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A proton exchange ionomer is one of the most important components in membrane electrode assemblies (MEAs) of polymer electrolyte membrane fuel cells (PEMFCs). It acts as both a proton conductor and a binder for nanocatalysts and carbon supports. The structure and the wetting conditions of the MEAs have a great impact on the microenvironment at the three-phase interphases in the MEAs, which can significantly influence the electrode kinetics such as the oxygen reduction reaction (ORR) at the cathode. Herein, by using the Pt(111)|X ionomer interface as a model system (X = Nafion, Aciplex, D72), we find that higher drying temperature lowers the onset potential for sulfonate adsorption and reduces apparent ORR current, while the current wave for OHad formation drops and shifts positively. Surprisingly, the intrinsic ORR activity is higher after properly correcting the blocking effect of Pt active sites by sulfonate adsorption and the poly(tetrafluoroethylene) (PTFE) skeleton. These results are well explained by the reduced water activity at the interfaces induced by the ionomer/PTFE, according to the mixed potential effect. Implications for how to prepare MEAs with improved ORR activity are provided.

The application of mixed catalysts in chemical to electrical energy transformation reactions can be a strategy for enhancing the catalysis of these reactions. Platinum and palladium exhibit significant catalytic activity in reactions of different natures, influenced not only by composition but also by structure. The present work presents a fundamental study of the characterization and electrochemical behavior of platinum-palladium bulk alloy single-crystal electrodes (Pt100−xPdx), prepared via a modified Clavilier protocol. Electrodes with varying mass ratios of Pt and Pd, compositions ranging from 0 to 15% Pd, and crystallographic orientations of (111) and (100) were manufactured. X-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED) reveal a well-correlated bulk and surface composition with ordered crystalline structures. Cyclic voltammetry in HClO4 and H2SO4 electrolytes indicates stronger anion interactions compared to pure platinum. Charge displacement experiments by CO adsorption estimate the effect of surface orientation and Pd content on the potential zero total charge (pztc). For Pt100−xPdx(111) surfaces, the pztc is very close to that of Pt(111), while surfaces with (100) orientation show decreasing pztc values with higher Pd content, favoring OH adsorption at lower potentials. Finally, the CO oxidation reaction on these Pt–Pd bulk alloy electrodes is studied by cyclic voltammetry, providing a profoundly comparative discussion of this reaction with Pt(111), Pt(100), and Pt(111) modified with Pd sub-monolayers.

Methanol oxidation is studied on well-defined Pt single-crystal surfaces to obtain information about the rate-determining step of the mechanism. For that, a voltammetric analysis of the kinetic isotopic effect using CH3OH and CD3OH at two different concentrations (10–4 and 10–2 M) has been carried out. For both concentrations, a significant diminution of the currents is observed when CD3OH is used, implying that the break of the C—H bond is involved in the rate-determining step of the reaction. The quantification of the Kinetic Isotope Effect (KIE) using the voltammetric currents shows values between 2.5 and 3.5, depending on the potential and surface orientation. This complex behavior is a consequence of the existence of several paths in the oxidation mechanism, whose rates strongly depend on the interfacial conditions. The different values are discussed considering the mechanism. On the other hand, when signals leading to the formation of CO on the Pt(100) electrode are analyzed, a KIE factor of 4.7 is obtained. All these numbers imply that in the rate-determining step of the mechanism, a C—H bond is broken.

This research explores the glycerol electrooxidation reaction (GEOR) on a platinum electrode, with a special emphasis on the role of the chemical properties of the anion present in the electrolyte composition. Essential knowledge of the mechanism and dynamics of glycerol electrooxidation is obtained through comprehensive studies that involve in situ FTIR measurements and the analysis of electrochemically oscillatory responses. This study focuses on the complex interplay between anion adsorption strength and the GEOR, focusing on the differences in CO adsorption coverage, which is the main strongly adsorbed intermediate. The anion adsorption strength, with the order HClO4 < H2SO4 < H3PO4, affects significantly not only the CO coverage on the platinum surface but also the overall glycerol electrooxidation rate. The observed differences in the electroactivity are attributed to competitive adsorption phenomena, in which specific coordinated ions have greater adsorption capabilities than perchlorate ions. These findings highlight the critical relevance of designing and optimizing electrocatalysts for glycerol electrooxidation and related processes with careful consideration of the electrolyte composition, notably the anion.

The ability to detect trace concentrations of arsenite, As (III), in real water solutions is impacted by co-contamination of other metals and co-occurring ions. The presence of copper (II) ions are the most likely co-contaminant in natural waters to interfere with electrochemical As (III) detection, due to the close oxidation potentials of Cu (II) and As (III). The use of well-oriented ultraflat Au(111) thin film electrodes provided increased peak separation and sensitivity for electrochemical deposition and oxidation of Cu (II) and As (III) in 0.5 M sulfuric acid compared to an Au wire electrode. However, mixtures of Cu (II) and As (III) altered the oxidation peak positions during both cyclic voltammetry (CV) and linear stripping voltammetry (LSV) analysis. Calibration curves using the standard additions method in trace concentrations were conducted for Cu, As, and Cu & As solutions. Sweeping the potential at 10 mV s−1 during CV in Cu & As mixtures resulted in a sequential deposition condition where a layer of Cu inhibited co-deposition of As to the electrode. In contrast, the rapid potential stepping of LSV to a potential where Cu and As reduction simultaneously occurs produced a peak profile different from Cu or As alone. A larger oxidation peak during LSV was also observed when both Cu and As were present. X-ray photoelectron spectroscopy indicates a Cu-As alloy is formed on the surface after LSV deposition. SYNOPSIS: Analysis of Cu (II), As (III) and Cu (II) & As (III) mixtures suggests that a Cu3As intermetallic phase is formed during LSV which impacts trace As detection even in trace Cu conditions. This has important implications for the ability to determine As concentrations near the MCL of 10 µg L−1 in natural water systems which may contain Cu (II) and other co-contaminants.