Showing papers in "ACS Catalysis in 2018"

Role of Interfaces in Two-Dimensional Photocatalyst for Water Splitting

Abstract: Hydrogen generation from the direct splitting of water by photocatalysis is regarded as a promising and renewable solution for the energy crisis The key to realize this reaction is to find an efficient and robust photocatalyst that ideally makes use of the energy from sunlight Recently, due to the attractive properties such as appropriate band structure, ultrahigh specific surface area, and more exposed active sites, two-dimensional (2D) photocatalysts have attracted significant attention for photocatalytic water splitting This Review attempts to summarize recent progress in the fabrication and applications of 2D photocatalysts including graphene-based photocatalysts, 2D oxides, 2D chalcogenides, 2D carbon nitride, and some other emerging 2D materials for water splitting The construction strategies and characterization techniques for 2D/2D photocatalysts are summarized Particular attention has been paid to the role of 2D/2D interfaces in these 2D photocatalysts as the interfaces and heterojunctions a

Toward the Decentralized Electrochemical Production of H2O2: A Focus on the Catalysis

Abstract: H2O2 is a valuable, environmentally friendly oxidizing agent with a wide range of uses from the provision of clean water to the synthesis of valuable chemicals. The on-site electrolytic production of H2O2 would bring the chemical to applications beyond its present reach. The successful commercialization of electrochemical H2O2 production requires cathode catalysts with high activity, selectivity, and stability. In this Perspective, we highlight our current understanding of the factors that control the cathode performance. We review the influence of catalyst material, electrolyte, and the structure of the interface at the mesoscopic scale. We provide original theoretical data on the role of the geometry of the active site and its influence on activity and selectivity. We have also conducted a series of original experiments on (i) the effect of pH on H2O2 production on glassy carbon, pure metals, and metal–mercury alloys, and (ii) the influence of cell geometry and mass transport in liquid half-cells in com...

Mechanism of CO2 Reduction at Copper Surfaces: Pathways to C2 Products

Abstract: On the basis of constraints from reported experimental observations and density functional theory simulations, we propose a mechanism for the reduction of CO2 to C2 products on copper electrodes. To model the effects of an applied potential bias on the reactions, calculations are carried out with a variable, fractional number of electrons on the unit cell, which is optimized so that the Fermi level matches the actual chemical potential of electrons (i.e., the applied bias); an implicit electrolyte model allows for compensation of the surface charge so that neutrality is maintained in the overall simulation cell. Our mechanism explains the presence of the seven C2 species that have been detected in the reaction, as well as other notable experimental observations. Furthermore, our results shed light on the difference in activities toward C2 products between the (100) and (111) facets of copper. We compare our methodologies and findings with those in other recent mechanistic studies of the copper-catalyzed C...

Phosphorus-Doped Co3O4 Nanowire Array: A Highly Efficient Bifunctional Electrocatalyst for Overall Water Splitting

Abstract: It is vitally essential to design highly efficient and cost-effective bifunctional electrocatalysts toward water splitting. Herein, we report the development of P-doped Co3O4 nanowire array on nickel foam (P-Co3O4/NF) from Co3O4 nanowire array through low-temperature annealing, using NaH2PO2 as the P source. As a 3D catalyst, such P-Co3O4/NF demonstrates superior performance for oxygen evolution reaction with a low overpotential (260 mV at 20 mA cm–2), a small Tafel slope (60 mV dec–1), and a satisfying durability in 1.0 M KOH. Density functional theory calculations indicate that P-Co3O4 has a reaction free-energy value that is much smaller than that of pristine Co3O4 for the potential determining step of the oxygen evolution reaction. Such P-Co3O4/NF also performs efficiently for hydrogen evolution reaction, and a two-electrode alkaline electrolyzer assembled by P8.6-Co3O4/NF as both anode and cathode needs only 1.63 V to reach a water-splitting current of 10 mA cm–2.

