NiFe Alloy Integrated with Amorphous/Crystalline NiFe Oxide as an Electrocatalyst for Alkaline Hydrogen and Oxygen Evolution Reactions.

The rational design of efficient and low-cost electrocatalysts based on earth-abundant materials is imperative for large-scale production of hydrogen by water electrolysis. Here we present a strategy to prepare highly active catalyst materials through modifying the crystallinity of the surface/interface of strongly coupled transition metal-metal oxides. We have thermally activated the catalysts to construct amorphous/crystalline Ni-Fe oxide interfaced with a conductive Ni-Fe alloy and systematically investigated their electrocatalytic performance toward the hydrogen evolution and oxygen evolution reactions (HER and OER) in alkaline solution.

Electronic States and Transport Phenomena of Pt Nanoparticle Catalysts Supported on Nb-Doped SnO for Polymer Electrolyte Fuel Cells.

Semiconducting oxide nanoparticles are strongly influenced by surface-adsorbed molecules and tend to generate an insulating depletion layer. The interface between a noble metal and a semiconducting oxide constructs a Schottky barrier, interrupting the electron transport. In the case of a Pt catalyst supported on the semiconducting oxide Nb-doped SnO with a fused-aggregate network structure (Pt/Nb-SnO) for polymer electrolyte fuel cells, the electronic conductivity increased abruptly with increasing Pt loading, going from 10 to 10 S cm.

Geometric control of nuclearity in copper(I)/dioxygen chemistry.

Copper(I) complexes supported by a series of N3-tridentate ligands bearing a rigid cyclic diamine framework such as 1,5-diazacyclooctane (L8, eight-membered ring), 1,4-diazacycloheptane (L7, seven-membered ring), or 1,4-diazacyclohexane (L6, six-membered ring) with a common 2-(2-pyridyl)ethyl side arm were synthesized and their reactivity toward O2 were compared. The copper(I) complex of L8 preferentially provided a mononuclear copper(II) end-on superoxide complex S as reported previously [Itoh, S., et al.

A copper complex supported by an N2S-tridentate ligand inducing efficient heterolytic O-O bond cleavage of alkylhydroperoxide.

We have recently reported a copper(II)-superoxide complex supported by an N3-tridentate ligand (L(N3)), which exhibits a similar structure and reactivity to those of a putative reactive intermediate involved in the catalytic reactions of copper monooxygenases such as peptidylglycine α-hydroxylating monooxygenase (PHM) and dopamine β-monooxygenase (DβM). In this study, we have synthesised and characterised copper complexes supported by a related sulphur-containing ligand (L(N2S)) to get insight into the notable electronic effect of the sulphur donor atom in the reaction with cumene hydroperoxide, inducing efficient heterolytic O-O bond cleavage.

Flavonolate complexes of M(II) (M = Mn, Fe, Co, Ni, Cu, and Zn). Structural and functional models for the ES (enzyme-substrate) complex of quercetin 2,3-dioxygenase.

A series of flavonolate complexes [M(II)L(fla)] (M = Mn (1), Fe (2), Co (3), Ni (4), Cu (5), and Zn (6), LH: 2-{[bis(pyridin-2-ylmethyl)amino]methyl}benzoic acid, fla: flavonolate) have been synthesized as structural and functional models for the ES (enzyme-substrate) complexes of the active site of various M(II)-containing quercetin 2,3-dioxygenase (2,3-QD) and their structures, spectroscopic features, and redox properties, as well as the reactivity toward molecular oxygen, have been investigated. The metal centers of [Fe(II)L(fla)]·H2O (2), [Co(II)L(fla)]·CH3OH (3), and [Ni(II)L(fla)] (4) exhibit a distorted octahedral geometry with two oxygen atoms of fla, one oxygen atom of the benzoate group of ligand L, and three nitrogen atoms of ligand L, in which oxygen atom of the carbonyl group of fla and one of the pyridine nitrogen atoms occupy the axial positions. The complexes [M(II)L(fla)] exhibit relatively high reactivity in the oxidative ring-opening of the bound flavonolate at lower temperature, presumably due to the existing carboxylate group in the supporting ligand.

Redox properties of a mononuclear copper(II)-superoxide complex.

Redox properties of a mononuclear copper(II) superoxide complex, (L)Cu(II)-OO(•), supported by a tridentate ligand (L = 1-(2-phenethyl)-5-[2-(2-pyridyl)ethyl]-1,5-diazacyclooctane) have been examined as a model compound of the putative reactive intermediate of peptidylglycine α-hydroxylating monooxygenase (PHM) and dopamine β-monooxygenase (DβM) (Kunishita et al. J. Am.

Active site models for the Cu(A) site of peptidylglycine α-hydroxylating monooxygenase and dopamine β-monooxygenase.

A mononuclear copper(II) superoxo species has been invoked as the key reactive intermediate in aliphatic substrate hydroxylation by copper monooxygenases such as peptidylglycine α-hydroxylating monooxygenase (PHM), dopamine β-monooxygenase (DβM), and tyramine β-monooxygenase (TβM). We have recently developed a mononuclear copper(II) end-on superoxo complex using a N-[2-(2-pyridyl)ethyl]-1,5-diazacyclooctane tridentate ligand, the structure of which is similar to the four-coordinate distorted tetrahedral geometry of the copper-dioxygen adduct found in the oxy-form of PHM (Prigge, S. T.

Reactivity of copper(II)-alkylperoxo complexes.

Copper(II) complexes 1a and 1b, supported by tridentate ligand bpa [bis(2-pyridylmethyl)amine] and tetradentate ligand tpa [tris(2-pyridylmethyl)amine], respectively, react with cumene hydroperoxide (CmOOH) in the presence of triethylamine in CH(3)CN to provide the corresponding copper(II) cumylperoxo complexes 2a and 2b, the formation of which has been confirmed by resonance Raman and ESI-MS analyses using (18)O-labeled CmOOH. UV-vis and ESR spectra as well as DFT calculations indicate that 2a has a 5-coordinate square-pyramidal structure involving CmOO(-) at an equatorial position and one solvent molecule at an axial position at low temperature (-90 °C), whereas a 4-coordinate square-planar structure that has lost the axial solvent ligand is predominant at higher temperatures (above 0 °C). Complex 2b, on the other hand, has a typical trigonal bipyramidal structure with the tripodal tetradentate tpa ligand, where the cumylperoxo ligand occupies an axial position.

Reactions of copper(II)-phenol systems with O2: models for TPQ biosynthesis in copper amine oxidases.

Copper(II) complexes supported by a series of phenol-containing bis(pyridin-2-ylmethyl)amine N(3) ligands (denoted as L(o)H, L(m)H, and L(p)H) have been synthesized, and their O(2) reactivity has been examined in detail to gain mechanistic insights into the biosynthesis of the TPQ cofactor (2,4,5-trihydroxyphenylalaninequinone, TOPA quinone) in copper-containing amine oxidases. The copper(II) complex of L(o)H (ortho-phenol derivative) involves a direct phenolate to copper(II) coordination and exhibits almost no reactivity toward O(2) at 60 °C in CH(3)OH. On the other hand, the copper(II) complex of L(m)H (meta-phenol derivative), which does not involve direct coordinative interaction between the phenol moiety and the copper(II) ion, reacts with O(2) in the presence of triethylamine as a base to give a methoxy-substituted para-quinone derivative under the same conditions.