Showing papers on "Noble metal published in 2015"

Noble metal-free hydrogen evolution catalysts for water splitting

Abstract: Sustainable hydrogen production is an essential prerequisite of a future hydrogen economy. Water electrolysis driven by renewable resource-derived electricity and direct solar-to-hydrogen conversion based on photochemical and photoelectrochemical water splitting are promising pathways for sustainable hydrogen production. All these techniques require, among many things, highly active noble metal-free hydrogen evolution catalysts to make the water splitting process more energy-efficient and economical. In this review, we highlight the recent research efforts toward the synthesis of noble metal-free electrocatalysts, especially at the nanoscale, and their catalytic properties for the hydrogen evolution reaction (HER). We review several important kinds of heterogeneous non-precious metal electrocatalysts, including metal sulfides, metal selenides, metal carbides, metal nitrides, metal phosphides, and heteroatom-doped nanocarbons. In the discussion, emphasis is given to the synthetic methods of these HER electrocatalysts, the strategies of performance improvement, and the structure/composition-catalytic activity relationship. We also summarize some important examples showing that non-Pt HER electrocatalysts could serve as efficient cocatalysts for promoting direct solar-to-hydrogen conversion in both photochemical and photoelectrochemical water splitting systems, when combined with suitable semiconductor photocatalysts.

Heteroatom-Doped Graphene-Based Materials for Energy-Relevant Electrocatalytic Processes

Abstract: To address aggravating energy and environment issues, inexpensive, highly active, and durable electrocatalysts as noble metal substitutes both at the anode and cathode are being actively pursued. Among them, heteroatom-doped graphene-based materials show extraordinary electrocatalytic performance, some even close to or outperforming the state-of-the-art noble metals, such as Pt- and IrO2-based materials. This review provides a concise appraisal on graphene doping methods, possible doping configurations and their unique electrochemical properties, including single and double doping with N, B, S, and P. In addition, heteroatom-doped graphene-based materials are reviewed as electrocatalysts for oxygen reduction, hydrogen evolution, and oxygen evolution reactions in terms of their electrocatalytic mechanisms and performance. Significantly, three-dimensional heteroatom-doped graphene structures have been discussed, and those especially can be directly utilized as catalyst electrodes without extra binders and s...

Molecular metal–N x centres in porous carbon for electrocatalytic hydrogen evolution

Abstract: Replacement of precious platinum with efficient and low-cost catalysts for electrocatalytic hydrogen evolution at low overpotentials holds tremendous promise for clean energy devices. Here we report a novel type of robust cobalt–nitrogen/carbon catalyst for the hydrogen evolution reaction (HER) that is prepared by the pyrolysis of cobalt–N4 macrocycles or cobalt/o-phenylenediamine composites and using silica colloids as a hard template. We identify the well-dispersed molecular CoNx sites on the carbon support as the active sites responsible for the HER. The CoNx/C catalyst exhibits extremely high turnover frequencies per cobalt site in acids, for example, 0.39 and 6.5 s−1 at an overpotential of 100 and 200 mV, respectively, which are higher than those reported for other scalable non-precious metal HER catalysts. Our results suggest the great promise of developing new families of non-precious metal HER catalysts based on the controlled conversion of homogeneous metal complexes into solid-state carbon catalysts via economically scalable protocols. Hydrogen evolution from water promises a future clean energy source, however the cost of noble metal catalysts, which are necessary for high efficiency, are very expensive. Here, the authors fabricate a porous cobalt–nitrogen/carbon catalyst which can deliver high activity and stability but at reduced cost.

Engineering Ordered and Nonordered Porous Noble Metal Nanostructures: Synthesis, Assembly, and Their Applications in Electrochemistry

Abstract: Nanostructures: Synthesis, Assembly, and Their Applications in Electrochemistry Chengzhou Zhu,† Dan Du,†,⊥ Alexander Eychmüller,‡ and Yuehe Lin*,†,§ †School of Mechanical and Materials Engineering, Washington State University, Pullman, Washington 99164-2920, United States Key Laboratory of Pesticide and Chemical Biology of the Ministry of Education, College of Chemistry, Central China Normal University, Wuhan 430079, P. R. China ‡Physical Chemistry, TU Dresden, Bergstrasse 66b, 01062 Dresden, Germany Pacific Northwest National Laboratory, Richland, Washington 99352, United States

Noble metal-comparable SERS enhancement from semiconducting metal oxides by making oxygen vacancies.