Suppression of Hydrogen Evolution Reaction in Electrochemical N2 Reduction Using Single-Atom Catalysts: A Computational Guideline

Abstract: We studied electrochemical nitrogen reduction reactions (NRR) to ammonia on single atom catalysts (SACs) anchored on defective graphene derivatives by density functional calculations. We find significantly improved NRR selectivity on SACs compared to that on the existing bulk metal surface due to the great suppression of the hydrogen evolution reaction (HER) on SACs with the help of the ensemble effect. In addition, several SACs, including Ti@N4 (0.69 eV) and V@N4 (0.87 eV), are shown to exhibit lower free energy for NRR than that of the Ru(0001) stepped surface (0.98 eV) due to a strong back-bonding between the hybridized d-orbital metal atom in SAC and π* orbital in *N2. Formation energies as a function of nitrogen chemical potential suggest that Ti@N4 and V@N4 are also synthesizable under experimental conditions.

Catalytic Strategies for the Cycloaddition of Pure, Diluted, and Waste CO2 to Epoxides under Ambient Conditions

Abstract: Cyclic organic carbonates represent a relevant class of chemicals that can be prepared from CO2 by cycloaddition to epoxides. The application of efficient catalysts is crucial in allowing the cycloaddition reaction to proceed under very mild conditions of temperature, pressure, and CO2 concentration, thus resulting in a sustainable and carbon-balanced approach to CO2 conversion. This is particularly the case if impure waste CO2 could be employed as a feedstock. In this Review, we have critically analyzed the burgeoning literature on the cycloaddition of CO2 to epoxides with the aim to provide state-of-the-art knowledge on the catalysts that can convert CO2 to carbonates under ambient conditions. These have been systematically organized in families of compounds and critically scrutinized in terms of catalytic activity, availability and mechanistic features. Finally, we provide an overview on the catalytic systems able to function using diluted and impure CO2 as a feedstock.

Facile Ammonia Synthesis from Electrocatalytic N2 Reduction under Ambient Conditions on N-Doped Porous Carbon

Abstract: Ammonia has been used in important areas such as agriculture and clean energy. Its synthesis from the electrochemical reduction of N2 is an attractive alternative to the industrial method that requires high temperature and pressure. Currently, electrochemical N2 fixation has suffered from slow kinetics due to the difficulty of N2 adsorption and N≡N cleavage. Here, N-doped porous carbon (NPC) is reported as a cost-effective electrocatalyst for ammonia synthesis from electrocatalytic N2 reduction under ambient conditions, where its N content and species were tuned to enhance N2 chemical adsorption and N≡N cleavage. The resulting NPC was effective for fixing N2 to ammonia with a high ammonia production rate (1.40 mmol g–1 h–1 at −0.9 V vs RHE). Experiments combined with density functional theory calculations revealed pyridinic and pyrrolic N were active sites for ammonia synthesis and their contents were crucial for promoting ammonia production on NPC. The energy-favorable pathway for ammonia synthesis was *...

Electrocatalytic C–H Activation

Abstract: C–H activation has emerged as a transformative tool in molecular synthesis, but until recently oxidative C–H activations have largely involved the use of stoichiometric amounts of expensive and toxic metal oxidants, compromising the overall sustainable nature of C–H activation chemistry. In sharp contrast, electrochemical C–H activation has been identified as a more efficient strategy that exploits storable electricity in place of byproduct-generating chemical reagents. Thus, transition-metal catalysts were shown to enable versatile C–H activation reactions in a sustainable manner. While palladium catalysis set the stage for C(sp2)–H and C(sp3)–H functionalizations by N-containing directing groups, rhodium and ruthenium catalysts allowed the use of weakly coordinating amides and acids. In contrast to these precious 4d transition metals, the recent year has witnessed the emergence of versatile cobalt catalysts for C–H oxygenations, C–H nitrogenations, and C–C-forming [4+2] alkyne annulations. Thereby, the ...

