Just over a century ago, Lewis published his seminal work on what became known as the covalent bond, which has since occupied a central role in the theory of making organic molecules. With the advent of covalent organic frameworks (COFs), the chemistry of the covalent bond was extended to two- and three-dimensional frameworks. Here, organic molecules are linked by covalent bonds to yield crystalline, porous COFs from light elements (boron, carbon, nitrogen, oxygen, and silicon) that are characterized by high architectural and chemical robustness. This discovery paved the way for carrying out chemistry on frameworks without losing their porosity or crystallinity, and in turn achieving designed properties in materials. The recent union of the covalent and the mechanical bond in the COF provides the opportunity for making woven structures that incorporate flexibility and dynamics into frameworks.

http://science.sciencemag.org/content/sci/355/6328/eaal1585.full.pdf

The atom, the molecule, and the covalent organic framework

Covalent organic frameworks (COFs) are a class of crystalline porous organic polymers with permanent porosity and highly ordered structures. Unlike other polymers, a significant feature of COFs is that they are structurally predesignable, synthetically controllable, and functionally manageable. In principle, the topological design diagram offers geometric guidance for the structural tiling of extended porous polygons, and the polycondensation reactions provide synthetic ways to construct the predesigned primary and high-order structures. Progress over the past decade in the chemistry of these two aspects undoubtedly established the base of the COF field. By virtue of the availability of organic units and the diversity of topologies and linkages, COFs have emerged as a new field of organic materials that offer a powerful molecular platform for complex structural design and tailor-made functional development. Here we target a comprehensive review of the COF field, provide a historic overview of the chemistry of the COF field, survey the advances in the topology design and synthetic reactions, illustrate the structural features and diversities, scrutinize the development and potential of various functions through elucidating structure-function correlations based on interactions with photons, electrons, holes, spins, ions, and molecules, discuss the key fundamental and challenging issues that need to be addressed, and predict the future directions from chemistry, physics, and materials perspectives.

Covalent Organic Frameworks: Design, Synthesis, and Functions.

Hydrogen fuel is considered as the cleanest renewable resource and the primary alternative to fossil fuels for future energy supply. Sustainable hydrogen generation is the major prerequisite to realize future hydrogen economy. The electrocatalytic hydrogen evolution reaction (HER), as the vital step of water electrolysis to H2 production, has been the subject of extensive study over the past decades. In this comprehensive review, we first summarize the fundamentals of HER and review the recent state-of-the-art advances in the low-cost and high-performance catalysts based on noble and non-noble metals, as well as metal-free HER electrocatalysts. We systemically discuss the insights into the relationship among the catalytic activity, morphology, structure, composition, and synthetic method. Strategies for developing an effective catalyst, including increasing the intrinsic activity of active sites and/or increasing the number of active sites, are summarized and highlighted. Finally, the challenges, perspectives, and research directions of HER electrocatalysis are featured.

Recent Advances in Electrocatalytic Hydrogen Evolution Using Nanoparticles.

Over the past few decades, the design and development of advanced electrocatalysts for efficient energy conversion technologies have been subjects of extensive study. With the discovery of graphene, two-dimensional (2D) nanomaterials have emerged as some of the most promising candidates for heterogeneous electrocatalysts due to their unique physical, chemical, and electronic properties. Here, we review 2D-nanomaterial-based electrocatalysts for selected electrocatalytic processes. We first discuss the unique advances in 2D electrocatalysts based on different compositions and functions followed by specific design principles. Following this overview, we discuss various 2D electrocatalysts for electrocatalytic processes involved in the water cycle, carbon cycle, and nitrogen cycle from their fundamental conception to their functional application. We place a significant emphasis on different engineering strategies for 2D nanomaterials and the influence these strategies have on intrinsic material performance, ...

Emerging Two-Dimensional Nanomaterials for Electrocatalysis

Covalent organic frameworks (COFs) are a class of crystalline porous polymer that allows the atomically precise integration of organic units into extended structures with periodic skeletons and ordered nanopores. One important feature of COFs is that they are designable; that is, the geometry and dimensions of the building blocks can be controlled to direct the topological evolution of structural periodicity. The diversity of building blocks and covalent linkage topology schemes make COFs an emerging materials platform for structural control and functional design. Indeed, COF architectures offer confined molecular spaces for the interplay of photons, excitons, electrons, holes, ions and guest molecules, thereby exhibiting unique properties and functions. In this Review, we summarize the major progress in the field of COFs and recent achievements in developing new design principles and synthetic strategies. We highlight cutting-edge functional designs and identify fundamental issues that need to be addressed in conjunction with future research directions from chemistry, physics and materials perspectives. Covalent organic frameworks are crystalline porous polymers with precisely ordered polygon architectures. In this Review we summarize recent advances in the design principles and synthetic reactions, highlight the current status in structural construction and functionality design, and predict challenging issues and future directions.