Abstract: Surface-enhanced Raman spectroscopy is widely used for rapid and sensitive molecular detection in chemistry and biology, but typically relies on noble metals. Here the authors report a non-stoichiometric semiconducting material with defect-rich surface that displays excellent detection limits and enhancement factors.

Noble metal alloy complex nanostructures: controllable synthesis and their electrochemical property

Abstract: Noble metal nanocrystals have been extensively utilized as promising catalysts for chemical transformations and energy conversion. One of their significant applications lies in electrode materials in fuel cells (FCs) due to their superior electrocatalytic performance towards the reactions both on anode and cathode. Nowadays, tremendous efforts have been devoted to improve the catalytic performance and minimize the usage of precious metals. Constructing multicomponent noble metal nanocrystals with complex structures provides the opportunity to reach this goal due to their highly tunable compositions and morphologies, leading to the modification of the related electrochemical properties. In this review, we first highlight the recent advances in the controllable synthesis of noble metal alloy complex nanostructures including nanoframes/nanocages, branched structures, concave/convex structures, core–shell structures and ultrathin structures. Then the effects of the well-defined nanocrystals on the modified and improved electrochemical properties are outlined. Finally, we make a conclusion with the points on the challenges and perspectives of the controllable synthesis of noble metal alloy complex nanostructures and their electrocatalytic performance.

Ultrastable single-atom gold catalysts with strong covalent metal-support interaction (CMSI)

Abstract: Supported noble metal nanoparticles (including nanoclusters) are widely used in many industrial catalytic processes While the finely dispersed nanostructures are highly active, they are usually thermodynamically unstable and tend to aggregate or sinter at elevated temperatures This scenario is particularly true for supported nanogold catalysts because the gold nanostructures are easily sintered at high temperatures, under reaction conditions, or even during storage at ambient temperature Here, we demonstrate that isolated Au single atoms dispersed on iron oxide nanocrystallites (Au-1/FeOx) are much more sinteringresistant than Au nanostructures, and exhibit extremely high reaction stability for CO oxidation in a wide temperature range Theoretical studies revealed that the positively charged and surface-anchored Au1 atoms with high valent states formed significant covalent metal-support interactions (CMSIs), thus providing the ultra-stability and remarkable catalytic performance This work may provide insights and a new avenue for fabricating supported Au catalysts with ultra-high stability

Molybdenum-Carbide-Modified Nitrogen-Doped Carbon Vesicle Encapsulating Nickel Nanoparticles: A Highly Efficient, Low-Cost Catalyst for Hydrogen Evolution Reaction

Abstract: Despite being promising substitutes for noble metal catalysts used in hydrogen evolution reaction (HER), the nonprecious metal catalysts (NPMCs) based on inexpensive and earth-abundant 3d transition metals (TMs) are still practically unfeasible due mainly to unsatisfactory activity and durability. Herein, a highly active and stable catalyst for HER has been developed on the basis of molybdenum-carbide-modified N-doped carbon vesicle encapsulating Ni nanoparticles (MoxC-Ni@NCV). This MoxC-Ni@NCV material was synthesized simply by the solid-state thermolysis of melamine-related composites of oxalate and molybdate with uniform Ni ions doping (Ni@MOM-com). Notably, the prepared MoxC-Ni@NCV was almost the most efficient NPMCs for HER in acidic electrolyte to date. Besides good long-term stability, MoxC-Ni@NCV exhibited a quiet low overpotential that was comparable to Pt/C. Thus, this work opens a new avenue toward the development of highly efficient, inexpensive HER catalysts.

Silver-catalysed reactions of alkynes: recent advances

Abstract: Silver is a less expensive noble metal. Superior alkynophilicity due to π-coordination with the carbon-carbon triple bond makes silver salts ideal catalysts for alkyne-based organic reactions. This review highlights the progress in alkyne chemistry via silver catalysis primarily over the past five years (ca. 2010-2014). The discussion is developed in terms of the bond type formed with the acetylenic carbon (i.e., C-C, C-N, C-O, C-Halo, C-P and C-B). Compared with other coinage metals such as Au and Cu, silver catalysis is frequently observed to be unique. This critical review clearly indicates that silver catalysis provides a significant impetus to the rapid evolution of alkyne-based organic reactions, such as alkynylation, hydrofunctionalization, cycloaddition, cycloisomerization, and cascade reactions.

