Silver Nanowires Cascaded Layered Double Hydroxides Nanocages with Enhanced Directional Electron Transport for Efficient Electrocatalytic Oxygen Evolution.

Designing and fabricating highly efficient oxygen evolution reaction (OER) electrocatalytic materials for water splitting is a promising and practical approach to green and sustainable low-carbon energy systems. Herein, a facile in situ growth self-template strategy by using ZIF-67 as a consumable layered double hydroxides (LDHs) template and silver nanowires (AgNWs) as 1D conductive cascaded substrate to controllably synthesize the target AgNWs@CoFe-LDH composites with unique hollow shell sugar gourd-like structure and enhanced directional electron transport effect is reported. The AgNWs exhibit the key functions of the close connection of CoFe-LDH nanocages and the support of the directional electron transport effect in the composite catalyst inducing electrons directionally moving from CoFe-LDH to AgNWs. Meanwhile, the CoFe-LDH nanocages with ultrathin nanosheets and hollow structural properties show abundant active sites for electrocatalytic oxygen generation. The versatile AgNWs@CoFe-LDH catalyst with optimized components, enhanced directional electron transport, and synergistic effect achieves high OER performance with the overpotential of 207 mV and long-term 50 h stability at 10 mA cm-2 in an alkaline medium. Moreover, in-depth insights into the microstructure, structure-activity relationships, identification of key intermediate species, and a proton-coupled four-electron OER mechanism based on experimental discovery and theoretical calculation are also demonstrated.

Tuning electronic structure of hedgehog-like nickel cobaltite via molybdenum-doping for enhanced electrocatalytic oxygen evolution catalysis.

As a typical spinel oxide, nickel cobaltite (NiCo2O4) is considered to be a promising and reliable oxygen evolution reaction (OER) catalyst due to its abundant oxidation states and the synergistic effect of multiple metal species. However, the electrocatalytic OER performance of NiCo2O4 has always been limited by the low specific surface area and poor intrinsic conductivity of spinels. Herein, the hedgehog-like molybdenum-doped NiCo2O4 (Mo-NiCo2O4) catalyst was prepared as an efficient OER electrocatalyst via a facile hydrothermal method followed with high-temperature annealing. The Mo-NiCo2O4-0.075 with Mo doping concentration of âˆ¼ 1.95 wt% exhibits excellent OER performance with a low overpotential of 265 mV at a current density of 10 mA·cm-2and a Tafel slope of 126.63 mV·dec-1, as well as excellent cyclingstability.The results demonstrated that the hedgehog-like structure provides Mo-NiCo2O4 with the high surface area and mesopores that enhance electrolyte diffusion and optimal active site exposure. The in-situ Raman spectra and density functional theory calculations show that the Mo cations doping improve the intrinsic conductivity of the NiCo2O4 while modulating the chemisorption of intermediates. Meanwhile, the energy barriers of *OH and O* formation decrease significantly after Mo doping, effectively facilitating water dissociation and optimizing the reaction kinetics.

Corrosion resistance and earth-abundance FeS-based heterojunction catalyst for seawater splitting at industrial grade density.

The strategic progression toward highly efficient transition metal electrocatalytic electrodes is crucial to achieving efficiency and long-term stability in hydrogen production from authentic seawater sources. This work reports the development of a self-supporting, heterogeneous and corrosion-resistant iron sulfur-based catalytic electrode via a streamlined, one-step process involving sulfide etching and electroless plating on an iron foam substrate (IF). This new electrode, named NiS-FeS@IF, involves a nanostructured NiS-FeS catalytic material that combines in situ, resulting in a thin, ultrathin nanospherical layer on the IF. This construction has low overpotentials of merely 322 mV for the hydrogen evolution reaction (HER) and 563 mV for the oxygen evolution reaction (OER) with a current density of 500 mA cm-2 in alkaline simulated seawater electrolytes. Importantly, the NiS-FeS@IF electrode enduring more than 500 h at an industrial grade high current density of 1 A cm-2 without noteworthy performance deterioration. The unique and uniformly dispersed morphology of NiS-FeS facilitates intensified interfacial electron transfer, optimizes active site exposure and provides efficient channels for the rapid release and mass transfer of gas bubbles. This work introduces a novel approach for the facile preparation of efficient electrode materials.

Intrinsic Electron Localization of Metastable MoS2 Boosts Electrocatalytic Nitrogen Reduction to Ammonia.

The advancement of efficient electrocatalysts toward the nitrogen reduction reaction (NRR) is critical in sustainable ammonia synthesis under ambient pressure and temperature. Manipulating the electronic configuration of electrocatalysts is particularly vital to form metal-nitrogen (MN) bonds during the NRR through regulating the active electronic states of sites. Here, in sharp contrast to stable 2H MoS2 without metal chains, MoMo bonding in metastable polymorphs of MoS2 bulk (zigzag chain in the 1T' phase and diamond chain in the 1T″' phase) is discovered to significantly increase intrinsic electron localization around the metal chains. This can enhance the charge transfer from the adsorbed nitrogen molecule to the metal chains, allowing for boosted NRR kinetics. The electrochemical experiments show that the NH3 yield rate and the faradaic efficiency of the metastable 1T″' MoS2 rich with abundant Mo-Mo bonds are about 9 and 12 times above average than those of 2H MoS2 , correspondingly. Theoretical simulations reveal the high local electron density surrounding the MoMo chains and sites can promote π back-donation, which is beneficial for increasing nitrogen adsorption, strengthening the MN bonds, and reducing the cleavage barrier of the triple NN bond.

