Synergistic Mn-Co catalyst outperforms Pt on high-rate oxygen reduction for alkaline polymer electrolyte fuel cells

Nature Communications, Journal Year: 2019, Volume and Issue: 10(1)

Published: April 3, 2019

Alkaline polymer electrolyte fuel cells are a class of that enable the use non-precious metal catalysts, particularly for oxygen reduction reaction at cathode. While there have been alternative materials exhibiting Pt-comparable activity in alkaline solutions, to best our knowledge none outperformed Pt fuel-cell tests. Here we report Mn-Co spinel cathode can deliver greater power, high current densities, than The power density cell employing reaches 1.1 W cm-2 2.5 A 60 oC. Moreover, this catalyst outperforms low humidity. In-depth characterization reveals remarkable performance originates from synergistic effects where Mn sites bind O2 and Co activate H2O, so as facilitate proton-coupled electron transfer processes. Such an electrocatalytic synergy is pivotal high-rate reduction, under water depletion/low humidity conditions.

Language: Английский

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Catalytic Alkene Carboaminations Enabled by Oxidative Proton-Coupled Electron Transfer

Journal of the American Chemical Society, Journal Year: 2015, Volume and Issue: 137(29), P. 9226 - 9229

Published: July 13, 2015

Here we describe a dual catalyst system comprised of an iridium photocatalyst and weak phosphate base that is capable both selectively homolyzing the N–H bonds N-arylamides (bond dissociation free energies ∼ 100 kcal/mol) via concerted proton-coupled electron transfer (PCET) mediating efficient carboamination reactions resulting amidyl radicals. This manner PCET activation, which finds its basis in numerous biological redox processes, enables formal homolysis stronger amide bond presence weaker allylic C–H bonds, selectivity uncommon conventional molecular H atom acceptors. Moreover, this transformation affords access to broad range structurally complex heterocycles from simple starting materials. The design, synthetic scope, mechanistic evaluation process are described.

Language: Английский

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Antioxidant Activity/Capacity Measurement. 2. Hydrogen Atom Transfer (HAT)-Based, Mixed-Mode (Electron Transfer (ET)/HAT), and Lipid Peroxidation Assays

Journal of Agricultural and Food Chemistry, Journal Year: 2016, Volume and Issue: 64(5), P. 1028 - 1045

Published: Jan. 25, 2016

Measuring the antioxidant activity/capacity levels of food extracts and biological fluids is useful for determining nutritional value foodstuffs diagnosis, treatment, follow-up numerous oxidative stress-related diseases. Biologically, antioxidants play their health-beneficial roles via transferring a hydrogen (H) atom or an electron (e(-)) to reactive species, thereby deactivating them. Antioxidant activity assays imitate this action; that is, are measured by H transfer (HAT) e(-) (ET) probe molecules. can be monitored wide variety with different mechanisms, including HAT, ET, mixed-mode (ET/HAT) assays, generally without distinct boundaries between Understanding principal advantages, disadvantages measurement important proper selection method valid evaluation properties in desired applications. This work provides general up-to-date overview HAT-based, (ET/HAT), lipid peroxidation available measuring chemistry behind them, critical advantages drawbacks.

Language: Английский

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Catalytic Olefin Hydroamidation Enabled by Proton-Coupled Electron Transfer

Journal of the American Chemical Society, Journal Year: 2015, Volume and Issue: 137(42), P. 13492 - 13495

Published: Oct. 6, 2015

Here we report a ternary catalyst system for the intramolecular hydroamidation of unactivated olefins using simple N-aryl amide derivatives. Amide activation in these reactions occurs via concerted proton-coupled electron transfer (PCET) mediated by an excited state iridium complex and weak phosphate base to furnish reactive amidyl radical that readily adds pendant alkenes. A series H-atom, electron, proton events with thiophenol cocatalyst product regenerate active forms photocatalyst base. Mechanistic studies indicate substrate can be selectively homolyzed PCET presence thiophenol, despite large difference bond dissociation free energies between functional groups.

Language: Английский

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A Continuum of Proton-Coupled Electron Transfer Reactivity

Accounts of Chemical Research, Journal Year: 2018, Volume and Issue: 51(10), P. 2391 - 2399

Published: Sept. 20, 2018

ConspectusProton-coupled electron transfer (PCET) covers a wide range of reactions involving the transfer(s) electrons and protons. The best-known PCET reaction, hydrogen atom (HAT), has been studied in detail for more than century. HAT is generally described as concerted (H• ≡ H+ + e–) from one group to another, Y H–X → Y–H X, but strict definition difficult establish. Distinctions are challenging when "H•" involves e– that to/from spatially distinct sites or even completely separate reagents (multiple-site proton–electron transfer, MS-CPET). MS-CPET reactivity increasingly proposed biological synthetic contexts, some typically resemble MS-CPET. Despite "look different," we argue here these lie on continuum, they governed by many same key parameters. This Account walks reader across this using series studies show strong similarities move protons seemingly different ways.To prepare our stroll, describe thermochemical kinetic frameworks driving force solution reaction most easily discussed difference bond dissociation free energies (BDFEs) reactants products. BDFEs can be analyzed sums proton steps therefore obtained pKa E° values. Even though do not make break bonds way HAT, description used with introduction an effective BDFE (BDFEeff). BDFEeff reductant/acid pair energy form H•, which values analogous fashion standard BDFE. When thermochemistry known, rate constants understood often predicted linear relationships (the Brønsted catalysis law) Marcus theory type approaches.After background, walk through continuum reactivity. Our journey begins study metal-mediated hydrocarbon substrates metal-oxo complex travels end spectrum, hydroxylamine TEMPOH two molecules. These examples, those between, all within thermodynamic framework. A first examples C–H uses framework highlights importance bonding preorganization. analyses along similar different, attempts divide into subcategories obscure much essential chemistry. We hope developing common features will help experts newcomers alike explore exciting new territories

Language: Английский

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