Single-Atom Catalysts for the Electroproduction of H₂O₂ in Optimized Acidic Conditions

The planet’s transitioning climate necessitates a societal shift towards a sustainable energy infrastructure. This can include the decentralized electroproduction of chemical commodities, such as H₂O₂ from PEM electrolysis reactors. This technology requires the development of electrocatalysts that are active, selective and stable during the operating conditions of scaled-up reactors. Single-atom catalysts anchored on nitrogen-carbon frameworks have promising potential for the selective electroreduction of oxygen to H₂O₂. The electrochemical testing of such single-atom catalysts is typically conducted with rotating ring disk electrode experiments, which tend to over-perform in comparison to their performances in scaled-up reactors. On the other hand, adapting electrocatalysts to scaled-up reactors is a difficult process that needs to be tailored to each catalyst being tested. Consequently, better methods for electrochemical testing are needed because the research field is limited to rotating ring disk experiments of minimal relevance or resource-intensive scaled-up reactor experiments. The floating electrode technique has shown promise for the oxygen reduction reaction by providing facile access of oxygen gas to the catalyst layer, but this has not yet been utilized for the selective electroreduction of oxygen to H₂O₂.
The modification of the floating electrode technique to test single-atom catalysts for the electroproduction of H₂O₂ was extensively explored. The results suggest that this floating electrode technique can provide both ideal and relevant conditions: the catalyst is not limited by the lack of oxygen at the higher overpotentials necessary for scaled-up operations, and the electroproduced H₂O₂ has facile escape channels from the abundant electrolyte. This project demonstrates a new application for the floating electrode technique, which has enabled the discovery of the iridium single-atom catalyst with comparable performances to the state-of-the-art cobalt single-atom catalyst in relevant operating conditions. Among the synthesized single-atom catalysts, the highly-active cobalt and iridium catalysts were more stable than the highly-selective platinum and palladium catalysts. In addition, potential degradation mechanisms are discussed, including metal agglomeration of single atom sites due to electrodeposition, and the electroreduction of H₂O₂ to H₂O.