Architectured Electrodes for Energy Conversion (Solid Oxide Fuel Cells and Solid Oxide Electrolyser Cells)

PhD grant from LABEX CEMAM - 2013-2016

Fuel cells provide an attractive solution for producing or stocking energy without CO2 emissions mainly due to the widespread use of fossil fuels. "Solid Oxide Cells" (SOCs) gather together all electrochemical systems based on an oxide ceramic electrolyte operating at high temperature. These technologies are still not used on a large scale because of problems related to durability, the use of hydrogen and costs.

An important bottle-neck related to durability in SOCs is the delamination of the oxygen electrode (anode) in Solid Oxide Electrolyser Cells (SOECs) and the chemical reactivity of this electrode with the electrolyte when working as a cathode in Solid Oxide Fuel cells (SOFCs). Moreover, the high operating temperature of SOFCs leads to severe constraints on materials assembling and on fabrication processes. Thermal expansion mismatches among materials limit stack-level power density, thermal cycling and stack life.

One natural strategy to remedy to these problems is to lower the operation temperature of SOCs to 700-850°C for a longer durability and reduced costs of the total system. However, this comes at the cost of increasing electrolyte ohmic losses and electrode polarizations. To overcome these bottlenecks, the design of an architectured electrode/electrolyte system is a promising solution. The elaboration of multimaterials with for instance porosity and compositional gradients (leading to improved gas diffusion without loss in mechanical strength) is a good example of this philosophy. An additional option is to incorporate a dense and thin buffer layer, which avoids chemical reactivity at the electrolyte/oxygen electrode interface.

The present PhD thesis aims to optimize the composition and the architectured microstructure with simultaneous graded porosity and composition of the oxygen electrode based on an electrode/electrolyte combination to improve the durability of IT-SOFCs and SOECs. This optimization will rely both on an experimental program (using electrostatic spray deposition, a powerful tool to elaborate the architectured multimaterials, impedance spectroscopy, SEM/FIB and nanotomography characterizations) and a simulation part, based on calculations on 3D microstructural reconstructed images in order to understand the link between electrical and electrochemical properties and detailed microstructure.

The added value of this PhD program rests on the synergy between an original fabrication process (ESD) and advanced characterizations coupled with the modeling of electrochemical properties using the microstructures studied by SEM/FIB and nano-tomography. This subject puts together three research groups which have competences recognized in elaboration and in solid state electrochemistry (LEPMI), in 3-D characterization (CMTC) and in modeling (C. SIMaP).

The PhD student will have competences in chemistry of materials and/or electrochemistry. The capacity to work in a team and a good knowledge of french or english language will be appreciated.

Contact: Elisabeth Djurado