Unraveling Dimensional Tuning: From 2D to 3D in Covalent Organic Frameworks for Enhanced 2e^- Oxygen Reduction...

Covalent organic frameworks (COFs) with a two-dimensional (2D) topology have recently emerged as promising catalyst systems for the electrosynthesis of hydrogen peroxide (H₂O₂) from oxygen (O₂). However, designing 2D catalysts to achieve higher H₂O₂ selectivity presents a significant challenge because of the extensive layer stacking and the aggregated active sites located in the basal planes. It results in lower atom utilization, which requires attention. In this study, we present two functionally similar COFs: one with a 2D rhombus topology (2D@BT_TPA-COF) and another with a three-dimensional (3D) noninterpenetrated pts topology (3D@BT_TPA-COF). Both COFs were utilized for the 2e^- oxygen reduction reaction (2e^- ORR). Tunning the dimensionality from 2D to 3D resulted in an increase in H₂O₂ selectivity from approximately ∼56% to approximately ∼96% (at 0.4 V) and a rise in the turnover frequency (TOF) from 0.05 to 0.08 s^-1 at 0.3 V. Nonaggregated active site distribution over 3D topology, featuring higher active site exposure, provides better access to the O₂/electrolyte and facilitates electron transfer leading to higher 2e^- ORR activity and selectivity compared to the 2D counterpart.