Phase change materials (PCMs) having a large latent heat during solid-liquid phase transition are promising for thermal energy storage applications. However, the relatively low thermal conductivity of the majority of promising PCMs (<10 W/(m ⋅ K)) limits the power density and overall storage efficiency. Developing pure or composite PCMs with high h. Solid-liquid phase change materials (PCMs) have been studied for decades, with application to thermal management and energy storage due to the large latent heat with a relatively low temperature or volume change. Recent advances and challenges associated with electrification (photovoltaics and wind), high-power-density electronic devices and machines, electrified transportation, energy conversion, and building air conditioning have re-invigorated interest in PCM thermal storage.1, 2, 3 Thermal storage using a PCM can buffer transient heat loads, balance generation and demand of renewable energy, store grid-scale energy, recover waste heat,4 and help achieve carbon neutrality.5 Compared with other energy storage methods such as electrochemical batteries, PCMs are attractive for their relatively low cost and ease of integration with readily available energy resources such as solar power.6,7Although the large latent heat of pure PCMs enables the storage of thermal energy, the cooling capacity and storage efficiency are limited by the relatively low thermal conductivity (∼1 W/(m ⋅ K)) when compared to metals (∼100 W/(m ⋅ K)).8,9 To achieve both high energy density and cooling capacity, PCMs having both high latent heat and high thermal conductivity are required. One method to increase the thermal conductivity of a PCM is to mix the PCM with a high ther. This work was supported by the National Science Foundation Engineering Research Center for Power Optimization of Electro-Thermal Systems (POETS), with cooperative agreement EEC-1449548. N.M. gratefully acknowledges funding support from the International Institute for Carbon-Neutral Energy Research, Kyushu University (WPI-I2CNER), sponsored by the J. Download : Download Acrobat PDF file (434KB)Document S1. Notes S1–S3, Figures S1 and S2, and Table S1.Download : Download Acrobat PDF file (3MB)Document S2. Article plus supplemental information.1.Z. Wang, Z. Tong, Q. Ye, H. Hu, X. Nie, C. Yan, W. Shang, C. Song, J. Wu, J. Wang, et al.Dynamic tuning of optical absorbers for accelerated solar-thermal energy storageNat. Commun., 8 (2017), p. 1View in ScopusGoogle Scholar2.K. Faraj, M. Khaled, J. Faraj, F. Hachem, C. CastelainPhase change material thermal energy storage systems for cooling applications in buildings: a reviewRenew. Sustain. Energy Rev., 119 (2020), p. 109View PDFView articleView in.