The catalytic asymmetric synthesis of P-chiral phosphorus compounds is an important way to construct P-chiral ligands. Herein, we report a new strategy that adopts the pyridinyl moiety as the coordination group in the cobalt-catalysed asymmetric nucleophilic addition/alkylation of secondary phosphine oxides. A series of tertiary phosphine oxides were generated with up to 99% yield and 99.5% ee with wide functional group tolerances. Mechanistic studies reveal that (R)-secondary phosphine oxides preferentially interact with the cobalt catalysts to produce P-stereogenic compounds.
https://ift.tt/3GWZRH9
Water electrolysis that results in green hydrogen is the key process towards a circular economy. The availabilities of the sustainable electricity and oxygen evolution reaction (OER) electrocatalyst are the main bottlenecks of the process for large-scale green hydrogen production. A broad range of OER electrocatalysts has been explored to decrease the overpotential and boost the kinetics of this sluggish half-reaction. Co, Ni, and Fe-based catalysts have been considered to be potential candidates to replace noble metals due to their tunable 3d electron configuration and spin state, versatility in the terms of crystal and electronic structures as well as abundance in nature. This review provides some basic principles of water electrolysis, key aspects of OER, and significant criteria for the development of the catalysts. It provides also some insights on recent advances of Co, Ni, and Fe-based oxides and a brief perspective on green hydrogen production and the challenges of water electrolysis.
https://ift.tt/3cRqMGW
The [Co–Fe–Pb]O x water oxidation anode catalyst facilitates long-term O2 evolution reaction in acidic electrolytes at elevated temperatures. Through a cobalt-selective self-healing mechanism, this catalyst operates in the absence of dissolved Pb2+ and Fe3+ precursors deeming it a prospective anode material for low-cost water electrolyzer systems.
Abstract
The instability and expense of anodes for water electrolyzers with acidic electrolytes can be overcome through the implementation of a cobalt-iron-lead oxide electrocatalyst, [Co–Fe–Pb]O x , that is self-healing in the presence of dissolved metal precursors. However, the latter requirement is pernicious for the membrane and especially the cathode half-reaction since Pb2+ and Fe3+ precursors poison the state-of-the-art platinum H2 evolving catalyst. To address this, we demonstrate the invariably stable operation of [Co–Fe–Pb]O x in acidic solutions through a cobalt-selective self-healing mechanism without the addition of Pb2+ and Fe3+ and investigate the kinetics of the process. Soft X-ray absorption spectroscopy reveals that low concentrations of Co2+ in the solution stabilize the catalytically active Co(Fe) sites. The highly promising performance of this system is showcased by steady water electrooxidation at 80±1 °C and 10 mA cm−2, using a flat electrode, at an overpotential of 0.56±0.01 V on a one-week timescale.
https://ift.tt/3gB3dF9
Promoting the initially deficient but cost‐effective catalysts to high‐performing competitors is of significance in developing better catalysts. Spinel zinc cobalt oxide (ZnCo 2 O 4 ) is not considered as a superior catalyst for the electrochemical oxygen evolution reaction (OER), which is the bottleneck reaction in water‐electrolysis. Herein, taking advantage of density functional theory (DFT) calculations, we find that the existence of low‐spin (LS) state cobalt cations hinders the OER activity of spinel zinc cobalt oxide, as the t 2g 6 e g 0 configuration gives rise to purely localized electronic structure and exhibits poor binding affinity to the key reaction intermediate. Increasing the spin state of cobalt cations in spinel ZnCo 2 O 4 is found to propagate a spin channel to promote spin‐selected charge transport during OER and generate better active sites for intermediates adsorption. The experiments find increasing the calcination temperature a facile approach to engineer high‐spin (HS) state cobalt cations in ZnCo 2 O 4 , while not working for Co 3 O 4 . The activity of the best spin‐state‐engineered ZnCo 2 O 4 outperforms other typical Co‐based oxides. Our work pinpoints the critical influence of the spinel composition on the splitting energy of the metals and further on the feasibility of spin state engineering.
