Quasi-Phthalocyanine Conjugated Covalent Organic Frameworks with Nitrogen-Coordinated Transition Metal Centers for High-Efficiency Electrocatalytic Ammonia Synthesis.

Developing high-performance nitrogen reduction reaction (NRR) electrocatalysts is an ongoing challenge. Herein, we report a pyrolysis-free synthetic method for introducing ordered quasi-phthalocyanine N-coordinated transition metal (Ti, Cu, or Co) centers into a conjugated two-dimensional (2D) covalent organic framework (COF) for enhanced NRR performance. Detailed experiments and characterizations revealed that the NRR activity of Ti-COF was clearly better than that of Cu-COF and Co-COF, because of the superior abilities of Ti metal centers in activating inert N2 molecules and suppressing the hydrogen evolution reaction (HER). The resulting Ti-COF exhibits a high NH3 yield of 26.89 µg h-1 mg-1cat. and a Faradaic efficiency of 34.62% for NRR. Density functional theory (DFT) calculations verify that Ti-COF can effectively adsorb and activate N2 molecules and inhibit HER compared with Cu-COF, Co-COF, and pristine COF catalysts. This work opens a new avenue for developing 2D-COF materials that contain abundant coordinated transition metal centers toward electrocatalytic NRR.

Pyrolysis-Free Synthesized Catalyst towards Acidic Oxygen Reduction by Deprotonation.

Acidic oxygen reduction is vital for renewable energy devices such as fuel cells. However, many aspects of the catalytic process are still uncertain-especially the large difference in activity in acidic and alkaline media. Thus, the design and synthesis of model catalysts to determine the active centers and the inactivation mechanism are urgently needed. We report a pyrolysis-free synthesis route to fabricate a catalyst (CPF-Fe@NG) for oxygen reduction in acidic conditions. By introducing a deprotonation process, we extended the oxygen reduction reaction (ORR) activity from alkaline to acidic conditions. CPF-Fe@NG demonstrated outstanding performance with a half-wave potential of 853 mV (vs. RHE) and good stability after 10000 cycles in 1 M HClO4 . The pyrolysis-free route could also be used to assemble fuel cells, with a maximum power density of 126 mW cm-2 . Our findings offer new insights into the ORR process to optimize catalysts for both mechanistic studies and practical applications.

A pyrolysis-free path toward superiorly catalytic nitrogen-coordinated single atom.

Nitrogen-coordinated single-atom catalysts (SACs) have emerged as a frontier for electrocatalysis (such as oxygen reduction) with maximized atom utilization and highly catalytic activity. The precise design and operable synthesis of SACs are vital for practical applications but remain challenging because the commonly used high-temperature treatments always result in unpredictable structural changes and randomly created single atoms. Here, we develop a pyrolysis-free synthetic approach to prepare SACs with a high electrocatalytic activity using a fully π-conjugated iron phthalocyanine (FePc)-rich covalent organic framework (COF). Instead of randomly creating Fe-nitrogen moieties on a carbon matrix (Fe-N-C) through pyrolysis, we rivet the atomically well-designed Fe-N-C centers via intermolecular interactions between the COF network and the graphene matrix. The as-synthesized catalysts demonstrate exceptional kinetic current density in oxygen reduction catalysis (four times higher than the benchmark Pt/C) and superior power density and cycling stability in Zn-air batteries compared with Pt/C as air electrodes.

In Situ Charge Exfoliated Soluble Covalent Organic Framework Directly Used for Zn-Air Flow Battery.

Covalent organic frameworks (COFs) are generally obtained as insoluble, cross-linked powders or films, hindering their superior processable properties especially for device implementation. Here, a soluble COF is created with atomically well-organized positive charged centers constrained in the planar direction, exhibiting exceptional solubility through an in situ charge exfoliation pathway. Once dissolved, the obtained true solution retains homogeneity even after standing over a year. Moreover, the as-designed soluble COF contains ordered N-coordinated Fe single atom centers and conjugated structures, providing a small work function (4.84 eV) and superior catalytic performance for oxygen reduction (high half-wave potential of ∼900 mV). The obtained COF true solution can be directly used as a highly efficient Pt-replaced catalyst for zinc-air flow batteries, generating prominent performance and outstanding stability.

[Biodegradation Characteristics and Kinetics of p-nitrophenol by Strain Arthrobacter sp. CN2].

To investigate the application potential of the p-nitrophenol-degrading bacterium Arthrobacter sp. CN2 in practice, the effects of pH, salinity and additional carbon source were determined, and the degradation kinetics of p-nitrophenol was analyzed. Strain CN2 could degrade p-nitrophenol efficiently in a wide range of pH (7.0-8.0) and elevated salinity (0-60 g · L(-1)). Investigation of additional glucose found that 0.5% of glucose could significantly increase the degrading speed and the time to reach 90% of degradation rate was shortened by 16 hours. These results indicated that strain CN2 could degrade p-nitrophenol efficiently under different conditions and had a great potential for application in practice.