An Unsaturated Bond Strategy to Regulate Active Centers of Metal-Free Covalent Organic Frameworks for Efficient Oxygen Reduction

Unsaturated environment is the key to affect catalytic activity of the oxygen reduction reaction (ORR). Unveiling the effect of unsaturated sites toward ORR activity is of importance due to the vague unsaturated states. Reported here is a proof-of-concept strategy on the evaluation of unsaturated bonds (UBs) on adjacent carbon environment by precisely developing two metal-free vinyl-/azo-decorated covalent organic frameworks (Vinyl-COF and Azo-COF) as catalysts. The as-prepared UB-COFs exhibit good performance than the control Py-COF and comparable to the most reported carbon catalysts. Supported by theory calculations and in situ Raman spectra-electrochemistry, it is revealed that the UBs in organic catalysts can produce para-activation, identifying the para C=N groups as active centers. Importantly, the intrinsic UBs can induce local charge redistribution, and make the molecular skeleton possess high isosurface map distribution, with an efficient affinity for oxygen intermediates.

Automated summary

This study developed two metal-free covalent organic frameworks as catalysts to evaluate the effect of unsaturated bonds on the catalytic activity of the oxygen reduction reaction. The results showed that the vinyl-/azo-decorated COFs exhibited better performance than the control sample and comparable to most reported carbon catalysts. Theoretical calculations and experimental results revealed that the unsaturated bonds in the organic catalysts can produce para-activation and have a high affinity for oxygen intermediates.