缺陷位工程在二维材料电催化析氢反应中的研究进展

面对不可再生资源的快速消耗和环境污染的日益加重,寻找清洁可再生能源势在必行.氢能是一种清洁可再生的能源,是目前最有希望替代化石燃料的一种能源.电化学水分解可用来产生高纯氢气,其中析氢催化剂起着至关重要的作用.尽管贵金属铂基催化剂表现出优异的析氢性能,然而稀缺性和高成本限制了其大规模应用.因此,开发高效和地球存量丰富的电...     

Boosting Size‐Selective Hydrogen Combustion in the Presence of Propene Using Controllable Metal Clusters Encapsulated in Zeolite

A strategy is presented for making metal clusters encapsulated inside microporous solids selectively accessible to reactant molecules by manipulating molecular sieve size and affinity for adsorbed molecules. This expands the catalytic capabilities of these materials to reactions demanding high selectivity and stability. Selective hydrogen combustion was achieved over Pt clusters encapsulated in LTA zeolite (KA, NaA, CaA) in a propene‐rich mixture obtained from propane dehydrogenation, showing pore‐size dependent selectivity and coking rate. Propene tended to adsorb at channels or external surfaces of zeolite, interfering the diffusion of hydrogen and oxygen. Tailoring the surface of LTA zeolite with additional alkali or alkaline earth oxides contributed to narrowing zeolite pore size and their affinity for propene. The thus‐modified Pt@KA catalyst displayed excellent hydrogen combustion selectivity (98.5 %) with high activity and superior anti‐coking and anti‐sintering properties.     

Elucidation of Metal‐Ion Accumulation Induced by Hydrogen Bonds on Protein Surfaces by Using Porous Lysozyme Crystals Containing RhIII Ions as the Model Surfaces

Metal‐ion accumulation on protein surfaces is a crucial step in the initiation of small‐metal clusters and the formation of inorganic materials in nature. This event is expected to control the nucleation, growth, and position of the materials. There remain many unknowns, as to how proteins affect the initial process at the atomic level, although multistep assembly processes of the materials formation by both native and model systems have been clarified at the macroscopic level. Herein the cooperative effects of amino acids and hydrogen bonds promoting metal accumulation reactions are clarified by using porous hen egg white lysozyme (HEWL) crystals containing Rh^III ions, as model protein surfaces for the reactions. The experimental results reveal noteworthy implications for initiation of metal accumulation, which involve highly cooperative dynamics of amino acids and hydrogen bonds: i) Disruption of hydrogen bonds can induce conformational changes of amino‐acid residues to capture Rh^III ions. ii) Water molecules pre‐organized by hydrogen bonds can stabilize Rh^III coordination as aqua ligands. iii) Water molecules participating in hydrogen bonds with amino‐acid residues can be replaced by Rh^III ions to form polynuclear structures with the residues. iv) Rh^III aqua complexes are retained on amino‐acid residues through stabilizing hydrogen bonds even at low pH (≈2). These metal–protein interactions including hydrogen bonds may promote native metal accumulation reactions and also may be useful in the preparation of new inorganic materials that incorporate proteins.     

MOF衍生的分层多孔三维N-CoPx/Ni2P大电流密度下加速析氢

氢气(H2)具有能量密度高、环境友好等优点,是一种很有前景的清洁能源载体.目前,电催化水裂解大规模制氢被认为是一种理想可行的方法.析氢反应(HER)涉及多个步骤,首先形成吸附的氢(Volmer步骤),然后是脱附步骤(Heyrovsky步骤)或两个相邻的吸附氢形成H2(Tafel步骤).与酸性介质相比,碱性介质中的HER...     

The Origin of the Catalytic Activity of a Metal Hydride in CO2 Reduction

Atomic hydrogen on the surface of a metal with high hydrogen solubility is of particular interest for the hydrogenation of carbon dioxide. In a mixture of hydrogen and carbon dioxide, methane was markedly formed on the metal hydride ZrCoH_x in the course of the hydrogen desorption and not on the pristine intermetallic. The surface analysis was performed by means of time‐of‐flight secondary ion mass spectroscopy and near‐ambient pressure X‐ray photoelectron spectroscopy, for the in situ analysis. The aim was to elucidate the origin of the catalytic activity of the metal hydride. Since at the initial stage the dissociation of impinging hydrogen molecules is hindered by a high activation barrier of the oxidised surface, the atomic hydrogen flux from the metal hydride is crucial for the reduction of carbon dioxide and surface oxides at interfacial sites.     

