Integrated Ultrafine Co0.85Se in Carbon Nanofibers: An Efficient and Robust Bifunctional Catalyst for Oxygen Electrocatalysis

Transition-metal selenides are emerging as alternative bifunctional catalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR); however, their activity and stability are still less than desirable. Herein, ultrafine Co_0.85Se nanoparticles encapsulated into carbon nanofibers (CNFs), Co_0.85Se@CNFs, is reported as an integrated bifunctional catalyst for OER and ORR. This catalyst exhibits a low OER potential of 1.58 V vs. reversible hydrogen electrode (RHE) (E_{J=10, OER}) to achieve a current density (J) of 10 mA cm⁻² and a high ORR potential of 0.84 V vs. RHE (E_{J=−1, ORR}) to reach −1 mA cm⁻². Thus, the potential between E_{J=10, OER} and E_{J=−1, ORR} is only 0.74 V, indicating considerable bifunctional activity. The excellent bifunctionality can be attributed to high electronic conduction, abundant electrochemically active sites, and the synergistic effect of Co_0.85Se and CNFs. Furthermore, this Co_0.85Se@CNFs catalyst displays good cycling stability for both OER and ORR. This study paves a new way for the rational design of hybrid catalysts composed of transition-metal selenides and carbon materials for efficiently catalyzing OER and ORR.     

A Bifunctional Hybrid Electrocatalyst for Oxygen Reduction and Evolution: Cobalt Oxide Nanoparticles Strongly Coupled to B,N-Decorated Graphene

The electrocatalyzed oxygen reduction and evolution reactions (ORR and OER, respectively) are the core components of many energy conversion systems, including water splitting, fuel cells, and metal–air batteries. Rational design of highly efficient non-noble materials as bifunctional ORR/OER electrocatalysts is of great importance for large-scale practical applications. A new strongly coupled hybrid material is presented, which comprises CoO_x nanoparticles rich in oxygen vacancies grown on B,N-decorated graphene (CoO_x NPs/BNG) and operates as an efficient bifunctional OER/ORR electrocatalyst. Advanced spectroscopic techniques were used to confirm formation of abundant oxygen vacancies and strong Co−N−C bridging bonds within the CoO_x NPs/BNG hybrid. Surprisingly, the CoO_x NPs/BNG hybrid electrocatalyst is highly efficient for the OER with a low overpotential and Tafel slope, and is active in the ORR with a positive half-wave potential and high limiting current density in alkaline medium.     

A Bifunctional Hybrid Electrocatalyst for Oxygen Reduction and Oxygen Evolution Reactions: Nano-Co3O4-Deposited La0.5Sr0.5MnO3 via Infiltration

For rechargeable metal–air batteries, which are a promising energy storage device for renewable and sustainable energy technologies, the development of cost-effective electrocatalysts with effective bifunctional activity for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) has been a challenging task. To realize highly effective ORR and OER electrocatalysts, we present a hybrid catalyst, Co₃O₄-infiltrated La_0.5Sr_0.5MnO_3-δ (LSM@Co₃O₄), synthesized using an electrospray and infiltration technique. This study expands the scope of the infiltration technique by depositing ~18 nm nanoparticles on unprecedented ~70 nm nano-scaffolds. The hybrid LSM@Co₃O₄ catalyst exhibits high catalytic activities for both ORR and OER (~7 times, ~1.5 times, and ~1.6 times higher than LSM, Co₃O₄, and IrO₂, respectively) in terms of onset potential and limiting current density. Moreover, with the LSM@Co₃O₄, the number of electrons transferred reaches four, indicating that the catalyst is effective in the reduction reaction of O₂ via a direct four-electron pathway. The study demonstrates that hybrid catalysts are a promising approach for oxygen electrocatalysts for renewable and sustainable energy devices.     

介孔CeO2负载的Co3O4催化剂催化富氢气体中的CO优先氧化反应

采用溶胶-凝胶法制备出介孔氧化铈(meso-CeO2)及其负载的氧化钴(Co3O4/meso-CeO2)催化剂,并将其应用于富氢气体中CO的优先氧化反应.通过N2物理吸附及X射线衍射表征考察了meso-CeO2和Co3O4/meso-CeO2的结构性质.活性评价结果表明,在高空速下,Co3O4/meso-CeO2催化剂上的CO优先氧化性能很好,但水和CO2对CO的氧化有一定的负作用.Co3O4/meso-CeO2催化剂的CO完全氧化温度窗口远大于沉淀法制备CeO2负载的氧化钴催化剂.     

