Showing papers on "Cobalt published in 2011"

Porphyrin-sensitized solar cells with cobalt (II/III)-based redox electrolyte exceed 12 percent efficiency (vol 334, pg 629, 2011)

Abstract: Simultaneous modification of the dye and redox shuttle boosts the efficiency of a dye-sensitized solar cell. The iodide/triiodide redox shuttle has limited the efficiencies accessible in dye-sensitized solar cells. Here, we report mesoscopic solar cells that incorporate a Co(II/III)tris(bipyridyl)–based redox electrolyte in conjunction with a custom synthesized donor-π-bridge-acceptor zinc porphyrin dye as sensitizer (designated YD2-o-C8). The specific molecular design of YD2-o-C8 greatly retards the rate of interfacial back electron transfer from the conduction band of the nanocrystalline titanium dioxide film to the oxidized cobalt mediator, which enables attainment of strikingly high photovoltages approaching 1 volt. Because the YD2-o-C8 porphyrin harvests sunlight across the visible spectrum, large photocurrents are generated. Cosensitization of YD2-o-C8 with another organic dye further enhances the performance of the device, leading to a measured power conversion efficiency of 12.3% under simulated air mass 1.5 global sunlight.

High-Performance Electrocatalysts for Oxygen Reduction Derived from Polyaniline, Iron, and Cobalt

Abstract: The prohibitive cost of platinum for catalyzing the cathodic oxygen reduction reaction (ORR) has hampered the widespread use of polymer electrolyte fuel cells. We describe a family of non-precious metal catalysts that approach the performance of platinum-based systems at a cost sustainable for high-power fuel cell applications, possibly including automotive power. The approach uses polyaniline as a precursor to a carbon-nitrogen template for high-temperature synthesis of catalysts incorporating iron and cobalt. The most active materials in the group catalyze the ORR at potentials within ~60 millivolts of that delivered by state-of-the-art carbon-supported platinum, combining their high activity with remarkable performance stability for non-precious metal catalysts (700 hours at a fuel cell voltage of 0.4 volts) as well as excellent four-electron selectivity (hydrogen peroxide yield <1.0%).

Splitting water with cobalt.

Abstract: The future of energy supply depends on innovative breakthroughs regarding the design of cheap, sustainable, and efficient systems for the conversion and storage of renewable energy sources, such as solar energy. The production of hydrogen, a fuel with remarkable properties, through sunlight-driven water splitting appears to be a promising and appealing solution. While the active sites of enzymes involved in the overall water-splitting process in natural systems, namely hydrogenases and photosystem II, use iron, nickel, and manganese ions, cobalt has emerged in the past five years as the most versatile non-noble metal for the development of synthetic H(2)- and O(2)-evolving catalysts. Such catalysts can be further coupled with photosensitizers to generate photocatalytic systems for light-induced hydrogen evolution from water.

The role of cobalt phosphate in enhancing the photocatalytic activity of α-Fe2O3 toward water oxidation.

Abstract: Transient absorption spectroscopy was used to probe the dynamics of photogenerated charge carriers in α-Fe2O3/CoOx nanocomposite photoelectrodes for water splitting. The addition of cobalt-based electrocatalysts was observed to increase the lifetime of photogenerated holes in the photoelectrode by more than 3 orders of magnitude without the application of electrical bias. We therefore propose that the enhanced photoelectrochemical activity of the composite electrode for water photooxidation results, at least in part, from reduced recombination losses because of the formation of a Schottky-type heterojunction.

Electocatalytic water oxidation by cobalt(III) hangman β-octafluoro corroles.

Abstract: Cobalt hangman corrole, bearing β-octafluoro and meso-pentafluorophenyl substituents, is an active water splitting catalyst. When immobilized in Nafion films, the turnover frequencies for the 4e–/4H+ process at the single cobalt center of the hangman platform approach 1 s–1. The pH dependence of the water splitting reaction suggests a proton-coupled electron transfer (PCET) catalytic mechanism.