Nickel‐Rich Layered Lithium Transition‐Metal Oxide for High‐Energy Lithium‐Ion Batteries

High energy‐density lithium‐ion batteries are in demand for portable electronic devices and electrical vehicles. Since the energy density of the batteries relies heavily on the cathode material used, major research efforts have been made to develop alternative cathode materials with a higher degree of lithium utilization and specific energy density. In particular, layered, Ni‐rich, lithium transition‐metal oxides can deliver higher capacity at lower cost than the conventional LiCoO₂. However, for these Ni‐rich compounds there are still several problems associated with their cycle life, thermal stability, and safety. Herein the performance enhancement of Ni‐rich cathode materials through structure tuning or interface engineering is summarized. The underlying mechanisms and remaining challenges will also be discussed.     

Nanoporous Metal Foams

Nanoporous metal foams (NMFs) have been a long sought‐after class of materials in the quest for high‐surface‐area conductive and catalytic materials. Herein we present an overview of newly developed synthetic strategies for producing NMFs along with an in‐depth discussion of combustion synthesis as a versatile and scalable approach for the preparation of nanoporous, nanostructured metal foams. Current applications of NMFs prepared using combustion synthesis are also presented including hydrogen storage and catalysis.     

Blending Cr2O3 into a NiO–Ni Electrocatalyst for Sustained Water Splitting

The rising H₂ economy demands active and durable electrocatalysts based on low‐cost, earth‐abundant materials for water electrolysis/photolysis. Here we report nanoscale Ni metal cores over‐coated by a Cr₂O₃‐blended NiO layer synthesized on metallic foam substrates. The Ni@NiO/Cr₂O₃ triphase material exhibits superior activity and stability similar to Pt for the hydrogen‐evolution reaction in basic solutions. The chemically stable Cr₂O₃ is crucial for preventing oxidation of the Ni core, maintaining abundant NiO/Ni interfaces as catalytically active sites in the heterostructure and thus imparting high stability to the hydrogen‐evolution catalyst. The highly active and stable electrocatalyst enables an alkaline electrolyzer operating at 20 mA cm^?2 at a voltage lower than 1.5 V, lasting longer than 3 weeks without decay. The non‐precious metal catalysts afford a high efficiency of about 15 % for light‐driven water splitting using GaAs solar cells.     

Strategies for the Improvement of the Hydrogen Storage Properties of Metal Hydride Materials

Metal hydrides are an important family of materials that can potentially be used for safe, efficient and reversible on‐board hydrogen storage. Light‐weight metal hydrides in particular have attracted intense interest due to their high hydrogen density. However, most of these hydrides have rather slow absorption kinetics, relatively high thermal stability, and/or problems with the reversibility of hydrogen absorption/desorption cycling. This paper discusses a number of different approaches for the improvement of the hydrogen storage properties of these materials, with emphasis on recent research on tuning the ionic mobility in mixed hydrides. This concept opens a promising pathway to accelerate hydrogenation kinetics, reduce the activation energy for hydrogen release, and minimize deleterious possible by‐products often associated with complex hydride systems.     

Enhanced Electron Penetration through an Ultrathin Graphene Layer for Highly Efficient Catalysis of the Hydrogen Evolution Reaction

Major challenges encountered when trying to replace precious‐metal‐based electrocatalysts of the hydrogen evolution reaction (HER) in acidic media are related to the low efficiency and stability of non‐precious‐metal compounds. Therefore, new concepts and strategies have to be devised to develop electrocatalysts that are based on earth‐abundant materials. Herein, we report a hierarchical architecture that consists of ultrathin graphene shells (only 1–3 layers) that encapsulate a uniform CoNi nanoalloy to enhance its HER performance in acidic media. The optimized catalyst exhibits high stability and activity with an onset overpotential of almost zero versus the reversible hydrogen electrode (RHE) and an overpotential of only 142 mV at 10 mA cm^?2, which is quite close to that of commercial 40 % Pt/C catalysts. Density functional theory (DFT) calculations indicate that the ultrathin graphene shells strongly promote electron penetration from the CoNi nanoalloy to the graphene surface. With nitrogen dopants, they synergistically increase the electron density on the graphene surface, which results in superior HER activity on the graphene shells.     

