Thermally Induced Oxygen Vacancies in BiOCl Nanosheets and Their Impact on Photoelectrochemical Performance**

Oxygen vacancies (OVs) have been reported to significantly alter the photocatalytic properties of BiOCl nanosheets. However, their formation mechanism and their role in the enhancement of photoelectrochemical performance remain unclear. In this work, thermally induced oxygen vacancies are introduced in BiOCl nanosheets by annealing in He atmosphere at various temperatures and their formation mechanism is investigated by in‐situ diffuse reflectance infrared (DRIFTS) measurements. The influence of OVs on band offset, carrier concentrations and photoelectrochemical performance are systematically studied. The results show that (1) the surface of BiOCl nanosheets is extremely sensitive to temperature and defects are formed at temperatures as low as 200 °C in inert atmosphere. (2) The formation of surface and bulk OVs in BiOCl is identified by a combination of XPS, in‐situ DRIFTS, and EPR experiments. (3) The photocurrent of BiOCl is limited by the concentration of charge carriers and shallow defect states induced by bulk oxygen vacancies, while the modulation of these parameters can effectively increase light absorption and carrier concentration leading to an enhancement of photoelectrochemical performance of BiOCl

Molybdenum Triamidoamine Systems. Reactions Involving Dihydrogen Relevant to Catalytic Reduction of Dinitrogen

[HIPTN[subscript 3]N]Mo(N[subscript 2]) (MoN[subscript 2]) ([HIPTN[subscript 3]N][superscript 3−] = [(HIPTNCH2CH2)3N]3− where HIPT = 3,5-(2,4,6-i-Pr[subscript 3]C[subscript 6]H[subscript 2])[subscript 2]C[subscript 6]H[subscript 3]) reacts with dihydrogen slowly (days) at 22 °C to yield [HIPTN[subscript 3]N]MoH[subscript 2] (MoH[subscript 2]), a compound whose properties are most consistent with it being a dihydrogen complex of Mo(III). The intermediate in the slow reaction between MoN[subscript 2] and H[subscript 2] is proposed to be [HIPTN[subscript 3]N]Mo (Mo). In contrast, MoN[subscript 2], MoNH[subscript 3], and MoH[subscript 2] are interconverted rapidly in the presence of H[subscript 2], N[subscript 2], and NH[subscript 3], and MoH[subscript 2] is the lowest energy of the three Mo compounds. Catalytic runs with MoH[subscript 2] as a catalyst suggest that it is competent for reduction of N[subscript 2] with protons and electrons under standard conditions. [HIPTN[subscript 3]N]MoH[subscript 2] reacts rapidly with HD to yield a mixture of [HIPTN[subscript 3]N]MoH[subscript 2], [HIPTN[subscript 3]N]MoD[subscript 2], and [HIPTN[subscript 3]N]MoHD, and rapidly catalyzes H/D exchange between H[subscript 2] and D[subscript 2]. MoH[subscript 2] reacts readily with ethylene, PMe[subscript 3], and CO to yield monoadducts. Reduction of dinitrogen to ammonia in the presence of 32 equiv of added hydrogen (vs Mo) is not catalytic, consistent with dihydrogen being an inhibitor of dinitrogen reduction.National Institutes of Health (U.S.) (GM 31978

A Selective Copper Based Oxygen Reduction Catalyst for the Electrochemical Synthesis of H 2 O 2 at Neutral pH

H2O2 is a bulk chemical used as "green" alternative in a variety of applications, but has an energy and waste intensive production method. The electrochemical O2 reduction to H2O2 is viable alternative with examples of the direct production of up to 20% H2O2 solutions. In that respect, we found that the dinuclear complex Cu2(btmpa) (6,6'-bis[[bis(2-pyridylmethyl)amino]methyl]-2,2'-bipyridine) reduces O2 to H2O2 with a selectivity up to 90 % according to single linear sweep rotating ring disk electrode measurements. Microbalance experiments showed that complex reduction leads to surface adsorption thereby increasing the catalytic current. More importantly, we kept a high Faradaic efficiency for H2O2 between 60 and 70 % over the course of 2 h of amperometry by introducing high potential intervals to strip deposited copper (depCu). This is the first example of extensive studies into the long term electrochemical O2 to H2O2 reduction by a molecular complex which allowed to retain the high intrinsic selectivity of Cu2(btmpa) towards H2O2 production leading to relevant levels of H2O2

Binuclear [(cod)(Cl)Ir(bpi)Ir(cod)]+ for Catalytic Water Oxidation

The binuclear iridium complex [(cod)(Cl)Ir(bpi)Ir(cod)]PF6 (bpi = (pyridin-2-ylmethyl)(pyridin-2-ylmethylene)amine; cod = 1,5-cyclooctadiene) reveals a noteworthy asymmetric binuclear coordination geometry, wherein the bpi ligand acts as a heteroditopic ligand and has an unusual π-coordinated imine moiety. This species is an effective precatalyst for water oxidation. After a short incubation time the catalyst reveals a turnover frequency of 3400 mol mol-1 s-1 with an overall turnover number >1000. © 2011 American Chemical Society.Financial support from the European Research Council (ERC Grant Agreement 202886-CatCIR), NWO-CW (VIDI grant 700.55.426, VENI grant 700.59.410), the MEC/FEDER (Project CTQ2008-03860, Spain), and the University of Amsterdam is gratefully acknowledged.Peer Reviewe