Enhanced Catalysis of Electrochemical Overall Water Splitting in Alkaline Media by Fe Doping in Ni3S2 Nanosheet Arrays

Abstract: The development of bifunctional electrocatalysts with high performance for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with earth-abundant elements is still a challenge in electrochemical water splitting technology. Herein, we fabricated a free-standing electrocatalyst in the form of vertically oriented Fe-doped Ni3S2 nanosheet array grown on three-dimensional (3D) Ni foam (Fe-Ni3S2/NF), which presented a high activity and durability for both HER and OER in alkaline media. On the basis of systematic experiments and calculation, the Fe-doping was evidenced to increase the electrochemical surface area, improve the water adsorption ability, and optimize the hydrogen adsorption energy of Ni3S2, which resulted in the enhancement of HER activity on Fe-Ni3S2/NF. Moreover, metal sites of Fe-Ni3S2/NF were proved to play a significant role in the HER process. During the catalysis of OER, the formation of Ni–Fe (oxy)hydroxide was observed on the near-surface section of Fe-Ni3S2/NF, and...

Single-Atomic Cu with Multiple Oxygen Vacancies on Ceria for Electrocatalytic CO2 Reduction to CH4

Abstract: The electrocatalytic reduction of CO2 into value-added chemicals such as hydrocarbons has the potential for supplying fuel energy and reducing environmental hazards, while the accurate tuning of electrocatalysts at the ultimate single-atomic level remains extremely challenging. In this work, we demonstrate an atomic design of multiple oxygen vacancy-bound, single-atomic Cu-substituted CeO2 to optimize the CO2 electrocatalytic reduction to CH4. We carried out theoretical calculations to predict that the single-atomic Cu substitution in CeO2(110) surface can stably enrich up to three oxygen vacancies around each Cu site, yielding a highly effective catalytic center for CO2 adsorption and activation. This theoretical prediction is consistent with our controlled synthesis of the Cu-doped, mesoporous CeO2 nanorods. Structural characterizations indicate that the low concentration (<5%) Cu species in CeO2 nanorods are highly dispersed at single-atomic level with an unconventionally low coordination number ∼5, su...

Engineering Crystal Facet of α-MnO2 Nanowire for Highly Efficient Catalytic Oxidation of Carcinogenic Airborne Formaldehyde

Abstract: The activity of exposed crystal facets directly determines its physicochemical properties. Thus, acquiring a high percentage of reactive facets by crystal facet engineering is highly desirable for improving the catalytic reactivity. Herein, single-crystalline α-MnO2 nanowires with major exposed high-index {310} facets were synthesized via a facile hydrothermal route with the assistance of a capping agent of oxalate ions. Comparing with two other low-index facets ({100} and {110}), the resulting α-MnO2 nanowires with exposed {310} facets exhibited much better activity and stability for carcinogenic formaldehyde (HCHO) oxidation, making 100% of 100 ppm of HCHO mineralize into CO2 at 60 °C, even better than some Ag supported catalysts. The density functional theory (DFT) calculations were used to investigate the difference in the catalytic activity of α-MnO2 with exposed {100}, {110}, and {310} facets. The experimental characterization and theoretical calculations all confirm that the {310} facets with high ...

Low-Temperature CO2 Methanation over CeO2-Supported Ru Single Atoms, Nanoclusters, and Nanoparticles Competitively Tuned by Strong Metal–Support Interactions and H-Spillover Effect

Abstract: CO2 hydrogenation for the acquisition of value-added chemicals is an economical means to deal with the CO2-relevant environmental problems, among which CO2 reduction to CH4 is an excellent model reaction for investigating the initial steps of CO2 hydrogenation. For the supported catalysts commonly used in such reactions, the tailoring of the interfacial effect between metal centers and supporting materials so as to obtain superior low-temperature CO2 methanation performance is a significant but challenging subject. In this work, we altered the size regimes of the Ru deposits in Ru/CeO2 assemblies and uncovered the competitive relationship between the strong metal–support interactions (SMSI) and the H-spillover effect in determining the methanation activities by some ex situ and in situ spectroscopic techniques coupled with density functional theory (DFT) calculations. For CeO2 nanowire supported single Ru atoms, Ru nanoclusters (ca. 1.2 nm in size), and large Ru nanoparticles (ca. 4.0 nm in size), the nan...

