Transition Metal-based Catalysts Research Articles

Fe-Co Co-Doped 1D@2D Carbon-Based Composite as an Efficient Catalyst for Zn-Air Batteries.

A Fe-Co dual-metal co-doped N containing the carbon composite (FeCo-HNC) was prepared by adjusting the ratio of iron to cobalt as well as the pyrolysis temperature with the assistance of functionalized silica template. Fe1Co-HNC, which was formed with 1D carbon nanotubes and 2D carbon nanosheets including a rich mesoporous structure, exhibited outstanding oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalytic activities. The ORR half-wave potential is 0.86 V (vs. reversible hydrogen electrode, RHE), and the OER overpotential is 0.76 V at 10 mA cm-2 with the Fe1Co-HNC catalyst. It also displayed superior performance in zinc-air batteries. This method provides a promising strategy for the fabrication of efficient transition metal-based carbon catalysts.

Cross-Coupling Between Aryl Halides and Aryl Alkynes Catalyzed by an Odd Alternant Hydrocarbon.

Catalytic cross-coupling between aryl halides and alkynes is considered an extremely important organic transformation (popularly known as the Sonogashira coupling) and it requires a transition metal-based catalyst. Accomplishing such transformation without any transition metal-based catalyst in the absence of any external stimuli such as heat, photoexcitation or cathodic current is highly challenging. This work reports transition-metal-free cross-coupling between aryl halides and alkynes synthesizing a rich library of internal alkynes without any external stimuli. A chemically double-reduced phenalenyl (PLY)-based molecule with the super-reducing property was employed for single electron transfer to activate aryl halides generating reactive aryl radicals, which subsequently react with alkyne. This protocol covers not only various types of aryl, heteroaryl and polyaryl halides but also applies to a large variety of aromatic alkynes at room temperature. With a versatile substrate scope successfully tested on more than 75 entries, this radical-mediated pathway has been explained by several control experiments. All the key reactive intermediates have been characterized with spectroscopic evidence. Detailed DFT calculations have been instrumental in portraying the mechanistic pathway. Furthermore, we have successfully extended this transition-metal-free catalytic strategy for the first time towards solvent-free cross-coupling between solid aryl halide and alkyne substrates.

Electrocatalytic Oxygen Reduction Using Metastable Zirconium Suboxide.

Strategies for discovery of high-performance electrocatalysts are important to advance clean energy technologies. Metastable phases such as low temperature or interfacial structures that are difficult to access in bulk may offer such catalytically active surfaces. We report here that the suboxide Zr3O, which is formed at Zr-ZrO2 interfaces but does not appear in the experimental Zr-O phase diagram exhibits outstanding oxygen reduction reaction (ORR) performance surpassing that of benchmark Pt/C and most transition metal-based catalysts. Addition of Fe3C nanoparticles to give a Zr-Zr3O-Fe3C/NC catalyst (NC = nitrogen-doped carbon) gives a half-wave potential (E1/2) of 0.914 V, outperforming Pt/C and showing only a 3 mV decrease after 20,000 electrochemical cycles. A zinc-air battery (ZAB) using this cathode material has a high power density of 241.1 mW cm-2 and remains stable for over 50 days of continuous cycling, demonstrating potential for practical applications. Zr3O demonstrates that interfacial or other phases that are difficult to stabilize may offer new directions for the discovery of high-performance electrocatalysts.

Carbon-free hydrogen production via plasma-catalytic ammonia decomposition over transition metal-based catalysts: In situ probing by DRIFTS and SVUV-PIMS

The lack of comprehensive understanding of the reaction mechanism hinders the development of plasma-catalytic ammonia (NH3) decomposition as a potential route for producing carbon-free hydrogen. Herein, we investigated the reaction process over transition metal-based catalysts in a dielectric barrier discharge (DBD) reactor. For the first time, a combination of an integrated in situ diffuse reflectance infrared Fourier transform spectroscopy-DBD (in situ DRIFTS-DBD) and Optical Emission Spectra (OES) were applied to reveal that as for Ni/Al2O3, less NH3* was observed in the gas phase and more NH3 adsorbed on the surface. Combined with online synchrotron vacuum ultraviolet-photoionization mass spectrometry (SVUV-PIMS) it was further illustrated that N2 desorbed more quickly from Ni/Al2O3 than other tested catalysts. Additionally, compared with thermal catalysis, plasma further enhanced the adsorption of NH3 on Lewis acid sites and facilitated the desorption of N2. This study provided a better understanding of the plasma-catalytic NH3 decomposition reaction.

