Copper-Tin Alloys for the Electrocatalytic Reduction of CO2 in an Imidazolium-Based Non-Aqueous Electrolyte

The ability to synthesize value-added chemicals directly from CO2 will be an important technological advancement for future generations. Using solar energy to drive thermodynamically uphill electrochemical reactions allows for near carbon-neutral processes that can convert CO2 into energy-rich carbon-based fuels. Here, we report on the use of inexpensive CuSn alloys to convert CO2 into CO in an acetonitrile/imidazolium-based electrolyte. Synergistic interactions between the CuSn catalyst and the imidazolium cation enables the electrocatalytic conversion of CO2 into CO at −1.65 V versus the standard calomel electrode (SCE). This catalyst system is characterized by overpotentials for CO2 reduction that are similar to more expensive Au- and Ag-based catalysts, and also shows that the efficacy of the CO2 reduction reaction can be tuned by varying the CuSn ratio.

Preferential Use of an Anode as an Electron Acceptor by an Acidophilic Bacterium in the Presence of Oxygen

ABSTRACT Several anaerobic metal-reducing bacteria have been shown to be able to donate electrons directly to an electrode. This property is of great interest for microbial fuel cell development. To date, microbial fuel cell design requires avoiding O2 diffusion from the cathodic compartment to the sensitive anodic compartment. Here, we show that Acidiphilium sp. strain 3.2 Sup 5 cells that were isolated from an extreme acidic environment are able to colonize graphite felt electrodes. These bacterial electrodes were able to produce high-density electrocatalytic currents, up to 3 A/m2 at a poised potential of +0.15 V (compared to the value for the reference standard calomel electrode) in the absence of redox mediators, by oxidizing glucose even at saturating air concentrations and very low pHs.

Covalent immobilization of urease on polypyrrole microspheres for application as a urea biosensor

Urease has been covalently immobilized on polypyrrole microspheres chemically linked to conducting polypyrrole-polyvinyl sulfonate (PPY-PVS) films. These films were electrochemically prepared during 5 - 7 min at a constant current of 2 mA using indium - tin oxide (ITO) glass plates as the working electrode, and a standard calomel electrode as the reference electrode. Urease covalently linked to polypyrrole microspheres (by reaction of protein amino groups with aldehyde groups on the surface of the microspheres) was entrapped/adsorbed onto electrochemically prepared conducting PPY-PVS films deposited on ITO. Potentiometric measurements undertaken on these conducting polymer electrodes using an ammonium ion analyzer reveal that they can be used for estimating the urea concentration in solutions from 5·10-3 mol/l to 6·10-2 mol/l.

Amperometric Determination of Total Cholesterol in Serum, with Use of Immobilized Cholesterol Ester Hydrolase and Cholesterol Oxidase

We describe an electrochemical method for simple, rapid, and economical assay of total serum cholesterol with use of immobilized cholesterol esterase (EC 3.1.1.13) and cholesterol oxidase (EC 1.1.3.6). A rotating porous cell was specially designed to hold the immobilized enzymes firmly and to allow the reaction mixture to pass through the en¬zyme layer easily, thus catalyzing the enzymatic trans¬formation quickly. Hydrogen peroxide resulting from the catalytic reactions was measured amperometrically at +0.60 V vs. a standard calomel electrode. The calibration curve for total serum cholesterol was linear from 0 to 5.00 g/liter. The method is specific, precise, and inexpensive. Our results correlate well with those obtained by the method of Abell et al. [Stand. Methods Clin. Chem. 2, 26 (1958)] , the correlation coefficient being 0.992. Ascorbic acid or bilirubin in concentrations up to 100 mg/liter do not interfere. The immobilized enzymes are stable, and the same immobilized-enzyme stirrer can be used for at least 200 accurate, reproducible assays.

Polarography of 2,2′-Bipyridyl Dimethiodide in Aqueous Solution

2,2′-Bipyridyl dimethiodide in aqueous solution in the pH range 5.0-8.9 gives a symmetrical one-electron reduction wave independent of pH and concentration at a potential of —0.96 V against a standard calomel electrode due to the formation of the corresponding radical cation. At a much lower potential it also shows a second reduction wave which is pH dependent.

Derivatives of 1,10-Phenanthroline-5,6-quinone

1,l0-Phenanthroline-5,6-quinone is prepared from 1,l0-phenanthroline via 5-nitro-1,l0-phenanthroline and 5-amino-1,l0-phenanthroline. It is converted by standard methods into 4,5-diazafluoren-9-one, 4,5-diazafluoren-9-ol,4,5-diazafluorene, and the new heterocyclic system dipyrido[3,2-a:2',3'-clphenazine. These four compounds each form a complex with cupric chloride. They thus represent a new series of chelating agents. By reaction with ethylene dibromide, dipyrido[3,2-a:2',3'-c]-phenaiine forms a diquaternary salt which is reduced in aqueous solution by a one-electron transfer to a highly coloured radical cation. Polarography experiments show that the reduction potential of the salt is -0.40 V against a standard calomel electrode.

The electrochemistry and the kinetics of the formation of ruthenium(II) nitrogen complexes

Electrolysis at a mercury cathode controlled at −0.50 V (vs. standard calomel electrode s.c.e.) in a H2SO4–K2SO4 electrolyte with pH of 2.6 and saturated with Ar gas has been used to prepare RuII–(NH3)5X. The reaction of this species with N2 in the aqueous base electrolyte at 26 °C has been studied and found to follow the equations:[Formula: see text]In base electrolyte saturated with N2 at 1 atm (CN2 ≈ 6 × 10−4 M) the value of the apparent first order constant, k′m is 4.4 × 10−5 s−1 and the value of kd is 4.2 × 10−2 1 mole−1 s−1.The electrochemistry of the various ruthenium species was also investigated in the H2SO4–K2SO4 electrolyte. At the dropping mercury electrode, RuIII (NH3)5Cl gave a well-defined one electron reduction wave with E1/2 = −0.27 V; RuII (NH3)5X gave a well-defined one electron oxidation wave with E1/2 = −0.25 V. The nitrogen complexes gave oxidation waves at a rotating platinum microelectrode, the monomer with E1/2 = +0.72 V and the dimer with E1/2 = +0.78 V.