## 1 Introduction  
Thermoelectric energy conversion can be used to capture electric power from waste heat in a variety of applications. Temperature fluctuations can affect very much not only the conversion efficiency but also converter life (thermoelectric semiconductors overheat at high temperature). Thermoelectric converter life can be assured by incorporating any high-temperature preventive measurement, while efficiency can be achieved by reducing temperature variation. Latent heat storage by use of phase change materials (PCM) appears as an appropriate technology to absorb temperature fluctuations, that way assuring thermoelectric converter life and efficiency. During a phase change process (melting and crystallization), the PCM material absorbs or releases heat, maintaining its temperature as constant. These phase change phenomena appear in a temperature-time diagram as a plateau.  
Efficiency is much more related to the thermal resistance of the heat sinks used in the thermoelectric converter. The lower the thermal resistance, the higher the converter efficiency.  
In this regard, the use of PCMs to absorb temperature fluctuations results in an increase in the heat sink thermal resistance [1, 2] due to PCMs' low thermal conductivity. Therefore, great care must be taken when defining a PCM-based heat sink [3, 4, 5], mainly with transient behavior [6, 7].  
Despite all of the work reported on PCM heat sinks [8, 9, 10] and the tremendous interest nowadays in TES in various industry branches as an energy-saving technology, few works have been carried out till now about high-temperature thermal storage and PCM-based heat sinks. In this regard, this work aims to present:  
* The thermophysical characterization of a high-temperature PCM: \(\odot\) Characterization of the PCM thermal properties (melting temperature and melting enthalpy); \(\odot\) PCM stability against thermal cycles when enclosed into a stainless-steel container.
* PCM and container's material compatibility for a specific application: \(\odot\) Corrosion test to check the compatibility of the PCM with different steels for the container.  
The application of interest in this work is to use a PCM to absorb possible temperature peaks at the hot side of the thermoelectric module that could damage a thermoelectric device designed to work up to 730 \({}^{\circ}\)C. This thermoelectric converter has been designed to recover part of the thermal energy of the combustion gases from a foundry. These gases go to the atmosphere at a temperature of 700 \({}^{\circ}\)C (high waste heat) but momentarily can reach peaks of temperature of 750-800 \({}^{\circ}\)C that could damage the device.  
The use of PCMs in low-temperature applications has been widely studied, and nowadays recent studies show novel forms of PCMs, such as nanocomposite PCMs or microtubule-encapsulated PCMs, which can reversibly store and release large amounts of thermal energy, making possible an efficient technology to ameliorate the energy crisis and environmental problems [11; 12; 13]. Nevertheless, to fulfil the objective of this application (protect the device from the temperature peaks), high-temperature PCMs (carbonates, metals, etc.) are required, so the aim of this work is the study and selection of a high-temperature PCM (700-850 \({}^{\circ}\)C) with stability against thermal cycles, high energy storage capacity and minimum corrosive effect.  
Figure 1 shows different PCM families with their corresponding melting temperature and enthalpy: metals, carbonates, fluorides and chlorides [14]. Not all of them fulfil the application requirement (melting temperature higher than 700 \({}^{\circ}\)C), just those inside the brown rectangle; some chlorides, some carbonates and some fluorides meet it.  
Figure 1: Families of PCMs depending on the melting temperature and its enthalpy.