Accelerated Stress Tests for Solid Oxide Cells via Artificial Aging of the Fuel Electrode

Solid Oxide Cells (SOCs) are under intensive development due to their great potential to meet the 2030 targets for decarbonization. One of their advantages is that they can work in reversible mode. However, in respect to durability, there are still some technical challenges. Although the quick development of experimental and modeling approaches gives insight into degradation mechanisms, an obligatory step that cannot be avoided is the performance of long‐term tests. Taking into account the target for a commercial lifetime is 80,000 h, experiments lasting years are not acceptable for market needs. This work aims to develop accelerated stress tests (ASTs) for SOCs by the artificial aging of the fuel electrode via redox cycling, which follows the degradation processes of calendar aging (Ni coarsening and migration). However, it can cause irreversible damage by the formation of cracks at the interface anode/electrolyte. The advantages of the developed procedure are that it offers a mild level of oxidation, which can be governed and regulated by the direct impedance monitoring of the Ni network resistance changes during oxidation/reduction on a bare anode sample. Once the redox cycling conditions are fixed and the anode/electrolyte sample is checked for cracks, the procedure is introduced for the AST in full‐cell configuration. The developed methodology is evaluated by a comparative analysis of current voltage and impedance measurements of pristine, artificially aged, and calendar‐aged button cells, combined with microstructural characterization of their anodes. It can be applied in both fuel cell and electrolyzer mode. The results obtained in this study from the electrochemical tests show that the artificially aged experimental cell corresponds to at least 3500 h of nominal operation. The number of hours is much bigger in respect to the microstructural aging of the anode. Taking into consideration that the duration of the performed 20 redox cycles is about 50 to 60 working hours, the acceleration factor in respect to experimental timing is estimated to be higher than 60, without any damaging of the sample. This result shows that the selected approach is very promising for a large decrease in testing times for SOCs

Impedance investigation of BaCe0.85Y0.15O3-delta properties for hydrogen conductor in fuel cells

International audienceThe influence of the sintering conditions on the electrochemical properties of the proton conducting electrolyte BaCe0.85Y0.15O3-delta (BCY15) and Ni - based BCY15 cermet anode for application in high temperature proton conducting fuel cell are investigated by electrochemical impedance spectroscopy. The results show that at lower sintering temperatures due to the formation of parasitic Y2O3 phase an increase of both the electrolyte and electrode resistances is observed. This effect is strongly reduced by enhancement of the sintering temperature. The obtained BCY15 conductivity (sigma = 2.5x10(-2) S/cm at 700 degrees C) is comparable with that of the best proton conducting materials, while the BCY15-Ni cermet (with ASR = 2.5 Omega cm(2) at 700 degrees C) needs further optimization. The results of impedance investigations of BCY15 as proton conducting electrolyte and cermet anode have been applied in development of innovative high temperature dual membrane fuel cell

Gases permeability study in dual membrane fuel cell

International audienceGases permeability in a porous mixed (proton and oxide ion) conductive membrane, which is a component of a new high temperature dual membrane fuel cell design is investigated by specially designed testing system based on measurements of the gas flow [ml/min] and pressure P (mm H2O) when penetrating through porous media. A strong correlation expressed in increase of the permeability with the decrease of the gases molecular weight is registered. The water vapor permeability decreases with the temperature. This is in agreement with data from the literature which show that the viscosity of gases, including water vapor, increases with the temperature. The results obtained suggest optimal porosity in respect to permeability, mechanical stability and conductivity in the range of 35-40%. They confirm the need of optimization concerning not only the pores fraction, but also the pores geometry and distribution, as well as the central membrane geometry and the configuration of the cell. This approach can be applied also for optimization of the electrodes porosity (pores concentration, geometry, distribution etc), especially in cases when gas mixtures (including water vapor) are used or produced

