Strengthening absorption ability of Co-N-C as efficient bifunctional oxygen catalyst by modulating the d band center using MoC

Co-N-C is a promising oxygen electrochemical catalyst due to its high stability and good durability.However,due to the limited adsorption ability improvement for oxygen-containing intermediates,it usually exhibits inadequate catalytic activity with 2-electron pathway and high selectivity of hydrogen peroxide.Herein,the adsorption of Co-N-C to these intermediates is modulated by constructing heterostructures using transition metals and their derivatives based on d-band theory.The heterostructured nanobelts with MoC core and pomegranate-like carbon shell consisting of Co nanoparticles and N dopant(MoC/Co-N-C)are engineered to successfully modulate the d band center of active Co-N-C sites,resulting in a remarkably enhanced electrocatalysis performance.The optimally performing MoC/Co-N-C exhibits outstanding bi-catalytic activity and stability for the oxygen electrochemistry,featuring a high wave-half potential of 0.865 V for the oxygen reduction reaction(ORR)and low overpotential of 370 mV for the oxygen evolution reaction(OER)at 10 mA cm^(-2).The zinc air batteries with the MoC/Co-N-C catalyst demonstrate a large power density of 180 mW cm^(-2)and a long cycling lifespan(2000 cycles).The density functional theory calculations with Hubbard correction(DFT+U)reveal the electron transferring from Co to Mo atoms that effectively modulate the d band center of the active Co sites and achieve optimum adsorption ability with"single site double adsorption"mode.

Metal-organic framework-based single-atom electro-/ photocatalysts: Synthesis, energy applications, and opportunities

Single-atom catalysts(SACs)have gained substantial attention because of their exceptional catalytic properties.However,the high surface energy limits their synthesis,thus creating significant challenges for further development.In the last few years,metal–organic frameworks(MOFs)have received significant consideration as ideal candidates for synthesizing SACs due to their tailorable chemistry,tunable morphologies,high porosity,and chemical/thermal stability.From this perspective,this review thoroughly summarizes the previously reported methods and possible future approaches for constructing MOF-based(MOF-derived-supported and MOF-supported)SACs.Then,MOF-based SAC's identification techniques are briefly assessed to understand their coordination environments,local electronic structures,spatial distributions,and catalytic/electrochemical reaction mechanisms.This review systematically highlights several photocatalytic and electrocatalytic applications of MOF-based SACs for energy conversion and storage,including hydrogen evolution reactions,oxygen evolution reactions,O_(2)/CO_(2)/N_(2) reduction reactions,fuel cells,and rechargeable batteries.Some light is also shed on the future development of this highly exciting field by highlighting the advantages and limitations of MOF-based SACs.

CoxP@NiCo-LDH heteronanosheet arrays as efficient bifunctional electrocatalysts for co-generation of value-added formate and hydrogen with less-energy consumption

The inefficiency of water splitting is mainly due to the sluggish anodic water oxidation reaction. Replacing water oxidation with thermodynamically more favorable selective methanol oxidation reaction and developing robust bifunctional electrocatalysts are of great significance. Herein, a hierarchical heteronanostructure with Ni–Co layered double hydroxide(LDH) ultrathin nanosheets coated on cobalt phosphide nanosheets arrays(CoxP@NiCo-LDH) are fabricated and used for co-electrolysis of methanol/water to co-produce value-added formate and hydrogen with saving energy. Benefiting from the fast charge transfer introduced by phosphide nanoarrays, the synergy in nanosheets catalysts with hetero-interface,CoxP@NiCo-LDH/Ni foam(NF) exhibits superior electrocatalytic performance(10 mA cm-2@ 1.24 V and-0.10 V for methanol selective oxidation and hydrogen evolution reaction, respectively). Furthermore,CoxP@NiCo-LDH/NF-based symmetric two-electrode electrolyzer drives a current density of 10 m A cm-2 with a low cell voltage of only 1.43 V and the Faradaic efficiency towards the generation of formate and H2 are close to 100% in the tested range of current density(from 40 to 200 m A cm-2). This work highlights the positive effect of hetero-interaction in the design of more efficient eletrocatalysts and might guide the way towards facile upgrading of alcohols and energy-saving electrolytic H2 co-generation.

