Toward sustainable and effective HER electrocatalysts: Strategies for the basal plane site activation of transition metal dichalcogenides

Due to their low cost and overall sustainability, transition metal dichalcogenides (TMDCs) are potential alternatives to noble metals as catalysts to produce green hydrogen. A promising route to improve their performances consists of activating their basal plane, both increasing the number of active sites or their specific activity. This can be accomplished by exploiting point defects, in-plane boundaries and strain. In particular, single atom adsorbed or incorporated into TMDCs have shown remarkable results in electrochemical half-cell tests. Topological curvature or grain boundaries (and related defects) can also be used to further boost the performances. A crucial point for the application of such strategies is related to the development of cost effective and sustainable methods for the scale-up of synthetic protocols.     

2D transition metal chalcogenides and van der Waals heterostructures: Fundamental aspects of their electrochemistry

The explosion of research on graphene has prompted a similar level of activity on materials with related structures, i.e. two-dimensional materials formed from solids with a laminar structure, which can be isolated in their monolayer form. The main focus of activity beyond graphene, in electrochemical and other contexts, has focussed on the transition metal dichalcogenides. This review will highlight important advances in the use of these materials in an electrochemical context. The existence of a “family” of two-dimensional materials has led to recent interest in the creation of “van der Waals heterostructures”, where dissimilar two-dimensional materials are assembled in a specific fashion to produce structures with distinct electronic properties. The application of these materials in electrochemistry is in its infancy but very recent works suggest this will be an extremely important area of research in the coming years.     

金属磷化物(NiCo)_2P/NF自支撑电极制备及其电催化研究

利用廉价的过渡金属作为催化剂催化水分解产氢和产氧是解决能源危机的重要途径.我们制备了一种中空过渡金属磷化物自支撑电极材料(NiCo)_2P/NF,该电极材料采用生长在泡沫镍上的类普鲁士蓝Ni_3[Co(CN)_6]_2作为前体,低温磷化后获得.该电极材料显示出高效的电催化水分解产氢和产氧能力,在1 mol/L氢氧化钾溶液中,达到10 mA/cm~2时,产氢和产氧过电位分别为159和210 mV,同时,将其组装成全解水装置后,仅需1.61 V电压即可达到10 mA/cm~2时,其全解水性能超过贵金属Pt/C-IrO_2(1.64 V),这使得该自支撑双金属磷化物电极有望替代贵金属用作电催化全解水催化剂.     

Effect of expired doxofylline drug on corrosion protection of soft steel in 1 M HCl: Electrochemical,quantum chemical and synergistic effect studies

The corrosion inhibition property of expired Doxofylline (DF) was tested for soft steel in 1 M hydrochloric acid solution by adopting mass change and electrochemical measurement techniques. At 200 ppm concentration of DF, maximum of 72.84% inhibition efficiency was noticed. However with addition of 50 ppm of KI, it enhances the percentage inhibition efficiency up to 88.48%. DF resists both anodic and cathodic reactions and functioned as mixed-inhibition mechanism. At higher temperatures, electrochemical impedance response noticed that, the diameter of the semicircle decreases as solution temperature increases As a result, in both absence and presence of the inhibitor the R_p values were decreased. Quantum chemical studies revealed about structural and electronic effects in relation to the inhibition efficiencies. Surface morphology of both inhibited and corroded soft steel was assessed by means of scanning electron microscopy (SEM)) and atomic force microscope (AFM). The SEM images of soft steel reflect the inhibitive property of the DF at optimized concentration and a significant decrease in the surface roughness was observed (surface roughness was reduced from 606 nm to 294 nm as measured by AFM)). UV-Visible absorption peaks signifies that CC and CO groups from the inhibitor were interacted with iron cations, which is the evidence for the formation protective film over the soft steel surface.     

