170 mW / cm²
After 51 months in total, the project was succesfully completed. Initialy scheduled for a duration of 48 Months, (November 2012 - October 2016), the project was extended for an additionaly 3 months period in September 2016, in order to overcome the last technical issues for the stack assembly. By the 31st of January 2017, the project was succesfully completed by the demonstration of the novel SOFC architecture at the stack level with a power density of 170 mW/cm².
Beyond the state of the art, the EVOLVE cell concept aims at combining the beneficial characteristics of the previous cell generations, the so called Anode Supported Cells (ASC) and Metals Supported Cells (MSC) while tackling key challenges like sulfur poisoning and redox stability, typical for state of art cells implementing nickel as electro-catalyst and structural component in the nickel / zirconia standard anodic cermet. The innovation of the EVOLVE cell concept remains in its anode compartment avoiding the use of pure nickel as structural component. The substrate, providing mechanical strength to the fuel cell is based on a robust metal alloy 3D porous backbone allowing the formation of a protective alumina layer enhancing stability during re-oxidation cycles and an electronic conducting material based on perovskite oxides.
An European consortium including academics and industrial partners with complementary backgrounds and expertise has been build up, and has been granted a financial support in 2011 by the Fuel Cells and Hydrogen Joint Understanding under the Grant Agreement n° 303429, for the development of the EVOLVE cell concept. The consortium EVOLVE included: the German Aerospace Center (Germany) assuming the leadership and the coordination, Alantum Europe GmbH (Germany), ARMINES (France), Ceramic Powder Technology AS (Norway), Consiglio Nazionale delle Ricerche (Italy), Institut Polytechnique de Grenoble (France), Saan Energi AB (Sweden) and Ceraco Ceramic Coating GmbH (Germany). The project ran from November 2012 until January 2017.
In a first step, set of materials were selected based on their physico-chemical properties and inter-compatibility for manufacturing a fuel cell. Namely a NiCrAl based metal foam provided by Alantum GmbH, as 3D metal alloy porous backbone, La0,1Sr0,9TiO3-δ, produced by CerPoTech AS, as electronic conducting material for the substrate and anodic electro-catalyst in combination with Gd doped ceria in the functional anode layer, yttria stabilized zirconia for the electrolyte, in combination with GDC as cathodic barrier layer and applied as thin film by EB PVD (Ceraco GmbH), and finally a LSCF based cathode.
Taking into consideration the properties of the material a specific modular manufacturing route was specifically designed for producing the EVOLVE cell. This route was divided into 5 consecutive modules consisting in 1) substrate manufacturing, 2) processing of anode functional layer (AFL) 3) Thin film Electrolyte Processing, 4) Cathode manufacturing, and 5) activation of the anode layer.
As level of electronic conductivity and electrocatalytic activity were limited, performance of the pure nickel free EVOLVE cells were limited to ca. 120 mW/cm² at 0.7V and 750°C with hydrogen as fuel. After the midterm evaluation of the project, it was thus decided to enhance the electronic conductivity in the substrate by replacing the LST material by a cermet LST-Ni (50:50), and boost the electro-catalytic activity of the anode functional layer by surface modification of the LST-CGO composite AFL with ca. 5 to 10wt % of nickel. With those modifications, the power density was increased up to 440 mW/cm² at 0.7V and 750°C with hydrogen as fuel. Comparable level of performance were achieved for cells built up on a standard ferritic stainless porous substrate, which confirmed the modularity of the processing route i.e. materials can be easily exchanged without redesigning a full manufacturing route.
The EVOLVE cell architecture with electrolyte thickness of less than 3μm could be successfully up-scaled to a size of 90 mm x 100 mm and could be successfully integrated into 1 cell stack, similarly to anode supported cells. The tested 1 cell stack achieved a power density up to 170 mW/cm² at 0.7V and 750°C with simulated syngas as fuel and air at the cathode. The stack could be successfully operated for more than 100 hours under constant current load. With less than 2% variation for 50 redox cycles, the Open Circuit Voltage showed an excellent stability, demonstrating that thin film electrolytes maintain integrity despite the harsh conditions.
At that point, the feasibility of the EVOLVE cell architecture has been demonstrated at the stack level. Further work would require assembly and tests of short stack fur further assessment, as well as implementation of technological improvements in the cell to enhance performance and durability.
The modular approach developed in the project for the cell manufacturing showed very promising characteristics for a quick implementation of advanced materials in the cell design and the possibility to involve different actors and processes in the fabrication process, which contrast with centralized cell production that can be observed nowadays in Europe. This modularity of the manufacturing route provides huge potential in terms of cost reduction potential on the basis of the principle of best performance / cost ratio and the flexibility offered regarding the materials that can be implemented.
More information and public deliverables are available upon request to the coordinator.