In this paper, the feasibility of using porous materials such as metal foams and expanded graphite to enhance the heat transfer capability of PCMs in high temperature thermal energy storage system is experimentally investigated. Experimental results showed that the heat transfer rate can be enhanced through addition of the porous materials by 2.5 times compared to that of pure NaNO3 in the heating process from 250-300 degrees C. However the heat transfer rate could be reduced by half in the liquid region since the natural convection can be severely suppressed by the porous structures. In an attempt to further reveal the natural convection effect in PCMs embedded in porous materials, two heating methods (boundary conditions) are examined. Finally the issue of corrosion process is briefly discussed. (C) 2011 Elsevier Ltd. All rights reserved.