Chemically exfoliated metallic MoS 2 nanosheets: A promising supporting co-catalyst for enhancing the photocatalytic performance of TiO 2 nanocrystals

Abstract: Electron-hole separation is a critical step to achieving efficient photocatalysis, towards which use of co-catalysts has become a widely used strategy. Despite the tremendous efforts and demonstrated functions of noble metal co-catalysts, seeking noble metal-free co-catalysts will always be the goal when designing cost-effective, high-performance hybrid photocatalysts. In this work, we demonstrate that MoS2 nanosheets with 1T phase (i.e., octahedral phase) can function as a co-catalyst with multiple merits: (1) Noble-metal-free; (2) high mobility for charge transport; (3) high density of active sites for H2 evolution on basal planes; (4) good performance stability; (5) high light transparency. As demonstrated in both photocatalytic hydrogen production and Rhodamine B degradation, the developed hybrid structure with TiO2 exhibits excellent performance, in sharp contrast to bare TiO2 and the hybrid counterpart with 2H-MoS2.

Trinary Layered Double Hydroxides as High‐Performance Bifunctional Materials for Oxygen Electrocatalysis

Abstract: Layered double hydroxides (LDHs) are a family of high-profile layer materials with tunable metal species and interlayer spacing, and herein the LDHs are first investigated as bifunctional electrocatalysts. It is found that trinary LDH containing nickel, cobalt, and iron (NiCoFe-LDH) shows a reasonable bifunctional performance, while exploiting a preoxidation treatment can significantly enhance both oxygen reduction reaction and oxygen evolution reaction activity. This phenomenon is attributed to the partial conversion of Co2+ to Co3+ state in the preoxidation step, which stimulates the charge transfer to the catalyst surface. The practical application of the optimized material is demonstrated with a small potential hysteresis (800 mV for a reversible current density of 20 mA cm−2) as well as a high stability, exceeding the performances of noble metal catalysts (commercial Pt/C and Ir/C). The combination of the electrochemical metrics and the facile and cost-effective synthesis endows the trinary LDH as a promising bifunctional catalyst for a variety of applications, such as next-generation regenerative fuel cells or metal–air batteries.

Noble metal aerogels-synthesis, characterization, and application as electrocatalysts.

Abstract: ConspectusMetallic and catalytically active materials with high surface area and large porosity are a long-desired goal in both industry and academia. In this Account, we summarize the strategies for making a variety of self-supported noble metal aerogels consisting of extended metal backbone nanonetworks. We discuss their outstanding physical and chemical properties, including their three-dimensional network structure, the simple control over their composition, their large specific surface area, and their hierarchical porosity. Additionally, we show some initial results on their excellent performance as electrocatalysts combining both high catalytic activity and high durability for fuel cell reactions such as ethanol oxidation and the oxygen reduction reaction (ORR). Finally, we give some hints on the future challenges in the research area of metal aerogels. We believe that metal aerogels are a new, promising class of electrocatalysts for polymer electrolyte fuel cells (PEFCs) and will also open great op...

Oxide-supported Ir nanodendrites with high activity and durability for the oxygen evolution reaction in acid PEM water electrolyzers

Abstract: Reducing the noble-metal catalyst content of acid Polymer Electrolyte Membrane (PEM) water electrolyzers without compromising catalytic activity and stability is a goal of fundamental scientific interest and substantial technical importance for cost-effective hydrogen-based energy storage. This study presents nanostructured iridium nanodendrites (Ir-ND) supported on antimony doped tin oxide (ATO) as efficient and stable water splitting catalysts for PEM electrolyzers. The active Ir-ND structures exhibited superior structural and morphological properties, such as particle size and surface area compared to commercial state-of-art Ir catalysts. Supported on tailored corrosion-stable conductive oxides, the Ir-ND catalysts exhibited a more than 2-fold larger kinetic water splitting activity compared with supported Ir nanoparticles, and a more than 8-fold larger catalytic activity than commercial Ir blacks. In single-cell PEM electrolyzer tests, the Ir-ND/ATO outperformed commercial Ir catalysts more than 2-fold at technological current densities of 1.5 A cm−2 at a mere 1.80 V cell voltage, while showing excellent durability under constant current conditions. We conclude that Ir-ND/ATO catalysts have the potential to substantially reduce the required noble metal loading, while maintaining their catalytic performance, both in idealized three-electrode set ups and in the real electrolyzer device environments.

