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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - PEGASUS (PEMFC based on platinum Group metAl free StrUctured cathodeS)

Teaser

Summary

Fuel cells, as an efficient energy conversion technology, and hydrogen, as a clean energy carrier, have a great potential to reduce carbon dioxide emissions, to reduce dependence on mainly imported hydrocarbons and to contribute to economic growth and a strong European competitiveness and thus to create employment in Europe.

Proton exchange membrane fuel cell (PEMFC) is the predilection fuel-cell technology for automotive applications with a large deployment horizon by 2025-2030. However, the increasing use of fuel cell electric vehicles (FCEV) is expected to lead to a quickly growing demand for Platinum Group Metals (PGMs) because fuel-cell vehicles require a multiple of the PGM amounts needed for conventional cars, between 30 and 50 gPt for a 100 kW full power stack. PGM production is not only itself related to some negative environmental impacts (e.g. through the use of fossil-fuel energy for mining and metallurgical plants), but also raises questions of long-term availability due to the limitation of reserves and Europeâ€™s economic dependence on the countries of the materialsâ€™ origin. In order to avoid future barriers for development and dissemination of FCH technologies, their materials demand and the related issues should hence be considered early enough in order to develop strategies to react on the changing markets and the new challenges â€“ as well as the opportunities â€“ they are posing.

Besides, durability and cost are also primary challenges to fuel cell commercialization. Fuel cell systems must compete with automotive internal combustion engines (ICEs) and other alternative technologies. The performance and durability of FCEV have already been proved for cars integrating high content of Pt based catalyst. To be also considered with incumbent and future competing technologies, the cost of automotive fuel cell systems needs to be competitive, both on the Total Cost of Ownership (TCO) and on initial cost basis (CAPEX). This cost must be achieved while ensuring that systems provide the performance and durability already demonstrated by high cost FCEV. One of the key issue lies on the fact that the cost of PEMFCs is driven by the use of Platinum (Pt), a very effective hydrogen oxidation and oxygen reduction catalyst, which represents an estimated 50% of the cost of the fuel cell stack. In addition, Pt is sensitive to contamination from impurities in hydrogen and certain air contaminants, which impose the use of high H2 purity and filter at the airside of the PEMFC system.

Hence, it is of high strategic importance that the transition to a next-generation PEMFC using Platinum Group Metals-free (PGM-free) catalysts is made as quickly as possible to ensure Europe\'s competitive position and to reduce market pressure on the use of scarce noble metals. While decreasing Pt loading in MEAs has been considered as an intermediary step, the ultimate industrial goal will be to manufacture PEMFC stacks for transport application with Non-PGM catalysts, and with performance and durability comparable to the targets defined currently with Pt.
In that perspective, the PEGASUS project is exploring a promising route towards the removal of Pt and other critical raw materials (CRMs) from PEMFC and their replacement by non-critical elements & structures enabling efficient and stable electrocatalysis conditions for an appropriate use as Pt-alternative competitive cathodic catalysts. The overall aim of this project is to bring up the experimental proof of concept for novel catalysts materials & structures.

Work performed

During the first period of the project, from February 2018 to July 2019, the consortium was able to produce four different PGM free catalyst technologies, following different synthetic routes, which are easily up scalable. This last point is important to facilitate a future mass production of the developed material.
Those catalysts are based on carbon, nitrogen and non-precious metal only (M/N/C). Among the different non-precious metals tested by the consortium, iron has presented the best activity. Therefore the prepared catalyst contain only atom which are very abundant on earth and neither PGM material nor CRM (critical raw material) as defined by the EU. They can be defined as non-precious metal catalyst (NMPC)
The different used synthetic routes followed in the project lead to catalysts with different microstructures and chemical compositions that allowed us to improve both oxygen reduction reaction kinetic and gas diffusion in the active layer. Those two last points are the main parameters to be tuned to improve the performance of a MEA (core of a fuel cell stack).
The developed materials have been successfully integrated in membrane electrode assemblies (MEA) and their performances characterized. The last results showed that the MEA integrating the best PEGASUS material gives higher performances than the MEA based on reference commercial PGM free catalyst. The achieved performances are comparable to the best-reported worldwide state of the art. Numerical results are given in the following section.
Then, the consortium fully characterized the newly developed material to provide:
- new insight on the nature of the active site, which is still an open question in the community
- ex situ evaluation of the intrinsic catalytic activity at the agglomerate level.

Final results

In Pegasus, many efforts are focussed on the integration of PGM free catalyst in MEA and their characterisation in single cell device, which is a mandatory step to validate the in situ catalyst performance. Recently, we were able to obtain MEA integrating PEGASUS catalyst providing higher performance than MEA integrating commercial PGM free catalyst. The catalyst intrinsic activity has been demonstrated to be higher than the commercial reference material thanks to the developed scanning electrochemical microscopy technique (SECM). To the best of our knowledge, it is the first time that this technique is used to perform electrochemical characterisation of PGM free catalyst for ORR.
The performance of MEA integrating 2 mgcat/cm2 Pegasus catalyst gives 280 mA/cm2geo @ 0,7 ViR-free under air, leading to 140 A/gcat. For comparison, the reported performance of MEA integrating PGM free catalyst in the 2018 US-DOE Annual Merit Review is 300 mA/cm2geo when using 4.8 mgcat/cm2, leading to 62,5 A/gcat. [P. Zelenay et al., DOE 2018 Annual Merit Review].
In the second period of the project, the consortium will run through the strategy defined in the project description, which can be grossly described as follows:
- Intrinsic catalyst activity improvement and validation by ex situ high level electrochemical technique (SECM)
- Tuning both the catalyst and active layer 3D structure to reduce transport loss at the cathode of the MEA.

As conclusion of the project, projection on cost of a stack integrating PGM free material to substitute the platinum at the cathode will be delivered.