Hydrodeoxygenation of guaiacol with CoMo catalysts. Part I: Promoting effect of cobalt on HDO selectivity and activity

Abstract: Unsupported and alumina-supported MoS2 and CoMoS catalysts have been compared in the hydrodeoxygenation (HDO) reaction of guaiacol (2-methoxyphenol), a typical model molecule for bio-oils coming from the pyrolysis of ligno-cellulosic biomass. The goal of this work was to understand the cobalt promoting effect on MoS2 phase in this type of catalytic reaction. It appeared clearly that in the presence of the CoMoS phase, the direct deoxygenation (DDO) pathway involved in guaiacol conversion was strongly increased as compared to the non-promoted MoS2 in the bulk or supported state. This effect is similar to the well-known increase of direct desulfurization (DDS) pathway by cobalt promoter in the hydrodesulfurization (HDS) of refractory sulfur compounds over molybdenum sulfide catalysts.

Co(1-x)S-graphene hybrid: a high-performance metal chalcogenide electrocatalyst for oxygen reduction.

Abstract: Owing to their high energy-conversion efficiency, low or even zero emission, and high energy and power density, fuel cells such as proton-exchange membrane fuel cells (PEMFC) and direct methanol fuel cells (DMFC) have drawn tremendous attention as potential clean and efficient power sources for both electric vehicles and portable electronics. 2] A major limiting factor of energy-conversion efficiency for present fuel cells is the sluggish kinetics of the oxygen reduction reaction (ORR) at the cathode. Platinum and its alloys have been so far the most active ORR catalysts. However, the prohibitive cost, scarcity, and declining activity of Pt-based catalysts have hindered widespread application and commercialization of fuel cells. Consequently, alternative electrocatalysts based on nonprecious metals have been actively pursued. Cobalt sulfides have been investigated as ORR catalyst with the highest activity among all chalcogenides of nonprecious metals in acidic solution. Theoretical studies predicted electrocatalytic activity of Co9S8 similar to that of Pt via a four-electron ORR pathway. However, current ORR catalysts based on cobalt sulfides and cobalt selenides have exhibited activities far lower than that of Pt. Moreover, it has been shown that two-electron reduction is the dominant reaction pathway for cobalt sulfide catalysts, especially at potentials higher than 0.5 V versus the reversible hydrogen electrode (RHE). It is thus highly desirable to design and synthesize high-performance cobalt chalcogenide based electrocatalyst materials capable of catalyzing fourelectron ORR. Here we describe a novel cobalt sulfide–graphene hybrid electrocatalyst for ORR, obtained by controlled two-step synthesis of Co1 xS nanoparticles on reduced graphene oxide (RGO). The RGO sheets underlying the Co1 xS nanoparticles provide an electrically conducting support for the catalyst, control the size of the catalyst particles, and enhance the ORR catalytic activity of the Co1 xS nanoparticles through strong electrochemical coupling. In 0.5m H2SO4, our Co1 xS/ RGO hybrid catalyst shows an ORR current onset at about 0.8 V versus RHE. When the electrode is rotated at 1600 rpm, the ORR current density is as high as about 1.1 mA cm 2 at 0.7 V versus RHE with a loading of about 100 mg cm . Measurements with both rotating disk electrode (RDE) and rotating ring disk electrode (RRDE) show that nearly fourelectron ORR can be achieved with the Co1 xS/RGO hybrid catalyst. The Co1 xS/RGO hybrid is the highest performance ORR catalyst among all cobalt chalcogenide based materials reported in the literature. Cobalt sulfide nanoparticles were synthesized on RGO sheets by a low-temperature solution-phase reaction followed by a high-temperature annealing step. Graphene oxide (GO) was made by a modified Hummers method (see Supporting Information), in which a six times lower concentration of KMnO4 was used (see Supporting Information) to give GO sheets with lower oxygen content than Hummers GO (ca. 15 vs. ca. 30 %, measured by X-ray photoelectron spectroscopy (XPS) and Auger spectroscopy). In the first reaction step, nanoparticles of cobalt sulfide precursor were selectively and uniformly coated onto GO surface by treating Co(OAc)2 with thioacetamide (TAA) in a GO/water suspension at 80 8C for 12 h (Figure S1, Supporting Information). The intermediate product was then annealed at 500 8C in 1 atm of Ar for 1 h to give the final hybrid material of cobalt sulfide nanoparticles on graphene (see Supporting Information for experimental details). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) clearly revealed that cobalt sulfide nanoparticles were selectively grown on RGO sheets without free growth of unattached nanoparticles in solution (Figure 1a, b, and d). The cobalt sulfide nanoparticles on RGO were crystalline with an average particle size of about 10–20 nm (Figure 1b and d). X-ray diffraction (XRD, Figure 1c) showed that the cobalt sulfide nanoparticles grown on RGO are a Co1 xS phase (ICDD PDF #00-0420826) with hexagonal structure in space group P63/mmc (no. 194). The lattice fringes of the Co1 xS nanocrystals (Figure 1d) and the electron diffraction pattern (Figure 1d inset) are consistent with the crystal structure. The Co1 xS/ RGO hybrid contains about 30 wt % of RGO with a designed Co/C ratio of 1/4. The ORR catalytic activity of Co1 xS/RGO was first characterized by loading the hybrid material onto glassy carbon electrode for cyclic voltammetry (CV) measurements in 0.5m H2SO4 at 25 8C (see Supporting Information for experimental details). Comparison of CV curves in O2versus Ar-saturated electrolyte clearly revealed the ORR catalytic activity of Co1 xS/RGO. The hybrid showed an ORR onset potential at about 0.8 V versus RHE, and the peak current was reached at about 0.73 V versus RHE (Figure 2a). Measurements with an RDE were carried out to reveal the ORR kinetics of the Co1 xS/RGO hybrid in 0.5m H2SO4 (Figure 2b). At 1600 rpm, the Co1 xS/RGO hybrid catalyst showed a current density of about 1.1 mAcm 2 at 0.7 V versus [*] H. Wang, Y. Liang, Y. Li, Prof. H. Dai Department of Chemistry, Stanford University, Keck Building 380 Roth Way, Stanford, CA 94305 (USA) E-mail: hdai@stanford.edu