Ultrathin Co3O4 Nanomeshes for the Oxygen Evolution Reaction

Abstract: Ultrathin transition-metal-based nanomeshes can perfectly combine the advantages of two-dimensional (2D) ultrathin nanosheets and porous nanostructures, which have wide applications in energy storage and conversion. In this work, we present an etch-free one-step approach to directly synthesize the ultrathin Co3O4 nanomeshes (Co-UNMs) by employing a CoCl2/K3Co(CN)6 cyanogel as the reaction precursor. The 2D planar structural unit and solid properties of the cyanogel result in the preferential assembly of generated crystal nuclei at the solid–liquid interface (i.e., cyanogel–solution interface) in the 2D direction, which plays a key role in the formation of nanomeshes. The as-prepared Co-UNMs with 1.5 nm thickness and abundant pores have high surface area and numerous defect atoms, resulting in enhanced activity for the oxygen evolution reaction (OER) in alkaline media, such as a low overpotential of 307 mV at 10 mA cm–2, a small Tafel slope of 76 mV dec–1, and attractive durability in 1 M KOH electrolyte.

Microporous Framework Induced Synthesis of Single-Atom Dispersed Fe-N-C Acidic ORR Catalyst and Its in Situ Reduced Fe-N4 Active Site Identification Revealed by X-ray Absorption Spectroscopy

Abstract: Developing highly efficient, low-cost oxygen reduction catalysts, especially in acidic medium, is of significance toward fuel cell commercialization. Although pyrolyzed Fe-N-C catalysts have been regarded as alternatives to platinum-based catalytic materials, further improvement requires precise control of the Fe-Nx structure at the molecular level and a comprehensive understanding of catalytic site structure and the ORR mechanism on these materials. In this report, we present a microporous metal–organic-framework-confined strategy toward the preferable formation of single-atom dispersed catalysts. The onset potential for Fe-N-C is 0.92 V, comparable to that of Pt/C and outperforming most noble-metal-free catalysts ever reported. A high-spin Fe3+-N4 configuration is revealed by the 57Fe Mossbauer spectrum and X-ray absorption spectroscopy for Fe L-edge, which will convert to Fe2+-N4 at low potential. The in situ reduced Fe2+-N4 moiety from high-spin Ox-Fe3+-N4 contributes to most of the ORR activity due t...

Engineering Cobalt Defects in Cobalt Oxide for Highly Efficient Electrocatalytic Oxygen Evolution

Abstract: Defect engineering is an effective way to modulate the electric states and provide active sites for electrocatalytic reactions. However, most studied oxygen vacancies are unstable and susceptible under the oxygen circumstance. Here, we fabricated cobalt-defected Co3–xO4 in situ for an efficient oxygen evolution reaction (OER). XAFS and PALS characterizations show that the crystals have abundant Co vacancies and a distorted structure. DFT calculations indicate that the metal defects lead to obvious electronic delocalization, which enhances the carrier transport to participate in water-splitting reactions along the defective conducting channels and the water adsorption/activation on the catalyst surface. Therefore, cobalt-defected Co3–xO4 shows remarkably high OER activity by delivering a much lower overpotential of 268 mV@10 mA cm–2 (with a small Tafel slope of 38.2 mV/dec) for OER in KOH electrolyte, in comparison with normal Co3O4 (376 mV), IrO2 (340 mV), and RuO2 (276 mV). This work opens up a promising...

Recent Advances in C–H Functionalization Using Electrochemical Transition Metal Catalysis

Abstract: Electrochemical transition metal catalysis is a powerful strategy for organic synthesis because it obviates the use of stoichiometric chemical oxidants and reductants. C–H bond functionalization offers a variety of useful conversions of simple and ubiquitous organic molecules into diverse functional groups in a single synthetic operation. This review summarizes recent progress in merging electrochemistry with transition metal-catalyzed C–H functionalization, specifically C–C, C–X (halogen), C–O, C–P, and C–N bond formation.

