Graphene inclusion controlling conductivity and gas sorption of metal-organic framework

A general approach to prepare composite films of metal–organic frameworks and graphene has been developed. Films of copper(ii)-based HKUST-1 and HKUST-1/graphene composites were grown solvothermally on glassy carbon electrodes. The films were chemically tethered to the substrate by diazonium electrografting resulting in a large electrode coverage and good stability in solution for electrochemical studies. HKUST-1 has poor electrical conductivity, but we demonstrate that the addition of graphene to HKUST-1 partially restores the electrochemical activity of the electrodes. The enhanced activity, however, does not result in copper(ii) to copper(i) reduction in HKUST-1 at negative potentials. The materials were characterised in-depth: microscopy and grazing incidence X-ray diffraction demonstrate uniform films of crystalline HKUST-1, and Raman spectroscopy reveals that graphene is homogeneously distributed in the films. Gas sorption studies show that both HKUST-1 and HKUST-1/graphene have a large CO(2)/N(2) selectivity, but the composite has a lower surface area and CO(2) adsorption capacity in comparison with HKUST-1, while CO(2) binds stronger to the composite at low pressures. Electron paramagnetic resonance spectroscopy reveals that both monomeric and dimeric copper units are present in the materials, and that the two materials behave differently upon hydration, i.e. HKUST-1/graphene reacts slower by interaction with water. The changed gas/vapour sorption properties and the improved electrochemical activity are two independent consequences of combining graphene with HKUST-1

A MOF-Based Spatial-Separation Layer to Enable a Uniform Favorable Microenvironment for Electrochemical CO2 Reduction

Regulating the local microenvironment of active sites to increase their specific CO2 concentration and pH gradient, is a promising approach to optimize the electrochemical CO2 reduction reaction (eCO2RR). However, currently reported morphological strategies display an uncertainty to the compatibility and distribution between catalytic sites and their microenvironment. Here, a uniform spatial-separation metal-organic framework (MOF) layer between active sites and bulk electrolyte is proposed, which enables each active site to locate in a similarly favorable microenvironment. Zinc oxide (ZnO) nanorods (NR), a representative electrocatalyst for eCO2RR, is covered with a Zeolitic imidazolate framework-8 (ZIF-8) thin layer to serve as a model system. The prepared ZnO NR@ZIF-8 exhibits an enhanced Faradaic efficiency toward CO at a wide range of potentials and reaches a maximum FE of CO (85%) at −1.05 V versus reversible hydrogen electrode, which is one of the best records till date. Moreover, the hydrophobic ZIF-8 layer protects ZnO against self-reduction. Such performance benefits from the porous ZIF-8 shell with high CO2 affinity, realizing efficient CO2 access and retaining an increased local pH near ZnO active sites

Steering carbon dioxide reduction toward C–C coupling using copper electrodes modified with porous molecular films

Copper offers unique capability as catalyst for multicarbon compounds production in the electrochemical carbon dioxide reduction reaction. In lieu of conventional catalysis alloying with other elements, copper can be modified with organic molecules to regulate product distribution. Here, we systematically study to which extent the carbon dioxide reduction is affected by film thickness and porosity. On a polycrystalline copper electrode, immobilization of porous bipyridine-based films of varying thicknesses is shown to result in almost an order of magnitude enhancement of the intrinsic current density pertaining to ethylene formation while multicarbon products selectivity increases from 9.7 to 61.9%. In contrast, the total current density remains mostly unaffected by the modification once it is normalized with respect to the electrochemical active surface area. Supported by a microkinetic model, we propose that porous and thick films increase both local carbon monoxide partial pressure and the carbon monoxide surface coverage by retaining in situ generated carbon monoxide. This reroutes the reaction pathway toward multicarbon products by enhancing carbon–carbon coupling. Our study highlights the significance of customizing the molecular film structure to improve the selectivity of copper catalysts for carbon dioxide reduction reaction

Low-valence Znδ+ (0<2) single-atom material as highly efficient electrocatalyst for CO2 reduction

A nitrogen-stabilized single-atom catalyst containing low-valence zinc atoms (Znδ+-NC) is reported. It contains saturated four-coordinate (Zn-N4) and unsaturated three-coordinate (Zn-N3) sites. The latter makes Zn a low-valence state, as deduced from X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, electron paramagnetic resonance, and density functional theory. Znδ+-NC catalyzes electrochemical reduction of CO2 to CO with near-unity selectivity in water at an overpotential as low as 310 mV. A current density up to 1 A cm−2 can be achieved together with high CO selectivity of >95 % using Znδ+-NC in a flow cell. Calculations suggest that the unsaturated Zn-N3 could dramatically reduce the energy barrier by stabilizing the COOH* intermediate owing to the electron-rich environment of Zn. This work sheds light on the relationship among coordination number, valence state, and catalytic performance and achieves high current densities relevant for industrial applications

Unexpected Mild Protection of Alcohols as 2-O-THF and 2-O-THP Ethers Catalysed by Cp2TiCl Reveal an Intriguing Role of the Solvent in the Single- Electron Transfer Reaction

A method for the conversion of primary, secondary and tertiary alcohols into the corresponding THF ethers at room temperature and primary and secondary alcohols into the corresponding THP ethers, has been developed using titanium(III) species generated from a catalytic amount of titanocene dichloride or (4R,5R)-(–)-2,2-dimethyl-α,α,α ,α -tetra(1-naphth-yl)-1,3-dioxolane-4,5-dimethanolatotitanium(IV) dichloride: acetonitrile adduct together with manganese(0) as a reductant and bromoform in THF or THP as the solvent. A radical mechanism is proposed for this transformation revealing an intriguing role of the solvent in the single-electron transfer reactions catalysed by the low valent TiIII system

Synthesis of RAFT Initiator on Metallic Surfaces

The aim of this project is to synthesise a RAFT initiator on a glassy carbon surface. The purpose of the initiators is to use them in a photocatalytic polymerisation of polymer brushes in water. The project will start to focus on two potential methods. Method 1 uses a disulfide diazonium salt as a grafting agent. By reducing the disulfide will cleave the disulfide, leaving a monolayer of the grafting agent. The thiolate might then react with carbondisulfide to form trithiocarbonate, which can react with a benzylic position to form a RAFT agent. Method 2 is another approach to form a RAFT agent. Diethylcarbamodithioate (DEDTC) will be added on the benzylic position in 1-(chloromethyl)-4-nitrobenzene. This will then be grafted on a surface. See "Home" under "Wiki" for an illustrative overview of the project