Showing papers on "Cobalt published in 2016"
TL;DR: Current progress in this field is summarized here, especially highlighting several important bifunctional catalysts, and various approaches to improve or optimize the electrocatalysts are introduced.
Abstract: Water electrolysis is considered as the most promising technology for hydrogen production. Much research has been devoted to developing efficient electrocatalysts for hydrogen production via the hydrogen evolution reaction (HER) and oxygen production via the oxygen evolution reaction (OER). The optimum electrocatalysts can drive down the energy costs needed for water splitting via lowering the overpotential. A number of cobalt (Co)-based materials have been developed over past years as non-noble-metal heterogeneous electrocatalysts for HER and OER. Recent progress in this field is summarized here, especially highlighting several important bifunctional catalysts. Various approaches to improve or optimize the electrocatalysts are introduced. Finally, the current existing challenges and the future working directions for enhancing the performance of Co-implicated electrocatalysts are proposed.
1,963 citations
TL;DR: Durability tests revealed that the Co single atoms exhibit outstanding chemical stability during electrocatalysis and thermal stability that resists sintering at 900 °C, which could facilitate new discoveries at the atomic scale in condensed materials.
Abstract: A new strategy for achieving stable Co single atoms (SAs) on nitrogen-doped porous carbon with high metal loading over 4 wt % is reported. The strategy is based on a pyrolysis process of predesigned bimetallic Zn/Co metal–organic frameworks, during which Co can be reduced by carbonization of the organic linker and Zn is selectively evaporated away at high temperatures above 800 °C. The spherical aberration correction electron microscopy and extended X-ray absorption fine structure measurements both confirm the atomic dispersion of Co atoms stabilized by as-generated N-doped porous carbon. Surprisingly, the obtained Co-Nx single sites exhibit superior ORR performance with a half-wave potential (0.881 V) that is more positive than commercial Pt/C (0.811 V) and most reported non-precious metal catalysts. Durability tests revealed that the Co single atoms exhibit outstanding chemical stability during electrocatalysis and thermal stability that resists sintering at 900 °C. Our findings open up a new routine for general and practical synthesis of a variety of materials bearing single atoms, which could facilitate new discoveries at the atomic scale in condensed materials.
1,779 citations
TL;DR: A room-temperature synthesis to produce gelled oxyhydroxides materials with an atomically homogeneous metal distribution that exhibit the lowest overpotential reported at 10 milliamperes per square centimeter in alkaline electrolyte and shows no evidence of degradation after more than 500 hours of operation.
Abstract: Earth-abundant first-row (3d) transition metal-based catalysts have been developed for the oxygen-evolution reaction (OER); however, they operate at overpotentials substantially above thermodynamic requirements. Density functional theory suggested that non-3d high-valency metals such as tungsten can modulate 3d metal oxides, providing near-optimal adsorption energies for OER intermediates. We developed a room-temperature synthesis to produce gelled oxyhydroxides materials with an atomically homogeneous metal distribution. These gelled FeCoW oxyhydroxides exhibit the lowest overpotential (191 millivolts) reported at 10 milliamperes per square centimeter in alkaline electrolyte. The catalyst shows no evidence of degradation after more than 500 hours of operation. X-ray absorption and computational studies reveal a synergistic interplay between tungsten, iron, and cobalt in producing a favorable local coordination environment and electronic structure that enhance the energetics for OER.
1,777 citations
TL;DR: In this paper, the state-of-the-art progress on various heterogeneous cobalt-based catalysts for sulfate radical-based advanced oxidation processes (SR-AOPs) is reviewed.
Abstract: Recently sulfate radical-based advanced oxidation processes (SR-AOPs) attract increasing attention due to their capability and adaptability in decontamination. The couple of cobalt and peroxymonosulfate (PMS) is an efficient way to produce reactive sulfate radicals. This article reviews the state-of-the-art progress on various heterogeneous cobalt-based catalysts for PMS activation, including cobalt oxides, cobalt-ferrite and supported cobalt by diverse substrates. We summarize the intrinsic properties of these catalysts and their fundamental behaviors in PMS activation, as well as synthetic approaches. In addition, influencing factors and synergistic techniques of Co/PMS systems in organic degradation and possible environmental applications are also discussed. Finally, we propose perspectives on challenges related to cobalt-based catalysts, heterogeneous Co/PMS systems and their potential applications in practical environmental cleanup.
