Electrocatalysis of oxygen reduction on multi-walled carbon nanotube supported copper and manganese phthalocyanines in alkaline media

Manganese phthalocyanine (MnPc) and copper phthalocyanine (CuPc)-modified electrodes were prepared using multi-walled carbon nanotubes (MWCNTs) as a support material. The catalyst materials were heat treated at four different temperatures to investigate the effect of pyrolysis on the oxygen reduction reaction (ORR) activity of these electrocatalysts. The MWCNT to metal phthalocyanine ratio was varied. Scanning electron microscopy (SEM) was employed to visualise the surface morphology of the electrodes and the x-ray photoelectron spectroscopic (XPS) study was carried out to analyse the surface composition of the most active catalyst materials. The ORR was studied in 0.1 M KOH solution employing the rotating disk electrode (RDE) method. Glassy carbon (GC) electrodes were modified with carbon nanotube-supported metal phthalocyanine catalysts using Tokuyama AS-4 ionomer. The RDE results revealed that the highest electrocatalytic activity for ORR was achieved upon heat treatment at 800 °C. CuPc-derived catalyst demonstrated lower catalytic activity as compared to the MnPc-derived counterpart, which is in good agreement with previous literature, whereas the activity of MnPc-based catalyst was higher than that reported earlier.     

Electrocatalysis of oxygen reduction on glassy carbon electrodes modified with anthraquinone moieties

Anthraquinone groups were electrochemically grafted to glassy carbon (GC) electrodes via methylene linker to study the oxygen reduction reaction (ORR) in alkaline medium. Two different anthraquinone derivatives, 2-bromomethyl-anthraquinone or 2-chloromethyl-anthraquinone, were used to modify the GC electrode surface. Several modification conditions encompassing potential cycling and electrolysis at a fixed potential were employed in order to vary the surface concentration of MAQ groups (Γ _MAQ) and to study the dependence of the O₂ reduction behaviour on electrografting procedure. Cyclic voltammetry confirmed the presence of anthraquinone moieties attached to the GC electrode and Γ _MAQ varied in the range of (0.5–2.4)?×?10^?10 mol cm^?2. Oxygen reduction was studied on MAQ-modified GC electrodes of various surface coverage using the rotating disc electrode (RDE) and rotating ring-disc electrode (RRDE) methods. The RDE and RRDE results of O₂ reduction reveal that GC/MAQ electrodes show rather similar electrocatalytic behaviour towards the ORR yielding hydrogen peroxide as the final product.     

Electrocatalytic oxygen reduction on transition metal macrocyclic complexes for anion exchange membrane fuel cell application

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Hydrogen adsorbed in a metal organic framework-5: coupled translation-rotation eigenstates from quantum five-dimensional calculations

We report rigorous quantum five-dimensional (5D) calculations of the coupled translation-rotation (T-R) eigenstates of a H(2) molecule adsorbed in metal organic framework-5 (MOF-5), a prototypical nanoporous material, which was treated as rigid. The anisotropic interactions between H(2) and MOF-5 were represented by the analytical 5D intermolecular potential energy surface (PES) used previously in the simulations of the thermodynamics of hydrogen sorption in this system [Belof et al., J. Phys. Chem. C 113, 9316 (2009)]. The global and local minima on this 5D PES correspond to all of the known binding sites of H(2) in MOF-5, three of which, α-, β-, and γ-sites are located on the inorganic cluster node of the framework, while two of them, the δ- and ε-sites, are on the phenylene link. In addition, 2D rotational PESs were calculated ab initio for each of these binding sites, keeping the center of mass of H(2) fixed at the respective equilibrium geometries; purely rotational energy levels of H(2) on these 2D PESs were computed by means of quantum 2D calculations. On the 5D PES, the three adjacent γ-sites lie just 1.1 meV above the minimum-energy α-site, and are separated from it by a very low barrier. These features allow extensive wave function delocalization of even the lowest translationally excited T-R eigenstates over the α- and γ-sites, presenting significant challenges for both the quantum bound-state calculations and the analysis of the results. Detailed comparison is made with the available experimental data.     

Oxygen reduction on electrodeposited silver catalysts in alkaline solution

In this study, silver was electrochemically deposited onto glassy carbon (GC) substrate using constant potential regime and tested for oxygen reduction reaction (ORR) in alkaline media. The surface morphology of Ag/GC electrodes was studied by scanning electron microscopy (SEM). It was established that after 10 s of deposition, a number of Ag nanoparticles with the size of 15 nm are produced that grow to about 45 nm after 300 s of electrodeposition. The ORR studies were conducted in 0.1 M KOH solution employing the rotating disk electrode (RDE) method. The Tafel slope at low current densities for electrodeposited silver is in the range from ?70 to ?80 mV. The RDE measurements showed that the electron transfer number (n) is 3.5 for smaller amounts of electrodeposited Ag, and it increases with increasing the loading of Ag on the GC surface. These n values suggest that the electroreduction of oxygen on Ag/GC electrodes proceeds mainly to water.     

NMR observation of rattling phonons in the pyrochlore superconductor KOs2O6

We report nuclear magnetic resonance studies on the beta-pyrochlore oxide superconductor KOs2O6. The nuclear relaxation at the K sites is entirely caused by fluctuations of the electric field gradient, which we ascribe to highly anharmonic low frequency oscillation (rattling) of K ions. A phenomenological analysis shows a crossover from overdamped to underdamped behavior of the rattling phonons with decreasing temperature and its sudden sharpening below the superconducting transition temperature T(c). Suppression of the Hebel-Slichter peak in the relaxation rate at the O sites below T(c) also indicates strong electron-phonon coupling.     

Crystal Structure-Guided Design of Bisubstrate Inhibitors and Photoluminescent Probes for Protein Kinases of the PIM Family

We performed an X-ray crystallographic study of complexes of protein kinase PIM-1 with three inhibitors comprising an adenosine mimetic moiety, a linker, and a peptide-mimetic (d-Arg)₆ fragment. Guided by the structural models, simplified chemical structures with a reduced number of polar groups and chiral centers were designed. The developed inhibitors retained low-nanomolar potency and possessed remarkable selectivity toward the PIM kinases. The new inhibitors were derivatized with biotin or fluorescent dye Cy5 and then applied for the detection of PIM kinases in biochemical solutions and in complex biological samples. The sandwich assay utilizing a PIM-2-selective detection antibody featured a low limit of quantification (44 pg of active recombinant PIM-2). Fluorescent probes were efficiently taken up by U2OS cells and showed a high extent of co-localization with PIM-1 fused with a fluorescent protein. Overall, the developed inhibitors and derivatives represent versatile chemical tools for studying PIM function in cellular systems in normal and disease physiology.     

Blocking Behavior of Covalently Attached Anthraquinone Towards Solution‐Based Redox Probes

The electrochemical properties of glassy carbon (GC) electrodes modified with 9,10‐anthraquinone (AQ) have been investigated. Electrografting of GC surface was carried out from the solution of the AQ diazonium derivative. The blocking action of GC/AQ electrodes for Fe(CN)$\rm{{_{6}^{3-}}}$ and Ru(NH₃)$\rm{{_{6}^{3+}}}$ redox probes was studied using cyclic voltammetry (CV) and the rotating disk electrode (RDE) method. It was established that the extent of blocking was a function of AQ surface concentration. A peculiar behavior was observed at the potentials of AQ reduction.