Thermally Stable 3,6‐Dinitropyrazolo[4,3‐c]pyrazole‐based Energetic Materials

3,6‐Dinitropyrazolo[4,3‐c]pyrazole was prepared using an efficient modified process. With selected cations, ten nitrogen‐rich energetic salts and three metal salts were synthesized in high yield based on the 3,6‐dinitropyrazolo[4,3‐c]pyrazolate anion. These compounds were fully characterized by IR and multinuclear NMR spectroscopies, as well as elemental analyses. The structures of the neutral compounds 4 and its salt 16 were confirmed by single‐crystal X‐ray diffraction showing extensive hydrogen‐bonding interactions. The neutral pyrazole precursor and its salts are remarkably thermally stable. Based on the calculated heats of formation and measured densities, detonation pressures (22.5–35.4 GPa) and velocities (7948–9005 m s^?1) were determined, and they compare favorably with those of TNT and RDX. Their impact and friction sensitivities range from 12 to >40 J and 80 to 360 N, respectively. These properties make them competitive as insensitive and thermally stable high‐energy density materials.     

Visible‐Light‐Mediated Metal‐Free Hydrosilylation of Alkenes through Selective Hydrogen Atom Transfer for Si−H Activation

Although there has been significant progress in the development of transition‐metal‐catalyzed hydrosilylations of alkenes over the past several decades, metal‐free hydrosilylation is still rare and highly desirable. Herein, we report a convenient visible‐light‐driven metal‐free hydrosilylation of both electron‐deficient and electron‐rich alkenes that proceeds through selective hydrogen atom transfer for Si−H activation. The synergistic combination of the organophotoredox catalyst 4CzIPN with quinuclidin‐3‐yl acetate enabled the hydrosilylation of electron‐deficient alkenes by selective Si−H activation while the hydrosilylation of electron‐rich alkenes was achieved by merging photoredox and polarity‐reversal catalysis.     

Layer‐by‐Layer Assemblies of Montmorillonite and Bacterial Cytochromes for Bioelectrocatalytic Devices

Clay‐based layer‐by‐layer architectures are studied in view of the development of new electrode materials for two highly attractive enzymatic reactions: metal bioremediation and hydrogen uptake. The buildup of layer‐by‐layer (LBL) assemblies of positively charged specific mediators of these enzymatic reactions and negatively charged montmorillonite nanoparticles were carried out onto gold and graphite electrodes. The structure and stability of the assemblies were examined using quartz crystal microgravimetry (QCM) and electrochemical techniques. Satisfactory catalytic efficiencies were observed through the LBL construction, either for bacterial cytochrome c₃‐mediated metal reduction, or hydrogen uptake via immobilized hydrogenase in the presence of an artificial shuttle, methylviologen. Interestingly, it is established that intercalating cytochrome c₃ layers between hydrogenase/montmorillonite layers not only protects hydrogenase from leaching, but allows H₂ uptake/evolution catalytic reaction without any additional diffusing redox mediator.     

Controlled Reactivity Tuning of Metal‐Functionalized Vanadium Oxide Clusters

Controlling the assembly and functionalization of molecular metal oxides [M_xO_y]^n? (M=Mo, W, V) allows the targeted design of functional molecular materials. While general methods exist that enable the predetermined functionalization of tungstates and molybdates, no such routes are available for molecular vanadium oxides. Controlled design of polyoxovanadates, however, would provide highly active materials for energy conversion, (photo‐) catalysis, molecular magnetism, and materials science. To this end, a new approach has been developed that allows the reactivity tuning of vanadium oxide clusters by selective metal functionalization. Organic, hydrogen‐bonding cations, for example, dimethylammonium are used as molecular placeholders to block metal binding sites within vanadate cluster shells. Stepwise replacement of the placeholder cations with reactive metal cations gives mono‐ and difunctionalized clusters. Initial reactivity studies illustrate the tunability of the magnetic, redox, and catalytic activity.     

Transition‐Metal‐Catalyzed Hydrogen‐Transfer Annulations: Access to Heterocyclic Scaffolds

The ability of hydrogen‐transfer transition‐metal catalysts, which enable increasingly rapid access to important structural scaffolds from simple starting materials, has led to a plethora of research efforts on the construction of heterocyclic scaffolds. Transition‐metal‐catalyzed hydrogen‐transfer annulations are environmentally benign and highly atom‐economical as they release of water and hydrogen as by‐product and utilize renewable feedstock alcohols as starting materials. Recent advances in this field with respect to the annulations of alcohols with various nucleophilic partners, thus leading to the formation of heterocyclic scaffolds, are highlighted herein.     