Crystalline-dependent surface reconstruction at low applied potential region for enhanced oxygen evolution reaction

Alkaline water electrolysis is apreferred technology for large-scale green hydrogen production. For most active transition metal-based catalysts during anodic oxygen evolution reaction (OER), the atomic structure of the anodic catalysts’ surface often undergoes reconstruction to optimize the reaction path and enhance their catalytic activity. The design and maintenance of highly active sites during this reconstruction process remain critical and challenging for most OER catalysts. In this study, we explored the effects of crystal structures in pre-catalysts on surface reconstruction at low applied potential. Through experimental observation and theoretical calculation, we found out that catalysts with specific crystal structures exhibit superior surface remodeling ability, which enables them to better adapt to the conditions of the oxygen evolution reaction and achieve efficient catalysis. The discharge process enables the formation of abundant phosphorus vacancies on the surface, which in turn affects the efficiency of the entire oxygen evolution reaction. The optimized crystal structure of the catalyst results in an increase as high as 58.5 mA/cm2 for Ni5P4, which is twice as high as that observed for Ni2P. These results provide essential theoretical foundations and technical guidance for designing more efficient catalysts for oxygen evolution reactions.

Design and synthesis of Co@NiSe catalyst for efficient 2e− ORR in neutral electrolyte: Effect of electronic structure engineering

Two-electron oxygen reduction reaction (2e− ORR) generating hydrogen peroxide (H2O2) in neutral electrolytes is currently encountering significant scientific challenges. Here, we adopted a direct electron transfer and defect engineering approach for synthesizing a Co-doped NiSe hybrid catalyst to boost the efficiency of this reaction system. The Co@NiSe catalyst with long-term stability over 160 h showed a 53.1 % increase in H2O2 selectivity comparing with the pristine NiSe material in neutral electrolyte, indicating the effective modulation of the electronic structure of NiSe via Co doping. Impressively, the 2e− ORR catalytic activity of the catalysts exhibited a positive linear dependence on the content of Ni2+ species. The present research proved the possibility for improving the activity of transition metal-based catalysts in neutral electrolytes via hetero-atom doping, which had built basic structure-function relations for designing highly efficient 2e− ORR system.

Enhancing nitroaromatics reduction through synergistic participation of Ni NPs and nickel ferrite/C nanocomposite: A path towards greener industrial viability

Ni/Fe-citrate gel was reduced in an H2/Ar, forming Ni NPs decorated NiFe2O4-C for eco-friendly nitroaromatics reduction. In-depth characterization of the catalyst highlighted the synergistic interaction between Ni NPs and NiFe2O4 (Ni/NiFe2O4-C), achieving ∼ 99 % conversion of nitroaromatics into amines at 70 °C and 0.5 MPa H2 in water. The cooperative effects of Ni NPs, NiFe2O4, and carbon were instrumental in enhancing the adsorption of hydrogen and nitroaromatics, and the kinetic study showed effectively reducing the activation barrier for the reduction. The HR-TEM, XPS, and H2-TPR provided valuable insights into the formation of Ni NPs and the NiFe2O4 framework, emphasizing their synergistic relationship. Raman spectroscopy and TGA analysis confirmed the formation of carbon. Remarkably, the highly active Ni/NiFe2O4-C catalyst recycled for five cycles without losing activity. p-Aminophenol on 7 g will receive significant attention, emphasizing the substantial promise of this sustainable transition metal-based catalyst for the eco-friendly hydrogenation of nitroaromatics.

