(Invited) Elucidating Active Structures of 2D Metal Organic Framework Catalysts for Electrochemical Two-Electron Oxygen Reduction

Abstract

Hydrogen peroxide (H2O2) is a widely produced green oxidant with applications in paper bleaching, chemical synthesis, and disinfection. H2O2 could be electrochemically produced safely, rapidly, and on-demand by using catalysts that are highly selective for a two-electron oxygen reduction reaction (2e- ORR) pathway as opposed to the complete four-electron (4e-) pathway, though development of such catalysts has been hindered by lack of systematic design principles. Recently, well-defined crystalline two-dimensional conductive metal organic frameworks (2D-MOFs) with a square planar metal-nitrogen (M-N4) motif have shown selective 2e- ORR but the origins of the catalytic activity and selectivity remain unclear. Here, we use a combination of theory and experiments to show a 2D-MOF based on metal hexaaminobenzene (M-HAB) as a highly active and selective catalyst for H2O2 electrosynthesis. Furthermore, operando X-ray absorption spectroscopy reveals highly stable metal coordination sites and charging of the organic linkers that occurs during ORR that directly competes with the production of H2O2. These results confirm that the organic linker can act as the dominant active site during ORR in these MOF catalysts and reveal a unique interplay between the material’s catalytic and redox properties that can guide the future design of similar MOFs for enhanced catalytic performance.