https://ift.tt/3fXBOx4
Journal of the American Chemical SocietyDOI: 10.1021/jacs.1c01525
Jieqiong Shan, Chao Ye, Shuangming Chen, Tulai Sun, Yan Jiao, Lingmei Liu, Chongzhi Zhu, Li Song, Yu Han, Mietek Jaroniec, Yihan Zhu, Yao Zheng, and Shi-Zhang Qiao
https://ift.tt/3tOgAoO
One stone, two birds: The twofold advantages of silver coupling with ordered mesoporous Co3O4 for OER are demonstrated. Metallic silver enhances the conductivity of the structure while Ag2O nanoclusters provide centers for Fe uptake from the KOH electrolyte and boost significantly the efficiency of the electrocatalyst.
Abstract
Herein, we show that the performance of mesostructured cobalt oxide electrocatalyst for oxygen evolution reaction (OER) can be significantly enhanced by coupling of silver species. Various analysis techniques including pair distribution function and Rietveld refinement, X‐ray absorption spectroscopy at synchrotron as well as advanced electron microscopy revealed that silver exists as metallic Ag particles and well‐dispersed Ag2O nanoclusters within the mesostructure. The benefits of this synergy are twofold for OER: highly conductive metallic Ag improves the charge transfer ability of the electrocatalysts while ultra‐small Ag2O clusters provide the centers that can uptake Fe impurities from KOH electrolyte and boost the catalytic efficiency of Co–Ag oxides. The current density of mesostructured Co3O4 at 1.7 VRHE is increased from 102 to 211 mA cm−2 with incorporation of silver spices. This work presents the dual role of silver moieties and demonstrates a simple method to increase the OER activity of Co3O4.
https://ift.tt/2Yw9Vlc
Unique ruthenium–cobalt oxide [(Ru–Co)O x ] hollow nanosheet arrays with an inter‐doped heterostructure are prepared on carbon cloth via a facile MOF template‐based strategy. The (Ru–Co)O x nanoarrays exhibit excellent catalytic activity for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), indicating an outstanding bifunctional electrocatalyst for alkaline overall water splitting.
Abstract
The development of transition‐metal‐oxides (TMOs)‐based bifunctional catalysts toward efficient overall water splitting through delicate control of composition and structure is a challenging task. Herein, the rational design and controllable fabrication of unique heterostructured inter‐doped ruthenium–cobalt oxide [(Ru–Co)O x ] hollow nanosheet arrays on carbon cloth is reported. Benefiting from the desirable compositional and structural advantages of more exposed active sites, optimized electronic structure, and interfacial synergy effect, the (Ru–Co)O x nanoarrays exhibited outstanding performance as a bifunctional catalyst. Particularly, the catalyst showed a remarkable hydrogen evolution reaction (HER) activity with an overpotential of 44.1 mV at 10 mA cm−2 and a small Tafel slope of 23.5 mV dec−1, as well as an excellent oxygen evolution reaction (OER) activity with an overpotential of 171.2 mV at 10 mA cm−2. As a result, a very low cell voltage of 1.488 V was needed at 10 mA cm−2 for alkaline overall water splitting.
https://ift.tt/3cvGW5Z
CoIII‐catalyzed site‐selective C8−H activation of quinoline N‐oxides is demonstrated, engaging allenes as dienylation partners under relatively mild reaction conditions. The combination of a carbonate leaving group on the allene and 30 mol % of a NaF additive was found to be crucial for the dienylation reaction with a broad range of quinoline N‐oxides and allenes, including late‐stage functionalizations. Mechanistic studies provide key insights into the reaction mechanism.