1,553 citations
TL;DR: In this paper, the role of the two different catalytic sites of pure cobalt and coexisting domains of cobalt metal and cobalt oxide has been evaluated, showing that surface cobalt atoms of the atomically thin layers have higher intrinsic activity and selectivity towards formate production, at lower overpotentials.
Abstract: Electroreduction of CO2 into useful fuels, especially if driven by renewable energy, represents a potentially 'clean' strategy for replacing fossil feedstocks and dealing with increasing CO2 emissions and their adverse effects on climate. The critical bottleneck lies in activating CO2 into the CO2(•-) radical anion or other intermediates that can be converted further, as the activation usually requires impractically high overpotentials. Recently, electrocatalysts based on oxide-derived metal nanostructures have been shown to enable CO2 reduction at low overpotentials. However, it remains unclear how the electrocatalytic activity of these metals is influenced by their native oxides, mainly because microstructural features such as interfaces and defects influence CO2 reduction activity yet are difficult to control. To evaluate the role of the two different catalytic sites, here we fabricate two kinds of four-atom-thick layers: pure cobalt metal, and co-existing domains of cobalt metal and cobalt oxide. Cobalt mainly produces formate (HCOO(-)) during CO2 electroreduction; we find that surface cobalt atoms of the atomically thin layers have higher intrinsic activity and selectivity towards formate production, at lower overpotentials, than do surface cobalt atoms on bulk samples. Partial oxidation of the atomic layers further increases their intrinsic activity, allowing us to realize stable current densities of about 10 milliamperes per square centimetre over 40 hours, with approximately 90 per cent formate selectivity at an overpotential of only 0.24 volts, which outperforms previously reported metal or metal oxide electrodes evaluated under comparable conditions. The correct morphology and oxidation state can thus transform a material from one considered nearly non-catalytic for the CO2 electroreduction reaction into an active catalyst. These findings point to new opportunities for manipulating and improving the CO2 electroreduction properties of metal systems, especially once the influence of both the atomic-scale structure and the presence of oxide are mechanistically better understood.
1,407 citations
TL;DR: In this article, it is demonstrated that amorphous cobalt boride (Co2B) prepared by the chemical reduction of CoCl2 using NaBH4 is an exceptionally efficient electrocatalyst for the oxygen evolution reaction (OER) in alkaline electrolytes and is simultaneously active for catalyzing the hydrogen evolution reaction.
Abstract: It is demonstrated that amorphous cobalt boride (Co2B) prepared by the chemical reduction of CoCl2 using NaBH4 is an exceptionally efficient electrocatalyst for the oxygen evolution reaction (OER) in alkaline electrolytes and is simultaneously active for catalyzing the hydrogen evolution reaction (HER). The catalyst achieves a current density of 10 mA cm−2 at 1.61 V on an inert support and at 1.59 V when impregnated with nitrogen-doped graphene. Stable performance is maintained at 10 mA cm−2 for at least 60 h. The optimized catalyst, Co2B annealed at 500 °C (Co2B-500) evolves oxygen more efficiently than RuO2 and IrO2, and its performance matches the best cobalt-based catalysts reported to date. Co2B is irreversibly oxidized at OER conditions to form a CoOOH surface layer. The active form of the catalyst is therefore represented as CoOOH/Co2B. EXAFS observations indicate that boron induces lattice strain in the crystal structure of the metal, which potentially diminishes the thermodynamic and kinetic barrier of the hydroxylation reaction, formation of the OOH* intermediate, a key limiting step in the OER.
677 citations
TL;DR: The plasma treatment significantly enhances the OER activity, as evidenced by a low overpotential to reach a current density of 10 mA cm(-2) , a small Tafel slope, and long-term durability in an alkaline electrolyte.