Electrical control of the ferromagnetic phase transition in cobalt at room temperature

Abstract: Electrical control of magnetic properties is crucial for device applications in the field of spintronics. Although the magnetic coercivity or anisotropy has been successfully controlled electrically in metals as well as in semiconductors, the electrical control of Curie temperature has been realized only in semiconductors at low temperature. Here, we demonstrate the room-temperature electrical control of the ferromagnetic phase transition in cobalt, one of the most representative transition-metal ferromagnets. Solid-state field effect devices consisting of a ultrathin cobalt film covered by a dielectric layer and a gate electrode were fabricated. We prove that the Curie temperature of cobalt can be changed by up to 12 K by applying a gate electric field of about ±2 MV cm(-1). The two-dimensionality of the cobalt film may be relevant to our observations. The demonstrated electric field effect in the ferromagnetic metal at room temperature is a significant step towards realizing future low-power magnetic applications.

Facile approach to prepare nickel cobaltite nanowire materials for supercapacitors

Abstract: Excellent electrochemical performance results from the coexistence of nickel and cobalt ions, with mesoporous characteristics and nanocrystal structure. Nickel cobalt nanowire is prepared by hydrothermal and thermal decomposition processes. High capacitance of 722 F g(-1) can be obtained at 1 A g(-1) in 6 M KOH, with a capacitance retention ratio of ca. 79% at 20 A g(-1) .