Abstract
An efficient Cp*CoIII‐catalyzed C8‐dienylation of quinoline‐N‐oxides was achieved by employing allenes bearing leaving groups at the α‐position as the dienylating agents. The reaction proceeds by CoIII‐catalyzed C−H activation of quinoline‐N‐oxides and regioselective migratory insertion of the allene followed by a β‐oxy elimination, leading to overall dienylation. Site‐selective C−H activation was achieved with excellent selectivity under mild reaction conditions, and 30 mol % of a NaF additive was found to be crucial for the efficient dienylation. The methodology features high stereoselectivity, mild reaction conditions, and good functional‐group tolerance. C8‐alkenylation of quinoline‐N‐oxides was achieved in the case of allenes devoid of leaving groups as coupling partners. Furthermore, gram‐scale preparation and preliminary mechanistic experiments were carried out to gain insights into the reaction mechanism.
https://ift.tt/2UYlMrs
Center of attention : Multifunctional platinum/lithium cobalt oxide (Pt/LiCoO2) heterostructures are prepared that allow the active center to be switched between Pt species for the hydrogen evolution reaction (HER) and LiCoO2 species for the oxygen evolution reaction (OER).
Abstract
Designing cost‐effective and efficient electrocatalysts plays a pivotal role in advancing the development of electrochemical water splitting for hydrogen generation. Herein, multifunctional active‐center‐transferable heterostructured electrocatalysts, platinum/lithium cobalt oxide (Pt/LiCoO2) composites with Pt nanoparticles (Pt NPs) anchored on LiCoO2 nanosheets, are designed towards highly efficient water splitting. In this electrocatalyst system, the active center can be alternatively switched between Pt species and LiCoO2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Specifically, Pt species are the active centers and LiCoO2 acts as the co‐catalyst for HER, whereas the active center transfers to LiCoO2 and Pt turns into the co‐catalyst for OER. The unique architecture of Pt/LiCoO2 heterostructure provides abundant interfaces with favorable electronic structure and coordination environment towards optimal adsorption behavior of reaction intermediates. The 30 % Pt/LiCoO2 heterostructured electrocatalyst delivers low overpotentials of 61 and 285 mV to achieve 10 mA cm−2 for HER and OER in alkaline medium, respectively.
https://ift.tt/3dG77sh
MgCo2O4, CoCr2O4, and Co2TiO4 were selected, where only Co3+ in the center of octahedron (Oh), Co2+ in the center of tetrahedron (Td), and Co2+ in the center of Oh can be active sites as model electrocatalysts for the oxygen evolution reaction. Co3+(Oh) sites are the best geometrical configuration; Co2+(Oh) sites exhibit better electrochemical activity than Co2+(Td).
Abstract
MgCo2O4, CoCr2O4, and Co2TiO4 were selected, where only Co3+ in the center of octahedron (Oh), Co2+ in the center of tetrahedron (Td), and Co2+ in the center of Oh, can be active sites for the oxygen evolution reaction (OER). Co3+(Oh) sites are the best geometrical configuration for OER. Co2+(Oh) sites exhibit better activity than Co2+(Td). Calculations demonstrate the conversion of O* into OOH* is the rate‐determining step for Co3+(Oh) and Co2+(Td). For Co2+(Oh), it is thermodynamically favorable for the formation of OOH* but difficult for the desorption of O2. Co3+(Oh) needs to increase the lowest Gibbs free energy over Co2+(Oh) and Co2+(Td), which contributes to the best activity. The coexistence of Co3+(Oh) and Co2+(Td) in Co3O4 can promote the formation of OOH* and decrease the free‐energy barrier. This work screens out the optimal geometrical configuration of cobalt cations for OER and gives a valuable principle to design efficient electrocatalysts.
https://ift.tt/2Q4Pby1
J. Am. Chem. Soc., 2016, 138 (17), pp 5615–5622
DOI: 10.1021/jacs.6b00737
https://pubs.acs.org/doi/10.1021/jacs.6b00737
Sci-Hub does not have the final version.
