Phase-change materials (PCMs) have emerged as a critical technology for thermal energy storage due to their ability to absorb and release large amounts of latent heat during phase transitions. Nanoengineering has significantly enhanced the performance of PCMs by addressing key challenges such as low thermal conductivity, leakage during phase transitions, and cycling instability. Advances in encapsulation techniques, thermal conductivity enhancement using carbon nanomaterials, and cycling stability improvements have expanded their applications in building climate control and industrial waste heat recovery systems.

Encapsulation techniques play a pivotal role in stabilizing PCMs and preventing leakage during melting. Nanocapsules and core-shell structures are among the most effective methods for confining PCMs at the nanoscale. Nanocapsules typically consist of a polymer or inorganic shell surrounding a PCM core, with diameters ranging from 100 to 500 nm. These structures provide a high surface-to-volume ratio, enabling efficient heat transfer while minimizing PCM leakage. Core-shell configurations, such as silica-coated paraffin or polyurethane-encapsulated fatty acids, offer enhanced mechanical strength and thermal stability. For instance, silica shells exhibit high thermal resistance and chemical inertness, making them suitable for high-temperature applications.

Thermal conductivity enhancement is another critical area where nanoengineering has made significant strides. Pure PCMs often suffer from low thermal conductivity, which limits heat transfer rates and reduces efficiency. Incorporating carbon-based nanomaterials such as graphene, carbon nanotubes (CNTs), or carbon nanofibers has proven effective in addressing this limitation. Graphene, with a thermal conductivity exceeding 3000 W/m·K, can dramatically improve heat diffusion within PCM composites. Studies have shown that adding just 5 wt% graphene to paraffin increases its thermal conductivity by over 200%. Similarly, CNTs form conductive networks within the PCM matrix, facilitating rapid heat absorption and release. Hybrid structures combining graphene oxide and metallic nanoparticles further enhance thermal performance by leveraging synergistic effects.

Cycling stability is a major concern for long-term PCM applications, as repeated phase transitions can lead to material degradation and reduced storage capacity. Nanoengineering approaches mitigate this issue through improved encapsulation and the use of stabilizing additives. For example, incorporating nanoscale clay particles into PCM composites prevents phase separation and suppresses supercooling effects. Additionally, cross-linked polymer networks within nanocapsules enhance mechanical durability, allowing thousands of cycles without significant performance loss. Research indicates that optimized nanocapsule formulations retain over 90% of their heat storage capacity after 10,000 thermal cycles, making them viable for industrial applications.

Applications in building climate control leverage nanoengineered PCMs for passive thermal regulation. Incorporating PCM nanocapsules into construction materials such as gypsum boards or concrete enables buildings to store excess heat during the day and release it at night, reducing energy consumption for heating and cooling. Simulations demonstrate that PCM-enhanced walls can lower indoor temperature fluctuations by up to 5°C, significantly decreasing HVAC loads. In industrial settings, waste heat recovery systems benefit from high thermal conductivity PCM composites. For instance, embedding CNT-enhanced PCMs in heat exchangers allows efficient capture and reuse of low-grade waste heat from manufacturing processes, improving overall energy efficiency.

Comparisons with sensible heat storage highlight the advantages of latent heat systems. Sensible heat storage relies on temperature changes in materials such as water or rocks, requiring large volumes to achieve comparable energy densities. In contrast, PCMs store 5 to 10 times more energy per unit volume due to their high latent heat capacity. For example, paraffin wax stores approximately 200 kJ/kg during melting, whereas water stores only 4.18 kJ/kg per °C temperature change. Additionally, nanoengineered PCMs operate within narrow temperature ranges, enabling precise thermal management that sensible heat systems cannot achieve.

Despite these advantages, challenges remain in scaling up nanoengineered PCM production and ensuring cost-effectiveness. Large-scale synthesis of uniform nanocapsules and homogeneous nanomaterial dispersions requires precise control over fabrication parameters. However, ongoing advancements in scalable techniques such as microfluidic encapsulation and spray drying are addressing these limitations.

In summary, nanoengineered PCMs represent a transformative approach to thermal energy storage, offering superior performance through advanced encapsulation, thermal conductivity enhancement, and cycling stability. Their integration into building materials and industrial systems demonstrates significant potential for energy savings and sustainable heat management. As research continues to optimize their properties and scalability, nanoengineered PCMs are poised to play a central role in global energy efficiency efforts.