Unraveling the relationship between Sr stoichiometry in Sr_(x)Fe_(1.5)Mo_(0.5)O_(6)-σ and its catalytic performance for high-temperature CO_(2) electrolysis

The solid oxide electrolytic cell(SOEC)is one of the most promising energy conversion and storage devices,which could convert CO_(2) to CO with high Faradaic efficiency and production rate.However,the lack of active and stable cathode materials impedes their practical applications.Here we focus on the promising perovskite oxide cathode material Sr_(2)Fe_(1.5)Mo_(0.5)O_(6)-σ,with the aim of understanding how A-atom stoichiometry and catalytic performance are linked.We find that increasing the strontium content in the perovskite improves the chemisorption of CO_(2) on its surface,forming a SrCO_(3) phase.This hinders the charge transfer and oxygen exchange processes.Simulta-neously,strontoium segregation to the cathode surface facilitates coking of the surface during CO_(2) electrolysis,which poisons the electrode.Consequently,a small number of Sr deficiencies are optimal for both electrochemical performance and long-term stability.Our results provide new insights for designing high-performance CO_(2) electrolysis cathode materials.

Coordination Effect-Promoted Durable Ni(OH)_(2) for Energy-Saving Hydrogen Evolution from Water/ Methanol Co-Electrocatalysis

Electrocatalytic water splitting is a viable technique for generating hydrogen but is precluded from the sluggish kinetics of oxygen evolution reactions(OER).Small molecule oxidation reactions with lower working potentials,such as methanol oxidation reactions,are good alternatives to OER with faster kinetics.However,the typically employed Ni-based electrocatalysts have poor activity and stability.Herein,a novel three-dimensional(3D)-networking Modoped Ni(OH)_(2) with ultralow Ni-Ni coordination is synthesized,which exhibits a high MOR activity of 100 mA cm^(−2) at 1.39 V,delivering 28 mV dec^(−1) for the Tafel slope.Meanwhile,hydrogen evolution with value-added formate co-generation is boosted with a current density of more than 500 mA cm^(−2) at a cell voltage of 2.00 V for 50 h,showing excellent stability in an industrial alkaline concentration(6 M KOH).Mechanistic studies based on density functional the-ory and X-ray absorption spectroscopy showed that the improved performance is mainly attributed to the ultralow Ni-Ni coordination,3D-networking structures and Mo dopants,which improve the catalytic activity,increase the active site density and strengthen the Ni(OH)_(2)3D-networking structures,respectively.This study paves a new way for designing electrocatalysts with enhanced activity and durability for industrial energy-saving hydrogen production.

Folic Acid Self-Assembly Enabling Manganese Single-Atom Electrocatalyst for Selective Nitrogen Reduction to Ammonia

Efficient and robust single-atom catalysts(SACs)based on cheap and earth-abundant elements are highly desirable for electrochemical reduction of nitrogen to ammonia(NRR)under ambient conditions.Herein,for the first time,a Mn-N-C SAC consisting of isolated manganese atomic sites on ultrathin carbon nanosheets is developed via a template-free folic acid self-assembly strategy.The spontaneous molecular partial dissociation enables a facile fabrication process without being plagued by metal atom aggregation.Thanks to well-exposed atomic Mn active sites anchored on two-dimensional conductive carbon matrix,the catalyst exhibits excellent activity for NRR with high activity and selectivity,achieving a high Faradaic efficiency of 32.02%for ammonia synthesis at−0.45 V versus reversible hydrogen electrode.Density functional theory calculations unveil the crucial role of atomic Mn sites in promoting N_(2) adsorption,activation and selective reduction to NH_(3) by the distal mechanism.This work provides a simple synthesis process for Mn-N-C SAC and a good platform for understanding the structure-activity relationship of atomic Mn sites.

Densely packed ultrafine SnO_(2) nanoparticles grown on carbon cloth for selective CO_(2) reduction to formate

Electrochemical reduction of CO_(2) to fuels and chemicals is a viable strategy for CO_(2) utilization and renewable energy storage.Developing free-standing electrodes from robust and scalable electrocatalysts becomes highly desirable.Here,dense SnO_(2) nanoparticles are uniformly grown on three-dimensional(3D)fiber network of carbon cloth(CC)by a facile dip-coating and calcination method.Importantly,Zn modification strategy is employed to restrain the growth of long-range order of SnO_(2) lattices and to produce rich grain boundaries.The hybrid architecture can act as a flexible electrode for CO_(2)-to-formate conversion,which delivers a high partial current of 18.8 m A cm-2 with a formate selectivity of 80%at a moderate cathodic potential of-0.947 V vs.RHE.The electrode exhibits remarkable stability over a 16 h continuous operation.The superior performance is attributed to the synergistic effect of ultrafine SnO_(2) nanoparticles with abundant active sites and 3D fiber network of the electrode for efficient mass transport and electron transfer.The sizeable electrodes hold promise for industrial applications.

