Exploring the interfacial neutral pH region of Pt(111) electrodes

The interfacial properties of Pt(111) single crystal electrodes have been investigated in the pH range 3 < pH < 5 in order to obtain information about the acidity of electrosorbed water. Proper experimental conditions are defined to avoid local pH changes while maintaining the absence of specifically adsorbed anions and preserving the cleanliness of the solution. For this purpose, buffer solutions resulting from mixtures of NaF and HClO4 are used. Total charge curves are obtained at different pHs from the integration of the voltammetric currents in combination with CO charge displacement experiments. Analysis of the composition of the interphase as a function of the pH provides information for the understanding of the notion of interfacial pH.

Towards the understanding of the interfacial pH scale at Pt(1 1 1) electrodes

The determination of the potentials of zero total and free charge, pztc and pzfc respectively, were made in a wide pH range by using the CO displacement method and the same calculation assumptions used previously for Pt(1 1 1) electrodes in contact with non-specifically adsorbing anions. Calculation of the pzfc involves, in occasions, long extrapolations that lead us to the introduction of the concept of potential of zero extrapolated charge (pzec). It was observed that the pztc changes with pH but the pzec is independent of this parameter. It was observed that the pztc > pzec at pH > 3.4 but the opposite is true for pH > 3.4. At the latter pH both pzec and pztc coincide. This defines two different pH regions and means that adsorbed hydrogen has to be corrected in the “acidic” solutions at the pztc while adsorbed OH is the species to be corrected in the “alkaline” range. The comparison of the overall picture suggests that neutral conditions at the interface are attained at significantly acidic solutions than those at the bulk.

Role of the interfacial water structure on electrocatalysis: Oxygen reduction on Pt(1 1 1) in methanesulfonic acid

Most of electrocatalytic reactions occur in an aqueous environment. Understanding the influence of water structure on reaction dynamics is fundamental in electrocatalysis. In this work, the role of liquid water structure on the oxygen reduction at Pt(1 1 1) electrode is analyzed in methanesulfonic (MTSA) and perchloric acids. This is because these different anions can exert a different influence on liquid water structure. Results reveal a lower ORR electrode activity in MTSA than in HClO4 solutions and they are discussed in light of anion's influence on water structural ordering. From them, the existence of an outer-sphere, rate determining, step in the ORR mechanism is suggested.

Diamond Surface Modification to Enhance Interfacial Thermal Conductivity in Al/Diamond Composites

Diamond/metal composites are very attractive materials for electronics because their excellent thermal properties make them suitable for use as heat sink elements in multifunctional electronic packaging systems. To enlarge the potential applications of these composites, current efforts are mainly focused on investigating different ways to improve the contact between metal and diamond. In the present work, a theoretical study has been carried out to determine the differences between the interfacial thermal conductance of aluminum/diamond and aluminum/graphite interfaces. Additionally, diamond particles were surface modified with oxygen to observe how it affects the quality of the diamond surface. The characterization of the surface of diamonds has been performed using different surface analysis techniques, especially x-ray photoelectron spectroscopy and temperature-programmed desorption.