Abstract: Electrochemical splitting of water to produce hydrogen and oxygen is an important process for many energy storage and conversion devices. Developing efficient, durable, low-cost, and earth-abundant electrocatalysts for the oxygen evolution reaction (OER) is of great urgency. To achieve the rapid synthesis of transition-metal nitride nanostructures and improve their electrocatalytic performance, a new strategy has been developed to convert cobalt oxide precursors into cobalt nitride nanowires through N2 radio frequency plasma treatment. This method requires significantly shorter reaction times (about 1 min) at room temperature compared to conventional high-temperature NH3 annealing which requires a few hours. The plasma treatment significantly enhances the OER activity, as evidenced by a low overpotential of 290 mV to reach a current density of 10 mA cm−2, a small Tafel slope, and long-term durability in an alkaline electrolyte.
648 citations
TL;DR: Carbon paper/carbon tubes/cobalt-sulfide is introduced as an integrated three-dimensional array electrode for cost-effective and energy-efficient HER and OER in alkaline medium and displays superior performance compared to non-noble metal catalysts reported previously.
Abstract: The development of an efficient catalytic electrode toward both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is of great significance for overall water splitting associated with the conversion and storage of clean and renewable energy. In this study, carbon paper/carbon tubes/cobalt-sulfide is introduced as an integrated three-dimensional (3D) array electrode for cost-effective and energy-efficient HER and OER in alkaline medium. Impressively, this electrode displays superior performance compared to non-noble metal catalysts reported previously, benefiting from the unique 3D array architecture with increased exposure and accessibility of active sites, improved vectorial electron transport capability, and enhanced release of gaseous products. Such an integrated and versatile electrode makes the overall water splitting proceed in a more direct and smooth manner, reducing the production cost of practical technological devices.
516 citations
TL;DR: Tuning of the atomic structure of one-dimensional single-crystal cobalt (II) oxide (CoO) nanorods by creating oxygen vacancies on pyramidal nanofacets shows that the surface atomic structure engineering is important for the fabrication of efficient and durable electrocatalysts.
Abstract: Engineering the surface structure at the atomic level can be used to precisely and effectively manipulate the reactivity and durability of catalysts. Here we report tuning of the atomic structure of one-dimensional single-crystal cobalt (II) oxide (CoO) nanorods by creating oxygen vacancies on pyramidal nanofacets. These CoO nanorods exhibit superior catalytic activity and durability towards oxygen reduction/evolution reactions. The combined experimental studies, microscopic and spectroscopic characterization, and density functional theory calculations reveal that the origins of the electrochemical activity of single-crystal CoO nanorods are in the oxygen vacancies that can be readily created on the oxygen-terminated {111} nanofacets, which favourably affect the electronic structure of CoO, assuring a rapid charge transfer and optimal adsorption energies for intermediates of oxygen reduction/evolution reactions. These results show that the surface atomic structure engineering is important for the fabrication of efficient and durable electrocatalysts.
516 citations
TL;DR: Nickel and cobalt incorporated MoS2 nanoboxes are synthesized via the reaction between Ni-Co Prussian blue analogue nanocubes and ammonium thiomolybdate to manifest enhanced electrochemical activity as an electrocatalyst for hydrogen evolution reaction.
Abstract: Nickel and cobalt incorporated MoS2 nanoboxes are synthesized via the reaction between Ni-Co Prussian blue analogue nanocubes and ammonium thiomolybdate. Due to the structural and compositional advantages, these well-defined nanoboxes manifest enhanced electrochemical activity as an electrocatalyst for hydrogen evolution reaction.
500 citations
TL;DR: These CoMnP nanoparticles are capable of catalyzing water oxidation at an overpotential of 0.33 V with a 96% Faradaic efficiency when deposited as an ink with carbon black and Nafion and a slight decrease in activity is observed after 500 cycles.
Abstract: The development of efficient water oxidation catalysts based on inexpensive and Earth-abundant materials is a prerequisite to enabling water splitting as a feasible source of alternative energy. In this work, we report the synthesis of ternary cobalt manganese phosphide nanoparticles from the solution-phase reaction of manganese and cobalt carbonyl complexes with trioctylphosphine. The CoMnP nanoparticles (ca. 5 nm in diameter) are nearly monodisperse and homogeneous in nature. These CoMnP nanoparticles are capable of catalyzing water oxidation at an overpotential of 0.33 V with a 96% Faradaic efficiency when deposited as an ink with carbon black and Nafion. A slight decrease in activity is observed after 500 cycles, which is ascribed to the etching of P into solution, as well as the oxidation of the surface of the nanoparticles. Manganese-based ternary phosphides represent a promising new system to explore for water oxidation catalysis.