Etching oxide overlayers of NiFe phosphide to facilitate surface reconstruction for oxygen evolution reaction

Transition-metal phosphides have been of concern as efficient electrocatalysts for oxygen evolution reaction(OER)due to its high conductivity and earth-abundance reserves.However,oxide overlayers formed on their surface by spontaneously atmospheric oxidation are usually neglected,thus confusing the establishment of structure–performance relationship.Herein,we successfully etched the oxide overlayers of NiFe phosphide(NiFeP)by a dielectric barrier discharge(DBD)plasma technique,aiming to reveal the influence of the oxide overlayers on its electrocatalytic performance for OER.It is found that etching the oxide overlayers can accelerate the surface reconstruction process of NiFeP and facilitate the formation of metal hydroxides,which are key intermediate phases for OER.Consequently,the etched NiFeP-DBD material shows remarkably enhanced OER activity with an overpotential of 265 mV at a current density of 10 mA cm^(-2).The finding of this work probably brings a significant impact to understand the structure–performance relationship of metal phosphide in electrooxidation reaction.

Co-and N-doped carbon nanotubes with hierarchical pores derived from metal-organic nanotubes for oxygen reduction reaction

Biomolecules with a broad range of structure and heteroatom-containing groups offer a great opportunity for rational design of promising electrocatalysts via versatile chemistry.In this study,uniform folic acid-Co nanotubes(FA-Co NTs) were hydrothermally prepared as sacrificial templates for highly porous Co and N co-doped carbon nanotubes(Co-N/CNTs) with well-controlled size and morphology.The formation mechanism of FA-Co NTs was investigated and FA-Co-hydrazine coordination interaction together with the H-bond interaction between FA molecules was characterized to be the driving force for growth of one-dimensional nanotubes.Such distinct metal-ligand interaction afforded the resultant CNTs rich Co-N_x sites,hierarchically porous structure and Co nanoparticle-embedded conductive network,thus an overall good electrocatalytic activity for oxygen reduction.Electrochemical tests showed that Co-N/CNTs-900 promoted an efficient 4 e ORR process with an onset potential of 0.908 V vs.RHE,a limiting current density of 5.66 mA cm^(-2) at 0.6 V and a H_2 O_2 yield lower than 5%,comparable to that of 20%Pt/C catalyst.Moreover,the catalyst revealed very high stability upon continuous operation and remarkable tolerance to methanol.

Hierarchical graphite foil/CoNi2S4 flexible electrode with superior thermal conductivity for high-performance supercapacitors

Effective heat dissipation is a crucial issue in electrochemical energy storage devices. Thus, it is highly desirable to develop high-performance electrode materials with high thermal conductivity. Here, we report a facile one-step electrodeposition method to synthesize ternary cobalt nickel sulfide（CoNi2S4）flower-like nanosheets which are grown on graphite foil（GF） as binder-free electrode materials for supercapacitors. The as-fabricated GF/CoNi2S4 integrated electrode manifested an excellent thermal conductivity of 620.1 W·m-1·K-1 and a high specific capacitance of 881 F·g-2 at 5 mA cm-2, as well as good rate capability and cycling stability. Ultimately, the all-solid-state symmetric supercapacitor based on these advanced electrodes demonstrated superior heat dissipation performance during the galvanostatic charge-discharge processes. This novel strategy provides a new example of effective thermal management for potential applications in energy storage devices.

γ-MnO_(2) nanorod-assembled hierarchical micro-spheres with oxygen vacancies to enhance electrocatalytic performance toward the oxygen reduction reaction for aluminum-air batteries

γ-MnO2 nanorod-assembled hierarchical micro-spheres with abundant oxygen defects are synthesized by a simple thermal treatment approach as oxygen reduction electrocatalysts for Al(aluminum)-air batteries. The rich oxygen vacancies on the surface of γ-MnO2 are verified by morphology, structure,electron paramagnetic resonance(EPR) and X-ray photoelectron spectroscopy(XPS) results. The oxygen reduction reaction(ORR) electrocatalytic activity of γ-MnO2 is significantly improved by the incoming oxygen vacancies. The γ-MnO2 nanorod-assembled hierarchical micro-spheres calcined under 300 °C in Ar atmosphere show the best ORR performance. The primary Al-air batteries using γ-MnO2 catalysts as the cathode, which demonstrates excellent peal power density of 318 m W cm^(-2) when applying theγ-MnO2 catalysts with optimal amount of oxygen vacancies.

