Enhancement of Thermal Conductivity in Phase Change Materials for Thermal Energy Storage Applications: A Comprehensive Review

International Journal of Research (IJR) e-ISSN: 2348-6848 p-ISSN: 2348-795X Vol. 12 Issue 11 November 2025 Received: 24 October 2025 265 Revised: 8 November 2025 Accepted: 18 November 2025 Copyright  authors 2025 DOI: HTTPS://DOI.ORG/10.5281/ZENODO.17642076 Enhancement of Thermal Conductivity in Phase Change Materials for Thermal Energy Storage Applications: A Comprehensive Review Nidhi¹, Jayesh Kumar² ¹²Department of Applied Sciences, Maharaja Surajmal Institute of Technology, New Delhi, India Corresponding Author email id: [email protected] Abstract Phase Change Materials (PCMs) are widely recognized for their high latent heat capacity and stable thermal performance, making them ideal for thermal energy storage (TES) applications. However, their inherently low thermal conductivity limits charging and discharging rates, reducing system efficiency. This review presents recent advancements in enhancing the thermal conductivity of PCMs through nanoparticle dispersion, structural modification, and hybrid enhancement strategies. Studies involving metallic and metal oxide nanoparticles (Cu, Al₂O₃, Ag, CuO), carbon-based nanomaterials (graphene, CNTs, graphite), and novel nanostructures (MnO₂ nanowires/nanotubes) are discussed. The effects of nanoparticle type, concentration, container geometry, and hybrid systems combining fins, heat pipes, and nanoparticles are systematically analyzed. The review concludes that graphene-based and MnO₂-based nanocomposites offer superior thermal performance with minimal impact on latent heat, making them promising candidates for future TES technologies. Keywords Phase Change Materials (PCMs); Thermal Energy Storage (TES); Nanoparticles; Graphene; Carbon Nanotubes (CNTs); Heat Pipes; Thermal Conductivity Enhancement; Nanocomposite PCM. 1. Introduction Latent heat storage materials have been extensively explored for their potential in thermal energy storage (TES) due to their ability to absorb and release large amounts of energy during phase transitions. The storage mechanism is based on solid–liquid or solid–solid transformations [1], with solid–liquid transitions being most preferred for TES systems owing to their high latent heat of fusion [2], small volume change, [3] and stable temperature-operation[4]. PCMs are broadly classified into inorganic (salts, salt hydrates, metals, and alloys) [5] and International Journal of Research (IJR) e-ISSN: 2348-6848 p-ISSN: 2348-795X Vol. 12 Issue 11 November 2025 Received: 24 October 2025 266 Revised: 8 November 2025 Accepted: 18 November 2025 Copyright  authors 2025 DOI: HTTPS://DOI.ORG/10.5281/ZENODO.17642076 organic (paraffin waxes, fatty acids, poly-alcohols) materials [6]. Among these, paraffin wax has gained significant attention because of its chemical stability, low cost, noncorrosive nature, and negligible supercooling. However, the low thermal conductivity[7] [8] of organic PCMs severely limits their heat transfer rate, posing a major barrier to their practical applications. To overcome this limitation, researchers have incorporated high thermal conductivity additives such as metallic fins, graphite, carbon nanotubes (CNTs), and graphene [9][10]. These fillers significantly enhance the effective thermal conductivity of PCMs, but high filler loading can lead to reduced latent heat and increased material cost. Consequently, optimizing filler concentration and morphology remains crucial to achieve the desired balance between thermal conductivity and energy storage capacity. In recent years, cool thermal energy storage (CTES) systems have gained prominence in building air-conditioning, food preservation, and electronic cooling. PCM-based systems are ideal for these applications as they enable efficient storage of cooling energy during off-peak hours and its release during peak demand, thus reducing energy costs and enhancing operational reliability. 2. Discussion Wu et al. [11] improved the thermal conductivity of paraffin (RT4) by incorporating carbon nanotubes (CNTs). With a 3% CNT concentration, solid and liquid thermal conductivities increased by 30.3% and 28.5%, respectively, with only slight reductions in latent heat. When applied to a refrigerated display cabinet, CNT-based PCMs significantly reduced temperature fluctuations, demonstrating improved cooling uniformity and energy efficiency. R.P. Singh et al. [12] identified graphene as the most effective nanoparticle among metals and metal oxides. In a LiNO₃–KCl eutectic salt system, graphene nanoplates enhanced thermal conductivity while slightly increasing viscosity. The optimized design reduced melting time by 57% compared to a conventional system, confirming graphene’s superior heat transfer efficiency. Ebadi et al. [13] conducted a combined numerical and experimental study using CuO nanoparticles dispersed in bio-based coconut oil PCM. They demonstrated that increasing the Rayleigh number and nanoparticle concentration