Pyridinium and its substituted derivatives are effective and stable homogeneous electrocatalysts for the aqueous multiple-electron, multiple-proton reduction of carbon dioxide to products such as formic acid, formaldehyde, and methanol. Importantly, high faradaic yields for methanol have been observed in both electrochemical and photoelectrochemical systems at low reaction overpotentials. Herein, we report the detailed mechanism of pyridinium-catalyzed CO2 reduction to methanol. At metal electrodes, formic acid and formaldehyde were observed to be intermediate products along the pathway to the 6e−-reduced product of methanol, with the pyridinium radical playing a role in the reduction of both intermediate products. It has previously been thought that metal-derived multielectron transfer was necessary to achieve highly reduced products such as methanol. Surprisingly, this simple organic molecule is found to be capable of reducing many different chemical species en route to methanol through six sequential e...

Using a one-electron shuttle for the multielectron reduction of CO2 to methanol: kinetic, mechanistic, and structural insights.

Permeable reactive barriers (PRBs) have shown great promise as an alternative to pump and treat for the remediation of groundwater containing a wide array of contaminants including organics, metals, and radionuclides. Analyses to date have focused on individual case studies, rather than considering broad performance issues. In response to this need, this study analyzed data from field installations of in situ zero-valent iron (ZVI) PRBs to determine what parameters contribute to PRB failure. Although emphasis has been placed on losses of reactivity and permeability, imperfect hydraulic characterization was the most common cause of the few PRB failures reported in the literature. Graphical and statistical analyses suggested that internal EH, influent pH, and influent concentrations of alkalinity, NO3 − and Cl− are likely to be the strongest predictors of PRBs that could be at risk for diminished performance. Parameters often cited in the literature such as saturation indices, dissolved oxygen, and total di...

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Long-Term Performance of Zero-Valent Iron Permeable Reactive Barriers: A Critical Review

Reactions of pipeline steels in carbon dioxide solutions

We have investigated the electrochemical synthetic mechanism of conductive polymer nanotubes in a porous alumina template using poly(3,4-ethylenedioxythiophene) (PEDOT) as a model compound. As a function of monomer concentration and potential, electropolymerization leads either to solid nanowires or to hollow nanotubes, and it is the purpose of these investigations to uncover the detailed mechanism underlying this morphological transition between nanowire and nanotube. Transmission electron microscopy was used to characterize electrochemically synthesized PEDOT nanostructures and measure the extent of their nanotubular portion quantitatively. The study on potential dependency of nanotubular portion shows that nanotubes are grown at a low oxidation potential (1.2 V vs Ag/AgCl) regardless of monomer concentration. This phenomenon is attributed to the predominance of electrochemically active sites on the annular-shape electrode at the pore bottom of a template. The explanation was supported by a further elec...

Controlled Electrochemical Synthesis of Conductive Polymer Nanotube Structures

Experimental results on the inception and propagation of streamers in water generated under the application of high electric fields are reviewed. Characteristic parameters, such as breakdown voltage, polarity of the applied voltage, propagation velocities and other phenomenological features, are compared with similar phenomena in other dielectric liquids and in gases. Consequently, parameters that are expected to influence the development of streamers in water are discussed with respect to the analogous well-established models and theories for the related mechanisms in gases. Most of the data support the notion that an initial low-density nucleation site or gas-filled bubble assists the initiation of a streamer. Details of this theory are laid out explaining the observed differences in the breakdown originating from the anode versus the cathode locations. The mechanisms can also be applied to streamer propagation, although some observations cannot be satisfactorily explained.

https://iopscience.iop.org/article/10.1088/0022-3727/41/23/234007/pdf

Streamers in water and other dielectric liquids

The behaviour of iron electrode in CO2− saturated neutral electrolyte—I. Electrochemical study

We report in situ electrochemical atomic force microscopic (EC-AFM) data and spectroelectrochemical results on doping-undoping of the films of regioregular poly(3-hexylthiophene) in propylene carbonate (PC) and aqueous solutions of 0.1 M LiClO 4 . The redox process of the polymer in propylene carbonate is accompanied by significant changes of the polymer thickness. This phenomenon is discussed in terms of polymer swelling and structural reconfiguration of the film, markedly delayed with respect to the charge transfer between the polymer and the substrate and exchange of the ions between the polymer matrix and the electrolyte solution. A large hysteresis for expansion and shrinking of the film is observed. In aqueous solutions, the hydrophobicity of alkyl chains limits the transfer of water molecules into the film and, in consequence, hinders the film reconfiguration. The thickness changes observed during polymer doping-undoping in water are about six times smaller than those observed in PC solution.

Marek Szklarczyk

Papers

The behaviour of iron electrode in CO2− saturated neutral electrolyte—I. Electrochemical study

Spectroelectrochemical and AFM studies of doping-undoping of poly(3-hexylthiophene) films in propylene carbonate and aqueous solutions of LiClO4

The behaviour of high polar organic solvents on platinum electrodes—I. The study of adsorption and electrode reactions of dimethylsulphoxide

The behaviour of high polar organic solvents at platinum electrode — II. Adsorption and electrode reactions of acetonitrile

The behaviour of iron electrode in CO2− saturated neutral electrolyte—II. Radiotracer study and corrosion considerations