Electrochemical Reduction of Carbon Dioxide in an MFC–MEC System with a Layer-by-Layer Self-Assembly Carbon Nanotube/Cobalt Phthalocyanine Modified Electrode

Electrochemical reduction of carbon dioxide (CO₂) to useful chemical materials is of great significance to the virtuous cycle of CO₂. However, some problems such as high overpotential, high applied voltage, and high energy consumption exist in the course of the conventional electrochemical reduction process. This study presents a new CO₂ reduction technique for targeted production of formic acid in a microbial electrolysis cell (MEC) driven by a microbial fuel cell (MFC). The multiwalled carbon nanotubes (MWCNT) and cobalt tetra-amino phthalocyanine (CoTAPc) composite modified electrode was fabricated by the layer-by-layer (LBL) self-assembly technique. The new electrodes significantly decreased the overpotential of CO₂ reduction, and as cathode successfully reduced CO₂ to formic acid (production rate of up to 21.0 ± 0.2 mg·L^–1·h^–1) in an MEC driven by a single MFC. Compared with the electrode modified by CoTAPc alone, the MWCNT/CoTAPc composite modified electrode could increase the current and formic acid production rate by approximately 20% and 100%, respectively. The Faraday efficiency for formic acid production depended on the cathode potential. The MWCNT/CoTAPc composite electrode reached the maximum Faraday efficiency at the cathode potential of ca<i>.</i> −0.5 V vs Ag/AgCl. Increasing the number of electrode modification layers favored the current and formic acid production rate. The production of formic acid was stable in the MFC–MEC system after multiple batches of CO₂ electrolysis, and no significant change was observed on the performances of the modified electrode. The coupling of the catalytic electrode and the bioelectrochemical system realized the targeted reduction of CO₂ in the absence of external energy input, providing a new way for CO₂ capture and conversion

Electrochemically Generated <i>cis</i>-Carboxylato-Coordinated Iron(IV) Oxo Acid–Base Congeners as Promiscuous Oxidants of Water Pollutants

The nonheme iron­(IV) oxo complex [Fe^IV(O)­(tpenaH)]²⁺ and its conjugate base [Fe^IV(O)­(tpena)]⁺ [tpena^– = <i>N</i>,<i>N</i>,<i>N</i>′-tris­(2-pyridylmethyl)­ethylenediamine-<i>N</i>′-acetate] have been prepared electrochemically in water by bulk electrolysis of solutions prepared from [Fe^III₂(μ-O)­(tpenaH)₂]­(ClO₄)₄ at potentials over 1.3 V (vs NHE) using inexpensive and commercially available carbon-based electrodes. Once generated, these iron­(IV) oxo complexes persist at room temperature for minutes to half an hour over a wide range of pH values. They are capable of rapidly decomposing aliphatic and aromatic alcohols, alkanes, formic acid, phenols, and the xanthene dye rhodamine B. The oxidation of formic acid to carbon dioxide demonstrates the capacity for total mineralization of organic compounds. A radical hydrogen-atom-abstraction mechanism is proposed with a reactivity profile for the series that is reminiscent of oxidations by the hydroxyl radical. Facile regeneration of [Fe^IV(O)­(tpenaH)]²⁺/ [Fe^IV(O)­(tpena)]⁺ and catalytic turnover in the oxidation of cyclohexanol under continuous electrolysis demonstrates the potential of the application of [Fe^III(tpena)]²⁺ as an electrocatalyst. The promiscuity of the electrochemically generated iron­(IV) oxo complexes, in terms of the broad range of substrates examined, represents an important step toward the goal of cost-effective electrocatalytic water purification