NMR Techniques for Noble Metal Nanoparticles

Abstract: Solution phase noble metal nanoparticle growth reactions are comprised of deceptively simple steps. Analytical methods with high chemical, spatial, and temporal resolution are crucial to understanding these reactions and subsequent nanoparticle properties. However, approaches for the characterization of solid inorganic materials and solution phase molecular species are often disparate. One powerful technique to address this gap is nuclear magnetic resonance (NMR) spectroscopy, which can facilitate routine, direct, molecular-scale analysis of nanoparticle formation and morphology in situ, in both the solution and the solid phase. A growing body of work indicates that NMR analyses should yield an exciting complement to the existing canon of routine nanoparticle characterization methods such as electron microscopy and optical absorption spectroscopy. Here, we discuss recent developments in the application of NMR techniques to the study of noble metal nanoparticle growth, surface chemistry, and physical prope...

Immobilizing highly catalytically active noble metal nanoparticles on reduced graphene oxide: a non-noble metal sacrificial approach

Abstract: In this work, we have developed a non-noble metal sacrificial approach for the first time to successfully immobilize highly dispersed AgPd nanoparticles on reduced graphene oxide (RGO). The Co3(BO3)2 co-precipitated with AgPd nanoparticles and subsequently sacrificed by acid etching effectively prevents the primary AgPd particles from aggregation. The resulted ultrafine AgPd nanoparticles exhibit the highest activity (turnover frequency, 2739 h(-1) at 323 K) among all the heterogeneous catalysts for the dehydrogenation of formic acid to generate hydrogen without CO impurity. The sacrificial approach opens up a new avenue for the development of high-performance metal nanocatalysts.

Noble metal modified reduced graphene oxide/TiO2 ternary nanostructures for efficient visible-light-driven photoreduction of carbon dioxide into methane

Abstract: The design and architecture of visible-light-active photocatalysts is a key aim among material scientists for the efficient utilization of renewable solar energy. In this paper, a series of noble metal (Pt, Pd, Ag and Au) nanoparticles supported on reduced graphene oxide/TiO2 (GT) were successfully synthesized through a dual step process. In the first step, GT nanocomposites were prepared using a solvothermal method. The as-prepared hybrid nanostructures were subsequently employed as supporting materials for the dispersion of metal nanoparticles. A simple polyol process was used to respectively reduce metal ions (PtCl62−, Pd2+, Ag+, and AuCl4−) into metal (Pt, Pd, Ag and Au) nanoparticles on GT. The three-component nanocomposites exhibited enhanced photocatalytic activities toward the photoreduction of CO2 into CH4 gas under the irradiation of typical daylight bulbs. This was attributed to the multiplex phenomena such as an enhanced utilization of visible light, efficient electron transfer in the noble metal-doped GT nanojunctions and interfacial electron transfer in the reduced graphene oxide (rGO) sheets, as evidenced by UV–vis and PL characterizations. Among the noble metals studied, the Pt-doped GT nanocomposites showed the highest efficiency in reducing CO2. A total CH4 yield of 1.70 μmol/gcat was achieved after 6 h of light irradiation, which was 2.6 and 13.2 folds higher in comparison to GT and commercial P25, respectively. Based on the experimental results obtained, a plausible mechanism for the photocatalytic process associated with Pt-GT was proposed.