Atomically dispersed Pd-Ru dual sites in an amorphous matrix towards efficient phenylacetylene semi-hydrogenation.

Optimizing the active sites to balance the conversion and selectivity of the target reaction has long been a challenging quest in developing noble metal-based catalysts. By dispersing Pd and Ru in an amorphous zirconium hydrogen phosphate matrix cross-linked by ionic inorganic oligomers, highly diluted noble metal (<0.2 mol%) can be utilized as dual single-atom sites in oxides for the semi-hydrogenation of phenylacetylene with optimized conversion and selectivity (both >90%) to styrene. In situ DRIFT-IR results suggested the fast generation of surface hydroxyl groups during the catalytic reaction, indicating the high efficiency of the single-atom sites to dissociate bound H2. This work provides an easily scaled-up method for the production of cost-effective single-atom catalysts extendable to various oxide matrices.

One-Step High-Temperature-Synthesized Single-Atom Platinum Catalyst for Efficient Selective Hydrogenation.

Although single-atom catalysts significantly improve the atom utilization efficiency, the multistep preparation procedures are complicated and difficult to control. Herein, we demonstrate that one-step in situ synthesis of the single-atom Pt anchored in single-crystal MoC (Pt1/MoC) by using facile and controllable arc-discharge strategy under extreme conditions. The high temperature (up to 4000°C) provides the sufficient energy for atom dispersion and overall stability by forming thermodynamically favourable metal-support interactions. The high-temperature-stabilized Pt1/MoC exhibits outstanding performance and excellent thermal stability as durable catalyst for selective quinoline hydrogenation. The initial turnover frequency of 3710 h-1 is greater than those of previously reported samples by an order of magnitude under 2 MPa H2 at 100°C. The catalyst also shows broad scope activity toward hydrogenation containing unsaturated groups of C=C, C=N, and C=O. The facile, one-step, and fast arc-discharge method provides an effective avenue for single-atom catalyst fabrication that is conventionally challenging.

Efficient Reduction of CO2 to CO Using Cobalt-Cobalt Oxide Core-Shell Catalysts.

The route of converting CO2 to CO by reverse water-gas shift (RWGS) reaction is of particular interest due to the direct use of CO as feedstock in many significant industrial processes. Here, an engineered cobalt-cobalt oxide core-shell catalyst (Co@CoO) with nanochains structure has been made for the efficient reduction of CO2 to useful CO. Owing to the excellent performance for H2 activation of metal nanoparticles and the enhanced absorption and activation for CO2 molecule of defective metal oxides, the unique synergistic effect of metallic Co and encapsulating coordinatively unsaturated CoO species shows high performance for clean generation of CO under moderate and practical conditions. Furthermore, with N-dopant into the defective CoO shell, the Co@CoO-N achieves the highest conversion of 19.2 % and an exceptional CO evolution rate of 96 mL min-1 gcat-1 at 523 K with a gas hourly space velocity (GHSV) of 42,000 mL gcat-1 h-1 , which is comparable with the previously reported materials under identical conditions.

Prominent Electron Penetration through Ultrathin Graphene Layer from FeNi Alloy for Efficient Reduction of CO2 to CO.

The chemical transformation of CO2 is an efficient approach in low-carbon energy system. The development of nonprecious metal catalysts with sufficient activity, selectivity, and stability for the generation of CO by CO2 reduction under mild conditions remains a major challenge. A hierarchical architecture catalyst composed of ultrathin graphene shells (2-4 layers) encapsulating homogeneous FeNi alloy nanoparticles shows enhance catalytic performance. Electron transfer from the encapsulated alloy can extend from the inner to the outer shell, resulting in an increased charge density on graphene. Nitrogen atom dopants can synergistically increase the electron density on the catalyst surface and modulate the adsorption capability for acidic CO2 molecules. The optimized FeNi3 @NG (NG=N-doped graphene) catalyst, with significant electron penetration through the graphene layer, effects exceptional CO2 conversion of 20.2 % with a CO selectivity of nearly 100 %, as well as excellent thermal stability at 523 K.

Direct synthesis of ethanol via CO2 hydrogenation using supported gold catalysts.

An efficient titania supported Au nanocluster (NC) has been prepared for the direct synthesis of useful EtOH from CO2 and H2. The unique creation of an excellent synergistic effect between Au NCs and the underlying TiO2 support, especially the anatase crystal phase with abundant oxygen vacancies, can achieve the high performance for EtOH synthesis under moderate and practical conditions.