TL;DR: A structure design and sequential synthesis of a highly active and stable hydrogen evolution electrocatalyst material based on pyrite-structured cobalt phosphosulfide nanoparticles grown on carbon nanotubes is reported.
Abstract: Rational design and controlled synthesis of hybrid structures comprising multiple components with distinctive functionalities are an intriguing and challenging approach to materials development for important energy applications like electrocatalytic hydrogen production, where there is a great need for cost effective, active and durable catalyst materials to replace the precious platinum. Here we report a structure design and sequential synthesis of a highly active and stable hydrogen evolution electrocatalyst material based on pyrite-structured cobalt phosphosulfide nanoparticles grown on carbon nanotubes. The three synthetic steps in turn render electrical conductivity, catalytic activity and stability to the material. The hybrid material exhibits superior activity for hydrogen evolution, achieving current densities of 10 mA cm(-2) and 100 mA cm(-2) at overpotentials of 48 mV and 109 mV, respectively. Phosphorus substitution is crucial for the chemical stability and catalytic durability of the material, the molecular origins of which are uncovered by X-ray absorption spectroscopy and computational simulation.
TL;DR: Electrochemical active surface area (EASA) evaluation and density functional theory (DFT) calculations revealed that the synergetic effect between the encapsulated cobalt nanoparticle and the N, B codoped carbon shell played the fundamental role in the superior HER catalytic performance.
Abstract: Low efficiency and poor stability are two major challenges we encounter in the exploration of non-noble metal electrocatalysts for the hydrogen evolution reaction (HER) in both acidic and alkaline environment. Herein, the hybrid of cobalt encapsulated by N, B codoped ultrathin carbon cages (Co@BCN) is first introduced as a highly active and durable nonprecious metal electrocatalysts for HER, which is constructed by a bottom-up approach using metal organic frameworks (MOFs) as precursor and self-sacrificing template. The optimized catalyst exhibited remarkable electrocatalytic performance for hydrogen production from both both acidic and alkaline media. Stability investigation reveals the overcoating of carbon cages can effectively avoid the corrosion and oxidation of the catalyst under extreme acidic and alkaline environment. Electrochemical active surface area (EASA) evaluation and density functional theory (DFT) calculations revealed that the synergetic effect between the encapsulated cobalt nanoparticl...
TL;DR: Various kinds of nanostructured materials including nanowires, nanosheets, hollow structures, porous structures, and oxide/carbon nanocomposites are discussed in terms of their LIB anode applications.
Abstract: Developing high-energy-density electrodes for lithium ion batteries (LIBs) is of primary importance to meet the challenges in electronics and automobile industries in the near future. Conversion reaction-based transition metal oxides are attractive candidates for LIB anodes because of their high theoretical capacities. This review summarizes recent advances on the development of nanostructured transition metal oxides for use in lithium ion battery anodes based on conversion reactions. The oxide materials covered in this review include oxides of iron, manganese, cobalt, copper, nickel, molybdenum, zinc, ruthenium, chromium, and tungsten, and mixed metal oxides. Various kinds of nanostructured materials including nanowires, nanosheets, hollow structures, porous structures, and oxide/carbon nanocomposites are discussed in terms of their LIB anode applications.
TL;DR: This study provides a theoretical basis for industrial-scale recycling resources from spent LIBs by using oxygen-free roasting and wet magnetic separation to in situ recycle of cobalt, Lithium Carbonate and Graphite from mixed electrode materials.
TL;DR: This work demonstrates a feasible method to achieve nanoporous carbon materials with tailored properties, including specific surface area, pore size distribution, degree of graphitization, and content of heteroatoms, and highlights the importance of precisely controlling the properties of the carbon materials.
