With the aim of obtaining a highly stable and active catalyst for oxygen evolution reaction (OER), a core–shell-like IrO2@RuO2 material was synthesized by using a surface modification/precipitation method in ethanol medium. The comparison of this catalyst with pure RuO2 and pure IrO2 showed that the obtained mixed oxide catalyst displayed the highest amount of active sites as well as a good accessibility for water. Moreover, this catalyst was shown to be highly stable toward repetitive redox cycling. Polarization curves of the three catalysts showed that the IrO2@RuO2 was the most active for the OER due to the large number and high accessibility of active sites. These catalytic benefic effects are attributed to an intimate contact between the two oxides in the IrO2-covered RuO2 nanocatalyst that combines the RuO2 intrinsic activity and the IrO2 stability. The present study contributes therefore to the rational design of efficient and stable electrocatalysts for water splitting in acidic media.

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Low-cost, efficient CO 2 -to-CO+O 2 electrochemical splitting is a key step for liquid-fuel production for renewable energy storage and use of CO 2 as a feedstock for chemicals. Heterogeneous catalysts for cathodic CO 2 -to-CO associated with an O 2 -evolving anodic reaction in high-energy-efficiency cells are not yet available. An iron porphyrin immobilized into a conductive Nafion/carbon powder layer is a stable cathode producing CO in pH neutral water with 90% faradaic efficiency. It is coupled with a water oxidation phosphate cobalt oxide anode in a home-made electrolyzer by means of a Nafion membrane. Current densities of approximately 1 mA/cm 2 over 30-h electrolysis are achieved at a 2.5-V cell voltage, splitting CO 2 and H 2 O into CO and O 2 with a 50% energy efficiency. Remarkably, CO 2 reduction outweighs the concurrent water reduction. The setup does not prevent high-efficiency proton transport through the Nafion membrane separator: The ohmic drop loss is only 0.1 V and the pH remains stable. These results demonstrate the possibility to set up an efficient, low-voltage, electrochemical cell that converts CO 2 into CO and O 2 by associating a cathodic-supported molecular catalyst based on an abundant transition metal with a cheap, easyto-prepare anodic catalyst oxidizing water into O 2 .CO 2 -to-CO conversion | carbon dioxide electrolyzer | electrochemistry | molecular catalysis | solar fuels T he production of carbon-based fuels or chemicals using the most abundant carbon source (CO 2 ) requires designing efficient, cheap, selective, and sustainable processes able to convert CO 2 into useful products (1-7). Carbon monoxide production is an important step to fuels because it can be used as a feedstock in the Fischer-Tropsch process. Compared with water splitting, electrochemical reduction of CO 2 into CO is a greater challenge. This is particularly true when aiming to carry out this reaction selectively in friendly conditions, namely at neutral pHs, ambient temperature, and with abundant and cheap materials as catalysts as opposed to solid-state high-temperature electrolyzers (8).We recently discovered that substitution of the four paraphenyl hydrogens of iron tetraphenylporphyrin by trimethylammonio groups provides a water-soluble iron porphyrin (WSCAT) able to catalyze selectively the electrochemical conversion of CO 2 into CO in neutral water in homogeneous conditions (9). The next challenge was to efficiently immobilize this molecular catalyst onto the cathode and to set up an integrated electrochemical cell able to split CO 2 and H 2 O into CO and O 2 according to[potentials referred to the standard hydrogen electrode (SHE)]. Immobilization of the catalyst was achieved by preparation of a suspension containing Nafion, WSCAT, and carbon powder (Materials and Methods) (10). This solution was then sprayed onto a carbon support (glassy carbon electrode for cyclic voltammetry experiments and carbon felt or carbon Toray for electrolysis) and air-dried. Interactions between the positively charged cataly...

Experimental data for viscosities, diffusion coefficients of ferrocene, and conductivities were obtained for three ionic liquid mixtures:  1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4), N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (bmpyNTf2), and N-methyl-N-hexylpyrrolidinium bis(trifluoromethylsulfonyl)imide (hmpyNTf2) + dimethylformamide (DMF) or + 3-picoline as cosolvents, in the range of temperature T = (295.2 to 325.2) K. At a given temperature, the viscosity decreases exponentially with the mole fraction of the added cosolvent, and the variation of the diffusion coefficient agrees with the Stokes−Einstein law. Concerning the conductivity, addition of the polar solvent dimethylformamide produces an increase much greater than the addition of 3-picoline. The viscosity, diffusion coefficient, and conductivity follow the Arrhenius model in the explored temperature range. Consequently, moderate heating and addition of a cosolvent are two good means for obtaining conditions well adapted to electrosynthetic applications in ionic liquids.

Electronic Supplementary Information (ESI) available: [N2-sorption measurements performed with SBA-15 used as hard template for the synthesis of mesoporous oxides. Pdf data obtained from the characterization of MnCo2O4-δ, NiCo2O4-δ, Co3O4-δ, NiO materials. Voltammogram recorded in supporting electrolyte (KOH 0.1 M) under N2 atmosphere at a scan rate of 50 mV s -1 with mesoporous NiO catalyst at room temperature. Overlay of EIS bode plots for Co3O4-δ and NiCo2O4-δ at 1.800 V vs. RHE]. SeeAbstract: Co3O4-δ, MnCo2O4-δ, NiCo2O4-δ materials were synthesized using a nanocasting process consisting in replicating a SBA-15 hard template. Catalysts powders obtained were characterized using different physico-chemical techniques (X-ray scattering, transmission electron microscopy, N2 physisorption and X-ray photoelectron spectroscopy) in order to deeply characterize their morphostructural properties. Electrochemical measurements performed with cyclic voltammetry and electrochemical impedance spectroscopy techniques have shown that these catalysts were liable to surface modifications induced by the applied electrode potential. These surface structural modifications as well as their effect on the electroactivity of the catalyst towards the OER in alkaline medium are discussed. The activated NiCo2O4-δ material showed particularly excellent catalytic ability towards the OER in 0.1 M KOH electrolyte In this material Co (IV) is found to be the active species in the catalyst composition for the OER. It exhibits an overpotential as low as 390 mV at a current density of 10 mA cm -2 . This catalytic activity is especially high since the oxide laoding is only of 0.074 mg cm -2 . Furthermore, this anode catalyst showed high stability during an accelerated durability test of 1500 voltammetric cycles.Please do not adjust margins Please do not adjust margins region at three potential values (0.7; 0.8 and 1 V vs. RHE) for each catalyst.

Two electrochemical techniques have been used to measure the pK(a) of N-bases in several ionic liquids (ILs). The first method corresponds to a potentiometric titration of a strong acid with the N-base using a platinized Pt indicator electrode immersed in the IL solution and maintained under dihydrogen atmosphere via gas bubbling. The second approach involves performing cyclic voltammetry at a platinized Pt electrode in a solution containing both strong acid and the conjugate weak acid of the N-base. Values of pK(a) obtained by one or the other approach are in good agreement with each other. The experimental data clearly demonstrated that acid/base chemistry in ILs is similar to that observed in molecular nonaqueous solvents; i.e., the relative strengths of the bases were in the right order and spaced (ΔpK(a)). It was also observed that the strength of N-bases is highly dependent on the anion of the ionic liquid; this observation indicates that pH-dependent reactions could be controlled by the appropriate choice of anion for bulk ILs or as an added co-ion to bulk IL.