Self-supported monometallic FeS2/FeOOH-ZnO@NF with abundant oxygen vacancies as efficient and stable electrocatalysts for the OER and HER

The construction of heterogeneous interfaces and oxygen vacancy (Ov) is a very useful method to enhance the catalytic activity performance of catalysts. In this work, the high-performance a monometallic iron based bifunctional electrocatalyst FeS2/FeOOH-ZnO@NF with oxygen vacancy (Ov) and heterogeneous interface is prepared by the ZnO template induced deposition method for the first time. Due to the synergistic effect of the heterogeneous interface of FeS2/FeOOH-ZnO@NF and the oxygen vacancies of the ZnO, the FeS2/FeOOH-ZnO@NF catalysts exhibited excellent hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activity in alkaline media, with a low overpotential of 74 mV and 177 mV at 10 mA cm−2, respectively. It should be emphasized that the FeS2/FeOOH-ZnO@NF || FeS2/FeOOH-ZnO@NF electrolytic cell has an ultra-low decomposition voltage, only 1.41 V at 10 mA cm−2 and 1.49 V at 20 mA cm−2, which is much lower than that currently reported in most literatures. This work will provide a new strategy and idea for the improvement of HER and OER electrocatalytic performance of transition metal-based catalyst.

Powering the Future by Iron Sulfide Type Material (FexSy) Based Electrochemical Materials for Water Splitting and Energy Storage Applications: A Review.

Water electrolysis is among the recent alternatives for generating clean fuels (hydrogen). It is an efficient way to produce pure hydrogen at a rapid pace with no unwanted by-products. Effective and cheap water-splitting electrocatalysts with enhanced activity, specificity, and stability are currently widely studied. In this regard, noble metal-free transition metal-based catalysts are of high interest. Iron sulfide (FeS) is one of the essential electrocatalysts for water splitting because of its unique structural and electrochemical features. This article discusses the significance of FeS and its nanocomposites as efficient electrocatalysts for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), and overall water splitting. FeS and its nanocomposites have been studied also for energy storage in the form of electrode materials in supercapacitors and lithium- (LIBs) and sodium-ion batteries (SIBs). The structural and electrochemical characteristics of FeS and its nanocomposites, as well as the synthesis processes, are discussed in this work. This discussion correlates these features with the requirements for electrocatalysts in overall water splitting and its associated reactions. As a result, this study provides a road map for researchers seeking economically viable, environmentally friendly, and efficient electrochemical materials in the fields of green energy production and storage.

Electronic Structure Design of Transition Metal-Based Catalysts for Electrochemical Carbon Dioxide Reduction.

With the increasingly serious greenhouse effect, the electrochemical carbon dioxide reduction reaction (CO2RR) has garnered widespread attention as it is capable of leveraging renewable energy to convert CO2 into value-added chemicals and fuels. However, the performance of CO2RR can hardly meet expectations because of the diverse intermediates and complicated reaction processes, necessitating the exploitation of highly efficient catalysts. In recent years, with advanced characterization technologies and theoretical simulations, the exploration of catalytic mechanisms has gradually deepened into the electronic structure of catalysts and their interactions with intermediates, which serve as a bridge to facilitate the deeper comprehension of structure-performance relationships. Transition metal-based catalysts (TMCs), extensively applied in electrochemical CO2RR, demonstrate substantial potential for further electronic structure modulation, given their abundance of d electrons. Herein, we discuss the representative feasible strategies to modulate the electronic structure of catalysts, including doping, vacancy, alloying, heterostructure, strain, and phase engineering. These approaches profoundly alter the inherent properties of TMCs and their interaction with intermediates, thereby greatly affecting the reaction rate and pathway of CO2RR. It is believed that the rational electronic structure design and modulation can fundamentally provide viable directions and strategies for the development of advanced catalysts toward efficient electrochemical conversion of CO2 and many other small molecules.

