Functional Grading by Key doping in Catalytic electrodes for Proton Ceramic Cells
About the Project
The European Commission’s Energy Union strategy supports technologies with the greatest impact on the EU's transformation to a low-carbon energy system, of which hydrogen technology is a vital part. Fuel cells and electrolysers are central components in hydrogen technology and among these, Proton Ceramic Cells (PCCs), comprising Fuel Cells (PCFCs) and Electrolysers (PCEs) are among the potentially most energy efficient. The performance of PCCs is currently limited by cell resistance, and by the efficiency of the positive electrode (positrode), which in these systems rely on ceramic materials with mixed protonic and electronic conductivity (MPECs). Recent studies have shown the significance of good MPEC materials for improved electrode functionality. But there are still several challenges to be met to produce up-scalable, stable and efficient positrodes for PCCs. The need for both proton conduction for extended electroactive area, and high electronic conduction for good current collection and utilization of the electrode volume is a tough nut to crack. Few materials offer both, and research groups tend to focus on one or the other. The most optimized MPEC materials furthermore often suffer from a severe mismatch of Thermal Expansion Coefficient (TEC) with respect to the electrolyte material, causing delamination, reduced active area and increased ohmic contact resistance. Finally, most positrodes are limited by slow surface kinetics, causing electrode polarization. In FunKeyCat we aim to produce graded electrodes with designed functional properties by co-doping MPECs with key elements for shifting the equilibrium
throughout the electrode thickness, and at the same time ensure a graded TEC mismatch to prevent delamination. The slow surface kinetics for the positrode reaction is the main obstacle for operation at lower temperatures. At high temperatures, the surfaces of the mixed conducting oxides present sufficient catalytic activity to avoid severe electrode polarisation, and at low temperatures, PEM cells struggle with expensive Pt catalysts. In the intermediate temperature range, however, additional catalysts will be needed to increase the rates of the surface mass transfer reaction. Manufacturing and addition of such catalysts is both tedious and costly, and coarsening and poisoning leads to deactivation and loss of cell performance over time. Therefore, FunKeyCat will explore a novel route for decoration of electrode surfaces by catalyst nanoparticles by in situ exsolution of nano-scaled oxides. The design of electrode materials with the ability to exsolve such catalysts is based on thermodynamic and defect chemical principles, and will represent a significant breakthrough. The investigation will be conducted on model systems, and expanded towards the end of the project to be applied also on the functionally graded systems, utilising an important exsolution driving force, namely lattice strain. Such strain may be caused by interfaces with different cell parameters, as is the case between the different functional layers in the graded electrodes. The outcome of the project will be fully integrated, highly catalytic electrodes with superior current collection properties and nano-scaled microstructures. The electrodes will exhibit regenerative catalytic properties after long-term degradation, improved functionality, increased thermomechanical and chemical stability, and the manufacturing process will ensure scalability for industrial processing at higher TRLs. The project will start at TRL2, where established principles for mixed conduction is applied to obtain the desired functionality and model electrodes are investigated, and end at TRL4, where button cells will be manufactured and tested for electrochemical performance.
FunkeyCat is an M-era.Net Project, financed by the National Research Council of where the partners are from.