Cu and Zn promoted Al-fumarate metal organic frameworks for electrocatalytic CO2 reduction.

Metal organic frameworks (MOFs) are attractive materials to generate multifunctional catalysts for the electrocatalytic reduction of CO2 to hydrocarbons. Here we report the synthesis of Cu and Zn modified Al-fumarate (Al-fum) MOFs, in which Zn promotes the selective reduction of CO2 to CO and Cu promotes CO reduction to oxygenates and hydrocarbons in an electrocatalytic cascade. Cu and Zn nanoparticles (NPs) were introduced to the Al-fum MOF by a double solvent method to promote in-pore metal deposition, and the resulting reduced Cu-Zn@Al-fum drop-cast on a hydrophobic gas diffusion electrode for electrochemical study. Cu-Zn@Al-fum is active for CO2 electroreduction, with the Cu and Zn loading influencing the product yields. The highest faradaic efficiency (FE) of 62% is achieved at -1.0 V vs. RHE for the conversion of CO2 into CO, HCOOH, CH4, C2H4 and C2H5OH, with a FE of 28% to CH4, C2H4 and C2H5OH at pH 6.8. Al-fum MOF is a chemically robust matrix to disperse Cu and Zn NPs, improving electrocatalyst lifetime during CO2 reduction by minimizing transition metal aggregation during electrode operation.

Carbon-Nanotube-Supported Copper Polyphthalocyanine for Efficient and Selective Electrocatalytic CO2 Reduction to CO.

Electroreduction of CO2 to CO is one of the simplest ways to valorise CO2 as a source of carbon. Herein, a cheap, robust, Cu-based hybrid catalyst consisting of a polymer of Cu phthalocyanine coated on carbon nanotubes, which proved to be selective for CO production (80 % faradaic yield) at relatively low overpotentials, was developed. Polymerisation of Cu phthalocyanine was shown to have a drastic effect on the selectivity of the reaction because molecular Cu phthalocyanine was instead selective for proton reduction under the same conditions. Although the material only showed isolated Cu sites in phthalocyanine-like CuN4 coordination, in situ and operando X-ray absorption spectroscopy showed that, under operating conditions, the Cu atoms were fully converted to Cu nanoparticles, which were likely the catalytically active species. Interestingly, this restructuring of the metal sites was reversible.

Copper-Substituted NiTiO3 Ilmenite-Type Materials for Oxygen Evolution Reaction.

Single Ni1-xCuxTiO3 (0.05 ≤ x ≤ 0.2) Ilmenite-type phases were successfully prepared through a solid-state reaction route using divalent metal nitrates as precursors and characterized. Their electrocatalytic performance for oxygen evolution reaction (OER) in alkaline media is presented. The Cu content was determined (0.05 ≤ x ≤ 0.2) by X-ray diffraction. A thorough powder neutron diffraction study was carried out to identify the subtle changes caused by copper substitution in the structure of NiTiO3. The evolution of the optical and magnetic properties with the Cu content was also investigated on the raw micrometer-sized particles. A reduction in particle size down to ≈15 nm was achieved by ball-milling the raw powder prepared by the solid-state reaction. The best catalytic activity for OER was obtained for nanometer-sized particles of Ni0.8Cu0.2TiO3 drop-casted on the Cu plate. For this electrode, a current density of 10 mA cm-2 for oxygen production was generated at 345 and 470 mV applied overpotentials with 1 and 0.1 M NaOH solutions as electrolytes, respectively. The catalyst retained this OER activity at 10 mA cm-2 for long-term electrolysis with a faradic efficiency of 90% for O2 production in a 0.1 M NaOH electrolyte.

Controlling Hydrogen Evolution during Photoreduction of CO2 to Formic Acid Using [Rh(R-bpy)(Cp*)Cl]+ Catalysts: A Structure-Activity Study.

The photochemical reduction of CO2 to formic acid catalyzed by a series of [Rh(4,4'-R-bpy)(Cp*)Cl]+ and [Rh(5,5'-COOH-bpy)(Cp*)Cl]+ complexes (Cp* = pentamethylcyclopentadienyl, bpy = 2,2'-bipyridine, and R = OCH3, CH3, H, COOC2H5, CF3, NH2, or COOH) was studied to assess how modifications in the electronic structure of the catalyst affect its selectivity, defined as the HCOOH:H2 product ratio. A direct molecular-level influence of the functional group on the initial reaction rate for CO2 versus proton reduction reactions was established. Density functional theory computations elucidated for the first time the respective role of the [RhH] and [Cp*H] tautomers, recognizing rhodium hydride as the key player for both reactions. In particular, our calculations explain the observed tendency of electron-donating substituents to favor CO2 reduction by means of decreasing the hydricity of the Rh-H bond, resulting in a lower hydride transfer barrier toward formic acid production as compared to substituents with an electron-withdrawing nature that favor more strongly the reduction of protons to hydrogen.