MOFs-Templated Co@Pd Core–Shell NPs Embedded in N-Doped Carbon Matrix with Superior Hydrogenation Activities

Abstract: Although MOFs supporting noble metal nanoparticles (NPs) have been widely used in heterogeneous catalysis, they are still limited in catalytic efficiency on a per-noble-metal-atom basis. Here we developed a MOFs-templated strategy to non-noble metal @noble metal core–shell nanocatalysts, which could far surpass the traditional MOFs supporting noble NPs in catalytic properties, by using MOFs-derived metal NPs as sacrificial templates to reduce noble metal ions via galvanic replacement reaction. As a model system, Co@Pd core–shell NPs embedded in the N-doped carbon matrix (Co@Pd/NC) were synthesized with an average size of ca. 9.4 nm and a ultrathin Pd shell by using ZIF-67 and Pd(NO3)2 as the precursor and Pd source, respectively. The highly exposed Pd atom on Co nanoparticles made it an attractive catalyst with high efficiency. When being used in the hydrogenation of nitrobenzene, the Co@Pd/NC exhibited an unprecedented high activity over Pd-based catalysts, yielding 98% conversion after 45 min reaction, ...

Stabilization of 4H hexagonal phase in gold nanoribbons

Abstract: Gold, silver, platinum and palladium typically crystallize with the face-centred cubic structure. Here we report the high-yield solution synthesis of gold nanoribbons in the 4H hexagonal polytype, a previously unreported metastable phase of gold. These gold nanoribbons undergo a phase transition from the original 4H hexagonal to face-centred cubic structure on ligand exchange under ambient conditions. Using monochromated electron energy-loss spectroscopy, the strong infrared plasmon absorption of single 4H gold nanoribbons is observed. Furthermore, the 4H hexagonal phases of silver, palladium and platinum can be readily stabilized through direct epitaxial growth of these metals on the 4H gold nanoribbon surface. Our findings may open up new strategies for the crystal phase-controlled synthesis of advanced noble metal nanomaterials.

Deactivation of Pd Catalysts by Water during Low Temperature Methane Oxidation Relevant to Natural Gas Vehicle Converters

Abstract: Effects of H2O on the activity and deactivation of Pd catalysts used for the oxidation of unburned CH4 present in the exhaust gas of natural-gas vehicles (NGVs) are reviewed. CH4 oxidation in a catalytic converter is limited by low exhaust gas temperatures (500–550 °C) and low concentrations of CH4 (400–1500 ppmv) that must be reacted in the presence of large quantities of H2O (10–15%) and CO2 (15%), under transient exhaust gas flows, temperatures, and compositions. Although Pd catalysts have the highest known activity for CH4 oxidation, water-induced sintering and reaction inhibition by H2O deactivate these catalysts. Recent studies have shown the reversible inhibition by H2O adsorption causes a significant drop in catalyst activity at lower reaction temperatures (below 450 °C), but its effect decreases (water adsorption becomes more reversible) with increasing reaction temperature. Thus above 500 °C H2O inhibition is negligible, while Pd sintering and occlusion by support species become more important. H2O inhibition is postulated to occur by either formation of relatively stable Pd(OH)2 and/or partial blocking by OH groups of the O exchange between the support and Pd active sites thereby suppressing catalytic activity. Evidence from FTIR and isotopic labeling favors the latter route. Pd catalyst design, including incorporation of a second noble metal (Rh or Pt) and supports high O mobility (e.g., CeO2) are known to improve catalyst activity and stability. Kinetic studies of CH4 oxidation at conditions relevant to natural gas vehicles have quantified the thermodynamics and kinetics of competitive H2O adsorption and Pd(OH)2 formation, but none have addressed effects of H2O on O mobility.

Low Pressure CO2 Hydrogenation to Methanol over Gold Nanoparticles Activated on a CeOx/TiO2 Interface

Abstract: Capture and recycling of CO2 into valuable chemicals such as alcohols could help mitigate its emissions into the atmosphere. Due to its inert nature, the activation of CO2 is a critical step in improving the overall reaction kinetics during its chemical conversion. Although pure gold is an inert noble metal and cannot catalyze hydrogenation reactions, it can be activated when deposited as nanoparticles on the appropriate oxide support. In this combined experimental and theoretical study, it is shown that an electronic polarization at the metal-oxide interface of Au nanoparticles anchored and stabilized on a CeO(x)/TiO2 substrate generates active centers for CO2 adsorption and its low pressure hydrogenation, leading to a higher selectivity toward methanol. This study illustrates the importance of localized electronic properties and structure in catalysis for achieving higher alcohol selectivity from CO2 hydrogenation.

