To find a cool storage phase-change materials (PCM) with large storage capacity, high heat transfer efficiency, and low supercooling, we investigated a water-based composite by using foam copper as the framework, which has been proved to enhance the thermal conductivity remarkably. We investigated the supercooling of water icing in pure foam copper with the help of differential scanning calorimetry, and found it was suppressed from 20.6 degrees C to 6.8 degrees C. By introducing AgI as the nucleation agent onto the foam copper coated with gold layer to prevent chemical reaction between the AgI and the copper, the supercooling was further suppressed down to 2.1 degrees C. Mechanism of the suppression of the supercooling was also discussed. Potential applications are expected for such PCM with high latent heat, relatively high thermal conductivity, and low supercooling, especially in the field required instantly high cold release power.