Dehydrogenation of Formic Acid at Room Temperature: Boosting Palladium Nanoparticle Efficiency by Coupling with Pyridinic-Nitrogen-Doped Carbon.

The use of formic acid (FA) to produce molecular H2 is a promising means of efficient energy storage in a fuel-cell-based hydrogen economy. To date, there has been a lack of heterogeneous catalyst systems that are sufficiently active, selective, and stable for clean H2 production by FA decomposition at room temperature. For the first time, we report that flexible pyridinic-N-doped carbon hybrids as support materials can significantly boost the efficiency of palladium nanoparticle for H2 generation; this is due to prominent surface electronic modulation. Under mild conditions, the optimized engineered Pd/CN0.25 catalyst exhibited high performance in both FA dehydrogenation (achieving almost full conversion, and a turnover frequency of 5530 h(-1) at 25 °C) and the reversible process of CO2 hydrogenation into FA. This system can lead to a full carbon-neutral energy cycle.

An aqueous rechargeable formate-based hydrogen battery driven by heterogeneous Pd catalysis.

The formate-based rechargeable hydrogen battery (RHB) promises high reversible capacity to meet the need for safe, reliable, and sustainable H2 storage used in fuel cell applications. Described herein is an additive-free RHB which is based on repetitive cycles operated between aqueous formate dehydrogenation (discharging) and bicarbonate hydrogenation (charging). Key to this truly efficient and durable H2 handling system is the use of highly strained Pd nanoparticles anchored on graphite oxide nanosheets as a robust and efficient solid catalyst, which can facilitate both the discharging and charging processes in a reversible and highly facile manner. Up to six repeated discharging/charging cycles can be performed without noticeable degradation in the storage capacity.

Partially reduced iridium oxide clusters dispersed on titania as efficient catalysts for facile synthesis of dimethylformamide from CO2, H2 and dimethylamine.

A novel bifunctional catalyst based on partially reduced iridium oxide supported on TiO2 was found to be exceedingly efficient for the organic-solvent-free synthesis of dimethylformamide from CO2, H2 and dimethylamine.

Efficient subnanometric gold-catalyzed hydrogen generation via formic acid decomposition under ambient conditions.

Formic acid (FA) has tremendous potential as a safe and convenient source of hydrogen for sustainable chemical synthesis and renewable energy storage, but controlled and efficient dehydrogenation of FA by a robust solid catalyst under ambient conditions constitutes a major challenge. Here, we report that a previously unappreciated combination of subnanometric gold and an acid-tolerant oxide support facilitates the liberation of CO-free H(2) from FA. Applying an ultradispersed gold catalyst comprising TEM-invisible gold subnanoclusters deposited on zirconia to a FA-amine mixture affords turnover frequencies (TOFs) up to 1590 per hour and a turnover number of more than 118,400 at 50 °C. The reaction was accelerated at higher temperatures, but even at room temperature, a significant H(2) evolution (TOFs up to 252 h(-1) after 20 min) can still be obtained. Preliminary mechanistic studies suggest that the reaction is unimolecular in nature and proceeds via a unique amine-assisted formate decomposition mechanism on Au-ZrO(2) interface.

Conversion of biomass-derived levulinate and formate esters into γ-valerolactone over supported gold catalysts.

The utilization of biomass has recently attracted tremendous attention as a potential alternative to petroleum for the production of liquid fuels and chemicals. We report an efficient alcohol-mediated reactive extraction strategy by which a hydrophobic mixture of butyl levulinate and formate esters, derived from cellulosic biomass, can be converted to valuable γ-valerolactone (GVL) by a simple supported gold catalyst system without need of an external hydrogen source. The essential role of the supported gold is to facilitate the rapid and selective decomposition of butyl formate to produce a hydrogen stream, which enables the highly effective reduction of butyl levulinate into GVL. This protocol simplifies the recovery and recycling of sulfuric acid, which is used for cellulose deconstruction.

Effect of optical absorbance on the Raman spectra of Ce(0.9)Tb(0.1)O(2-delta) solid solution.

Concentration of oxygen vacancies, optical absorption and microstructure of Ce(0.9)Tb(0.1)O(2-) (delta) material under different atmospheres (O(2), He and H(2)) and temperatures are characterized by in situ X-ray diffraction, in situ Raman spectroscopy and confocal microscopy. In this paper, we focus on how the change in optical absorption of the sample significantly affects the observed Raman information (peak intensity and the variation rule of oxygen vacancy concentration) under in situ conditions. With increasing temperature, the optical absorption of the sample decreases because of the release of oxygen and consequent changes of the microstructure. The decline in the optical absorption enables the Raman laser to increase its sampling depth, therefore, the deeper layer phonons in the structure are also sampled and contribute to the Raman scattering when the same excitation laser line is used. A more pronounced effect is observed when 514 nm laser line is used rather than 785 nm excitation, because both Tb and oxygen vacancies are enriched on the surface of the material and the 514 nm light provides surface information, while 785 nm light provides almost complete information on the sample.