The Cover Feature shows the cycling of a phase‐change material in the context of solar‐thermal energy storage application. Energy in the form of heat is harvested from the sun during the day, causing the melting of the phase‐change material. The energy is stored in the liquid form and can be slowly released after sunset. Phase‐change materials can be a promising solution for the intermittency of renewable energy sources. More information can be found in the Full Paper by K. Matuszek et al. on page 159 in Issue 1, 2020 (DOI: 10.1002/cssc.201902601).

Phase change materials (PCMs) which melt in the temperature range of 100-230 °C, are a promising alternative for the storage of thermal energy. In this range, large amounts of energy available from solar-thermal, or other forms of renewable heat, can be stored and applied to domestic or industrial processes, or to an Organic Rankine Cycle (ORC) engine to generate electricity. The amount of energy absorbed is related to the latent heat of fusion (ΔH_f) and is often connected to the extent of hydrogen bonding in the PCM. Herein, we report fundamental studies, including crystal structure and Hirshfeld surface analysis, of a family of guanidinium organic salts that exhibit high values of ΔH_f, demonstrating that the presence and strength of H-bonds between ions plays a key role in this property.