IDEAL Cell: Work Package 5 "Dual Cell Optimization and Integration"

Objectives

The main objectives of this work package are:

• Optimization of the central membrane in terms of advanced materials and materials architecture;
• Development and application of theoretical and modelling tools to assist materials design and architectural design of the dual cell and a short-stack;
• Optimization of operating conditions and performance of the dual cell;
• Development of the stack design and integration of the dual cell into a short-stack;
• Evaluation of performance and durability of a dual cell short-stack and comparison with an IT-SOFC short-stack.

Description of work

Task 5.1: Central membrane optimization and forming of the optimized dual cell (Partner 1, Partner 3, Partner 4, Partner 5, Partner 6, Partner 7)

The key factor for central membrane optimisation is to obtain high anionic and protonic conductivities and to realize the proper connectivity among different phases (proton conductor, oxygen ion conductor, open porosity for water evacuation), avoiding tortuous and/or resistive paths. A percolating network of anionic carriers will be formed by precipitation of ceria particles during sintering of Ba-deficient BCY15. A mixed conductor with minimal possible interfacial resistance should be obtained. BCY15 powder doped with trivalent elements (e.g. Sm) (developed in Task3.1) will be also studied to favour an intrinsic mixed conduction.

Modelling activity will be performed that addresses the relationship between materials properties such as composition and particle size distribution, electrode morphology (e.g. connectivity, active zone area, porosity) and apparent physical properties (e.g. conductivity, permeability to species in the gas phase), using percolation theory and conductivity models in disordered media.

Dual cells will be fabricated using the appropriate forming process, previously chosen. EIS measurements on working cells will be performed at different conditions (temperature ranges, pressure, gas flows, etc) for optimization of the central membrane. Selected data will be analysed by Differential Impedance Analysis for deeper information, which will be used in the optimization.

Task 5.2: Thermodynamic and electrochemical description and modelling of the influence of operating parameters on cell performance (Partner 3, Partner 4, Partner 9)

Investigation and modeling of the mechanisms of mass transfer and reaction in composite electrodes with reference to micro fabricated dense and patterned electrodes will be performed.

The cell performance achieved in WP 4 will be analyzed in detail by CFD modelling for verification of species distribution, electrochemical surface reactions and generated heat distribution. As input the parameters gained by advanced material characterization in task 5.1 will be used.

Modelling and simulation of new stack concepts and new balance of plant components, including analysis of flows (air, fuel) and energy balance, will be carried out. Process control strategies will be elaborated and modelling work will be performed to determine optimum operating conditions and techno-economic impact. Technical results and other relevant considerations obtained in task 5.2 will be used for benchmarking in WP6.

Task 5.3: Optimization of operating conditions (Partner 4, Partner 5)

In this task the cell integrity and its stability over time will be proved and the operating conditions and the practical cell performance will be optimized. EIS measurements will be carried in order to optimize the central membrane as well as to test the full dual cell performance at different conditions. Selected EIS measurements will be analyzed by Differential Impedance Analysis (after elimination of the parasitic inductance) for optimization of the cell’s operating conditions.

Electrochemical characterization of full dual cells by I-V measurements will be done. The cell’s behaviour will be investigated by varying the operating parameters and monitoring the cell behaviour. Long-term measurements over 1000 hours will be performed and post mortem analysis using optical microscopy, SEM/EDX and XRD will be done to study the durability behaviour and potential degradation phenomena of the cell. If needed, more sophisticated techniques (TEM, HRTEM, SIMS), available within the consortium, will be applied.

Task 5.4: Development of cell, cell integration and cell and stack design (Partner 2, Partner 3, Partner 4, Partner 8)

Theoretical tools developed in WP 4 and in task 5.1 and 5.2 will be integrated and implemented to predict the overall cell performance as a function of physical and morphological properties of materials, operating conditions (temperature and gas composition) and geometry (thickness and diameter). The gas supply of the reactive zones will be evaluated with CFD modelling. Detailed models, based on the consideration of significant physical, chemical and electrochemical processes occurring in a porous electrode, will be developed. The results of model simulations will be compared with experimental data of cell polarization. Simplified models will be derived for routine design purposes.

Based on the modelling results and due to the special nature of the dual fuel cell developed in this project (dead end gas chambers with no gas dilution), an appropriate cell and stack design with an integrated cell will be developed. A short-stack of 2 dual cells will be assembled for testing.

For integration of the dual cell into a stack, metallic interconnects will be used. An essential feature of the dual cell is the absence of water vapour at both metal-electrode interfaces. This enables the use of standard metallic interconnects, i.e. commercial ferritic steels (Crofer22APU from VDM KruppThyssen and F17Nb from UGINE) that in common fuel cells are subjected to heavy corrosion phenomena, drastically introducing ohmic losses. However, the deposition of protective layers will be considered to avoid decrease of conductivity due to the formation of an oxide layer at the metal-gas interface on the cathode side. The case of the exhaust of pure water vapour from the central membrane will be considered. MOCVD, screen printing and PLD treatments will be applied, followed by conventional characterization (XRD, SIMS, AES and Area Specific Resistance –ASR– stability over time).

Task 5.5: Fabrication of a GDC-based IT-SOFC short-stack for comparative studies (Partner 4)

The performance of the dual cell short-stack will be compared with that of IT-SOFC short-stack. GDC-based SOFC cells will be fabricated and assembled with ferritic interconnects in a 2-cell short-stack. The cells will be manufactured by plasma spray technology. Glass seals will be used for sealing the cells in the stack.

Task 5.6: Evaluation of performance of a dual cell short-stack and comparison with SOFC short-stack performance (Partner 4, Partner 9)

The dual cell short-stack manufactured in task 5.4 and the IT-SOFC short-stack manufactured in task 5.5 will be electrochemically characterized by performing I-V characteristics measurements. The electrochemical results obtained under varying operating conditions as well as the performance and durability behaviour of both fuel cell types will be analyzed for further benchmarking.

Deliverables

• D5.1 Technical report on the results obtained in the 6 tasks of WP5 (Year 4).