Abstract: Single metal-organic frameworks (MOFs), constructed from the coordination between one-fold metal ions and organic linkers, show limited functionalities when used as precursors for nanoporous carbon materials. Herein, we propose to merge the advantages of zinc and cobalt metals ions into one single MOF crystal (i.e., bimetallic MOFs). The organic linkers that coordinate with cobalt ions tend to yield graphitic carbons after carbonization, unlike those bridging with zinc ions, due to the controlled catalytic graphitization by the cobalt nanoparticles. In this work, we demonstrate a feasible method to achieve nanoporous carbon materials with tailored properties, including specific surface area, pore size distribution, degree of graphitization, and content of heteroatoms. The bimetallic-MOF-derived nanoporous carbon are systematically characterized, highlighting the importance of precisely controlling the properties of the carbon materials. This can be done by finely tuning the components in the bimetallic MOF precursors, and thus designing optimal carbon materials for specific applications.
TL;DR: In this paper, a nitrogen-enriched graphene shell was used to encapsulate metallic cobalt nanoparticles by a nitrogen−enriched carbon dioxide (NO 2 ) shell, which makes an excellent bifunctional electrocatalyst and zinc-air battery cathode material.
Abstract: Encapsulating metallic cobalt nanoparticles by a nitrogen‐enriched graphene shell makes an excellent bifunctional electrocatalyst and zinc–air battery cathode material.
TL;DR: A review of cobalt complex-catalyzed hydrosilylation of alkenes and alkynes from the early studies in the 1960s until now, with the objective of providing readers with the status of the field and the underlying late 3D metal chemistry that is meaningful for new nonprecious metal catalyst design is provided in this paper.
Abstract: The demand for economical and environmentally benign catalysts for important chemical transformations has recently initiated great efforts on nonprecious metal-catalyzed hydrosilylation reactions. The special chemical properties of cobalt enable the development of diverse cobalt complex-based catalysts for hydrosilylation reactions. This paper reviews the significant advances of cobalt complex-catalyzed hydrosilylation of alkenes and alkynes from the early studies in the 1960s until now, with the objective of providing readers with the status of the field and the underlying late 3d metal chemistry that is meaningful for new nonprecious metal catalyst design. Progress, problems, and perspectives in this vibrant field are discussed.
TL;DR: The cobalt-based layered MOF electrode exhibits a high specific capacitance and excellent cycling stability, and may be ascribed to the intrinsic nature of Co-LMOF, enough space available for the storage and diffusion of the electrolyte, and the particles of nanoscale size.
Abstract: Metal–organic frameworks (MOFs) have recently received increasing interest due to their potential application in the energy storage and conversion field. Herein, cobalt-based layered MOF ({[Co(Hmt)(tfbdc)(H2O)2]·(H2O)2}n, Co–LMOF; Hmt = hexamethylenetetramine; H2tfbdc = 2,3,5,6-tetrafluoroterephthalic acid) has been evaluated as an electrode material for supercapacitors. The Co–LMOF electrode exhibits a high specific capacitance and excellent cycling stability. Its maximum specific capacitance is 2474 F g–1 at a current density of 1 A g–1, and the specific capacitance retention is about 94.3% after 2000 cycles. The excellent electrochemical property may be ascribed to the intrinsic nature of Co–LMOF, enough space available for the storage and diffusion of the electrolyte, and the particles of nanoscale size.
TL;DR: A novel bi-functional electrocatalyst towards the ORR and OER: Co nanoparticle-embedded N-doped carbon nanotube (CNT)/porous carbon (PC) by pyrolyzing metal organic framework (MOF) encapsulated Co3O4 by pyrotechnics exhibited highly efficient electrocatalytic activity.
TL;DR: A facile method is demonstrated to engineer the eg filling of perovskite cobaltite LaCoO3 for improving the oxygen evolution reaction activity, comparable to those of recently reported cobalt oxides with eg∼1.2 configurations.
Abstract: The activity of electrocatalysts exhibits a strongly dependence on their electronic structures. Specifically, for perovskite oxides, Shao-Horn and co-workers have reported a correlation between the oxygen evolution reaction activity and the eg orbital occupation of transition-metal ions, which provides guidelines for the design of highly active catalysts. Here we demonstrate a facile method to engineer the eg filling of perovskite cobaltite LaCoO3 for improving the oxygen evolution reaction activity. By reducing the particle size to ∼80 nm, the eg filling of cobalt ions is successfully increased from unity to near the optimal configuration of 1.2 expected by Shao-Horn’s principle. Consequently, the activity is significantly enhanced, comparable to those of recently reported cobalt oxides with eg∼1.2 configurations. This enhancement is ascribed to the emergence of spin-state transition from low-spin to high-spin states for cobalt ions at the surface of the nanoparticles, leading to more active sites with increased reactivity. The activity of electrocatalysts exhibits a strong dependence on their electronic structures. Here, the authors manipulate the eg filling of perovskite cobaltite LaCoO3nanoparticles by changing particle size and show improved oxygen evolution activity with increased numbers of surface high-spin cobalt ions.