NiCo2O4/MXene Hybrid as an Efficient Bifunctional Electrocatalyst for Oxygen Evolution and Reduction Reaction

For the advancement of electrochemical energy conversion and storage technologies, bifunctional electrocatalysts are crucial for efficiently driving both the oxygen evolution (OER) and reduction reactions (ORR). Cobalt-based spinel oxides are a class of promising bifunctional electrocatalysts. However their low electrical conductivity and stability may hinder further improvement. A novel composite material composed of NiCo₂O₄ nanoparticles integrated with emerging two dimensional MXene nanosheets (NiCo₂O₄/MXene) was developed. The successful integration of NiCo₂O₄ with MXene brings about a number of attractive structural features. This includes synergistic effects between NiCo₂O₄ and MXene, highly accessible surface areas, complete exposure of numerous active sites, and excellent electronic conductivity, all of which collectively contribute to the desirability of composite material for OER and ORR. The synthesized NiCo₂O₄/MXene composite showed extraordinary OER electrocatalytic activity with a lower overpotential of 360 mV at a current density of 10 mA/cm², and a small Tafel slope of 64 mV/dec compared to NiCo₂O₄, MXene and NiCo₂O₄+MXene (physically mixed). Additionally, NiCo₂O₄/MXene displays an ORR limiting current density of −4 mA/cm² and exhibited highest onset potential and half wave potential of 0.92 V and 0.72 V vs. RHE, respectively, for the ORR in alkaline media compared to NiCo₂O₄, MXene and NiCo₂O₄+MXene (physically mixed).     

N,P‐Codoped Carbon Networks as Efficient Metal‐free Bifunctional Catalysts for Oxygen Reduction and Hydrogen Evolution Reactions

The high cost and scarcity of noble metal catalysts, such as Pt, have hindered the hydrogen production from electrochemical water splitting, the oxygen reduction in fuel cells and batteries. Herein, we developed a simple template‐free approach to three‐dimensional porous carbon networks codoped with nitrogen and phosphorus by pyrolysis of a supermolecular aggregate of self‐assembled melamine, phytic acid, and graphene oxide (MPSA/GO). The pyrolyzed MPSA/GO acted as the first metal‐free bifunctional catalyst with high activities for both oxygen reduction and hydrogen evolution. Zn–air batteries with the pyrolyzed MPSA/GO air electrode showed a high peak power density (310 W g^?1) and an excellent durability. Thus, the pyrolyzed MPSA/GO is a promising bifunctional catalyst for renewable energy technologies, particularly regenerative fuel cells.     

酸性和碱性溶液中金属氮碳材料氧还原和氢析出反应的理论研究

单原子催化剂(SAC)由于其低成本和在各种电催化反应中潜在的高催化活性而被认为是铂族金属的有前景的替代材料,但仍然缺乏对不同金属氮碳材料催化剂之间活性差异的原子机理的理解.在此,通过实验和理论研究相结合,研究了非贵金属氮碳材料(Me-N-C,Me = Fe和Co)作为模型催化剂,以探索在普遍的pH值下氧还原反应(ORR...     

Self-Assembled Two-Dimensional NiO/CeO2 Heterostructure Rich in Oxygen Vacancies as Efficient Bifunctional Electrocatalyst for Alkaline Hydrogen Evolution and Oxygen Evolution

The development of high-efficiency bifunctional electrocatalysts toward the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline surroundings is essential and challenging for the large-scale generation of clean hydrogen. Herein, a novel self-assembled two-dimensional (2 D) NiO/CeO₂ heterostructure (HS) consisting of NiO and CeO₂ nanocrystals is prepared through a facile two-step approach, and utilized as an enhanced bifunctional electrocatalyst for the HER and OER under alkaline conditions. It is concluded that this 2 D NiO/CeO₂ HS, rich in oxygen vacancies, demonstrates attractive electrocatalytic properties for both the HER and OER in 1 m KOH, including low onset overpotential (η₁), η₁₀ and Tafel slope, excellent durability, as well as large active surface area. Therefore, the self-assembled 2 D NiO/CeO₂ HS is believed to be an efficient bifunctional electrocatalyst toward the HER and OER.     

