The nucleation of Ag onto vitreous carbon from aqueous 3 M NaCl or 0.6 M NaClO4 and deep eutectic solvent (DES) 1:2 molar mixture of choline cloride:urea solutions containing Ag + , has been studied analyzing the chronoamperometric response to single potential steps. From the coordinates of the maxima observed in the current responses, the nucleation frequencies A (s-1) and number densities of nucleation sites N0 (cm-2) were obtained from the standard model of nucleation with diffusion-controlled three-dimensional growth. Analysis of the overpotential dependence of nucleation frequencies using the classical electrochemical nucleation theory allowed to calculate the Gibbs free energy of nucleation and critical nucleus size nc as well as the exchange current density j0, transfer coefficient and surface tension of silver nuclei. The kinetics of Ag + reduction is two orders of magnitude slower in DES compared to both aqueous systems studied, and values of << 0.5 where found in both aqueous and DES media, indicating either that the intermediate state for metal ion reduction is located close to the initial state, i.e., the solvated or complexed metal ion in solution, or that the metal ion is specifically adsorbed on the surface and the symmetry factor involved requires an alternative electron transfer formalism. The low and nc values observed indicate that the discharge of a single Ag ion on the surface already becomes a supercritical nucleus, involving a very low Gibbs energy barrier, characteristic of a non-activated process.
The hydrogen evolution reaction is one of the most studied processes in electrochemistry and platinum is by far the best catalyst for this reaction. Despite the importance of this reaction on platinum, detailed and accurate kinetic measurements of the steps that lead to the main reaction are still lacking, particularly because of the fast rate of the reaction. Hydrogen adsorption on Pt(111) has been taken as a benchmark system in a large number of computational studies but reliable experimental data to compare with the computational studies is very scarce. To gain further knowledge on this matter, a temperature study of the hydrogen adsorption reaction has been carried out to obtain kinetic information for this process on Pt(111), in alkaline solution. This was achieved by measuring electrochemical impedance spectra and cyclic voltammograms in the range of 278 ≤ T ≤ 318 (K), to obtain the corresponding surface coverage by adsorbed species and the faradaic charge transfer resistance. From this data, the standard rate constant has been extracted with a kinetic model assuming a Frumkin type 1 Page 1 of 22 ACS Paragon Plus Environment ACS Applied Materials & Interfaces isotherm, resulting in values of 2.60 × 10 −7 ≤ k 0 ≤ 1.68 × 10 −6 (s −1 ) respectively. The Arrehnius plot gives an activation energy of 32 kJ mol −1 . Comparisons are made with reported values for the overall HER and those calculated by computational methods, giving a reference frame to support future studies on hydrogen catalysis.
Application specific Pt-grown carbon nanofibers for H2O2 detection were characterized and the roles of dissolved oxygen and chloride ions on the electrochemical performance were assessed in detail.
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