Elucidation of the Structure of a Thiol Functionalized Cu-tmpa Complex Anchored to Gold via a Self-Assembled Monolayer

Metals in Catalysis, Biomimetics & Inorganic Material

Elucidation of the Electrocatalytic Nitrite Reduction Mechanism by Bio-Inspired Copper Complexes

Mononuclear copper complexes relevant to the active site of copper nitrite reductases (CuNiRs) are known to be catalytically active for the reduction of nitrite. Yet, their catalytic mechanism has thus far not been resolved. Here, we provide a complete description of the electrocatalytic nitrite reduction mechanism of a bio-inspired CuNiR catalyst Cu(tmpa) (tmpa = tris(2-pyridylmethyl)amine) in aqueous solution. Through a combination of electrochemical studies, reaction kinetics, and density functional theory (DFT) computations, we show that the protonation steps take place in a stepwise manner and are decoupled from electron transfer. The rate-determining step is a general acid-catalyzed protonation of a copper-ligated nitrous acid (HNO2) species. In view of the growing urge to convert nitrogen-containing compounds, this work provides principal reaction parameters for efficient electrochemical nitrite reduction. This contributes to the investigation and development of nitrite reduction catalysts, which is crucial to restore the biogeochemical nitrogen cycle

Mechanistic Investigations into the Selective Reduction of Oxygen by a MCO T3 site-inspired Copper Complex

Understanding how multicopper oxidases (MCOs) efficiently and selectively reduce oxygen in the trinuclear copper cluster (TNC) is of great importance. Previously it was reported that when the T2-site is removed from the TNC, all O2 binding activity at the dinuclear T3-site is lost. Computational studies attribute this loss of activity to the flexibility of the protein active site, where the T3-copper centers move apart to minimize electrostatic repulsions. To address the question if and how a more constrained T3-site will catalyze the reduction of oxygen, we herein report a mechanistic investigation into the oxygen reduction reaction (ORR) activity of the dinuclear copper complex [Cu2L(μ-OH)]3+ (L=2,7-bis[bis(2-pyridylmethyl)aminomethyl]-1,8-naphthyridine). This T3-inspired complex confines the Cu centers in a rigid scaffold in close proximity instead of the flexible scaffold found in the protein active site and we demonstrate that under these constraints the dinuclear copper site displays ORR activity. Compared to the ORR mechanism of MCOs, we show that electrochemical reduction of [Cu2L(μ-OH)]3+ follows a similar pathway as the reduction of the resting enzyme due to the presence of the Cu-OH-Cu motif. By identification of key intermediates along the catalytic cycle of [Cu2L(μ-OH)]3+ we provide for the first time evidence that metal-metal cooperativity takes place during electrocatalysis of the ORR by a copper-based catalyst, which is achieved by the ability of the rigid ligand framework to bind two copper atoms in close proximity. Electrochemical studies show that the mechanisms of the ORR and hydrogen peroxide reduction reaction (HPRR) found for [Cu2L(μ-OH)]3+ are different from the ones found for analogous mononuclear copper catalysts. In addition, the metal-metal cooperativity results in an improved selectivity for the four-electron ORR of more than 70%. This selectivity is achieved by better stabilization of reaction intermediates between both copper centers, which is also essential for the ORR mechanism observed in MCOs. Overall, the mechanism of the [Cu2L(μ-OH)]3+-catalyzed ORR in this work gives insight into the ORR activity of a T3-site and contributes to understanding of how the ORR activity and selectivity are established in MCOs

Catalytic Activity of an Iron-Based Water Oxidation Catalyst: Substrate Effects of Graphitic Electrodes

The synthesis, characterization, and electrochemical studies of the dinuclear complex [(MeOH)­Fe­(Hbbpya)-μ-O-(Hbbpya)­Fe­(MeOH)]­(OTf)₄ (<b>1</b>) (with Hbbpya = <i>N,N</i>-bis­(2,2′-bipyrid-6-yl)­amine) are described. With the help of online electrochemical mass spectrometry, the complex is demonstrated to be active as a water oxidation catalyst. Comparing the results obtained for different electrode materials shows a clear substrate influence of the electrode, as the complex shows a significantly lower catalytic overpotential on graphitic working electrodes in comparison to other electrode materials. Cyclic voltammetry experiments provide evidence that the structure of complex <b>1</b> undergoes reversible changes under high-potential conditions, regenerating the original structure of complex <b>1</b> upon returning to lower potentials. Results from electrochemical quartz crystal microbalance experiments rule out that catalysis proceeds via deposition of catalytically active material on the electrode surface