Covalent organic frameworks: a materials platform for structural and functional designs

In this work, the activity of bimetallic PtRu/C with varying amounts of Ru for the hydrogen oxidation/evolution reactions (HOR/HER) was determined. The results demonstrate that surface Ru is not necessary for high activity, which shows that the improved activity of the bimetallic PtRu comes from the electronic interaction of Ru with Pt and the tuning of the hydrogen binding energy (HBE). Using the charge transfer coeffiecient from Butler-Volmer fitting and kinetic modeling, it was determined that Ru affects the HOR/HER mechanism in two ways: changing the pathway from Tafel-Volmer to Heyrovsky-Volmer, and lowering of the activation barrier of the Volmer step. Utilizing catalysts with Heyrovsky-Volmer(RDS) mechanism as well as focusing on tuning the HBE might help improve the activity of non-precious metal catalysts; allowing PGM-free fuel cells to become economically viable.

https://iopscience.iop.org/article/10.1149/2.051181jes/pdf

Mechanistic Study of the Hydrogen Oxidation/Evolution Reaction over Bimetallic PtRu Catalysts

Dynamic Hydrothermal Synthesis of a b-Oriented MFI Zeolite Film

Gaseous HCl by-product is often produced from chlorination processes using Cl2 gas. Onsite Cl2 regeneration from HCl is highly desirable as it eliminates the need to buy new Cl2 and dispose HCl waste. Herein a gaseous HCl electrolysis with Fe3+/Fe2+ redox-mediated cathode is demonstrated for Cl2 regeneration. HCl is oxidized to generate Cl2 and proton in anode while Fe3+ is reduced to Fe2+ in cathode. Simultaneously Fe3+ is regenerated chemical oxidation of Fe2+ by oxygen (air) that also produces water. Low operational voltage and high coulombic efficiency are achieved by using a novel composite porous membrane and hydrophobic anode. Specifically, a cell voltage of only 0.64 V is needed at the typical current density of 4 kA m−2, leading to a low energy consumption of 483 kWh tCl2−1 (124 kJ molCl2−1) that is about 50-55% of state-of-the-art HCl electrolysis processes. These new concepts may also help other challenging processes such as H2S splitting and electrochemical NH3 synthesis.

Low-voltage gaseous HCl electrolysis with an iron redox-mediated cathode for chlorine regeneration

Hydrogen chloride (HCl) by-product is often produced from chlorine-consuming processes. Traditional electrochemical processes for converting HCl to chlorine (Cl2) are completed by anodic oxidation reaction coupled with cathodic reduction reactions (two major types: hydrogen evolution reaction and oxygen reduction reaction). Herein, a triiodide (I3−)/iodide (I−) redox-mediated cathode is implemented for the first time for converting HCl to Cl2. The iodide (I−) can be converted back to triiodide (I3−) by air in a reactor external to the eletrolyzer. The desirable redox potential and facile kinetics of I3−/I− offer a substantially lower operational cell voltage, reducing energy consumption by 20%–25% at a typical current density of 4 kA m−2 and improving the efficiency of Cl2 recovery. © The Author(s) 2017. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. [DOI: 10.1149/2.0461707jes] All rights reserved.

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Iodine Redox-Mediated Electrolysis for Energy-Efficient Chlorine Regeneration from Gaseous HCl

The invention discloses a synthesis method of tetra-substituted iminazole shown by a formula III The method comprises the following steps of: reacting alkenyl azide shown by a formula I and nitrone shown by a formula II as raw materials in the presence of anhydrous magnesium sulfate as an accelerant and 1,2-dichloroethane as a solvent at 50-80 DEG C for 24-48 h, and performing TLC (thin-layer chromatography) detection until the alkenyl azide disappears; after the reaction is over, cooling and concentrating the reaction liquid, and performing column chromatography elution by taking a mixed solvent of petroleum ether and ethyl acetate at a volume ratio of 10:1 as an eluent; collecting the elution liquid of all monitored products; and performing rotary evaporation to remove the solvent to obtain the 1,2,4,5-tetra-substituted iminazole The synthesis method disclosed by the invention has the beneficial effects of no catalyst used, mild reaction, high yield and good selectivity, is easy to operate and realizes convenient post-treatment

Jie Zheng

Papers

Mechanistic Study of the Hydrogen Oxidation/Evolution Reaction over Bimetallic PtRu Catalysts

Dynamic Hydrothermal Synthesis of a b-Oriented MFI Zeolite Film

Low-voltage gaseous HCl electrolysis with an iron redox-mediated cathode for chlorine regeneration

Iodine Redox-Mediated Electrolysis for Energy-Efficient Chlorine Regeneration from Gaseous HCl

Synthesis method of tetra-substituted iminazole