Reduced Graphene Oxide-Based Silver Nanoparticle-Containing Composite Hydrogel as Highly Efficient Dye Catalysts for Wastewater Treatment

Abstract: New reduced graphene oxide-based silver nanoparticle-containing composite hydrogels were successfully prepared in situ through the simultaneous reduction of GO and noble metal precursors within the GO gel matrix. The as-formed hydrogels are composed of a network structure of cross-linked nanosheets. The reported method is based on the in situ co-reduction of GO and silver acetate within the hydrogel matrix to form RGO-based composite gel. The stabilization of silver nanoparticles was also achieved simultaneously within the gel composite system. The as-formed silver nanoparticles were found to be homogeneously and uniformly dispersed on the surface of the RGO nanosheets within the composite gel. More importantly, this RGO-based silver nanoparticle-containing composite hydrogel matrix acts as a potential catalyst for removing organic dye pollutants from an aqueous environment. Interestingly, the as-prepared catalytic composite matrix structure can be conveniently separated from an aqueous environment after the reaction, suggesting the potentially large-scale applications of the reduced graphene oxide-based nanoparticle-containing composite hydrogels for organic dye removal and wastewater treatment.

Strongly Coupled 3D Hybrids of N‐doped Porous Carbon Nanosheet/CoNi Alloy‐Encapsulated Carbon Nanotubes for Enhanced Electrocatalysis

Abstract: A novel 3D nanoarchitecture comprising in situ-formed N-doped CoNi alloy-encapsulated carbon nanotubes (CoNi-NCNTs) grown on N-doped porous carbon nanosheets (NPCNs) is designed and constructed for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). When evaluated as an electrocatalyst for ORR, the hybrid shows efficient catalytic activity, high selectivity, superior durability, and strong tolerance against methanol crossover compared with the commercial Pt/C catalyst. Such good oxygen reduction reaction performance is comparable to most of the previously reported results and the synergistic effect is found to boost the catalytic performance. Moreover, the constructed hybrid exhibits an excellent ORR activity with a current density of 10 mA cm(-2) at 1.59 V and an onset potential of 1.57 V, even beyond the state-of-the-art Ir/C catalyst in alkaline media. The enhancement in electrochemical performance can be attributed to the unique morphology and defect structures, high porosity, good conductive networks, and strongly interacting CoNi-NCNT and NPCN in the hybrid. These results suggest the possibility for the development of effective nanocarbon electrocatalysts to replace commercial noble metal catalysts for direct use in fuel cells and water splitting devices.

“Black” TiO2 Nanotubes Formed by High-Energy Proton Implantation Show Noble-Metal-co-Catalyst Free Photocatalytic H2-Evolution

Abstract: We apply high-energy proton ion-implantation to modify TiO2 nanotubes selectively at their tops. In the proton-implanted region, we observe the creation of intrinsic cocatalytic centers for photocatalytic H2-evolution. We find proton implantation to induce specific defects and a characteristic modification of the electronic properties not only in nanotubes but also on anatase single crystal (001) surfaces. Nevertheless, for TiO2 nanotubes a strong synergetic effect between implanted region (catalyst) and implant-free tube segment (absorber) can be obtained.

Reversibility of Noble Metal-Catalyzed Aprotic Li-O2 Batteries

Abstract: The aprotic Li-O2 battery has attracted a great deal of interest because, theoretically, it can store far more energy than today’s batteries. Toward unlocking the energy capabilities of this neotype energy storage system, noble metal-catalyzed high surface area carbon materials have been widely used as the O2 cathodes, and some of them exhibit excellent electrochemical performances in terms of round-trip efficiency and cycle life. However, whether these outstanding electrochemical performances are backed by the reversible formation/decomposition of Li2O2, i.e., the desired Li-O2 electrochemistry, remains unclear due to a lack of quantitative assays for the Li-O2 cells. Here, noble metal (Ru and Pd)-catalyzed carbon nanotube (CNT) fabrics, prepared by magnetron sputtering, have been used as the O2 cathode in aprotic Li-O2 batteries. The catalyzed Li-O2 cells exhibited considerably high round-trip efficiency and prolonged cycle life, which could match or even surpass some of the best literature results. How...