Low-cost high-efficiency system for solar-driven conversion of CO2 to hydrocarbons.

Conversion of carbon dioxide into hydrocarbons using solar energy is an attractive strategy for storing such a renewable source of energy into the form of chemical energy (a fuel). This can be achieved in a system coupling a photovoltaic (PV) cell to an electrochemical cell (EC) for CO2 reduction. To be beneficial and applicable, such a system should use low-cost and easily processable photovoltaic cells and display minimal energy losses associated with the catalysts at the anode and cathode and with the electrolyzer device. In this work, we have considered all of these parameters altogether to set up a reference PV-EC system for CO2 reduction to hydrocarbons. By using the same original and efficient Cu-based catalysts at both electrodes of the electrolyzer, and by minimizing all possible energy losses associated with the electrolyzer device, we have achieved CO2 reduction to ethylene and ethane with a 21% energy efficiency. Coupled with a state-of-the-art, low-cost perovskite photovoltaic minimodule, this system reaches a 2.3% solar-to-hydrocarbon efficiency, setting a benchmark for an inexpensive all-earth-abundant PV-EC system.

A Dendritic Nanostructured Copper Oxide Electrocatalyst for the Oxygen Evolution Reaction.

To use water as the source of electrons for proton or CO2 reduction within electrocatalytic devices, catalysts are required for facilitating the proton-coupled multi-electron oxygen evolution reaction (OER, 2 H2 O→O2 +4 H+ +4 e- ). These catalysts, ideally based on cheap and earth abundant metals, have to display high activity at low overpotential and good stability and selectivity. While numerous examples of Co, Mn, and Ni catalysts were recently reported for water oxidation, only few examples were reported using copper, despite promising efficiencies. A rationally designed nanostructured copper/copper oxide electrocatalyst for OER is presented. This material derives from conductive copper foam passivated by a copper oxide layer and further nanostructured by electrodeposition of CuO nanoparticles. The generated electrodes are highly efficient for catalyzing selective water oxidation to dioxygen with an overpotential of 290 mV at 10 mA cm-2 in 1 m NaOH solution.

Porous dendritic copper: an electrocatalyst for highly selective CO2 reduction to formate in water/ionic liquid electrolyte.

Copper is currently extensively studied because it provides promising electrodes for carbon dioxide electroreduction. The original combination, reported here, of a nanostructured porous dendritic Cu-based material, characterized by electron microcopy (SEM, TEM) and X-ray diffraction methods, and a water/ionic liquid mixture as the solvent, contributing to CO2 solubilization and activation, results in a remarkably efficient (large current densities at low overpotentials), stable and selective (large faradic yields) electrocatalytic system for the conversion of CO2 into formic acid, a product with a variety of uses. These results provide new directions for the further improvement of Cu electrodes.

CO2 Reduction to CO in Water: Carbon Nanotube-Gold Nanohybrid as a Selective and Efficient Electrocatalyst.

A gold-based nanostructure has been demonstrated as promising materials for the selective electroreduction of CO2 to CO in aqueous conditions. In this work, we present a carbon nanotube-gold nanohybrid as a selective and efficient electrocatalyst for the reduction of CO2 in 0.5 m NaHCO3 . The hybrid material exhibits remarkable activity with a current density of 10 mA cm(-2) at -0.55 V versus standard hydrogen electrode with a stable CO production rate (0.52 µmol s(-1) ) after 4 h electrolysis. Monodispersed gold nanoparticles anchored on carbon nanotubes through a layer-by-layer method allows very little Au loading and thus minimization of the cost of electrode fabrication with a mass activity up to 100 A g(-1) at -0.55 V versus reversible hydrogen electrode. It is 33 times higher than a previous report for monodisperse Au nanoparticles (3 A g(-1) ) while ensuring selectivity (70 % faradaic yield of CO) at comparable reduction potential.

Cu/Cu2 O Electrodes and CO2 Reduction to Formic Acid: Effects of Organic Additives on Surface Morphology and Activity.

Copper/copper oxide (Cu/Cu2 O) electrodes are known to display interesting electrocatalytic performances for the reduction of CO2 , and thus, deserve further investigation for optimization. Here, we show that the addition of nitrogen-based organic additives greatly improves the activity of these electrodes (higher current densities, greater selectivity, and higher faradaic yields). The best effector is found to be tetramethyl cyclam. For example, electrolysis at -2.0 V versus Fc+ /Fc in CO2 -saturated DMF/H2 O (99:1, v/v) in the presence of this effector results in formic acid with almost 90 % faradaic yield. SEM and XPS analysis of the electrode surface reveals that the organic additive promotes the formation of active Cu0 nanoparticles from Cu2 O during electrolysis. This simple approach provides a straightforward strategy toward the optimization of Cu/Cu2 O electrodes.