Activity and Stability of Ruddlesden–Popper‐Type Lan+1NinO3n+1 (n=1, 2, 3, and ∞) Electrocatalysts for Oxygen Reduction and Evolution Reactions in Alkaline Media

Increasing energy demands have stimulated intense research activity on cleaner energy conversion such as regenerative fuel cells and reversible metal–air batteries. It is highly challenging but desirable to develop low‐cost bifunctional catalysts for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), the lack of which is currently one of the major limiting components towards commercialization of these technologies. Here, we have conducted a systematic study on the OER and ORR performances of the Ruddlesden–Popper family of La_n+1Ni_nO_3n+1 (n=1, 2, 3, and ∞) in an alkaline medium for the first time. It is apparent that the Ni?O bond lengths and the hyperstoichiometric oxides in the rock‐salt layers correlate with the ORR activities, whereas the OER activities appear to be influenced by the OH^? content on the surface of the compounds. In our case, the electronic configuration fails to predict the electrocatalytic activity of these compounds. This work provides guidelines to develop new electrocatalysts with improved performances.     

Status Quo on Graphene Electrode Catalysts for Improved Oxygen Reduction and Evolution Reactions in Li-Air Batteries

Reduced global warming is the goal of carbon neutrality. Therefore, batteries are considered to be the best alternatives to current fossil fuels and an icon of the emerging energy industry. Voltaic cells are one of the power sources more frequently employed than photovoltaic cells in vehicles, consumer electronics, energy storage systems, and medical equipment. The most adaptable voltaic cells are lithium-ion batteries, which have the potential to meet the eagerly anticipated demands of the power sector. Working to increase their power generating and storage capability is therefore a challenging area of scientific focus. Apart from typical Li-ion batteries, Li-Air (Li-O₂) batteries are expected to produce high theoretical power densities (3505 W h kg⁻¹), which are ten times greater than that of Li-ion batteries (387 W h kg⁻¹). On the other hand, there are many challenges to reaching their maximum power capacity. Due to the oxygen reduction reaction (ORR) and oxygen evolution reaction (OES), the cathode usually faces many problems. Designing robust structured catalytic electrode materials and optimizing the electrolytes to improve their ability is highly challenging. Graphene is a 2D material with a stable hexagonal carbon network with high surface area, electrical, thermal conductivity, and flexibility with excellent chemical stability that could be a robust electrode material for Li-O₂ batteries. In this review, we covered graphene-based Li-O₂ batteries along with their existing problems and updated advantages, with conclusions and future perspectives.     

Hexagonal La2O3 Nanocrystals Chemically Coupled with Nitrogen-Doped Porous Carbon as Efficient Catalysts for the Oxygen Reduction Reaction

The construction of nano-scale hybrid materials with a smart interfacial structure, established by using rare earth oxides and carbon as building blocks, is essential for the development of economical and efficient catalysts for oxygen reduction reactions (ORRs). In this work, hexagonal La₂O₃ nanocrystals on a nitrogen-doped porous carbon (NPC) derived from crop radish, served as building bricks, are prepared by chemical precipitation and then calcination at elevated temperatures. The obtained La₂O₃/NPC hybrid exhibits a very high ORR activity with a half-wave potential of 0.90 V, exceeding that of commercial Pt/C (0.83 V). Both DFT theoretical and experimental results have verified that the significantly enhanced catalytic performance is ascribed to the formation of the C−O−La covalent bonds between carbon and La₂O₃. Through the covalent bonds, electrons can transfer from the carbon to La₂O₃ and occupy the unfilled e_g orbital of the La₂O₃ phase. This results in the accelerated adsorption of active oxygen and the facilitated desorption of the surface hydroxides (OH_ad⁻), thereby promoting the ORR over the catalyst.     

