Metal‐Free Carbon‐Based Covalent Organic Frameworks with Heteroatom‐Free Units Boost Efficient Oxygen Reduction. Issue 7 (18th December 2022)

• Record Type: Journal Article
• Authors: You, Zhihu; Wang, Bingbing; Zhao, Zijie; Zhang, Qiankun; Song, Weichen; Zhang, Chuanhui; Long, Xiaojing; Xia, Yanzhi
• Is Part Of: Advanced materials. Volume 35:Issue 7(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-12-18
• Subjects: active centers -- conjugated organic frameworks -- heteroatom‐free -- metal‐free -- oxygen reduction; Materials -- Periodicals; Chemical vapor deposition -- Periodicals; 620.11
• DOI: 10.1002/adma.202209129
• Languages: English
• ISSNs: 0935-9648

Abstract

Abstract: Accurate identification of carbon‐based metal‐free electrocatalyst (CMFE) activity and enhancing their catalytic efficiency for O2 conversion is an urgent and challenging task. This study reports a promising strategy to simultaneously develop a series of covalent organic frameworks (COFs) with well‐defined heterocyclic‐free biphenyl or fluorenyl units. Unlike heteroatom doping, the developed method not only supplies methyl‐induced molecular configuration to promote activity, but also provides a direct opportunity to identify heteroatom‐free carbon active centers. The introduction of methyl groups (MGs) with reversible valence bonds into a pristine biphenyl‐based COF results in an excellent performance with a half‐wave potential of 0.74 V versus the reversible hydrogen electrode (RHE), which is among the highest values for CMFE‐COFs as oxygen reduction reaction (ORR) electrocatalysts. Combined with in situ Raman spectra and theoretical calculations, the MG‐bound skeleton (DAF‐COF ) is found to produce ortho activation, confirming the ortho carbon (site‐5) adjacent to MGs as active centers. This may be attributed to the opening and binding of MGs, which effectively regulate the molecular configuration and charge redistribution, as well as improve charge transfer and reduce the energy barrier. This study provides insight into the design of highly efficient metal‐free organic electrocatalysts via the regulation of valence bonds. Abstract : A novel strategy to regulate the charge redistribution of active centers of metal‐free organic electrocatalysts by using heteroatom‐free methyl groups (MGs) is reported. MGs can produce ortho activation, confirming the ortho carbon (site‐5) as active centers. This study provides insight into the design of highly efficient metal‐free organic electrocatalysts via the regulation of valence bonds.