NaOH溶液中Ni基石墨修饰电极上甲醇电氧化过程中钴与铜的协同效应

在NaOH溶液(0.1 mol/L)中考察了Ni, Co和Cu二元和三元合金修饰的石墨电极上甲醇电氧化反应性能.采用循环伏安法、计时电流法和电化学阻抗谱(EIS)等技术研究了修饰电极的催化活性和协同效应.这些催化剂在含有Ni, Cu和Co离子溶液的阴极电位上反复浸渍石墨电极制得.结果表明,在甲醇存在下, Ni基三元合金修饰电极(G/NiCuCo)对甲醇氧化反应的响应值明显高于其它样品.阳极峰值电流与扫描速率的平方根呈线性关系,表明该过程受扩散控制.在CA区域,该反应遵循Cottrellin特性,甲醇扩散系数为6.25×10–6 cm2/s.甲醇氧化反应速率常数为40×107 cm3/(mol·s).另外,采用EIS研究了修饰电极表面上甲醇催化氧化反应.     

原子层沉积：一种多相催化剂“自下而上”气相制备新策略

多相催化剂是极为重要的一类催化剂,在许多重要工业反应中扮演关键角色。然而,传统的湿化学合成手段在很多情况下难以做到对催化剂活性位点的结构、组成以及其周围局部环境的原子级精细调控,继而给优化催化剂性能、理解多相催化机理带来较大的挑战。原子层沉积(ALD)是一种气相催化剂合成技术,其原理是基于两种前驱体蒸汽交替进样并在载体表面上发生分子层面上的“自限制”反应,实现目标材料在载体表面上的精准沉积。利用其分子层面上的“自限制”反应特性,并通过改变沉积周期数、次序和种类等方法可以实现对催化剂活性位结构的原子级精细控制,进而为人们提供了一种催化剂“自下而上”精细可控合成的新策略。在本文中,我们总结了利用ALD方法在负载型单金属和双金属催化剂精细设计方面的进展,讨论了ALD方法在设计高效催化剂方面的特点与优势。特别地,我们总结了利用ALD方法制备单原子和双原子结构金属催化剂的方法与策略。此外,我们总结了利用氧化物可控沉积精准调控金属催化活性中心周围的微环境,从而实现提升催化剂活性、选择性和稳定性的方法。最后我们展望了ALD技术在催化剂制备领域中应用的潜力。     

Selectivity effects related to the diversity of active sites operating on nanostructured multifunctional catalysts

The goal of the present study was to gain a better understanding of the selectivity of processes over multifunctional catalysts exhibiting diversity of operating active sites. The concept is that the concurrent performance of different types of active sites may provoke effects on the process selectivity comparable to the effects resulting from the kinetic regularities and activation energies of the occurring reactions. Accordingly, in the kinetic model the authors introduce specific parameters reflecting the contribution of distinct types of active sites, facilitating different reaction routes. Reasons are adduced how suchlike parameters serve to account the impact of various reaction routes occurring on different types of sites. The suggested approach links the deactivation-caused selectivity changes to dissimilarities in the vulnerability of different types of active sites. This work relates the probabilities for action of different types of sites to the size of active-phase islands. Various reaction mechanism patterns are modeled to examine relevant selectivity effects.     

Fe原子吸附对单层WS_2结构和性质的影响

本文采用基于密度泛函理论(DFT)的第一性原理方法研究了Fe原子吸附对单层WS_2结构和性质的影响。研究结果表明:Fe原子吸附在W原子的顶位最稳定,相应的原子吸附能为1.84 eV。Fe与衬底间的相互作用削弱了紧邻W―S键,使其键长增大0.011 nm。由于衬底原子的影响,Fe原子d轨道的电子重新分布,形成了2μB左右的局域原子磁矩。在低覆盖度下(0.125和0.25 ML),磁性作用以超交换作用为主,铁磁序不稳定。而在高覆盖度下(0.5和1.0 ML),Fe原子间距减小,磁性作用以RKKY作用为主,铁磁序稳定。电子结构的计算结果显示,在高覆盖度下,Fe/WS_2结构在费米能级处的电子自旋极化率等于100%。自旋向上与向下通道分别为间接带隙的半导体和金属。在1.0 ML覆盖度下,自旋向上的禁带宽度约为0.94 eV。这说明Fe原子吸附可以将直接带隙的WS_2半导体转变成半金属,形成一种潜在的自旋电子器件材料。     

Synergistic effects of catalysts and plasmas on the synthesis of ammonia and hydrazine

