Two types of form-stable phase change materials (PCMs) were developed by impregnation of Na2CO3 center dot 10H(2)O-Na2HPO4 center dot 12H(2)O eutectic hydrated salt (EHS) into expanded graphite (EG) and expanded graphite oxide (EGO). The effects and mechanisms of chemical structures of EG and EGO on thermal properties were thoroughly discussed, in which the chemical structures were revealed by XPS, Raman spectra and XRD, and the thermal properties were assessed using the DSC analysis and thermal conductivity test. The results indicated that the EHS/EGO composite possessed higher latent heat, favorable thermal conductivity and lower supercooling degree because of the more surface oxygen-containing groups and surface defects as well as larger interlayer spacing in the EGO. Furthermore, the EHS/EGO composite remained thermally stable after 200 thermal cycles. This work will provide insights into the performance improvement of form-stable PCM composites by means of tailoring the chemical structures of porous supports. (C) 2017 Elsevier Ltd. All rights reserved.