Cobalt Imidazolate Framework as Precursor for Oxygen Reduction Reaction Electrocatalysts

Abstract: We demonstrate a new approach of preparing a non-platinum group metal (PGM) electrocatalyst for oxygen reduction reaction through rational design by using cobalt imidazolate framework—a subclass of metal-organic framework (MOF) material—as the precursor with potential to produce uniformly distributed catalytic center and high active-site density. MOFs represent a new type of materials, and have recently been under broad exploration of various important applications due to their amenability to rational design for different functionalities at molecular level. In particular, their high surface areas, well-defined porous structures, and building block variety not only distinguish them from the conventional materials in gas adsorption and separation, but also offer new promises in catalysis application. However, the application of porous MOFs for electrocatalysis in fuel cell has yet to be exploited. The oxygen reduction reaction (ORR) at the cathode of a proton exchange membrane fuel cell (PEMFC) represents a very important electrocatalytic reaction. At present, the catalyst materials of choice are platinum group metals (PGMs). The high costs and limited reserves of PGMs, however, created a major barrier for large-scale commercialization of PEMFCs. Intensive efforts have been dedicated to the search of low-cost alternatives. The discovery of ORR activity on cobalt phthalocyanine stimulated extensive investigations of using Co–N4 or Fe–N4 macromolecules as precursors for preparation of transition metal (TM) based, non-PGM catalysts. The ORR activity over a cobalt–polypyrrole composite was observed, of which a Co ligated by pyrrolic nitrogens was proposed as the catalytic site. Activation in an inert atmosphere of the similar TM– polymer composite through pyrolysis further improved the catalytic activity. More recently, significant enhancement in ORR activity was demonstrated in a carbon-supported iron-based catalysts, and it was suggested that micropores (width <20 ) have critical influence on the formation of the active site with an ionic Fe coordinated by four pyridinic nitrogens after high-temperature treatment. The onset potential for an Fe-based catalyst is found to be 0.1 V higher than that of a Co-based system although the latter is more stable under PEMFC operating condition. These previous studies proposed the nitrogen-ligated TM entities either as the precursors or the active centers for the catalytic ORR process. Another challenge for non-PGM ORR catalysts is their relatively low turn-over-frequency in comparison with Pt. To compensate low activity without using excessive amount of catalyst, thus causing thick electrode layer and poor mass transport, it is desirable to produce the highest possible catalytic-site density, that are evenly distributed and accessible to gas diffusion through a porous framework. Herein we report the first experimental demonstration of porous MOF as a new class of precursor for preparing ORR catalysts. Different from previous approaches, MOFs have the following advantages when used to prepare non-PGM electrocatalysts: MOFs have clearly-defined three-dimensional structures. The initial entities such as TM–N4 can be grafted into MOFs with the highest possible volumetric density through regularly arranged cell structure. The MOF surface area and pore size are tunable by the length of the linker. The organic linkers would be converted to carbon during thermal activation while maintaining the porous framework, leading to catalysts with high surface area and uniformly distributed active sites without the need of a second carbon support or pore forming agent. Furthermore, the TM–ligand composition can be rationally designed with wide selection of metal–linker combinations for systematical investigation on the relationship between precursor structure and catalyst activity. Our studies demonstrate the initial step to achieve such advantages. [a] Dr. S. Ma, Dr. G. A. Goenaga, Dr. D.-J. Liu Chemical Sciences & Engineering Division Argonne National Laboratory, Argonne, IL 60439 (USA) Fax: (+1) 630-252-4176 E-mail : djliu@anl.gov [b] A. V. Call Department of Materials Science and Engineering Northwestern University, Evanston, IL 60208 (USA) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201003080.

Hybrid structure of cobalt monoxide nanowire @ nickel hydroxidenitrate nanoflake aligned on nickel foam for high-rate supercapacitor

Abstract: A new hybrid nanostructure of porous cobalt monoxide nanowire @ ultrathin nickel hydroxidenitrate nanoflake is directly synthesized on a 3D nickel foam by a facile two-step hydrothermal route, which demonstrates a specific capacitance of ∼798.3 F g−1 at the current density of ∼1.67 A g−1 and good rate performance when used as electrode material for supercapacitors. The capacitance loss is less than 5% after 2000 charge–discharge cycles.