The synergistic effects o1 driving frequency of the discharge and catalysis of iron and molybdenum wires when then are placed in nitrogen-h ydrogen radio-frequency and microwave plasmas mere investigated. The ammonia Yield increased in the plasmas prepared using both driving frequencies. but the hydrazine yield increased only in fire radio-frequency discharge with the catalysts. The direct adsorption of NH_x formed in the plasma on the catalyst surface followed by the formation of NH₃ and N₂H₄ are considered as a reaction scheme in the radio-frequency discharge. On the other hand, the adsorption of N atoms and/or formation of the metal- N bond favors the formation of ammonia but does not affect the hydrazine formation in the microwave discharge.     

Electrochemical reduction of nitrogen to ammonia: Progress,challenges and future outlook

Ammonia is an important chemical used in the production of fertilizers. The electrochemical nitrogen reduction reaction (NRR) to synthesize ammonia has emerged to be a potential alternative approach. Here, we provide a short opinion of the current progress and challenges of nitrogen reduction reaction from the recent literature. Different types of electrocatalysts with their performances and design principles are briefly outlined. However, most of the electrocatalysts showed unsatisfactory catalytic performance for NRR because of various factors, such as the competing side reactions and the large thermodynamic energy barrier. Hence, the concept of conducting NRR should be re-evaluated. We provide our opinion on the future possible outlook on how to improve the NRR performance. Alternative external energy input should be coupled with the electrochemical reduction of nitrogen to help with the activation of nitrogen to ammonia. Some possible energy input could be the use of cold plasma and surface plasmon resonance.     

非金属与金属的协同作用对镁基储氢合金电化学性能的影响

用机械球磨法分别以Ti、B、复合物TiB对非晶态Mg45Ti3V2Ni50储氢合金进行了表面修饰.实验结果表明,恰当比例的TiB球磨修饰对镁基储氢合金循环稳定性远好于Ti、B同比例单独修饰合金电极的效果.Mg45Ti3V2Ni50与TiB质量比为2∶1的Mg45Ti3V2Ni50-TiB(2∶1)复合合金电极的初始放电容量为529.4mAh·g-1,第50次循环放电容量仍为277.1mAh·g-1.复合物TiB中Ti、B元素之间和复合合金中合金元素与TiB之间产生了金属与非金属的协同作用,导致复合合金新的立体褶皱结构的生成,增强了修饰层与合金间的作用,Mg45Ti3V2Ni50-TiB(2∶1)合金电极表面活性增强,循环稳定性显著提高.     

The magic of integration:Exploring the construction of dithienylethene-based infinite coordination polymers and their synergistic effect for gaseous ammonia probe applications

Infinite coordination polymers are recognized as excellent platform for functionalization.Dithienylethene motifs,which are one of the most attractive functional moieties,were incorporated into an infinite coordination polymer,to deliver a‘‘smart’’porous material that can response to external stimuli.The obtained dithienylethene-based infinite coordination polymers(named Cu-DTEDBA)share the advantages of both infinite coordination polymers(porosity and stability)and dithienylethene motifs(photochromism).The physical and chemical properties of Cu-DTEDBA were characterized by FTIR,TEM,SEM,XRD,TGA,UV–vis,EDX and BET.Moreover,the combination of dithienylethene and infinite coordination polymers gives rise to a synergistic effect,which induces functional behaviors of ammonia sensor applications.Both open and closed forms of Cu-DTEDBA exhibit distinct colorimetric change upon exposure to gaseous ammonia,which is not observed in dithienylethene free molecules.     

A DFT study on structural stability and electronic property of VIIIB transition metal-doped carbon nanocaps

Carbon nanocap (CNC) was selected for the systems doped with VIIIB transition metal (TM) atoms. The geometrical structures and electronic properties of TM-doped CNCs were calculated using the density functional theory method. It was found that TM atoms can interact with CNC to form TM–CNC complexes, which corresponded with the large partial charge transfer. All of molecular orbitals of TM–CNC complexes were localized in vicinity doping site. The density of states of these TM-doped CNCs were exhibited mostly metallic or narrow–gap semiconductor.     