Highly efficient thermal decomposition of AP through intimately encapsulating in 3DOM CoFe2O4 spinel

Designing highly active catalysts and constructing the interface between ammonium perchlorate (AP) and catalysts are effective strategies for achieving efficient thermal decomposition of AP, which is an urgent need for developing AP based composite solid propellants. Herein, we report an impregnation vacuum freeze-drying strategy to encapsulate AP in an independent three-dimensionally ordered macroporous (3DOM) CoFe2O4 (3D CFO) spinel, resulting in a novel 3D CFO encapsulated AP nanocomposite materials (AP-3DCNCs). The connected pores of 3D CFO provide a model structure for the growth of AP nanocrystals, while the impregnation vacuum freeze-drying strategy ensures the uniform distribution of AP crystals in pores, effectively achieving the size effect of AP nanocrystals (39.88 ∼ 55.50 nm). By adjusting the loading capacity of the AP, the AP-3DCNCs configuration was effectively controlled. The thermal decomposition of AP-3DCNCs is greatly enhanced due to their unique configuration. The high-temperature decomposition temperature is significantly reduced by 180.06–141.78 °C, and the maximum equivalent heat release increased by 2.03 times. It can be foreseen AP-3DCNCs are attractive nanocomposites for the thermal decomposition of AP, and these results provide a convenient strategy for the preparation of transition metal-based composite catalysts with promising applications in the field of solid propellants.

Microscopic-Level Insights into P-O-Induced Strong Electronic Coupling Over Nickel Phosphide with Efficient Benzyl Alcohol Electrooxidation.

Electrooxidation of biomass into fine chemicals coupled with energy-saving hydrogen production for a zero-carbon economy holds great promise. Advanced anode catalysts determine the cell voltage and electrocatalytic efficiency greatly, further the rational design and optimization of their active site coordination remains a challenge. Herein, a phosphorus-oxygen terminals-rich species (Ni2 P-O-300) via an anion-assisted pyrolysis strategy is reported to induce strong electronic coupling and high valence state of active nickel sites over nickel phosphide. This ultimately facilitates the rapid yet in-situ formation of high-valence nickel with a high reaction activity under electrochemical conditions, and exhibits a low potential of 1.33V vs. RHE at 10mAcm-2 , exceeding most of reported transition metal-based catalysts. Advanced spectroscopy, theoretical calculations, and experiments reveal that the functional P-O species can induce the favorable local bonding configurations for electronic coupling, promoting the electron transfer from Ni to P and the adsorption of benzyl alcohol (BA). Finally, the hydrogen production efficiency and kinetic constant of BA electrooxidation by Ni2 P-O-300 are increased by 9- and 2.8- fold compared with the phosphorus-oxygen terminals-deficient catalysts (Ni2 P-O-500). This provides an anion-assisted pyrolysis strategy to modulate the electronic environment of the Ni site, enabling a guideline for Ni-based energy/catalysis systems.

Developing high-power Li||S batteries via transition metal/carbon nanocomposite electrocatalyst engineering.

The activity of electrocatalysts for the sulfur reduction reaction (SRR) can be represented using volcano plots, which describe specific thermodynamic trends. However, a kinetic trend that describes the SRR at high current rates is not yet available, limiting our understanding of kinetics variations and hindering the development of high-power Li||S batteries. Here, using Le Chatelier's principle as a guideline, we establish an SRR kinetic trend that correlates polysulfide concentrations with kinetic currents. Synchrotron X-ray adsorption spectroscopy measurements and molecular orbital computations reveal the role of orbital occupancy in transition metal-based catalysts in determining polysulfide concentrations and thus SRR kinetic predictions. Using the kinetic trend, we design a nanocomposite electrocatalyst that comprises a carbon material and CoZn clusters. When the electrocatalyst is used in a sulfur-based positive electrode (5 mg cm-2 of S loading), the corresponding Li||S coin cell (with an electrolyte:S mass ratio of 4.8) can be cycled for 1,000 cycles at 8 C (that is, 13.4 A gS-1, based on the mass of sulfur) and 25 °C. This cell demonstrates a discharge capacity retention of about 75% (final discharge capacity of 500 mAh gS-1) corresponding to an initial specific power of 26,120 W kgS-1 and specific energy of 1,306 Wh kgS-1.

Organic Dye-Sensitized Nitrene Generation: Intermolecular Aziridination of Unactivated Alkenes.