Spirally oriented Au microelectrode array sensor for detection of Hg (II).

A simple and reproducible carbon microelectrode array (CMA), designed to eliminate diffusive interference among the microelectrodes, has been fabricated and used as a frame to build a gold (Au) microelectrode array (GMA) sensor. To prepare the CMA initially, rather than use an uncontrollable large number of carbon fibers, only 60 carbon fibers of regular size were used to ensure manageable and reproducible arrangement for array construction. In addition, for efficient spatial arrangement of the microelectrode and easy sensor preparation, carbon fibers were oriented in a spiral fashion by rolling around a Cu wire. The distance between carbon fibers was carefully determined to avoid overlap among individual diffusion layers, one of the important factors governing steady-state current response and sensor-to-sensor reproducibility. After the preparation of a spirally arranged CMA, Au was electrochemically deposited on the surface of individual carbon electrodes to build a final GMA sensor. Then, the GMA sensor was used to measure Hg(2+) in a low concentration range. Simultaneously, multiple GMA sensors were independently prepared to examine reproducibility in sensor fabrication as well as electrochemical measurement (sensor-to-sensor reproducibility). Overall, highly sensitive detection of Hg(2+) was possible using the proposed GMA sensor due to efficient arrangement of microelectrodes and the sensor-to-sensor reproducibility was superior owing to simplicity in sensor fabrication.

A three-dimensional gold nanodendrite network porous structure and its application for an electrochemical sensing.

A three dimensional (3D) gold (Au) nanodendrite network porous structure constructed by a simple electrochemical synthetic method has been presented, and its utility for sensitive electrochemical measurement was demonstrated in this study. The 3D nanodendrite network porous structure was constructed on a platinum surface through electrodeposition of Au under the presence of hydrogen bubbles generated from the same surface. Iodide, used as a co-reagent, played an important role in the construction of the nanodendrite network by preventing continual growth of Au into larger agglomerates as well as inhibiting coalescence of neighboring nanodendrites. An electrochemical sensor incorporating the structure was built and used to detect As(III) in ultra low concentration range. For the purpose of comparison, bare gold and gold nanoparticle-incorporated electrodes were also prepared. With the use of 3D nanodendrite network porous structure, a much more sensitive detection of As(III) was possible due to its large surface area.

Sensitive detection of an anthrax biomarker using a glassy carbon electrode with a consecutively immobilized layer of polyaniline/carbon nanotube/peptide.

Sensitivity of Anthrax protective antigen (PA) detection has been improved by directly immobilizing a PA-specific peptide onto a multi-wall carbon nanotube (MWCNT). The MWCNT was covalently immobilized onto a polyaniline (PANI) electrode, which was prepared via electropolymerization of the aniline monomer onto a glassy carbon electrode (GCE). Then, the PA-specific peptide was covalently immobilized to the MWCNT layer for measurement. When comparing this technique to that of PA immobilization on an insulting self assembled organic layer, the advantages of the MWCNT are clear. The MWCNT sensor resulted in enhanced electron transfer across the sensing layer. The resulting limit of detection (LOD) was 0.4 pM, a 13-fold improvement over that of our previous self-assembled organic layer was used for immobilization of the same peptide. Neither positive nor negative interferences were observed when a sample containing both 100 pM PA and bovine serum albumin (BSA) was measured, indicating good selectivity of the proposed sensor.

Square wave voltammetric detection of Anthrax utilizing a peptide for selective recognition of a protein biomarker.

A short chain peptide (16mer) has been successfully utilized for the selective electrochemical detection of the protein biomarker, protective antigen (PA), for the diagnosis of Anthrax. The major motivation of using a peptide instead of an antibody for the development of a biosensor is that there are advantages associated with the smaller size, better biological stability and easy synthesizability of a peptide. PA-selective peptide was synthesized and conjugated on a binding layer previously immobilized onto gold electrode. The same sensing scheme using a conventional antibody instead of a peptide was also tested for the purpose of comparison. Since the size of the peptide is approximately 1-2 orders of magnitude smaller than that of the antibody, a more populated immobilization of peptide on the sensing layer is possible and will eventually lead to improved sensitivity for PA detection. The selectivity of the peptide-based sensor was evaluated by observing the reduction peaks of samples containing PA with different concentrations of bovine serum albumin (BSA). The resulting responses were interference-free from BSA. The results of this study demonstrate the strong analytical potential of a peptide-based biosensor for diverse applications, especially in disease diagnosis where detection of a specific protein biomarker is particularly demanding.