Chemical and Physical Solutions for Hydrogen Storage

Hydrogen is a promising energy carrier in future energy systems. However, storage of hydrogen is a substantial challenge, especially for applications in vehicles with fuel cells that use proton‐exchange membranes (PEMs). Different methods for hydrogen storage are discussed, including high‐pressure and cryogenic‐liquid storage, adsorptive storage on high‐surface‐area adsorbents, chemical storage in metal hydrides and complex hydrides, and storage in boranes. For the latter chemical solutions, reversible options and hydrolytic release of hydrogen with off‐board regeneration are both possible. Reforming of liquid hydrogen‐containing compounds is also a possible means of hydrogen generation. The advantages and disadvantages of the different systems are compared.     

Orthogonally Self‐Assembled Multifunctional Block Copolymers

We report the synthesis of telechelic poly(norbornene) and poly(cyclooctene) homopolymers by ring‐opening metathesis polymerization (ROMP) and their subsequent functionalization and block copolymer formation based on noncovalent interactions. Whereas all the poly(norbornene)s contain either a metal complex or a hydrogen‐bonding moiety along the polymer side‐chains, together with a single hydrogen‐bonding‐based molecular recognition moiety at one terminal end of the polymer chain. These homopolymers allow for the formation of side‐chain‐functionalized AB and ABA block copolymers through self‐assembly. The orthogonal natures of all side‐ and main‐chain self‐assembly events were demonstrated by ¹H NMR spectroscopy and isothermal titration calorimetry. The resulting fully functionalized block copolymers are the first copolymers combining both side‐ and main‐chain self‐assembly, thereby providing a high degree of control over copolymer functionalization and architecture and bringing synthetic materials one step closer to the dynamic self‐assembly structures found in nature.     

Hydrogen‐Bonded Organic Aromatic Frameworks for Ultralong Phosphorescence by Intralayer π–π Interactions

Ultralong organic phosphorescence (UOP) based on metal‐free porous materials is rarely reported owing to rapid nonradiative transition under ambient conditions. In this study, hydrogen‐bonded organic aromatic frameworks (HOAFs) with different pore sizes were constructed through strong intralayer π–π interactions to enable ultralong phosphorescence in metal‐free porous materials under ambient conditions for the first time. Impressively, yellow UOP with a lifetime of 79.8 ms observed for PhTCz‐1 lasted for several seconds upon ceasing the excitation. For PhTCz‐2 and PhTCz‐3, on account of oxygen‐dependent phosphorescence quenching, UOP could only be visualized in N₂, thus demonstrating the potential of phosphorescent porous materials for oxygen sensing. This result not only outlines a principle for the design of new HOFs with high thermal stability, but also expands the scope of metal‐free luminescent materials with the property of UOP.     

Transition‐Metal–Boron Intermetallics with Strong Interatomic d–sp Orbital Hybridization for High‐Performance Electrocatalysis

A theoretical and experimental study gives insights into the nature of the metal–boron electronic interaction in boron‐bearing intermetallics and its effects on surface hydrogen adsorption and hydrogen‐evolving catalytic activity. Strong hybridization between the d orbitals of transition metal (T_M) and the sp orbitals of boron exists in a family of fifteen T_M–boron intermatallics (T_M:B=1:1), and hydrogen atoms adsorb more weakly to the metal‐terminated intermetallic surfaces than to the corresponding pure metal surfaces. This modulation of electronic structure makes several intermetallics (e.g., PdB, RuB, ReB) prospective, efficient hydrogen‐evolving materials with catalytic activity close to Pt. A general reaction pathway towards the synthesis of such T_MB intermetallics is provided; a class of seven phase‐pure T_MB intermetallics, containing V, Nb, Ta, Cr, Mo, W, and Ru, are thus synthesized. RuB is a high‐performing, non‐platinum electrocatalyst for the hydrogen evolution reaction.     

True Boundary for the Formation of Homoleptic Transition‐Metal Hydride Complexes

Despite many exploratory studies over the past several decades, the presently known transition metals that form homoleptic transition‐metal hydride complexes are limited to the Groups 7–12. Here we present evidence for the formation of Mg₃CrH₈, containing the first Group 6 hydride complex [CrH₇]^5?. Our theoretical calculations reveal that pentagonal‐bipyramidal H coordination allows the formation of σ‐bonds between H and Cr. The results are strongly supported by neutron diffraction and IR spectroscopic measurements. Given that the Group 3–5 elements favor ionic/metallic bonding with H, along with the current results, the true boundary for the formation of homoleptic transition‐metal hydride complexes should be between Group 5 and 6. As the H coordination number generally tends to increase with decreasing atomic number of transition metals, the revised boundary suggests high potential for further discovery of hydrogen‐rich materials that are of both technological and fundamental interest.