## 2 Comparison of Experimental Devices
### HSLU  
The setup used at Lucerne University of Applied Sciences and Arts (HSLU) is based on the commercial device Easymax 102 (METTLER TOLEDO AG., CH), which is used as a cycling device and synthesis station (Figure 6). The Easymax is operated between \(-30\) and \(180\)\({}^{\circ}\)C. Two heating chambers with various adapters allow the measurement with one to five vessels (\(1\times 100\) mL, \(3\times 25\) mL, \(5\times 8\) mL) per chamber (Figure 7a). Magnetic or mechanical stirring can be applied. Easymax 102 contains one temperature sensor per chamber. Therefore, an external logging device to record the temperature of the other vessels is used. Different heating and cooling rates can be applied, either using a fixed rate or by controlled heating so that a temperature difference between the sample temperature (\(T_{\rm r}\)) and the temperature of the jacket (\(T_{\rm j}\)) is not exceeded. If more than one vessel per chamber is measured, only heating by rate is possible (Figure 8). During the experiments, the jacket temperature \(T_{\rm j}\) and the reaction temperature \(T_{\rm r}\) are measured. With the addition of a reaction calorimetry unit (Figure 7b), the phase change enthalpy, heat transfer coefficient, and specific heat can be determined as well. Typically, ten thermal cycles per day are carried out. Figure 5: Pictures of stability testing device “EHU”; thermostatic bath (**a**), glass tube and cap (**b**), thermally cycled samples (**c**). Figure 8: Typical temperature profiles of the stability testing device “HSLU” (fixed heating and cooling rate (**a**), constant temperature difference upon heating and fixed cooling rate (**b**)); jacket temperature \(T_{j}\), and reaction temperature \(T_{r}\). Figure 6: Picture of stability testing device “HSLU”. Figure 7: Sample containers of the stability testing device “HSLU” (**a**), reaction calorimetry unit (**b**). ISE Capsules  
The test facility \"ISE capsules\" consists of an open bath in which the encapsulated PCM samples are immersed. Circulating tap water is applied as a heat transfer fluid. The flow rate can be adjusted manually by means of a pump with a downstream restriction. The bath temperature is controlled by a thermostat that supplies heat to the test circuit by a heat exchanger. Temperature sensors at the flow and return line of the bath and a volume flow sensor allow the thermal balancing of the heat stored in the PCM macro-capsules. The schematic of the setup is shown in Figure 9.  
The typical temperature profile is comprised of temperature steps (1 K-min-1 heating and cooling rate), which are repeated cyclically. The set temperatures depend on the PCM under investigation and are usually set 5 K below and above the melting temperature of the PCM. Typically, ten thermal cycles per day are carried out. ISE Peltier  
This is a flexible Peltier test rig for cycling in the temperature range \(-\)30 to 200 \({}^{\circ}\)C. Up to 16 Peltier modules with a maximum heating and cooling power of 30 W each and a surface of \(65\times 65\) mm can be flexibly combined in the x and z directions. Each Peltier module has two Peltier elements: one on the bottom and one on top. The upper Peltier elements are single point fixed to compensate for non-parallel surfaces. The contact pressure of the upper Peltier element can be controlled by pressurized air. A picture of the Peltier test rig is shown in Figure 10.  
Up to eight individual temperature controllers are used to control the temperature of samples. Peltier elements can be individually attached to each controller. Temperature profiles are composed of basic segments. Basic segments are the sudden temperature change, ramp, or isotherms. Heating and cooling rates can be defined individually. Sample crucibles are designed as needed. In line stability check is not foreseen. External stability check via DSC, optical inspection, or others is necessary. Measured data are the temperatures of the PCM (middle or surface) and the temperature of the Peltier surface. Up to 24 thermal cycles per day are carried out.