Electrochemical performance of grown layer of Ni(OH)2 on nickel foam and treatment with phosphide and selenide for efficient water splitting

Active nanocomposites synthesized by the electrochemical approach play a vital role in energy generation, conversion, and storage technologies. Recently, scientists began to explore the use of earth-rich transition metal-based materials to replace precious metal-based catalysts. Transition metals (TMs) based nickel (Ni) and their pnictides compounds such as phosphides and selenides exhibit good activity for hydrogen evaluation reaction (HER) and the entire water electrolysis process. In this study, we first prepared Ni(OH)₂ and grown its layer on Ni foam (NF) and treated it with selenide (Se) and phosphide (P) then nickel-based selenide-phosphide catalyst (Ni–P–Se) was prepared by simultaneous selenization and phosphidation process for the first time. The as-obtained composite was then analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), elemental mapping and transmission electron microscope (TEM) means to study the composition, structure, and micro-morphology of materials. Furthermore, we also observed electrocatalytic water splitting activity using electrochemical cell. The results of electrochemical tests depicted that the selenization and phosphidation treatments significantly enhanced the electrocatalytic HER activity of the starting materials. The overpotentials required for Ni–P–Se to reach 10 ?mA ?cm^?2 and 100 ?mA ?cm^?2 were only 242 ?mV and 282 ?mV. The Tafel slope of Ni–P–Se is 151 ?mV dec^?1, which is lower than that of nickel phosphide, selenide, and hydroxide indicating that selenide-phosphide enhances the HER reaction kinetics of the material, which in turn increases hydrogen output rate as compared with previous studies.     

Relativistic and electron correlation effects on thed-d spectrum of transition metal fluorides

Summary The electronic spectra of the transition metal complexes CoF ₆ ^2– , RhF ₆ ^2– and IrF ₆ ^2– that occur in the solids Cs₂MeF₆ are calculated. Hartree-Fock and Dirac-Fock calculations followed by non-relativistic and relativistic CI calculations respectively are used to study the influence of relativity and electron correlation. The calculated transitions are found to agree fairly well with experiment, the largest discrepancies arising from the neglect of differential dynamical electron correlation effects.     

H-, C-NMR and ethylene polymerization studies of zirconocene/MAO catalysts: effect of the ligand structure on the formation of active intermediates and polymerization kinetics

Using ¹H- and ¹³C-NMR spectroscopies, cationic intermediates formed by activation of L₂ZrCl₂ with methylaluminoxane (MAO) in toluene were monitored at Al/Zr ratios from 50 to 1000 (L₂ are various cyclopentadienyl (Cp), indenyl (Ind) and fluorenyl (Flu) ligands). The following catalysts were studied: (Cp-R)₂ZrCl₂ (R=Me, 1,2-Me₂, 1,2,3-Me₃, 1,2,4-Me₃, Me₄, Me₅, n-Bu, t-Bu), rac-ethanediyl(Ind)₂ZrCl₂, rac-Me₂Si(Ind)₂ZrCl₂, rac-Me₂Si(1-Ind-2-Me)₂ZrCl₂, rac-ethanediyl(1-Ind-4,5,6,7-H₄)₂ZrCl₂, (Ind-2-Me)₂ZrCl₂, Me₂C(Cp)(Flu)ZrCl₂, Me₂C(Cp-3-Me)(Flu)ZrCl₂ and Me₂Si(Flu)₂ZrCl₂. Correlations between spectroscopic and ethene polymerization data for catalysts (Cp-R)₂ZrCl₂/MAO (R=H, Me, 1,2-Me₂, 1,2,3-Me₃, 1,2,4-Me₃, Me₄, Me₅, n-Bu, t-Bu) and rac-Me₂Si(Ind)₂ZrCl₂ were established. The catalysts (Cp-R)₂ZrCl₂/AlMe₃/CPh₃⁺B(C₆F₅)₄⁻ (R=Me, 1,2-Me₂, 1,2,3-Me₃, 1,2,4-Me₃, Me₄, n-Bu, t-Bu) were also studied for comparison of spectroscopic and polymerization data with MAO-based systems. Complexes of type (Cp-R)₂ZrMe⁺←Me⁻-Al≡MAO (IV) with different [Me-MAO]⁻ counteranions have been identified in the (Cp-R)₂ZrCl₂/MAO (R=n-Bu, t-Bu) systems at low Al/Zr ratios (50-200). At Al/Zr ratios of 500-1000, the complex [L₂Zr(μ-Me)₂AlMe₂]⁺[Me-MAO]⁻ (III) dominates in all MAO-based reaction systems studied. Ethene polymerization activity strongly depends on the Al/Zr ratio (Al/Zr=200-1000) for the systems (Cp-R)₂ZrCl₂/MAO (R=H, Me, n-Bu, t-Bu), while it is virtually constant in the same range of Al/Zr ratios for the catalytic systems (Cp-R)₂ZrCl₂/MAO (R=1,2-Me₂, 1,2,3-Me₃, 1,2,4-Me₃, Me₄) and rac-Me₂Si(Ind)₂ZrCl₂/MAO. The data obtained are interpreted on assumption that complex III is the main precursor of the active centers of polymerization in MAO-based systems.     