Synthesis of Magnetite/Graphene Oxide Composite and Application for Cobalt(II) Removal

Abstract: A magnetite/graphene oxide (M/GO) composite was synthesized via a chemical reaction with a magnetite particle size of 10–15 nm and was developed for the removal of heavy metal ions from aqueous solutions. The composite was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The sorption of Co(II) on the M/GO composite was carried out under various conditions, that is, contact time, sorbent content, pH, ionic strength, foreign ions, and temperature. The sorption isotherms of Co(II) on the M/GO composite could be described well by the Langmuir model. The thermodynamic parameters (ΔH0, ΔS0, and ΔG0) calculated from the temperature-dependent isotherms indicated that the sorption reaction of Co(II) on the M/GO composite was an endothermic and spontaneous process. M/GO can be separated and recovered by magnetic separation. Results show that the magnetic M/GO composite is a promising sorbent material for the preconcentration an...

Electrocatalytic water oxidation beginning with the cobalt polyoxometalate [Co4(H2O)2(PW9O34)2]10-: identification of heterogeneous CoOx as the dominant catalyst.

Abstract: The question of “what is the true catalyst?” when beginning with the cobalt polyoxometalate (POM) [Co4(H2O)2(PW9O34)2]10– in electrochemical water oxidation catalysis is examined in pH 8.0 sodium phosphate buffer at a glassy carbon electrode. Is [Co4(H2O)2(PW9O34)2]10– a true water oxidation catalyst (WOC), or just a precatalyst? Electrochemical, kinetic, UV–vis, SEM, EDX, and other data provide four main lines of compelling evidence that, under the conditions used herein, the dominant WOC is actually heterogeneous CoOx and not homogeneous [Co4(H2O)2(PW9O34)2]10–.

Molecular Cobalt Pentapyridine Catalysts for Generating Hydrogen from Water

Abstract: A set of robust molecular cobalt catalysts for the generation of hydrogen from water is reported. The cobalt complex supported by the parent pentadentate polypyridyl ligand PY5Me2 features high stability and activity and 100% Faradaic efficiency for the electrocatalytic production of hydrogen from neutral water, with a turnover number reaching 5.5 × 104 mol of H2 per mole of catalyst with no loss in activity over 60 h. Control experiments establish that simple Co(II) salts, the free PY5Me2 ligand, and an isostructural PY5Me2 complex containing redox-inactive Zn(II) are all ineffective for this reaction. Further experiments demonstrate that the overpotential for H2 evolution can be tuned by systematic substitutions on the ancillary PY5Me2 scaffold, presaging opportunities to further optimize this first-generation platform by molecular design.

Highly active cobalt phosphate and borate based oxygen evolving catalysts operating in neutral and natural waters

Abstract: A high surface area electrode is functionalized with cobalt-based oxygen evolving catalysts (Co-OEC = electrodeposited from pH 7 phosphate, Pi, pH 8.5 methylphosphonate, MePi, and pH 9.2 borate electrolyte, Bi). Co-OEC prepared from MePi and operated in Pi and Bi achieves a current density of 100 mA cm−2 for water oxidation at 442 and 363 mV overpotential, respectively. The catalyst retains activity in near-neutral pH buffered electrolyte in natural waters such as those from the Charles River (Cambridge, MA) and seawater (Woods Hole, MA). The efficacy and ease of operation of anodes functionalized with Co-OEC at appreciable current density together with its ability to operate in near neutral pH buffered natural water sources bodes well for the translation of this catalyst to a viable renewable energy storage technology.