Regulating the Electron Localization of Metallic Bismuth for Boosting CO_(2)Electroreduction

Electrochemical reduction of CO_(2)to formate is economically attractive but improving the reaction selectivity and activity remains challenging.Herein,we introduce boron(B)atoms to modify the local electronic structure of bismuth with positive valence sites for boosting conversion of CO_(2)into formate with high activity and selectivity in a wide potential window.By combining experimental and computational investigations,our study indicates that B dopant differentiates the proton participations of rate-determining steps in CO_(2)reduction and in the competing hydrogen evolution.By comparing the experimental observations with the density functional theory,the dominant mechanistic pathway of B promoted formate generation and the B concentration modulated effects on the catalytic property of Bi are unravelled.This comprehensive study offers deep mechanistic insights into the reaction pathway at an atomic and molecular level and provides an effective strategy for the rational design of highly active and selective electrocatalysts for efficient CO_(2)conversion.

Water-oxidation intermediates enabling electrochemical propylene epoxidation

In the production of propylene oxide(PO),reliance on hazardous chemical oxidants,such as molecular chlorine(Cl_(2))or peroxides,is a common practice.A promising alternative to current epoxidation methods involves a selective direct propylene epoxidation pathway utilizing water as the oxygen source through water-oxidation intermediates.This approach presents a robust substitute for existing epoxidation techniques.

High-temperature transport properties of BaSn_(1−x)Sc_(x)O_(3−δ) ceramic materials as promising electrolytes for protonic ceramic fuel cells

Protonic ceramic fuel cells(PCFCs)offer a convenient means for electrochemical conversion of chemical energy into electricity at intermediate temperatures with very high efficiency.Although BaCeO_(3)-and BaZrO_(3)-based complex oxides have been positioned as the most promising PCFC electrolytes,the design of new protonic conductors with improved properties is of paramount importance.Within the present work,we studied transport properties of scandium-doped barium stannate(Sc-doped BaSnO_(3)).Our analysis included the fabrication of porous and dense BaSn_(1−x)Sc_(x)O_(3−δ)ceramic materials(0≤x≤0.37),as well as a comprehensive analysis of their total,ionic,and electronic conductivities across all the experimental conditions realized under the PCFC operation:both air and hydrogen atmospheres with various water vapor partial pressures(p(H2O)),and a temperature range of 500–900℃.This work reports on electrolyte domain boundaries of the undoped and doped BaSnO_(3)for the first time,revealing that pure BaSnO_(3)exhibits mixed ionic–electronic conduction behavior under both oxidizing and reducing conditions,while the Sc-doping results in the gradual improvement of ionic(including protonic)conductivity,extending the electrolyte domain boundaries towards reduced atmospheres.This latter property makes the heavilydoped BaSnO_(3)representatives attractive for PCFC applications.

A facile approach to fabricating graphene/waterborne epoxy coatings with dual functionalities of barrier and corrosion inhibitor

A facile and environmentally-friendly method is developed to prepare graphene/waterborne epoxy(WEP)composite coatings.The graphene nanosheets are produced with electrochemical-exfoliation in the solution containing surfactants,cetyl trimethyl ammonium bromide(CTAB)and sodium dodecyl sulfate(SDS).The nanosheets containing solution thus formed are subjected to a quick dialysis and then directly used as a diluent for WEP without any further treatment.This preparation method overcomes the commonly identified problems of aggregations and‘corrosion promotion’effect associated with graphene,and increases the impedance of the composite coatings by more than two orders of magnitude.The analysis of anticorrosion performance suggested that the presence of surfactants not only improves the dispersibility of graphene nanosheets but also endows the composite coatings with both barrier and corrosion inhibition capabilities.The strategy reported herein may pave the path to the large-scale production of graphene anticorrosion coatings.

Copper-based metal-organic frameworks for electrochemical reduction of CO_(2)

The electrochemical CO_(2)reduction reaction(CO_(2)ER)is an emerging process that involves utilizing CO_(2)to produce valuable chemicals and fuels by consuming excess electricity from renewable sources.Recently,Cu and Cu-based nanoparticles,as earth-abundant and economical metal sources,have been attracting significant interest.The chemical and physical properties of Cu-based nanoparticles are modified by different strategies,and CO_(2)can be converted into multicarbon products.Among various Cu-based nanoparticles,Cu-based metal-organic frameworks(MOFs)are gaining increasing interest in the field of catalysis because of their textural,topological,and electrocatalytic properties.In this minireview,we summarized and highlighted the main achievements in the research on Cu-based MOFs and their advantages in the CO_(2)ER as electrocatalysts,supports,or precursors.

