Phase Change Materials (PCMs) are widely recognized for their potential in thermal energy storage systems due to their high latent heat capacity. However, their practical application is significantly hindered by low thermal conductivity, which limits the charging and discharging rates of energy. This review provides a comprehensive and critical synthesis of recent passive techniques developed to enhance the thermal performance of PCMs. These include finned structures, porous media, nanoparticle dispersion, geometrical modifications, and multi-PCM strategies. Quantitative comparisons show that the use of fins can reduce melting time by up to 65 %, while metallic porous matrices can improve thermal conductivity by over 500 %. Incorporation of nanoparticles has demonstrated up to 25 % enhancement in heat transfer rates, albeit with increased viscosity. Geometrical innovations and multi-PCM layering have enabled tailored thermal responses across temperature ranges, suitable for applications such as solar thermal systems and building-integrated energy storage. Furthermore, this review identifies trade-offs associated with each method, including design complexity, cost, and material compatibility, and presents a comparative performance table to guide selection based on system requirements. Hybrid enhancement strategies, such as nanoparticle-doped PCMs embedded in metal foams, are also proposed as a promising direction for future research. The review concludes with specific, forward-looking insights, highlighting opportunities for PCM-based solutions in solar desalination, cold-chain transport, and passive building cooling under real-world constraints.