Efficient Light-Driven Carbon-Free Cobalt-Based Molecular Catalyst for Water Oxidation

Abstract: The abundant-metal-based polyoxometalate complex [Co4(H2O)2(PW9O34)2]10− is a hydrolytically and oxidatively stable, homogeneous, and efficient molecular catalyst for the visible-light-driven catalytic oxidation of water. Using a sacrificial electron acceptor and photosensitizer, it exhibits a high (30%) photon-to-O2 yield and a large turnover number (>220, limited solely by depletion of the sacrificial electron acceptor) at pH 8. The photocatalytic performance of this catalyst is superior to that of the previously reported precious-metal-based polyoxometalate water oxidation catalyst [{Ru4O4(OH)2(H2O)4}(γ-SiW10O36)2]10−.

Cemented carbide phase diagrams: A review

Abstract: One of the main topics of the actual research in the field of cemented carbides concerns the development of new composites, with partial or total substitution of the traditional cobalt binder by other more economic and less toxic materials. Composites with partial substitution of cobalt by nickel and iron are currently entering in industrial production. However, the total cobalt replacement is envisaged and Ni–Fe or Ni–Fe–Cr alloys are being currently investigated for such a purpose. The actual knowledge on phase diagrams for WC and different binders will be extremely useful and opportune regarding the need to choose initial compositions leading to a desired final phase composition and to select adequate sintering cycle conditions. In the present review, the existent phase diagrams of W–C–M with M = (Co, Fe, Ni, Fe–Ni, Fe–Al, Co–Fe–Ni, Cr and Cr–Fe) are presented and discussed.

Sequential crystallization of sea urchin-like bimetallic (Ni, Co) carbonate hydroxide and its morphology conserved conversion to porous NiCo2O4 spinel for pseudocapacitors

Abstract: We report kinetic control over and mechanistic studies on the formation of sea urchin-like, bimetallic (Ni, Co) carbonate hydroxidevia a sequential crystallization process, which was facilely converted to porous NiCo2O4 spinel with a conserved morphology, an excellent candidate material for pseudocapacitors. The formation of bimetallic carbonate hydroxide was found to start with the nucleation of monometallic nickel carbonate hydroxide evolving into flower-like microspheres. This was followed by the nucleation and growth of the bimetallic carbonate hydroxide nanorods from and on the nanoplates in the flower-like microspheres by localized dissolution-recrystallization, leading finally to the sea urchin structure. After calcination, a morphology conserved NiCo2O4 spinel nanostructure was formed, which uniquely comprises hierarchical, interconnected pores with high specific surface areas suitable for fast electron and electrolyte transport. This, in tandem with the rich redox reactions of nickel cobaltite spinel and their at least two orders of magnitude higher electric conductivity than those of nickel oxides and cobalt oxides alone, renders the novel nanostructures ideal candidates for pseudocapacitors. Indeed, the porous NiCo2O4 nanostructure with a specific surface area of up to 198.9 m2 g−1 has exhibited higher specific capacitances (658 F g−1 at 1 A g−1) than the monometallic cobalt oxides (60 F/g at 1 A g−1) and nickel oxides (194 F g−1 at 1 A g−) with similar porous nanostructures. Significantly, even at a high current density of 10 A g−1, the pseudocapacitor made of NiCo2O4 porous materials retained high specific capacitances of 530 F g−1 with excellent cycling stability. In all, the simple, scalable syntheses and the excellent supercapacitor performance reported here portend large scale applications of these novel materials in energy storage.

Morphology-controllable synthesis of cobalt oxalates and their conversion to mesoporous Co3O4 nanostructures for application in supercapacitors.