A Dinuclear Cobalt Cryptate as a Homogeneous Photocatalyst for Highly Selective and Efficient Visible-Light Driven CO2 Reduction to CO in CH3CN/H2O Solution

A dinuclear cobalt complex [Co₂(OH)L¹](ClO₄)₃ ( 1 , L¹=N[(CH₂)₂NHCH₂(m-C₆H₄)CH₂NH(CH₂)₂]₃N) displays high selectivity and efficiency for the photocatalytic reduction of CO₂ to CO in CH₃CN/H₂O (v/v=4:1) under a 450 nm LED light irradiation, with a light intensity of 100 mW cm⁻². The selectivity reaches as high as 98 %, and the turnover numbers (TON) and turnover frequencies (TOF) reach as high as 16896 and 0.47 s⁻¹, respectively, with the calculated quantum yield of 0.04 %. Such high activity can be attributed to the synergistic catalysis effect between two Co^II ions within 1 , which is strongly supported by the results of control experiments and DFT calculations.     

SrNb0.1Co0.7Fe0.2O3−δ Perovskite as a Next‐Generation Electrocatalyst for Oxygen Evolution in Alkaline Solution

The perovskite SrNb_0.1Co_0.7Fe_0.2O_3?δ (SNCF) is a promising OER electrocatalyst for the oxygen evolution reaction (OER), with remarkable activity and stability in alkaline solutions. This catalyst exhibits a higher intrinsic OER activity, a smaller Tafel slope and better stability than the state‐of‐the‐art precious‐metal IrO₂ catalyst and the well‐known BSCF perovskite. The mass activity and stability are further improved by ball milling. Several factors including the optimized e_g orbital filling, good ionic and charge transfer abilities, as well as high OH^? adsorption and O₂ desorption capabilities possibly contribute to the excellent OER activity.     

Pd/Co3O4纳米颗粒负载于Al2O3纳米片高效催化甲烷燃烧

We report an efficient catalyst composed of ternary components prepared by inlaying Pd/Co₃O₄ nanoparticles in alkaline Al₂O₃ nanosheets for catalytic oxidation of methane. Pd/Co₃O₄ inlaid in alkaline Al₂O₃ exhibited a higher ability to break the C-H bond of methane than Pd/Co₃O₄ supported on SiO₂, ZrO₂, CeO₂, and acidic or neutral Al₂O₃. Our results show more oxygen vacancies and higher amounts of surface adsorbed oxygen on the surface of Pd/Co₃O₄/alkaline Al₂O₃ than on other catalysts, which is responsible for methane activation and conversion. Further, the Pd/Co₃O₄/alkaline Al₂O₃ catalyst can almost restore to its initial value in the absence of water when 5% (volume fraction) vapor water was cut off, although a decrease in activity occurred when water vapor was introduced to the reaction system. Even under a condition similar to the exhaust of a lean-burn natural gas engine, the catalytic performance of the Pd/Co₃O₄/alkaline Al₂O₃ catalyst is excellent, that is, methane could be completely converted when the sample temperature in the reaction atmosphere was ramped to 400℃.     

Theoretical Investigation on the Hydrogen Evolution,Oxygen Evolution,and Oxygen Reduction Reactions Performances of Two-Dimensional Metal-Organic Frameworks Fe3(C2X)12 (X = NH,O, S)

Two-dimensional metal-organic frameworks (2D MOFs) inherently consisting of metal entities and ligands are promising single-atom catalysts (SACs) for electrocatalytic chemical reactions. Three 2D Fe-MOFs with NH, O, and S ligands were designed using density functional theory calculations, and their feasibility as SACs for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) was investigated. The NH, O, and S ligands can be used to control electronic structures and catalysis performance in 2D Fe-MOF monolayers by tuning charge redistribution. The results confirm the Sabatier principle, which states that an ideal catalyst should provide reasonable adsorption energies for all reaction species. The 2D Fe-MOF nanomaterials may render highly-efficient HER, OER, and ORR by tuning the ligands. Therefore, we believe that this study will serve as a guide for developing of 2D MOF-based SACs for water splitting, fuel cells, and metal-air batteries.     