Aziridines are important structural motifs and intermediates, and several synthetic strategies for the direct aziridination of alkenes have been introduced. However, many of these strategies require an excess of activated alkene, suffer from competing side-reactions, have limited functional group tolerance, or involve precious transition metal-based catalysts. Herein, we demonstrate the direct aziridination of alkenes by combining sulfonyl azides as a triplet nitrene source with a catalytic amount of an organic dye functioning as photosensitizer. We show how the nature of the sulfonyl azide, in combination with the triplet-excited state energy of the photosensitizer, affects the aziridination yield and provide a mechanistic rationale to account for the observed dependence of the reaction yield on the nature of the organic dye and sulfonyl azide reagents. The optimized reaction conditions enable the aziridination of structurally diverse and complex alkenes, carrying various functional groups, with the alkene as the limiting reagent.

Tunable-pH Environment Induced by Local Anchor Effect of High Lewis Basicity Conductive Polymers toward Glycerol Upgrading Assisted Hydrogen Evolution.

Hybrid organic/inorganic composites with the organic phase tailored to modulate the local chemical environment at the transition metal-based catalyst surface arise as an enchanting category of catalysts for electrocatalysis. A fundamental understanding of how the conductive polymers of different Lewis basicities affect the reaction path is, however, still lacking to guide rational catalyst design. Herein, polyaniline (PANI), poly(3,4-ethylenedioxythiophene) (PEDOT), and poly(vinyl alcohol) (PVA) manifesting different Lewis basicities are compared for their regulatory roles on the hydrogen evolution reaction (HER) and glycerol electrooxidation (GOR) pathways regarding local proton coverage. Concerted efforts from in situ Raman and DFT theoretical calculations unveil that conductive polymer/V2O5 surface with tunable local pH regulated by Lewis acidity/basicity. As a result of the tailored chemical environment, the restructured V2O5/PANI/NF composite demonstrates a low overall potential of 1.55 V at the partial current density of 50 mA cm-2 for formate. The glycerol upgrading assisted hydrogen evolution device composed of V2O5/PANI/NF exhibits excellent electrochemical performance at a maximal Faraday efficiency of 82%, ranking among state of the art.

Solvent-free synthesis of foam board-like CoSe2 alloy to selectively generate singlet oxygen via peroxymonosulfate activation for sulfadiazine degradation

Singlet oxygen (1O2) is a highly effective reactive species in selectively oxidizing organic pollutants. However, it is still challenging to rationally design robust catalysts for the selective generation of 1O2. Herein, the coordination and engineering architecture of the foam board-like CoSe2 alloy were facilely constructed through a green solvent-free method and displayed almost 100% 1O2 production selectivity. The CoSe2 alloy showed excellent catalytic ability for the efficient and fast removal of organic pollutants via peroxymonosulfate (PMS) activation compared with previously reported cobalt-based catalysts. The CoSe2/PMS system exhibited strong resistance for a broad pH range (3.0–11.0) and various coexisting inorganic ions owing to the advantage of the strong bonding of Co-Se in CoSe2 alloy. Mechanism studies revealed that 1O2 was the only reactive oxygen species in the CoSe2/PMS system. Theoretical calculations demonstrated that Co was the dominant adsorption site for PMS in CoSe2, and the production pathway of 1O2 was PMS* → *OH → *O → 1O2. In addition, it was proved that *OH and *O served as the rate-determining steps for the formation of 1O2 by PMS activation on CoSe2 alloy. These findings provide a rational strategy for preparing a series of low-cost transition metal-based alloy catalysts for PMS activation to achieve high-efficiency 1O2 production in the elimination of organic pollutants.