enhanced natural convection and melting performance, improving energy storage without altering the phase change pattern. Khodadadi and Hosseinizadeh [14] numerically examined Cu nanoparticle-based NEPCMs. The addition of nanoparticles enhanced both thermal conductivity and heat release rates while slightly reducing latent heat. Their results confirmed that NEPCMs enable faster charging and discharging in TES systems. International Journal of Research (IJR) e-ISSN: 2348-6848 p-ISSN: 2348-795X Vol. 12 Issue 11 November 2025 Received: 24 October 2025 267 Revised: 8 November 2025 Accepted: 18 November 2025 Copyright  authors 2025 DOI: HTTPS://DOI.ORG/10.5281/ZENODO.17642076 Wang et al. [15] prepared PEG8000/MWCNT nanocomposite PCMs and observed that thermal conductivity increased from 0.295 to 0.531 W/m·K, while latent heat decreased slightly. The composite demonstrated excellent form stability and faster melting/solidification, indicating suitability for TES applications. Harish [16] investigated the thermal conductivity and viscosity of CuO–octadecane nanofluids, finding that conductivity increased up to 9%, while viscosity rose by 60% with higher nanoparticle concentration. The addition of nanoparticles changed the fluid behavior from Newtonian to shear-thinning, enhancing its convective heat transfer capability. S. Harish et al. [17] prepared lauric acid–graphene nanocomposites and reported a 230% increase in thermal conductivity with just 1 vol% graphene. Graphene outperformed CNTs and metallic nanoparticles due to its high aspect ratio and low interfacial resistance, while latent heat and melting temperature remained nearly constant. This demonstrates graphene’s strong potential for high-efficiency TES systems. M. Mahdavi et al. [18] proposed a hybrid enhancement technique combining heat pipes and nanoparticles (Al₂O₃, Ag, Cu, CuO). The inclusion of heat pipes significantly reduced melting and solidification times, and nanoparticle addition further accelerated heat transfer. The study revealed a synergistic relationship between heat pipe number and nanoparticle type, highlighting the effectiveness of hybrid conductive mechanisms. W. Liang et al. [19] incorporated MnO₂ nanowires and nanotubes into organic PCMs, achieving a 377% improvement in thermal conductivity while retaining high latent heat (140–206 J/g). XRD analysis confirmed the preservation of crystalline structure. The composites showed excellent cyclic stability, with only 2.8% loss in latent heat after 100 cycles, making them highly durable for long-term TES use. Kumar et al. [20] numerically studied Cu nanoparticle-enhanced paraffin PCMs in a magnetic field. The optimal nanoparticle concentration was found to be 2% for maximum melting rate and 0.5% for maximum energy storage. A stronger magnetic field suppressed natural convection, reducing both melting rate and storage efficiency. M.E. Zayed et al. [21] reviewed heat transfer enhancement techniques including fin design, container geometry, and hybrid configurations. Rectangular containers and longitudinal fins were found to enhance performance most effectively. They recommended combining fins, graphite, and heat pipes in future designs for improved efficiency. V. Mayilvelnathan et al. [22] investigated erythritol-based PCM with 1 wt% graphene in a shell-and-helical tube configuration. The helical design ensured uniform phase front movement, reducing melting time by 30% and solidification time by 20%. The system achieved superior thermal uniformity and efficiency, ideal for medium-temperature TES applications. 3. Conclusions International Journal of Research (IJR) e-ISSN: 2348-6848 p-ISSN: 2348-795X Vol. 12 Issue 11 November 2025 Received: 24 October 2025 268 Revised: 8 November 2025 Accepted: 18 November 2025 Copyright  authors 2025 DOI: HTTPS://DOI.ORG/10.5281/ZENODO.17642076 This review highlights the remarkable progress made in enhancing the thermal conductivity and heat transfer efficiency of phase change materials through nanotechnology and design innovations. Among all studied approaches: Graphene-based nanocomposites provide the highest conductivity enhancement with minimal effect on latent heat. Metal oxide nanoparticles like CuO and MnO₂ improve heat transfer and maintain structural stability. Hybrid systems integrating fins, heat pipes, and nanoparticles achieve rapid melting/solidification while maintaining good energy storage density. Optimized geometries, such as helical or conical storage systems, ensure uniform heat distribution and enhanced system reliability. Overall, the integration of nanostructures and advanced heat transfer mechanisms significantly improves PCM performance, paving the way for next-generation efficient, compact, and durable TES systems for applications in HVAC, renewable energy, and industrial thermal management. 4. References [1] M. K. Rathod and J. Banerjee, “Thermal stability of phase change materials used in latent heat energy storage systems: A review,” Renew. Sustain. 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