (PCMs) used in LHS usually suffer from low thermal conductivity. In this work, the expanded graphite (EG) was applied to support n-eicosane (C20) via vacuum impregnation to prepare C20/EG composite PCMs. The DSC analysis indicated that the C20/EG 15 has latent heat values of 199.4 J g −1 for melting and 199.2 J g −1 for freezing, exhibiting a large thermal storage capacity. The effect of EG on thermal performance was investigated and results suggested that the thermal conductivity of the composite with 15 wt.% EG (3.56 W m −1 K −1 ) is 14.4 times than that of pure C20 (0.25 W m −1 K −1 ), and the heating and cooling curves confirmed the EG has substantially improved the thermal transfer rate of samples. Furthermore, the electro-to-heat conversion measurement was carried out under small voltage (1.9–2.1 V), and the C20/EG 15 exhibits high electro-to-heat storage efficiency (65.7%) under the voltage of 2.1 V. In all, the composite C20/EG 15 is a potential candidate not only for electro-to-heat conversion but also for other thermal storage applications due to large latent heat capacity and high thermal conductivity.