Unveiling Active Sites of CO2 Reduction on Nitrogen-Coordinated and Atomically Dispersed Iron and Cobalt Catalysts

Abstract: Herein, we report the exploration of understanding the reactivity and structure of atomically dispersed M–N4 (M = Fe and Co) sites for the CO2 reduction reaction (CO2RR). Nitrogen coordinated Fe or Co site atomically dispersed into carbons (M–N–C) containing bulk- and edge-hosted M–N4 coordination were prepared by using Fe- or Co-doped metal–organic framework precursors, respectively, which were further studied as ideal model catalysts. Fe is intrinsically more active than Co in M–N4 for the reduction of CO2 to CO, in terms of a larger current density and a higher CO Faradaic efficiency (FE) (93% vs. 45%). First principle computations elucidated that the edge-hosted M–N2+2–C8 moieties bridging two adjacent armchair-like graphitic layers is the active sites for the CO2RR. They are much more active than previously proposed bulk-hosted M–N4–C10 moieties embedded compactly in a graphitic layer. During the CO2RR, when the dissociation of *COOH occurs on the M–N2+2–C8, the metal atom is the site for the adsorpt...

An Electrocatalytic Approach to the Radical Difunctionalization of Alkenes

Abstract: Given its many distinct characteristics, electrochemistry represents an attractive approach to meet the prevailing trends in organic synthesis. In particular, electrocatalysis—a process that integrates electrochemistry and small-molecule catalysis—has the potential to substantially improve the scope of synthetic electrochemistry and provide a wide range of useful transformations. Recently, we have demonstrated new catalytic approaches that combine electrochemistry and redox-metal catalysis for the oxidative difunctionalization of alkenes to access a diverse array of vicinally functionalized structures. This Perspective details our design principles underpinning the development of electrochemical diazidation, dichlorination, and halotrifluoromethylation of alkenes, which were built on foundational work by others in the areas of synthetic electrochemistry, radical chemistry, and transition-metal catalysis. The introduction of redox-active Mn catalysts allows the generation of radical intermediates from read...

Boron Carbon Nitride Semiconductors Decorated with CdS Nanoparticles for Photocatalytic Reduction of CO2

Abstract: Ternary boron carbon nitride (BCN) semiconductors have been developed as emerging metal-free photocatalysts for visible-light reduction of CO2, but the achieved efficiency is still not satisfying. Herein, we report that the CO2 photoreduction performance of a bulk BCN semiconductor can be substantially improved by surface engineering with CdS nanoparticles. The CdS/BCN photocatalysts are characterized completely by diverse tests (e.g., XRD, FTIR, XPS, DRS, SEM, TEM, N2 sorption, PL, and transient photocurrent spectroscopy). Performance of the CdS/BCN heterostructures is evaluated by reductive CO2 conversion reactions with visible light under benign reaction conditions. Compared with bare BCN material, the optimized CdS/BCN photocatalyst exhibits a 10-fold-enhanced CO2 reduction activity and high stability, delivering a considerable CO production rate of 12.5 μmol h–1 (250 μmol h–1 g–1) with triethanolamine (TEOA) as the reducing agent. The reinforced photocatalytic CO2 reduction activity is mainly assigne...

Multi-Level Architecture Optimization of MOF-Templated Co-Based Nanoparticles Embedded in Hollow N-Doped Carbon Polyhedra for Efficient OER and ORR

Abstract: Emerging clean energy technologies such as regenerative fuel cells and rechargeable metal–air batteries have attracted increasing global interest because of their high efficiency and environmental benignity, but the lack of highly active bifunctional electrocatalysts at low cost for both oxygen reduction and evolution reactions (ORR and OER) greatly hinders their commercial applications. Here, we report the multilevel architecture optimization of Co-based nanoparticles (NPs) embedded in hollow N-doped carbon polyhedra for boosting the ORR and OER, which are fabricated by a two-step pyrolysis–oxidation strategy with a Co-based MOF (ZIF-67) as precursor. The key for this strategy lies in the precise and effective control of the oxidation processes of Co NPs, which enables the synthesis of a series of Co–Co3O4-based nanoarchitectures that are embedded in hollow nitrogen-doped carbon polyhedra (HNCP), including core–shell Co/Co3O4, yolk@shell Co@Co3O4, and hollow Co3O4 NPs. Benefiting from its abundant oxygen...

