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Protection of Redox Catalysts for Cathodic Processes in Redox Matrices.

Periodic Reporting for period 3 - REDOX SHIELDS (Protection of Redox Catalysts for Cathodic Processes in Redox Matrices.)

Reporting period: 2020-03-01 to 2020-08-31

The transition to sustainable energy schemes on a global scale requires catalysts that are robust, highly active and scalable. Currently, precious metals are used in commercially available devices such as H2/O2 fuel cells or electrolyzers for H2 generation. However their limited abundancy is a major barrier toward their widespread adoption in clean energy technology. Alternative catalysts based on earth abundant metals have demonstrated activity that compete with the one of precious metals and open promising perspective for their global implementation. However their stability is insufficient to maintain high performances under the operating conditions of energy converting devices. The objective of the ERC project REDOX SHIELDS is to establish novel concepts to protect highly active but fragile catalysts made from abundant sources so that they can be used in fuel cell and electrolyzers to enable storage and use of energy from renewable sources.
The research achievements of the first half of the project REDOX SHIELDS are the results from a combination of theoretical and experimental investigations.

Extensive modeling activities in cooperation with the group of Christophe Léger at the CNRS Marseille led us to a complete understanding of the protection of catalysts under oxidative conditions even in thin films (<10 µm). We demonstrate that the life time of the catalysts scales exponentially with the film thickness. This is important because it makes it possible to theoretically increase the life time of protection from just 10 min in a 3 µm thick film, to 1 year in a 6 µm film, and even to 22000 years in a 8 µm film! This remarkable protection enables to finely tune the film properties for a best compromise in terms of current output, stability and catalyst utilization which are the primary requirements for technological applicability of such catalysts in energy conversion. This breakthrough now enables to reconsider catalysts that were previously discarded for the integration into devices.

The protection from O2 was also further extended to protection from other deactivating molecules such as H2O2 which is often a side product from O2 generation. We have combined the ability of a redox polymer to reduce O2 to H2O2 with the catalytic activity of an electrolyte containing iodide for the dismutation of H2O2 to H2O. We demonstrated experimentally that this approach is extremely valuable for protecting highly fragile catalysts such as the hydrogenase for as long as 9 days under constant exposure to O2 which would normally destroy the catalyst whitin seconds. This exceptional performance consolidates the possibility for using highly O2 sensitive catalyst in technological device for energy conversion.
Before the end of the project we aim at explaining the mechanism of protection of thin films for fragile catalysts that are highly active for H2 generation. Based on this knowledge we will design a protection matrix with the ideal properties for protecting such catalysts quasi-inifinitely from deactivating molecules. Demonstration of this possibility will be performed by constructing an electrolyzer for H2 evolution based on the catalysts from Nature, the hydrogenase, which is among the most active but also the most fragile catalyst for generating H2. Succeeding in protecting such a fragile catalysts in the harsh conditions of an operating electrolyzer will validate the general applicability of the protection concept to any other artificial or natural catalysts and thus open up their use in devices for clean energy conversion.
Protection matrices for fragile electrocatalysts