Dipeptide coacervates as artificial membraneless organelles for bioorthogonal catalysis

Artificial organelles can manipulate cellular functions and introduce non-biological processes into cells. Coacervate droplets have emerged as a close analog of membraneless cellular organelles. Their biomimetic properties, such as molecular crowding and selective partitioning, make them promising components for designing cell-like materials. However, their use as artificial organelles has been limited by their complex molecular structure, limited control over internal microenvironment properties, and inherent colloidal instability. Here we report the design of dipeptide coacervates that exhibit enhanced stability, biocompatibility, and a hydrophobic microenvironment. The hydrophobic character facilitates the encapsulation of hydrophobic species, including transition metal-based catalysts, enhancing their efficiency in aqueous environments. Dipeptide coacervates carrying a metal-based catalyst are incorporated as active artificial organelles in cells and trigger an internal non-biological chemical reaction. The development of coacervates with a hydrophobic microenvironment opens an alternative avenue in the field of biomimetic materials with applications in catalysis and synthetic biology.

Electrochemical water splitting enhancement by introducing mesoporous NiCoFe-trimetallic phosphide nanosheets as catalysts for the oxygen evolution reaction.

Transition metal-based catalysts are widely used in electrocatalysis, especially in the field of water splitting, due to their excellent electrochemical performance, which focuses on improving the efficiency of the complex oxygen evolution reaction (OER) that occurs at the anode. Transition metal-based catalysts will undergo electrochemical surface reconstruction and form (oxy)hydroxide-based hybrids, which consider the actual active sites for OER. So many efforts have been made to know the origin of the effect of electrochemical surface reconstruction on the performance of the OER. Herein, NiCoFe-phosphide catalyst nanosheets were constructed by a simple one-step hydrothermal reaction by adding oleylamine and ethanol to water solvent during the preparation of the catalyst precursor and high-temperature gas-phase phosphating and significantly showed high effectiveness catalytic activity and conductivity in comparison to normal and traditional preparation methods. Electrochemical analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) demonstrate that the surface was constructed during the electrochemical reaction and formed an amorphous layer of MOx(OH)y active sites, which increased the electrochemical surface area and promoted charge transfer. As well, the synthesized NiCoFePx-PNSs catalyst nanosheets exhibit excellent catalytic activity with a low overpotential equal to 259 mV to achieve the OER at a current density of 10 mA cm-2 and a low Tafel slope of 50.47 mV dec-1 which is better than for most reported transition metal-based electrocatalysts. This work provides a new design for a transition metal-based catalyst for OER as well as further insights into the effect of electrochemical surface reconstruction on intrinsic activity and OER performance.

Boosting oxygen evolution reaction rates with mesoporous Fe-doped MoCo-phosphide nanosheets.

Transition metal-based catalysts are commonly used for water electrolysis and cost-effective hydrogen fuel production due to their exceptional electrochemical performance, particularly in enhancing the efficiency of the oxygen evolution reaction (OER) at the anode. In this study, a novel approach was developed for the preparation of catalysts with abundant active sites and defects. The MoCoFe-phosphide catalyst nanosheets were synthesized using a simple one-step hydrothermal reaction and chemical vapor deposition-based phosphorization. The resulting MoCoFe-phosphide catalyst nanosheets displayed excellent electrical conductivity and a high number of electrochemically active sites, leading to high electrocatalytic activities and efficient kinetics for the OER. The MoCoFe-phosphide catalyst nanosheets demonstrated remarkable catalytic activity, achieving a low overpotential of only 250 mV to achieve the OER at a current density of 10 mA cm-2. The catalyst also exhibited a low Tafel slope of 43.38 mV dec-1 and maintained high stability for OER in alkaline media, surpassing the performance of most other transition metal-based electrocatalysts. The outstanding OER performance can be attributed to the effects of Mo and Fe, which modulate the electronic properties and structures of CoP. The results showed a surface with abundant defects and active sites with a higher proportion of Co2+ active sites, a larger specific surface area, and improved interfacial charge transfer. X-ray photoelectron spectroscopy (XPS) analysis revealed that the catalyst's high activity originates from the presence of Mo6+/Mo4+ and Co2+/Co3+ redox couples, as well as the formation of active metal (oxy)hydroxide species on its surface.

Quantum Embedding for Molecules with Auxiliary Particles - The Ghost Gutzwiller Ansatz

Strong/static electronic correlation mediates the emergence of remarkable phases of matter, and underlies the exceptional reactivity properties in transition metal-based catalysts. Modeling strongly correlated molecules and solids calls for multi-reference...