Passive suppression of supercooling in water-based cold storage using copper oxide nanowire–modified copper foam

Phase change materials are widely used in thermal energy storage systems due to their high energy density and ability to store and release heat at nearly constant temperatures. Among these, water and salt hydrates are particularly attractive because of their high latent heat and low cost. However, their practical deployment is often limited by supercooling, a phenomenon that delays crystallization, extends the metastable liquid phase, and makes heat release unpredictable. This work presents a passive, additive-free method to suppress supercooling by growing copper oxide nanowires directly on open-cell copper foam, forming a stable, highly wettable nucleation framework. The nanowires were synthesized via controlled chemical oxidation and annealing, resulting in dense nanostructures that increased surface roughness and enhancing the surface hydrophilicity. Isothermal cooling experiments with deionized water, conducted across bath temperatures from −6 °C to −14 °C, demonstrated that bare copper foam significantly reduced the degree of supercooling compared to pure water. More notably, the nanowires-modified foam nearly eliminated supercooling, achieving an 89.9–99.9% reduction. While overall freezing times remained similar across foam-based samples, nucleation occurred earlier and more consistently with the copper oxide nanowires. This surface-engineering approach offers a scalable and robust solution to stabilize water-based latent heat storage systems by actively controlling nucleation through nanostructured interfaces. • In-situ CuO nanowires on copper foam effectively suppress DI water supercooling. • Isothermal tests quantify supercooling at −6 to −14 °C bath temperatures. • Nanowire-modified foam reduces DI water supercooling by 89.9–99.9%. • 135 cycles confirm high repeatability with minimal supercooling degree variance. • Nanowire-modified foam nearly eliminates DI water nucleation delay time.