Enhanced Electrochemical Reduction of CO2 to CO on Ag/SnO2 by a Synergistic Effect of Morphology and Structural Defects

Silver (Ag)-based materials are considered to be promising materials for electrochemical reduction of CO₂ to produce CO, but the selectivity and efficiency of traditional polycrystalline Ag materials are insufficient; there still exists a great challenge to explore novel modified Ag based materials. Herein, a nanocomposite of Ag and SnO₂ (Ag/SnO₂) for efficient reduction of CO₂ to CO is reported. HRTEM and XRD patterns clearly demonstrated the lattice destruction of Ag and the amorphous SnO₂ in the Ag/SnO₂ nanocomposite. Electrochemical tests indicated the nanocomposite containing 15% SnO₂ possesses highest catalytic selectivity featured by a CO faradaic efficiency (FE) of 99.2% at −0.9 V versus reversible hydrogen electrode (vs RHE) and FE>90% for the CO product at a wide potential range from −0.8 V to −1.4 V vs RHE. Experimental characterization and analysis showed that the high catalytic performance is attributed to not only the branched morphology of Ag/SnO₂ nanocomposites (NCs), which endows the maximum exposure of active sites, but also the special adsorption capacity of abundant defect sites in the crystal for *COOH (the key intermediate of CO formation), which improves the intrinsic activity of the catalyst. But equally important, the existed SnO₂ also plays an important role in inhibiting hydrogen evolution reaction (HER) and anchoring defect sites. This work demonstrates the use of crystal defect engineering and synergy in composite to improve the efficiency of electrocatalytic CO₂ reduction reaction (CO₂RR).     

Toluene abatement on Ag-CeO2/SBA-15 catalysts: synergistic effect of silver and ceria

As a typical volatile organic compound, toluene is a hazardous material for human health and the environment, and currently, the development of catalysts for its oxidation into CO₂ and water is crucial. The series of Ag-CeO₂/SBA-15 catalysts is synthesized by wetness impregnation techniques and characterized by a number of physical-chemical methods (nitrogen [N₂] physisorption, small angle X-ray scattering [SAXS], transmission electron microscopy [TEM], and temperature-programmed reduction [TPR]). The toluene sorption and catalytic properties in toluene oxidation are studied. Small silver [Ag] and cerium oxide [ceria, CeO_2] particles with sizes below 3 nm are predominantly formed in the ordered structure of Santa Barbara Amorphous-15 [SBA-15]. The interactions between the Ag and CeO₂ nanoparticles are established. Temperature-programmed desorption of toluene [TPD-C₇H₈] analysis shows that physical adsorption of toluene occurs on pristine SBA-15 material, while the introduction of either silver or ceria to SBA-15 leads to the appearance of additional strongly bound chemisorbed toluene on such sites. When both Ag and CeO₂ are introduced, only chemisorbed toluene is formed over the Ag-CeO₂/SBA-15 catalyst, and the highest catalytic activity in toluene oxidation is observed over this catalyst (T_98% = 233 °C, 0.2% C₆H₅CH₃) that is attributed to the synergistic effect of ceria [CeO_2] and silver [Ag].