Three weeks ago I had a user bring me a computer from a lab (like a science lab, it drove some laser gear). The computer had a failed disk. Very dead. Two weeks ago I returned the computer with a new disk and a fresh XP install (required for the old software). Some time last last week I disassembled the disk, as it is our standard policy to not throw them out for fear of leaking data. Also magnets. Magnets are cool.
This disk was one of those failures where the heads had collided with the platters and turned the surface (that holds the data) into a fine dust. It was definitely way dead.
Today I had another user come in asking for the disk back. She "has connections" that could recover from dead disks. No, I told her, the platter is physically destroyed. I showed her a platter with the same symptoms. No, her connections have ways of recovering from that.
I'd already disassembled the disk so I didn't know which broken platters were hers anyway. "But it was only a few days ago!". No, I have the ticket here, this was weeks ago.
I'm almost surprised she didn't just ask for our whole platter connection collection so her "connections" could find things from that. The things she was after was the lab software. They apparently don't have a backup copy of it anywhere...
edit: whopps typos
The instability and expense of anodes for water electrolyzers with acidic electrolytes can be overcome through the implementation of the cobalt‐iron‐lead oxide electrocatalyst, [Co‐Fe‐Pb]Ox, that is self‐healing in the presence of dissolved metal precursors. However, the latter requirement is pernicious for the membrane and especially the cathode half‐reaction since Pb2+ and Fe3+ precursors poison the state‐of‐the‐art platinum H2 evolving catalyst. To address this, we demonstrate the invariably stable operation of [Co‐Fe‐Pb]Ox in acidic solutions through a cobalt‐selective self‐healing mechanism without the addition of Pb2+ and Fe3+ and investigate the kinetics of the process. Soft X‐ray absorption spectroscopy reveals that low concentrations of Co2+ in the solution stabilize the catalytically active Co(Fe) sites. The highly promising performance of this system is showcased by steady water electrooxidation at 80 °C and 10 mA cm−2, using a flat electrode, at an overpotential of 0.56 ± 0.01 V on a one‐week timescale.
https://ift.tt/3gB3dF9
One stone, two birds : The twofold advantages of silver coupling with ordered mesoporous Co3O4 for OER are demonstrated. Metallic silver enhances the conductivity of the structure while Ag2O nanoclusters provide centers for Fe uptake from the KOH electrolyte and boost significantly the efficiency of the electrocatalyst.
Abstract
Herein, we show that the performance of mesostructured cobalt oxide electrocatalyst for oxygen evolution reaction (OER) can be significantly enhanced by coupling of silver species. Various analysis techniques including pair distribution function and Rietveld refinement, X‐ray absorption spectroscopy at synchrotron as well as advanced electron microscopy revealed that silver exists as metallic Ag particles and well‐dispersed Ag2O nanoclusters within the mesostructure. The benefits of this synergy are twofold for OER: highly conductive metallic Ag improves the charge transfer ability of the electrocatalysts while ultra‐small Ag2O clusters provide the centers that can uptake Fe impurities from KOH electrolyte and boost the catalytic efficiency of Co–Ag oxides. The current density of mesostructured Co3O4 at 1.7 VRHE is increased from 102 to 211 mA cm−2 with incorporation of silver spices. This work presents the dual role of silver moieties and demonstrates a simple method to increase the OER activity of Co3O4.
https://ift.tt/2Yw9Vlc
Herein, we show that performance of mesostructured cobalt oxide electrocatalyst for oxygen evolution reaction (OER) can be significantly enhanced with coupling of silver species. Various analysis techniques including pair distribution function and Rietveld, X‐ray absorption spectroscopy at synchrotron as well as advanced electron microscopy revealed that silver exists as metallic Ag particles and well‐dispersed Ag2O nanoclusters within mesostructure. The benefits of this synergy are twofold for OER: highly conductive metallic Ag improves the charge transfer ability of the electrocatalyst while ultra‐small Ag2O clusters provide the centers that can uptake Fe impurities from KOH electrolyte and boost the catalytic efficiency of Co‐Ag oxides. The current density of mesostructured Co3O4 at 1.7 VRHE is increased from 102 to 211 mA/cm2 with incorporation of silver spices. This work presents the dual role of silver moieties and demonstrates a simple method to increase the OER activity of Co3O4.