Homogeneous Catalysis by Cobalt and Manganese Pincer Complexes

Abstract: Homogeneous catalysis of organic transformations by metal complexes has been mostly based on complexes of noble metals. In recent years, tremendous progress has been made in the field of base-metal catalysis, mostly with pincer-type complexes, such as iron, cobalt, nickel, and manganese pincer systems. Particularly impressive is the explosive growth in the catalysis by Mn-based pincer complexes, the first such complexes being reported as recently as 2016. This review covers recent progress in the field of homogeneously catalyzed reactions using pincer-type complexes of cobalt and manganese. Various reactions are described, including acceptorless dehydrogenation, hydrogenation, dehydrogenative coupling, hydrogen borrowing, hydrogen transfer, H–X additions, C–C coupling, alkene polymerization and N2 fixation, including their scope and brief mechanistic comments.

Interfacial Interaction between FeOOH and Ni–Fe LDH to Modulate the Local Electronic Structure for Enhanced OER Electrocatalysis

Abstract: Toward the pursuit of high-performance Ni2+/Co2+/Fe3+-relevant oxygen evolution reaction (OER) electrocatalysts, the modulation of local electronic structure of the active metal sites provides the fundamental motif, which could be achieved either through direct modifications of local chemical environment or interfacial interaction with a second metal substrate which possesses high electronegativity (typically noble metal Au). Herein, we report that the local electronic structure of Ni–Fe layered double hydroxide (LDH) could be favorably modulated through strong interfacial interactions with FeOOH nanoparticles (NPs). The biphasic and multiscale composites FeOOH/LDH demonstrated an increasingly pronounced synergy effect for OER catalysis when the average size of FeOOH NPs decreases from 18.0 to 2.0 nm. Particularly, the composite with average size of FeOOH NPs of 2.0 nm exhibited an overpotential of 174 mV at 10 mA cm–2 and a tafel slope of 27 mV dec–1 in 1.0 M KOH, outmatching all the noble and non-noble ...

Challenges and Prospects in Solar Water Splitting and CO2 Reduction with Inorganic and Hybrid Nanostructures

Abstract: The inexorable rise of carbon dioxide level in the atmosphere, already exceeding 400 ppm, highlights the need for reduction of CO2 emissions. Harvesting solar energy to drive reverse chemical reactions to fuel combustion offers a possible solution. The produced chemical fuels (e.g. hydrogen, methane, or methanol) are also a convenient means of energy storage, not available in photovoltaic cells. This Review is focused on the heterogeneous photocatalytic water splitting and on CO2 reduction with nanostructured semiconductors, metals, and their hybrids. The stages of light absorption, charge separation and transfer, and surface reactions are discussed, together with possible energy-loss mechanisms and means of their elimination. Many novel materials have been developed in this active field of research, and this Review describes the concepts underpinning the continued progress in the field. The approaches which hold promise for substantial improvement in terms of efficiency, cost, and environmental sustainab...

Direct Production of Lower Olefins from CO2 Conversion via Bifunctional Catalysis

Abstract: Direct conversion of carbon dioxide (CO2) into lower olefins (C2=–C4=), generally referring to ethylene, propylene, and butylene, is highly attractive as a sustainable production route for its great significance in greenhouse gas control and fossil fuel substitution, but such a route always tends to be low in selectivity toward olefins. Here we present a bifunctional catalysis process that offers C2=–C4= selectivity as high as 80% and C2–C4 selectivity around 93% at more than 35% CO2 conversion. This is achieved by a bifunctional catalyst composed of indium–zirconium composite oxide and SAPO-34 zeolite, which is responsible for CO2 activation and selective C–C coupling, respectively. We demonstrate that both the precise control of oxygen vacancies on the oxide surface and the integration manner of the components are crucial in the direct production of lower olefins from CO2 hydrogenation. No obvious deactivation is observed over 150 h, indicating a promising potential for industrial application.

Incorporation of Imidazolium-Based Poly(ionic liquid)s into a Metal–Organic Framework for CO2 Capture and Conversion

Abstract: The rational integration of multiple functional components into a composite material could result in enhanced activity tailored for specific applications. Herein, imidazolium-based poly(ionic liquid)s (denoted as polyILs) have been confined into the metal–organic framework (MOF) material MIL-101 via in situ polymerization of encapsulated monomers. The resultant composite polyILs@MIL-101 exhibits good CO2 capture capability that is beneficial for the catalysis of the cycloaddition of CO2 with epoxides to form cyclic carbonates at subatmospheric pressure in the absence of any cocatalyst. The significantly enhanced activity of polyILs@MIL-101, compared to either MIL-101 or polyILs, is attributed to the synergistic effect among the good CO2 enrichment capacity, the Lewis acid sites in the MOF, as well as the Lewis base sites in the polyILs.

