A Review of Carbon Nanoparticles-Enhanced Salt-Based Phase Change Materials for Thermal Energy Storage Applications

Thermal energy storage (TES) is critical to improving energy efficiency and integrating intermittent renewable energy systems. Among various TES technologies, latent heat TES systems employing phase change materials (PCMs) offer high energy storage density but suffer from inherently low thermal conductivity, which limits charging and discharging rates. Carbon nanostructures have emerged as promising thermal conductivity enhancers because of their exceptional intrinsic thermal properties and large surface area. This review critically examines the incorporation of carbon nanostructures, including carbon nanotubes, graphene, expanded graphite, and carbon nanofibers, into salt-based PCMs. The review emphasizes their influence on thermal conductivity, specific heat capacity, phase transition behavior, cyclic stability, and overall energy storage performance. The mechanisms responsible for thermal enhancement, including percolation network formation, phonon transport facilitation, and interfacial thermal resistance reduction, are discussed in detail. A comparative analysis of reported literature highlights the trade-offs between conductivity enhancement and latent heat reduction, dispersion challenges, and long-term reliability concerns. Finally, key research gaps and future directions for optimizing nano-enhanced PCMs (NePCMs) for large-scale TES applications are identified. This review provides a structured and mechanistic perspective to guide the design of high-performance carbon-based composite PCMs. Unlike previous broad NePCM reviews, this work focuses exclusively on inorganic salt-based PCMs and incorporates the recent literature, including a systematic comparative table of carbon nanostructure performance metrics alongside a critical discussion of measurement methodology uncertainties that affect the reliability of reported values.