https://ift.tt/2Yw9Vlc
An efficient Cp*Co(III)‐catalyzed C‐8 dienylation of quinoline‐ N ‐oxides was achieved employing allenes bearing leaving groups at the α ‐position as the dienylating agents. The reaction proceeds via a Co(III)‐catalyzed C‐H activation of quinoline‐ N ‐oxides, regioselective migratory insertion of allene followed by β ‐oxy elimination leading to overall dienylation. Site‐selective C‐H activation was achieved with excellent selectivity under mild conditions and inquisitively 30 mol% of NaF additive was found to be crucial for the efficient dienylation. The methodology features high stereoselectivity, mild conditions, and good functional group tolerance. C‐8 Alkenylation of quinoline‐ N ‐oxides was achieved in case of allenes devoid of leaving groups as coupling partners. Furthermore, gram‐scale preparation and preliminary mechanism experiments were carried out to gain insights on the reaction mechanism.
https://ift.tt/2UYlMrs
Designing cost‐effective and efficient electrocatalysts plays a pivotal role in advancing the development of electrochemical water splitting for hydrogen generation. Herein, multifunctional active‐center‐transferable heterostructured electrocatalysts, platinum/lithium cobalt oxide (Pt/LiCoO2) composites with Pt nanoparticles (Pt NPs) anchored on LiCoO2 nanosheets, are designed towards highly efficient water splitting. In this electrocatalyst system, the active center can be alternatively switched between Pt species and LiCoO2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Specifically, Pt species are the active centers and LiCoO2 acts as the co‐catalyst for HER, whereas the active center transfers to LiCoO2 and Pt turns into the co‐catalyst for OER. The unique architecture of Pt/LiCoO2 heterostructure provides abundant interfaces with favorable electronic structure and coordination environment towards optimal adsorption behavior of reaction intermediates. The 30% Pt/LiCoO2 heterostructured electrocatalyst delivers low overpotentials of 61 and 285 mV to achieve 10 mA cm‐2 for HER and OER in alkaline medium, respectively. This study will diversify the design strategies for the development of efficient electrocatalysts via interface engineering towards water splitting and beyond.
https://ift.tt/3dG77sh
MgCo2O4, CoCr2O4, and Co2TiO4 were selected, where only Co3+ in the center of octahedron (Oh), Co2+ in the center of tetrahedron (Td), and Co2+ in the center of Oh can be active sites as model electrocatalysts for the oxygen evolution reaction. Co3+(Oh) sites are the best geometrical configuration; Co2+(Oh) sites exhibit better electrochemical activity than Co2+(Td).
Abstract
MgCo2O4, CoCr2O4, and Co2TiO4 were selected, where only Co3+ in the center of octahedron (Oh), Co2+ in the center of tetrahedron (Td), and Co2+ in the center of Oh, can be active sites for the oxygen evolution reaction (OER). Co3+(Oh) sites are the best geometrical configuration for OER. Co2+(Oh) sites exhibit better activity than Co2+(Td). Calculations demonstrate the conversion of O* into OOH* is the rate‐determining step for Co3+(Oh) and Co2+(Td). For Co2+(Oh), it is thermodynamically favorable for the formation of OOH* but difficult for the desorption of O2. Co3+(Oh) needs to increase the lowest Gibbs free energy over Co2+(Oh) and Co2+(Td), which contributes to the best activity. The coexistence of Co3+(Oh) and Co2+(Td) in Co3O4 can promote the formation of OOH* and decrease the free‐energy barrier. This work screens out the optimal geometrical configuration of cobalt cations for OER and gives a valuable principle to design efficient electrocatalysts.
https://ift.tt/2Q4Pby1