Efficient Electrochemical Hydrogen Peroxide Production from Molecular Oxygen on Nitrogen-Doped Mesoporous Carbon Catalysts

Abstract: Electrochemical hydrogen peroxide (H2O2) production by two-electron oxygen reduction is a promising alternative process to the established industrial anthraquinone process. Current challenges relate to finding cost-effective electrocatalysts with high electrocatalytic activity, stability, and product selectivity. Here, we explore the electrocatalytic activity and selectivity toward H2O2 production of a number of distinct nitrogen-doped mesoporous carbon catalysts and report a previously unachieved H2O2 selectivity of ∼95–98% in acidic solution. To explain our observations, we correlate their structural, compositional, and other physicochemical properties with their electrocatalytic performance and uncover a close correlation between the H2O2 product yield and the surface area and interfacial zeta potential. Nitrogen doping was found to sharply boost H2O2 activity and selectivity. Chronoamperometric H2O2 electrolysis confirms the exceptionally high H2O2 production rate and large H2O2 faradaic selectivity f...

Oxygen Vacancies Confined in Nickel Molybdenum Oxide Porous Nanosheets for Promoted Electrocatalytic Urea Oxidation

Abstract: The direct urea fuel cell (DUFC), as an efficient technology for generating power from urea, shows great potential for energy-sustainable development but is greatly hindered by the slow kinetics of the urea oxidation reaction (UOR). Herein, we highlighted a defect engineering strategy to design oxygen vacancy-rich NiMoO4 nanosheets as a promising platform to study the relationship between O vacancies and UOR activity. Experimental/theoretical results confirm that the rich O vacancies confined in NiMoO4 nanosheets successfully bring synergetic effects of higher exposed active sites, faster electron transport, and lower adsorption energy of urea molecules, giving rise to largely improved UOR activity. As expected, the r-NiMoO4/NF 3D electrode exhibits a higher current density of 249.5 mA cm–2, which is about 1.9 and 5.0 times larger than those of p-NiMoO4/NF and Ni-Mo precursor/NF at a potential of 0.6 V. Our finding will be a promising pathway to develop non-noble materials as highly efficient UOR catalysts.

Single Co Atoms Anchored in Porous N-Doped Carbon for Efficient Zinc−Air Battery Cathodes

Abstract: Exploration of cheap, efficient, and highly durable transition-metal-based electrocatalysts is critically important for the renewable energy chain, including both energy storage and energy conversi...

A Perspective on the Selective Catalytic Reduction (SCR) of NO with NH3 by Supported V2O5–WO3/TiO2 Catalysts

Abstract: The selective catalytic reduction (SCR) of NOx with NH3 to harmless N2 and H2O plays a crucial role in reducing highly undesirable NOx acid gas emissions from large utility boilers, industrial boilers, municipal waste plants, and incinerators. The supported V2O5–WO3/TiO2 catalysts have become the most widely used industrial catalysts for these SCR applications since introduction of this technology in the early 1970s. This Perspective examines the current fundamental understanding and recent advances of the supported V2O5–WO3/TiO2 catalyst system: (i) catalyst synthesis, (ii) molecular structures of titania-supported vanadium and tungsten oxide species, (iii) surface acidity, (iv) catalytic active sites, (v) surface reaction intermediates, (vi) reaction mechanism, (vii) rate-determining-step, and (viii) reaction kinetics.

Oxygen Vacancy Promoting Dimethyl Carbonate Synthesis from CO2 and Methanol over Zr-Doped CeO2 Nanorods

Abstract: The synthesis of dimethyl carbonate (DMC) from CO2 and methanol by Zr-doped CeO2 nanorods with different ratios of Zr/Ce has been studied at 6.8 MPa and 140 °C. The catalysts were characterized ext...