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Homogeneous, aqueous solutions of the natural compound riboflavin were investigated for their electrocatalytic oxygen to hydrogen peroxide (H2O2) reduction performance using cyclic voltammetry and electrolysis. In addition to pH dependencies, interestingly the choice of carbon‐based electrode material had a strong impact on the electrocatalytic performance. Therefore, the three electrode materials, glassy carbon, carbon paper (CP), and carbon felt were electrochemically compared and afterwards investigated with scanning electron microscopy. Attributed to the deprotonation of riboflavin, pH = 13 was identified as the best performing condition. Using CP at pH = 13, the addition of riboflavin enhanced the H2O2 production by a factor of 14 up to 355 μmol after 6 h at an average faradaic efficiency of around 80%. [ABSTRACT FROM AUTHOR]

Abstract: We report on a self‐assembled system comprising a molecular copper‐porphyrin photoelectrocatalyst, 5‐(4‐carboxy‐phenyl)‐10,15,20‐triphenylporphyrinatocopper(II) (CuTPP‐COOH), covalently bound to self‐organized, anodic titania nanotube arrays (TiO2 NTs) for photoelectrochemical reduction of oxygen. Visible light irradiation of the porphyrin‐covered TiO2 NTs under cathodic polarization up to −0.3 V vs. Normal hydrogen electrode (NHE) photocatalytically produces H2O2 in pH neutral electrolyte, at room temperature and without need of sacrificial electron donors. The formation of H2O2 upon irradiation is proven and quantified by direct colorimetric detection using 4‐nitrophenyl boronic acid (p‐NPBA) as a reactant. This simple approach for the attachment of a small molecular catalyst to TiO2 NTs may ultimately allow for the preparation of a low‐cost H2O2 evolving cathode for efficient photoelectrochemical energy storage under ambient conditions. [ABSTRACT FROM AUTHOR]

We present a study on a microbial electrolysis cell with methanogenic microorganisms adapted to reduce CO2 to CH4 with the direct injection of electrons and without the artificial addition of H2 or an additional carbon source except gaseous CO2. This is a new approach in comparison to previous work in which both bicarbonate and gaseous CO2 served as the carbon source. The methanogens used are known to perform well in anaerobic reactors and metabolize H2 and CO2 to CH4 and water. This study shows the biofilm formation of those microorganisms on a carbon felt electrode and the long-term performance for CO2 reduction to CH4 using direct electrochemical reduction. CO2 reduction is performed simply by electron uptake with gaseous CO2 as the sole carbon source in a defined medium. This 'electrometabolism' in such microbial electrolysis cells depends strongly on the potential applied as well as on the environmental conditions. We investigated the performance using different adaption mechanisms and a constant potential of −700 mV vs. Ag/AgCl for CH4 generation at 30-35 °C. The experiments were performed by using two-compartment electrochemical cells. Production rates with Faradaic efficiencies of around 22 % were observed. [ABSTRACT FROM AUTHOR]

The alkynyl-substituted ReI complex [Re(5,5′-bisphenylethynyl-2,2′-bipyridyl)(CO)3Cl] was immobilized by electropolymerization onto a Pt-plate electrode. The polymerized film exhibited electrocatalytic activity for the reduction of CO2 to CO. Cyclic voltammetry studies and bulk controlled-potential electrolysis experiments were performed by using a CO2-saturated acetonitrile solution. The CO2 reduction, determined by cyclic voltammetry, occurs at approximately −1150 mV versus the normal hydrogen electrode (NHE). Quantitative analysis by GC and IR spectroscopy was used to determine a Faradaic efficiency of approximately 33 % for the formation of CO. Both values of the modified electrode were compared to the performance of the homogenous monomer [Re(5,5′-bisphenylethynyl-2,2′-bipyridyl)(CO)3Cl] in acetonitrile. The polymer formation and its properties were studied by using SEM, AFM, and attenuated total reflectance (ATR) FTIR and UV/Vis spectroscopy. [ABSTRACT FROM AUTHOR]