In situ redox growth of mesoporous Pd-Cu2O nanoheterostructures for improved glucose oxidation electrocatalysis

Interfaces of metal-oxide heterostructured electrocatalyst are critical to their catalytic activities due to the significant interfacial effects. However, there are still obscurities in the essence of interfacial effects caused by crystalline defects and mismatch of electronic structure at metal-oxide nanojunctions. To deeply understand the interfacial effects, we engineered crystalline-defect Pd-Cu2O interfaces through nonepitaxial growth by a facile redox route. The Pd-Cu2O nanoheterostructures exhibit much higher electrocatalytic activity toward glucose oxidation than their single counterparts and their physical mixture,which makes it have a promising potential for practical application of glucose biosensors.Experimental study and density functional theory(DFT) calculations demonstrated that the interfacial electron accumulation and the shifting up of d bands center of Cu-Pd toward the Fermi level were responsible for excellent electrocatalytic activity. Further study found that Pd(3 1 0) facets exert a strong metaloxide interface interaction with Cu2O(1 1 1) facets due to their lattice mismatch. This leads to the sinking of O atoms and protruding of Cu atoms of Cu2O, and the Pd crystalline defects, further resulting in electron accumulation at the interface and the shifting up of d bands center of Cu-Pd, which is different from previously reported charge transfer between the interfaces. Our findings could contribute to design and development of advanced metal-oxide heterostructured electrocatalysts.

Copper-cobalt-nickel oxide nanowire arrays on copper foams as self-standing anode materials for lithium ion batteries

Numerous scientists are in the pursuit of energy storage materials with high energy and high power density by assembly of electrochemically active materials into conductive scaffolds,owing to the emerging need for next-generation energy storage devices.In this architectures,the active materials bonded to the conductive scaffold can provide a robust and free-standing structure,which is crucial to the fabrication of materials with high gravimetric capacity.Thus,hierarchical copper-cobalt-nickel ternary oxide(CuCoNi-oxide) nanowire arrays grown from copper foam were successfully fabricated as freestanding anode materials for lithium ion batteries(LIBs).CuCoNi-oxide nanowire arrays could provide more active sites owing to the hyperbranched structure,leading to a better specific capacity of 1191 mAh/g,cycle performance of 73% retention in comparison to CuO nanowire structure,which exhibited a specific capacity of 1029 mAh/g and capacity retention of 43%,respectively.

Highly selective conversion of methane to ethanol over CuFe_(2)O_(4)-carbon nanotube catalysts at low temperature

Conversion of methane into liquid alcohol such as ethanol at low temperature in a straight,selective and low energy consumption process remains a topic of intense scientific research but a great challenge.In this work,CuFe_(2)O_(4)/CNT composite is successfully synthesized via a facile co-reduction method and used as catalysts to selectively oxidize methane.At a low temperature of 150℃,methane is directly converted to ethanol in a single process on the as-prepared CuFe_(2)O_(4)/CNT composite with high selectivity.A mechanism is also proposed for the significant methane selective oxidation performance of the CuFe_(2)O_(4)/CNT composite catalysts.

Mesoporous CeO_(2)-C hybrid spheres as efficient support for platinum nanoparticles towards methanol electrocatalytic oxidation

The development of direct methanol fuel cells(DMFCs) is partially limited by the poor kinetics of methanol oxidation reaction(MOR) at the anode side.It was reported that the interaction between Pt and CeO_(2) enhances the electrocatalytic performance of Pt catalyst for MOR.In this work,a hybrid material(CeO_(2)-C) composed of CeO_(2) and carbon was successfully prepared by a simple hydrothermal method followed by calcination in inert atmosphere.The hierarchically porous nanostructure and especially good electronic conductivity of CeO_(2)-C make it an excellent support for Pt particles for application in electrocatalytic process.TEM investigation reveals that triple-phase interface of Pt,carbon and CeO_(2) forms in Pt/CeO_(2)-C catalyst.Performance of the as-prepared catalyst for MOR was studied in alkaline medium.The Pt/CeO_(2)-C catalyst shows superior catalytic performance for MOR compared with Pt/CeO_(2) and the physical mixture of Pt/CeO_(2) and acetylene black(Pt/CeO_(2)+C).The significantly improved performance can be attributed to the synergetic effect between Pt particles and CeO_(2)-C support,and the better conductivity of CeO_(2)-C.This study provides a possible method to expand the application potential of CeO_(2) materials in MOR,and may also be used in other electrocatalytic process.