Proof of cOncept of a multi-functional reverSible Electrochemical hYbriD cell Operating at iNtermediate temperature – POSEYDON

POSEYDON, is a 48-month "PRC" project, fitting the "Sustainable, clean, safe and efficient energy" challenge. It deals with the production of clean energy via the fuel cell, the production of hydrogen by electrolysis of water and the valorisation of CO2 (production of high added value products by co-electrolysis of H2O/CO2). The novelty with high ambition is to design a unique reversible electrochemical cell to address these three operation modes, called hybrid cell, using a composite electrolyte combining molten salts and solid oxide, operating in the 550-700°C temperature range. Three academic partners (IRCP, ICMCB, ICGM) are involved with complementary skills: high temperature electrochemistry (fuel cells, H2O and CO2 electrolysis) based on molten salts and/or solid oxide by protons and/or oxide ions, composite electrolyte, electrode materials (design and elaboration), electrochemical performances, electrochemical impedance spectroscopy. This project is based on the very promising results obtained independently by the three partners on electrodes and electrolyte materials, as well as on the development of new architectures and compatible elaboration methods for the assembly of the components to design a complete cell.

The project will be organized around three main scientific tasks. The task 1 will address the selection of the best materials. We are considering an original electrolyte, resulting from recent researches leaded by IRCP and ICGM. Thanks to the analyses of the transport mechanisms and the identification of the involved species, a three-phase composite electrolyte will be considered: a mixture of molten salts (a priori a ternary eutectic of Li, Na and K carbonates) associated with not one but two oxide phases: a cerium oxide-based phase conducting mainly oxide ions, and a barium cerate-type phase for its proton conduction. This constitutes a real originality of POSEYDON. For the electrode materials, we will use strontium-doped lanthanum (or barium) ferro-cobaltites, the most studied materials as oxygen electrode in Solid Oxide Cells. We will move on to promising materials evidenced by ICMCB, based on Pr oxide and ceria, shaped by infiltration. The oxygen electrode is a major issue in this project, as it must meet the usual criteria in the field and must also be compatible with CO2-rich atmospheres. In case of failure, we will keep the usual materials of molten carbonate cells, i.e. in situ lithiated NiO . For the hydrogen electrode, recent advances in Ni, Cu and doped ceria based cermets are promising to address the reversibility of the hybrid cell. The task 2 concerns the manufacture of complete cells, the three partners developing complementary synthesis/shaping methods. The insertion of electrode/electrolyte interfacial layers, based on ceria, present in the electrolyte and the electrodes, has proven to be efficient to increase the performances, and will be therefore maintained. The task 3 will consist on the study of the electrochemical performances of the complete cells, for the 3 modes of operation already mentioned. We are aware that this project is very ambitious. Nevertheless, the exploration of new materials and new architectures will be suitable for at least one mode of operation (fuel cell), with a targeted power density of 0.5 W.cm-2 at 600°C (the explored range is 550-700°C), and a durability >1000 hours. Scientific and technological advances are strongly expected through this POSEYDON project, very useful in the hydrogen sector for further development: both for socio-economic benefits to lower the cost of hydrogen produced via non-noble and accessible materials, as well as to decrease the operation temperature compared to the existing one, for an higher production.