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.
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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.
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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.
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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.
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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
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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
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