Newly N-S-C coordination-structured active sites, originating from the integrity of edged thiophene S, graphitic N, and pentagon defects, were reconstructed by N-modified S defects in carbon aerogel with a 3D hierarchical macro-mesomicroporous structure. This metal-free material exhibited outstanding oxygen reduction reaction (ORR) activity (e.g., half-wave potentials of 0.76 V in 0.5 M H 2 SO 4 and 0.1 M HClO 4 ; 0.85 V in 0.1 M KOH) with good stability and high current density in both acidic and alkaline electrolytes. The experimental and computational results reveal that the pentagon S defect is essential for the ORR in acidic electrolytes because it provides a remarkable increase in reactivity. One graphitic-type N in the meta-position of the pentagon defect further significantly improves the reactivity as a result of locally precise control of the electronic structure, thus forming highly active sites for ORR in acid.

Defective or heteroatom-doped metal-free carbon materials (MFCMs) have been regarded as efficient oxygen reduction reaction (ORR) catalysts in the past decade. However, the active centers for ORR in MFCMs are hard to confirm precisely and synthesize controllably through common methods such as high-temperature pyrolysis or heteroatom doping. To verify the precise structure acting as the active center for the ORR, we first report two crystalline metal-free thiophene-sulfur covalent organic frameworks (MFTS-COFs) as ORR catalysts. The MFTS-COFs show more positive catalytic capability than the thiophenefree COF, indicating that pentacyclic thiophene-sulfur building blocks act as active centers to induce ORR catalytic activity. MFTS-COFs with higher contents of thiophene-sulfur exhibit better ORR performance. The experimental identification is supported by density functional theory calculations. These results thus demonstrate that rational design and precise synthesis of metal-free crystalline organic materials can promote the development of new ORR catalysts.

The development of three-dimensional (3D) functionalized covalent organic frameworks (COFs) is of critical importance for expanding their potential applications. However, the introduction of functional groups in 3D COFs remains largely unexplored. Herein we report the first example of 3D Salphenbased COFs (3D-Salphen-COFs) and their metal-containing counterparts (3D-M-Salphen-COFs), the later being further used as catalytic antioxidants. These Salphen-based COFs exhibit high crystallinity and specific surface area in addition to excel lent chemical stability. Furthermore, the Cu(II)-Salphen COF displayed high activity in the removal of superoxide radicals. This study not only presents a new pathway to construct 3D functionalized COFs, but also promotes their applications in biology and medicine.

The functionalization of three-dimensional (3D) covalent organic frameworks (COFs) is essential to broaden their applications. However, the introduction of organic groups with electroactive abilities into 3D COFs is still very limited. Herein we report the first case of 3D tetrathiafulvalene-based COFs (3D-TTF-COFs) with non- or 2-fold interpenetrated pts topology and tunable electrochemical activity. The obtained COFs show high crystallinity, permanent porosity, and large specific surface area (up to 3000 m2/g). Furthermore, these TTF-based COFs are redox active to form organic salts that exhibit tunable electric conductivity (as high as 1.4 × 10–2 S cm–1 at 120 °C) by iodine doping. These results open a way toward designing 3D electroactive COF materials and promote their applications in molecular electronics and energy storage.