Electroreduction of CO2 in a Non-aqueous Electrolyte-The Generic Role of Acetonitrile

Transition metal carbides, especially Mo2C, are praised to be efficient electrocatalysts to reduce CO2 to valuable hydrocarbons. However, on Mo2C in an aqueous electrolyte, exclusively the competing hydrogen evolution reaction takes place, and this discrepancy to theory was traced back to the formation of a thin oxide layer at the electrode surface. Here, we study the CO2 reduction activity at Mo2C in a non-aqueous electrolyte to avoid such passivation and to determine products and the CO2 reduction reaction pathway. We find a tendency of CO2 to reduce to carbon monoxide. This process is inevitably coupled with the decomposition of acetonitrile to a 3-aminocrotonitrile anion. Furthermore, a unique behavior of the non-aqueous acetonitrile electrolyte is found, where the electrolyte, instead of the electrocatalyst, governs the catalytic selectivity of the CO2 reduction. This is evidenced by in situ electrochemical infrared spectroscopy on different electrocatalysts as well as by density functional theory calculations.

Deactivation and regeneration of a benchmark Pt/C catalyst toward oxygen reduction reaction in the presence of poisonous SO2 and NO

Adsorbed SO2 on Pt sites can be substituted by NO; adsorbed NO can be completely reduced to NH4+ and removed in a reduction potential range.

Electrochemical behaviour and surface characterisation of Zr exposed to an SBF solution containing glycine, in view of dental implant applications

Zr and Ti alloys are extensively used in the biomedical field owing to their optimal mechanical properties and excellent corrosion resistance. Fully ceramic implants based on zirconia are appealing with respect to the traditional Ti-based metallic ones for several reasons, such as: (i) improved aesthetic impact, (ii) better biocompatibility and (iii) better osteointegration. Nevertheless, fully ceramic implants exhibit serious mechanical and clinical drawbacks, chiefly brittleness and impossibility of post-implant position adjustments. In this paper we propose the novel approach of using a metal-based system, consisting of metallic Zr, for the bulk of the implant and an electrochemically grown zirconia coating, ensuring contact of the ceramic with the biological environment and isolation from the underlying metal. This solution combines the outstanding mechanical properties of the metal in the bulk with the optimal biochemical properties exclusively where they are needed: at the surface. The present paper-focussed on the electrochemical behaviour of the proposed system at the implant-wound and implant-growing bone interface-reports a time-dependent electrochemical corrosion study of zirconia-coated zirconium, performed in the following ways: (i) exposure and measurements in SBF (simulating the inorganic part of human plasma, relevant to wound chemistry), (ii) exposure and measurements in SBF with added glycine (the simplest, ubiquitous amino acid found in proteins), (iii) exposure in SBF with added glycine and measurements in SBF. Electrochemical impedance spectra were measured and interpreted with the equivalent-circuit approach, yielding estimates of the time-variation of the oxide film thickness and resistance were estimated. FT-IR, Surface Raman and VIS reflectance spectroscopies were used to characterise the surface before and after the exposure to SBF solutions. Spectroelectrochemical measurements revealed an higher corrosion resistance of the oxide films formed on Zr in the presence of glycine in the SBF matrix and a smoother electrode surface.