Fine‐Tuning the Reactivity and Stability by Systematic Ligand Variations in CpCoI Complexes as Catalysts for [2+2+2] Cycloaddition Reactions

CpCo^I‐olefin‐phosphite and CpCo^I‐bisphosphite complexes were systematically prepared and their reactivity in [2+2+2] cycloaddition reactions compared with highly active [CpCo(H₂C?CHSiMe₃)₂] ( 1 ). Whereas 1 is an excellent precursor for the synthesis of [CpCo(olefin)(phosphite)] complexes ( 2 a – f ), [CpCo(phosphite)₂] complexes ( 3 a – e ) were prepared photochemically from [CpCo(cod)]. The complexes were evaluated in the cyclotrimerization reaction of diynes with nitriles yielding pyridines. For [CpCo(olefin)(phosphite)], as well as some of the [CpCo(phosphite)₂] complexes, reaction temperatures as low as 50 °C were sufficient to perform the cycloaddition reaction. A direct comparison showed that the order of reactivity for the complex ligands was olefin₂>olefin/phosphite>phosphites₂. The complexes with mixed ligands favorably combine reactivity and stability. Calculations on the ligand dissociation from [CpCo(olefin)(phosphite)] proved that the phosphite is dissociating before the olefin. [CpCo(H₂C?CHSiMe₃){P(OPh)₃}] ( 2 a ) was investigated for the co‐cyclization of diynes and nitriles and found to be an efficient catalyst at rather mild temperatures.     

Carboxylated,Fe‐Filled Multiwalled Carbon Nanotubes as Versatile Catalysts for O2 Reduction and H2 Evolution Reactions at Physiological pH

The development of new electrocatalysts for the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) at physiological pH is critical for several fields, including fuel cells and biological applications. Herein, the assembly of an electrode based on carboxyl‐functionalised hydrophilic multiwalled carbon nanotubes (MWCNTs) filled with Fe phases and their excellent performance as electrocatalysts for ORR and HER at physiological pH are reported. The encapsulated Fe dramatically enhances the catalytic activity, and the graphitic shells play a double role of efficiently mediating the electron transfer to O₂ and H₂O reactants and providing a cocoon that prevents uncontrolled Fe oxidation or leaching.     

脊椎状NiCo2O4纳米棒的制备及其析氧和氧还原性能研究

以水热法并进一步焙烧合成脊椎状NiCo₂O₄纳米棒,通过透射电子显微镜（TEM）、X射线衍射仪（XRD）、X射线光电子能谱仪（XPS）和热重分析仪（TG）等来表征其结构形态及热稳定性.采用线性扫描法（LSV）、循环伏安（CV）研究所制备催化剂的在玻碳和旋转圆盘电极上的电催化活性：在0.1 mol·L^-1 KOH溶液中的电催化析氧反应（OER）和电催化氧还原反应（ORR）.研究结果表明,所制备的脊椎状NiCo₂O₄纳米棒有大量的不饱和态,200℃焙烧制备的脊椎状NiCo₂O₄纳米棒析氧过电位最小可达309 mV,Tafel斜率145.6 mV/dec,其氧还原极限电流密度在1600 rmp可达到5.095 mA·cm^-2,电子转移数在3.2~3.8之间,接近四电子转移机理,其优良电化学性能可能是由于暴露了更多的边缘缺陷的缘故.     

Carbon Dots Integrated NiCo2O4 Hierarchical Nanoneedle Arrays Supported on Ni Foam as Efficient and Stable Electrode for Hydrogen and Oxygen Evolution Reactions

The production of hydrogen and oxygen via water electrolysis has become a sustainable and encouraging pathway for the establishment of new energy sources. Herein, we report the successful growth of hierarchical NiCo₂O₄‐carbon dots (CDs) nanoneedle arrays supported on nickel foam through a simple and environmentally benign hydrothermal self‐assembly technique. The designed material acts as a binder free electrode and shows bifunctional electrocatalytic activity for both hydrogen evolution reaction (HER) as well as oxygen evolution reaction (OER) in alkaline medium. An electrocatalyst sample with an optimal loading of CDs (25 mg) requires a low overpotential of 146 mV to achieve a current density of 10 mA/cm² for the HER in an alkaline medium, whereas it requires an overpotential of 390 mV to achieve a current density of 50 mA/cm² for the OER in the same alkaline medium. The excellent electrocatalytic activities of the sample with loading of CD can be ascribed due to the presence of large number of exposed active sites offered by CD/NiCo₂O₄ and the enhanced electron transfer processes occurring as a result of hierarchical structure composed of three‐dimensional nickel foam and the NiCo₂O₄?CDs nanoneedle arrays. Thus, the synthesis method introduced in this present work is a facile and cost‐effective approach for the construction of bifunctional electrocatalysts with high reactivity and excellent durability.