• Electrocatalysis of O 2 reduction in solution often requires special electrode materials. • Our subtraction method allows electrochemical analysis with conventional GC/Pt RRDE. • Information about excess current and excess efficiency can be provided. • Upon rotation the excess current and electrocatalytic potentials are affected. The state-of-the-art procedure for investigating homogenous and heterogeneous electrocatalysts is cyclic voltammetry (CV). However, this technique usually requires an inactive electrode material. One common problem arising e. g. in studying the oxygen reduction reaction (ORR) is the significant background contribution to the overall ORR current provided by many carbon-based and metal-based electrode materials. Furthermore, rotating ring-disc electrodes (RRDEs) made of common materials like glassy carbon/platinum (GC/Pt) can be affected by overlapping reduction potentials on the disc. Interference from overlapping reactions on the ring might also occur, particularly in connection with oxygen reduction and hydrogen peroxide oxidation in ORR studies. We present herein a novel subtraction method which allows a semi-quantitative description of homogeneous electrocatalysts and helps to overcome the overlapping problems described above using anthraquinone-2-sulfonate (AQS) as a "case study material" for the ORR. [ABSTRACT FROM AUTHOR]

The electrocatalytic reduction of carbon dioxide (CO 2 ) is an attractive option to efficiently bind electrical energy from renewable resources in artificial carbon fuels and feedstocks. The strategy is considered as crucial part in closing the anthropogenic carbon cycle. In particular, the electrosynthetic production of C1 species such as carbon monoxide (CO) would radiate immense power, since these building blocks offer a versatile chemistry to higher carbon products and fuels. In the present study we report the exploration of the catalytic behavior of semiconducting Co 3 O 4 nanofibers for the conversion of CO 2 to CO predominantly with a Faradaic efficiency of 65%. We assist the process by expanding the electrode network with nanofibrous interconnections and hence are able to demonstrate the electrosynthesis of CO without applying any metal supplement. We use polyacrylnitrile (PAN) as template polymer to generate highly crystalline Co 3 O 4 fibers to expand the catalytically active surface to volume ratio. The stability of the nanofibrous electrodes remains for 8 h at a geometric current density of approximately 0.5 mA/cm 2 on a flat surface. The ease of synthesis and the comparatively high Faradaic yield for CO makes Co 3 O 4 nanofibers a potential candidate for future large scale electrode utilization. [ABSTRACT FROM AUTHOR]

Herein we report a highly efficient molecular catalyst of novel Re(I) complex (ReTPS) containing 4,4′-bis(4-(triphenylsilyl)phenyl)-2,2′-bipyridine as a specific ligand. Photophysical studies and density functional theory (DFT) as well as time-dependent DFT (TDDFT) calculations show efficient expansion of π-system by the arylsilyl units, with a minimal electronic effect on the parent Re(I) complex. Electrochemical studies reveal an electron-reservoir characteristic of ReTPS by storing two electrons in the ligand before the Re(I) center is reduced. Faradaic efficiency of 76% and turnover number of 130 were recorded for electrocatalytic and photocatalytic reduction of CO 2 , respectively. [ABSTRACT FROM AUTHOR]

The article reports on the use of biofunctionalized conductive polymers for electrocatalysis of carbon dioxide in generating renewable carbon feedstock and synthetic fuels. It is said that polydopamine could offer the combination of efficient electrical conduction, together with rendered active catalytic sites.

Abstract: The rhenium complex fac-(5,5′-bisphenylethynyl-2,2′-bipyridyl)Re(CO)3Cl was used as a novel catalyst for the electro- and photochemical reduction of CO2 to CO in homogeneous solution. The results were compared to (2,2′-bipyridyl)Re(CO)3Cl as a benchmark compound. Cyclic voltammetric studies as well as bulk controlled potential electrolysis experiments were performed using a CO2 saturated solution in acetonitrile. (5,5′-bisphenylethynyl-2,2′-bipyridyl)Re(CO)3Cl showed a 6.5-fold increase in current density under CO2 at −1750 mV versus normal hydrogen electrode (NHE) as compared to the operation without CO2. Quantitative analysis by gas chromatography (GC) and infrared spectroscopy showed a Faradaic efficiency of around 45% for the formation of CO. [Copyright &y& Elsevier]