Chemical synthesis and application of palladium nanoparticles

Abstract: In the past, palladium as a member of the platinum group metals was mainly known as an expensive noble metal. Probably, only fast hydrogen absorption into bulk palladium reminded of its unique catalytic activity. At the beginning of the twenty-first century, detailed studies of the electron structure of palladium atom/nanocluster/nanoparticles launched a new understanding of the selective catalytic activity of this noble metal. This review presents the simplest and most useful methods of synthesizing palladium in a nano scale. In addition, the most famous and required applications of nano-palladium are described in the second half of the review. With the rapid development of nanotechnologies, palladium nanoparticles are becoming prospective selective catalysts for complex chemical reactions.

The effect of noble metal (Au, Pd and Pt) nanoparticles on the gas sensing performance of SnO2-based sensors: a case study on the {221} high-index faceted SnO2 octahedra

Abstract: Surface modification with noble metals is considered as an effective strategy to enhance sensitivity and selectivity of metal oxide-based gas sensors. This enhancement with noble metal decoration is generally attributed to the formation of a heterogeneous interface between the noble metal and metal oxide. However, the sensitization mechanism of noble metals on the specific facets of the metal oxide support lacks a unified understanding. In this work, three gas sensing hybrid nanostructures based on noble metal (Au, Pd and Pt) decorated {221} faceted octahedral SnO2 nanocrystals were specifically constructed. Our results showed that, on these {221} specific facets of SnO2, Au exhibited a positive effect for enhancing the sensitivity and selectivity of SnO2 sensors, while Pd and Pt played the opposite roles. It is considered that the sensitization effects of noble metals are related to their surface chemical states and interaction with the metal oxide support. The methodology demonstrated in this work is beneficial to probing into the sensitization mechanisms of noble metals in semiconductor/metal hybrid sensors.

Efficient Water Splitting Using a Simple Ni/N/C Paper Electrocatalyst

Abstract: An efficient water splitting electrocatalyst is presented. Cheap and sustainable cellulose filter paper, infiltrated with nickel acetate as the nickel source, and phenanthroline as a ligand and nitrogen source are carbonized together. Nitrogen functionalities turn out to be crucial coordination sites for the supported Ni/NiO(OH) particles. This simple and scalable one step procedure leads to powders, but also to complete membranes made of ≈10 wt% Ni, supported on nitrogen functionalized carbon. The non-noble catalyst shows a low onset potential (330 mV vs reversible hydrogen electrode), high current density (e.g., j > 25 mA cm−­2 at η = 430 mV), excellent kinetics (Tafel slope of 44 mV dec−1), and a very favorable stability (<5% decay after 10 h electrolysis) in the oxygen evolution. The performance is similar or even better compared to state-of-the-art noble metal catalysts (e.g., IrO2, Ir/C, Ru/C, and Pt/C). Because of the simple, cheap, and scalable preparation procedure the catalyst is highly promising for practical low price/tech applications. Interestingly, the system is also active in the hydrogen evolution reaction, leading to a promising bifunctional catalyst. The benchmark characteristics are η10 = 390 mV for oxygen evolution and η10 = 190 mV for hydrogen evolution, that is, an overall efficiency of 68% at 10 mA current density.

Electrocatalytic H2 production from seawater over Co, N-codoped nanocarbons

Abstract: One of the main barriers blocking sustainable hydrogen production is the use of expensive platinum-based catalysts to produce hydrogen from water. Herein we report the cost-effective synthesis of catalytically active, nitrogen-doped, cobalt-encased carbon nanotubes using inexpensive starting materials—urea and cobalt chloride hexahydrate (CoCl2·6H2O). Moreover, we show that the as-obtained nanocarbon material exhibits a remarkable electrocatalytic activity toward the hydrogen evolution reaction (HER); and thus it can be deemed as a potential alternative to noble metal HER catalysts. In particular, the urea-derived carbon nanotubes synthesized at 900 °C (denoted as U-CNT-900) show a superior catalytic activity for HER with low overpotential and high current density in our study. Notably also, U-CNT-900 has the ability to operate stably at all pH values (pH 0–14), and even in buffered seawater (pH 7). The possible synergistic effects between carbon-coated cobalt nanoparticles and the nitrogen dopants can be proposed to account for the HER catalytic activity of U-CNT-900. Given the high natural abundance, ease of synthesis, and high catalytic activity and durability in seawater, this U-CNT-900 material is promising for hydrogen production from water in industrial applications.