TL;DR: In this paper, the authors report a purposely designed route for the synthesis of a promising carbon-based electrocatalyst for both ORR (oxygen reduction reaction) and OER (oxoxygen evolution reaction) from zeolitic imidazolate frameworks (ZIFs).
Abstract: We report a purposely designed route for the synthesis of a promising carbon-based electrocatalyst for both ORR (oxygen reduction reaction) and OER (oxygen evolution reaction) from zeolitic imidazolate frameworks (ZIFs). Firstly, precursor ZIFs are rationally designed with a blend of volatile zinc to induce porosity and stable cobalt to induce graphitic domains. Secondly, the self-modulated cobalt–nitrogen–carbon system (SCNCS) is shown to be an effective ORR catalyst after graphitization at mild temperatures. Finally, the best OER catalyst is developed by enhancing graphitization of the SCNCS. For the first time, solely by switching the graphitization conditions of SCNCS, excellent ORR or OER performance is realized. This approach not only opens up a simple protocol for simultaneous optimization of nitrogen doping and graphitization at controlled cobalt concentrations, but also provide a facile method of developing such active catalysts without the use of extensive synthesis procedures.
TL;DR: In this paper, a series of cobalt phosphide-based electrocatalysts were synthesized successfully via a facile thermal decomposition approach to further explore the influence of phase structure and support effect on the catalytic activity for HER.
Abstract: Cobalt phosphides have been used as promising electrocatalysts for catalyzing the hydrogen evolution reaction (HER) in acidic aqueous solutions. In order to further explore the influence of phase structure and support effect on the catalytic activity for HER, herein, a series of cobalt phosphide-based electrocatalysts, including Co2P, CoP, Co2P/CNTs, CoP/CNTs, Co2P/NCNTs and CoP/NCNTs, were synthesized successfully via a facile thermal decomposition approach. The crystalline phase can be controlled by changing the phosphide source species. When the phosphide source was trioctylphosphine, CoP-based catalysts were obtained. However, Co2P-based catalysts can be obtained by using triphenylphosphine as the phosphide source. Then the phase catalytic activity and stability of the as-synthesized cobalt phosphide-based catalysts for hydrogen evolution were compared. The results show that the catalytic activity followed the order CoP/NCNTs > Co2P/NCNTs > CoP/CNTs > Co2P/CNTs > CoP > Co2P, which can be attributed to the different atomic ratios of Co to P, the strong interaction between cobalt phosphide and carbon species and the doping of N atoms into CNTs. Our studies indicate that the HER catalytic efficiency of transition metal phosphide catalysts can be improved significantly by adjusting active phase and carbon species structures.
TL;DR: When Ru(bpy)3(2+) was replaced by the organic dye sensitizer purpurin, TONs of 790 and 1365 were achieved in N,N-dimethylformamide for the cobalt and iron catalysts, respectively.
Abstract: The design of highly efficient and selective photocatalytic systems for CO2 reduction that are based on nonexpensive materials is a great challenge for chemists. The photocatalytic reduction of CO2 by [Co(qpy)(OH2)2]2+ (1) (qpy = 2,2′:6′,2″:6″,2‴-quaterpyridine) and [Fe(qpy)(OH2)2]2+ (2) have been investigated. With Ru(bpy)32+ as the photosensitizer and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole as the sacrificial reductant in CH3CN/triethanolamine solution under visible-light excitation (blue light-emitting diode), a turnover number (TON) for CO as high as 2660 with 98% selectivity can be achieved for the cobalt catalyst. In the case of the iron catalyst, the TON was >3000 with up to 95% selectivity. More significantly, when Ru(bpy)32+ was replaced by the organic dye sensitizer purpurin, TONs of 790 and 1365 were achieved in N,N-dimethylformamide for the cobalt and iron catalysts, respectively.
