IL-PCM : Sustainable Ionic Liquids (IL) as Phase Change Materials (PCM) for Energy Storage in Smart Buildings

The 2.3 Mio buildings in Switzerland are responsible for around 50% of the energy consumption, from which ca. 80% are dedicated to thermal energy (heating, hot water, air conditioning, etc.). The largest part of the heat production for buildings today takes place still through oil and gas heating units what makes the building sector responsible for around 40% of Swiss CO₂ emissions. This energy consumption and its related CO₂-emission must be strongly reduced to achieve the Swiss “2050 Energy Strategy” goals. One way to do it is by novel and innovative energy storage concepts like the integration of latent heat storage devices in buildings.

Latent heat storage devices use a phase transition of the storage material to store thermal energy; such phase change materials (PCM) can absorb peak energy in solar plants, act in buildings as passive temperature stabilization or allow an active control of the building temperature as proved by the previous SLL project “Smart-PCM Walls”. PCM can delay the temperature change in a building and stabilize it around the PCM fusion temperature (passive) or be used as a real thermal battery with a full control of the charge and discharge process (active).

Chemicals used today as PCMs are either from fossil resources (paraffin’s), hydrated salts or fatty acids. The current problems and challenges of these materials are costs, sustainability, corrosion, toxicity, fusion-solidification temperature, hysteresis, material purity, small temperature conductivity, thermal cycling stability, and packaging.

There is also only a modest number of manufacturers and commercial products. We propose to use ionic liquids (IL) as novel and innovative PCMs. ILs are organic salts with melting temperature typically below 100°C. The advantage of ILs is the endless number of cation/anion combinations that allows synthesizing IL for specific applications. The goal is, based on our experience in ILs and PCM, to use natural and renewable chemicals to prepare novel PCM-ionic liquids and perform direct material characterizations to allow sustainable applications in the building and energy sector for latent heat storage.

We see this project as an advanced feasibility and proof-of-concept study. There is already a lot of know-how inhouse available regarding ionic liquids and phase change materials and the goal is to bring this expertise together to evaluate scope and limits of ionic liquids (IL) to store heat via their phase change from solid/liquid.

For the execution of this project, we have identified three main goals:

1. Screening and evaluation based on industrial requirements of biobased ILs for PCM applications, including synthesis of novel IL’s;
2. Create a short-list of candidate ionic liquids that are ideally suited as PCM and test them in a “proof-of-concept” small-scale demonstrator developed within this project;
3. Evaluation and assessment of potential partners (academia & industry) for further development.