Abstract: In this work, one-dimensional and layered parallel folding of cobalt oxalate nanostructures have been selectively prepared by a one-step, template-free, water-controlled precipitation approach by simply altering the solvents used at ambient temperature and pressure. Encouragingly, the feeding order of solutions played an extraordinary role in the synthesis of nanorods and nanowires. After calcination in air, the as-prepared cobalt oxalate nanostructures were converted to mesoporous Co(3)O(4) nanostructures while their original frame structures were well maintained. The phase composition, morphology, and structure of the as-obtained products were studied in detail. Electrochemical properties of the Co(3)O(4) electrodes were carried out using cyclic voltammetry (CV) and galvanostatic charge-discharge measurements by a three-electrode system. The electrochemical experiments revealed that the layered parallel folding structure of mesoporous Co(3)O(4) exhibited higher capacitance compared to that of the nanorods and nanowires. A maximum specific capacitance of 202.5 F g (-1) has been obtained in 2 M KOH aqueous electrolyte at a current density of 1 A g(-1) with a voltage window from 0 to 0.40 V. Furthermore, the specific capacitance decay after 1000 continuous charge-discharge cycles was negligible, revealing the excellent stability of the electrode. These characteristics indicate that the mesoporous Co(3)O(4) nanostructures are promising electrode materials for supercapacitors.

Effects of Driving Forces for Recombination and Regeneration on the Photovoltaic Performance of Dye-Sensitized Solar Cells using Cobalt Polypyridine Redox Couples

Abstract: Dye-sensitized solar cells (DSCs) with open-circuit potentials above 1 V were obtained by employing the triphenylamine based organic dye D35 in combination with cobalt phenanthroline redox couples. ...

Powerful amide synthesis from alcohols and amines under aerobic conditions catalyzed by gold or gold/iron, -nickel or -cobalt nanoparticles.

Abstract: Considering the importance of the development of powerful green catalysts and the omnipresence of amide bonds in natural and synthetic compounds, we report here on reactions between alcohols and amines for amide bond formation in which heterogeneous gold and gold/iron, -nickel, or -cobalt nanoparticles are used as catalysts and molecular oxygen is used as terminal oxidant. Two catalysts show excellent activity and selectivity, depending on the type of alcohols used. A wide variety of alcohols and amines, including aqueous ammonia and amino acids, can be used for the amide synthesis. Furthermore, the catalysts can be recovered and reused several times without loss of activity.

Catalytic Hydrolysis of Ammonia Borane via Cobalt Palladium Nanoparticles

Abstract: Monodisperse 8 nm CoPd nanoparticles (NPs) with controlled compositions were synthesized by the reduction of cobalt acetylacetonate and palladium bromide in the presence of oleylamine and trioctylphosphine. These NPs were active catalysts for hydrogen generation from the hydrolysis of ammonia borane (AB), and their activities were composition dependent. Among the 8 nm CoPd catalysts tested for the hydrolysis of AB, the Co35Pd65 NPs exhibited the highest catalytic activity and durability. Their hydrolysis completion time and activation energy were 5.5 min and 27.5 kJ mol–1, respectively, which were comparable to the best Pt-based catalyst reported. The catalytic performance of the CoPd/C could be further enhanced by a preannealing treatment at 300 °C under air for 15 h with the hydrolysis completion time reduced to 3.5 min. This high catalytic performance of Co35Pd65 NP catalyst makes it an exciting alternative in pursuit of practical implementation of AB as a hydrogen storage material for fuel cell applic...

Rapid water reduction to H2 catalyzed by a cobalt bis(iminopyridine) complex.

Abstract: A cobalt bis(iminopyridine) complex is a highly active electrocatalyst for water reduction, with an estimated apparent second order rate constant kapp ≤ 107 M–1s–1 over a range of buffer/salt concentrations. Scan rate dependence data are consistent with freely diffusing electroactive species over pH 4–9 at room temperature for each of two catalytic reduction events, one of which is believed to be ligand based. Faradaic H2 yields up to 87 ± 10% measured in constant potential electrolyses (−1.4 V vs SCE) confirm high reactivity and high fidelity in a catalyst supported by the noninnocent bis(iminopyridine) ligand. A mechanism involving initial reduction of Co2+ and subsequent protonation is proposed.