TL;DR: Among the as-synthesized metal phosphides, nickel cobalt phosphides quasi-hollow nanocubes exhibit the best electrocatalytic activity for hydrogen evolution reaction in terms of lower overpotential and smaller Tafel slope in alkaline solution.
01 Sep 2016
TL;DR: In this paper, needle-shaped narrow hexagonal phase 1D nanostructures of dicobalt phosphide (Co2P) are reported as efficient electrocatalysts for the oxygen evolution reaction (OER).
Abstract: Needle-shaped narrow hexagonal phase 1D nanostructures of dicobalt phosphide (Co2P) are reported as efficient electrocatalysts for the oxygen evolution reaction (OER). Without other metal incorporation, which was typically followed for enhancing the OER activity, the electrochemical performance was observed to be superior in comparison to all reported cobalt-based nanostructured metal phosphides. For anodic metamorphosis, these nanostructures, like all other metal phosphides, undergo surface oxidation but remain more active and superior to pure cobalt oxides as well as surface-oxidized different shaped monocobalt phosphides. Moreover, the synthesis was also followed by adopting a moderate synthetic protocol where PH3 gas was used as a phosphorus source and also scaled up to the gram level. In addition, the hydrogen evolution reaction (HER) performance of these phosphides was further studied, and the performance was observed to be comparable to that in the best reports.
TL;DR: Peapod-like carbon-encapsulated cobalt chalcogenide nanowires are designed and synthesized by a facile method and show excellent electrochemical performance for sodium storage, suggesting that chalCogenides, especially selenides, have potential as advanced anodes for sodium-ion batteries.
Abstract: Peapod-like carbon-encapsulated cobalt chalcogenide nanowires are designed and synthesized by a facile method. The nanowires show excellent electrochemical performance for sodium storage, suggesting that chalcogenides, especially selenides, have potential as advanced anodes for sodium-ion batteries.
TL;DR: A novel cobalt-catalyzed stereodivergent transfer hydrogenation of alkynes to Z- and E-alkenes based on a rational catalyst design that allows for the synthesis of more than 50 alkenes with good chemo- and stereoselectivity.
Abstract: Herein, we report a novel cobalt-catalyzed stereodivergent transfer hydrogenation of alkynes to Z- and E-alkenes. Effective selectivity control is achieved based on a rational catalyst design. Moreover, this mild system allows for the transfer hydrogenation of alkynes bearing a wide range of functional groups in good yields using catalyst loadings as low as 0.2 mol %. The general applicability of this procedure is highlighted by the synthesis of more than 50 alkenes with good chemo- and stereoselectivity. A preliminary mechanistic study revealed that E-alkene product was generated via sequential alkyne hydrogenation to give Z-alkene intermediate, followed by a Z to E alkene isomerization process.
TL;DR: In this paper, the authors present a review of the most promising cobalt and nickel-based catalysts for the decomposition of ammonia but metal dispersion needs to be increased in order to become more attractive candidates.
Abstract: The wide-spread implementation of the so-called hydrogen economy is currently partially limited by an economically feasible way of storing hydrogen. In this context, ammonia has been commonly presented as a viable option for chemical storage due its high hydrogen content (17.6 wt%). However, its use as an energy carrier requires the development of catalytic systems capable of releasing hydrogen at adequate rates and conditions. At the moment, the most active catalytic systems for the decomposition of ammonia are based on ruthenium, however its cost and scarcity inhibit the wide scale use of these catalysts. This issue has triggered research on the development of alternative catalysts based on more sustainable systems using more readily available, non-noble metals mainly iron, cobalt and nickel as well as a series of transition metal carbides and nitrides and bimetallic systems, which are reviewed herein. There have been some promising cobalt- and nickel-based catalysts reported for the decomposition of ammonia but metal dispersion needs to be increased in order to become more attractive candidates. Conversely, there seems to be less scope for improvement of iron-based catalysts and metal carbides and nitrides. The area with the most potential for improvement is with bimetallic catalysts, particularly those consisting of cobalt and molybdenum.