Guanidinium Organic Salts as Phase-Change Materials for Renewable Energy Storage

A dearth of inexpensive means of energy storage is constraining the expansion of intermittent renewable energy sources such as sun and wind. Thermal energy storage technology utilizing phase-change materials (PCMs) is a promising solution, enabling storage of large quantities of thermal energy at a relatively low cost. Guanidinium mesylate, which melts at 208 °C with latent heat of fusion of ΔH_f =190 J g^-1 is a promising PCM candidate for these applications.^[1] Here, studies on guanidinium organic salts were conducted, including heat capacity, thermal conductivity, advanced thermal stability, long-term cycling, and economic analysis. The data place guanidinium mesylate among the best PCMs operating in the 100-220 °C temperature region in terms of thermal energy storage, with total volumetric energy storage measured as 622 MJ m^-3 (173 kWh m^-3 ). Additionally, it was shown to be stable during cycling, with over 400 cycles performed. Simple economic analysis indicated a cost of 6 USD per MJ of stored thermal energy. This study proves that guanidinium mesylate and potentially other similar salts can be feasible as PCMs for inexpensive energy storage for renewable energy storage applications.