Rational Design Two- or Four-Electron Reaction Pathway Covalent Organic Frameworks for Efficient and Selective...

Covalent organic frameworks (COFs) are often employed in oxygen reduction reactions (ORR) for hydrogen peroxide production due to their tunable structures and compositions. However, COF electrocatalysts require precise structural engineering, such as heteroatoms or metal site doping, to modulate the reaction pathway during the ORR process. In this work, we designed a tetraphenyl-p-phenylenediamine based COF electrocatalyst, namely TPDA-BDA, which exhibited excellent two-electron (2e) ORR performance with high H₂O₂ selectivity of 89.7 % and faraday efficiency (FE) of 86.7 %, higher than the reported COFs to date for H₂O₂ electrosynthesis. The theoretical and experimental results showed that the rate-determining step energy barrier for reduction of O₂ to OOH* intermediates was significantly reduced by replacing of bipyridine with biphenyl blocks, changing from 4e to 2e ORR reaction pathway. Also, the donor-acceptor characteristic and narrower optical band gap of TPDA-BDA COF enhanced the electronic conductivity and reduction ability, thus elevating the catalytic activity. As a result, the H₂O₂ selectivity was maintained above 85 % even after 50 h stability test. This work reveals the structure-property relationship of COF electrocatalysts and provides a new strategy for rational design of high performance 2e ORR COF electrocatalysts for efficient and selective hydrogen peroxide production.