<p>Phase change materials (PCMs) provide promising thermal energy solutions as they store and release thermal energy during phase shifts. The thermal energy stored in PCMs can be integrated with advanced energy storage and thermal conversion applications. Furthermore, it improves thermal management through heat dissipation efficiency and extends effective heat absorption and dissipation durations. However, some challenges such as liquid phase leakage and low thermal conductivity of pure PCMs need to be solved. This work presented a novel method to overcome these difficulties by synthesizing shape-stable composite PCMs (ss-PCM) from waste rice husk ash (RHA) and expanded graphite (EG) by vacuum impregnation method. The resulting RHA: EG-based ss-PCM has uniform distribution within RHA pores and improves thermal conductivity with maintaining functional group integrity as confirmed by SEM, thermal conductivity analyzer and FTIR analyses, respectively. UV–vis spectroscopy shows 600% increase in absorbance over pure PCM, which indicates better light absorption capability. Thermal conductivity is 0.45 W&#xa0;m⁻¹&#xa0;K⁻¹ with trade-off of 25% loss of latent heat. The thermal stability of composites shown up to 403.15&#xa0;K without any degradation was confirmed by TGA analysis, and the composite shows good chemical and thermal reliability after 500 cycles. The prepared composites can be utilized for thermal regulation and energy storage applications with waste materials as an environmental concern. Therefore, the study advocates sustainable energy solutions and pollution mitigation against climate change.</p> Graphical abstract <p></p>