A shape-stabilized composite phase change material (SCPCM) made of n-nonadecane infused by capillary forces in a compressed reduced graphene oxide-activated carbon matrix (EFB(rGOAC)-M) was prepared from oil palm empty fruit bunch. The composite exhibited improved thermal properties and was used to fabricate an SCPCM by impregnation, in which the pores of the EFB(rGOAC)-M served as the support, while n-nonadecane was the central envelope. The EFB(rGOAC)-M exhibited a specific surface area of 680 m2 g-1 and an average pore size of 22 Å. The successful infiltration of n-nonadecane into the pores of EFB(rGOAC)-M was confirmed via nitrogen gas adsorption-desorption isotherms and scanning electron micrographs. According to the differential scanning calorimeter analysis, the composite SCPCM-5 exhibited melting and freezing temperatures of 37.25 °C and 25.58 °C, respectively, and an associated latent heat value of 82.72 J g-1 and -62.22 J g-1, respectively. There was no seepage during the phase change process (from solid to liquid, as the n-nonadecane was uniformly dispersed in the pores of the carbon matrix (EFB(rGOAC)-M) and held by the capillary and the surface tension forces of the carbon matrix. This innovative, inexpensive and environmentally friendly shape-stabilized phase change material could be applied for thermal energy storage applications.