Electro-to-heat energy conversion/storage provides a new direction for the development of phase change materials (PCMs). However, conversion rate and energy storage density of the existing PCMs are limited by their low intrinsic electrical and thermal conductivities and poor compressive strength. In this work, a novel form-stable phase change material (FSPCM) has been prepared via ligand replacement followed by the embedment of acetylene black conductive network. The addition of 20 wt% acetylene black reduces the resistivity of the polyethylene glycol-based PCM from 10(7) - 10(12) Omega.m to 0.3 Omega.m, while its thermal conductivity is increased by 300%. The resulting conductive composite possesses the ability to store heat at voltage as low as 1.8 V and high electro-to-heat conversion efficiency. The composite compressive strength reaches 10(5) Pa at an ambient temperature of 110 degrees C, while the temperature is 60 degrees C more than that of phase transition temperature of PCM. Further, the magnitude of the temperature change in the electrothermal conversion curves recorded after 50 solid-liquid phase transition cycles does not exceed 2.0%. The excellent electrical and thermal conductivities as well as good mechanical properties of the synthesized composite suggest a promising route for manufacturing novel materials with high power capacity for thermal storage applications.