Dual membrane fuel cell -impedance approach for proof of concept

International audienceThe dual membrane fuel cell (DMFC) is an innovative SOFC architecture in which an oxygen compartment (cathode and oxide ion conducting electrolyte) is combined with a hydrogen compartment (anode and proton conducting electrolyte) through a porous mixed conducting central membrane (CM) where the two types of ions react and produce water which is evacuated through the pores. This concept is proved on a model cell via sets of investigations based on D.C. testing and Impedance Spectroscopy. For optimization of the three DMFC compartments (oxygen, hydrogen and CM) with regard to materials and technological conditions for the deposition of the functional layers, impedance studies were carried out on symmetrical half cells. Special attention was given to some new experiments elucidating the processes of water formation and propagation through the central membrane

Redox - Cycling - a tool for artificial electrochemical aging of solid oxide cells

In this work a procedure for accelerated stress tests of Solid Oxide Cell (SOC) by artificial aging of the anode via redox cycling is presented. This approach eliminates the interrelation of different degradation processes and ensures a clear picture of the anode degradation on the total cell performance. The level of oxidation is monitored in situ on bare anode samples by impedance measurements of the Ni network resistance changes during oxidation/reduction cycling which ensures governing of the oxidation level with high reproducibility by selection of appropriate experimental conditions. Once fixed on bare anode samples, the selected redox cycling regime is further applied in full cell configuration. The developed methodology is evaluated by comparative analysis of current-voltage and impedance measurements of artificially aged and calendar aged button cells. The results for 8 redox cycles are comparable to those obtained for more than 600 hours operation in standard conditions

Impedance studies of porous electrolyte with mixed ion conductivity

International audienceIn this study mixed ion conductivity of a composite material based on proton conducting BaCe0,85Y0,15O2,925 (BCY15) and oxide ion conducting Ce0,85Y0,15O1,925 (YDC15) electrolytes has been investigated by Electrochemical Impedance Spectroscopy in relation to its application as a membrane (named central membrane CM) in an innovative design of a high temperature Dual Membrane Fuel Cell (DMFC). One of the most important advantages of the new architecture is the separation of hydrogen, oxygen and exhaust water in three independent chambers. The key-point of the DMFC development is the design and fabrication of the porous CM, which has to combine high mixed ion (proton and oxide ion) conductivity with sufficient porosity necessary for the evacuation of the water produced in this layer. In order to understand and evaluate the processes taking place in the CM, impedance studies were carried out and presented in this work. The obtained results show that a composite central membrane with 50 v % BCY15 and 50 v % YDC15 and porosity about 35-40 % obtained by addition of pore former (graphite) could be used for the fabrication of the first (Proof of the Concept) generation Dual Membrane Fuel Cell

Reversibility in dual membrane fuel cell

A promising direction in the development of solid oxide fuel cells (SOFC) is the reversible approach in which the device operates as fuel cell and as electrolyzer. Reversibility is very important for coupling with RES. A serious problem is the asymmetry of the system when operating in the two modes. A definitive breakthrough is the separation of the water production/consumption from the two electrodes. For fuel cell mode this idea has been realized in the innovative concept of the dual membrane fuel cell (DMFC), recently developed and proved in a FP7 project. The cell consists of three independent chambers for hydrogen, oxygen and water. They can be separately optimized. This work presents reversibility studies of the DMFC. The first results are very promising. They show good reversibility without application of a special catalyst for enhancement of the water splitting. The electrolyzer mode has lower overvoltage and thus lower internal resistance

Reversibility in monolithic dual membrane fuel cell

International audienceA promising direction in the development of solid oxide fuel cells (SOFC) is the reversible approach in which the device operates as a fuel cell and as an electrolyzer. A serious problem is the asymmetry of the system when operating in the two modes. A definitive breakthrough is the separation of the water production/consumption from the two electrodes. For fuel cell mode this idea has been realized in the innovative concept of the dual membrane fuel cell (dmFC). The cell consists of three independent chambers for hydrogen, oxygen and water. This work presents the reversibility studies of the dmFC. The first results are very promising. They show good reversibility without application of a special catalyst for enhancement of the water splitting