Electrochemical dissolution of gold and platinum in 0.1 M HClO 4 , 0.1 M H 2 SO 4 , and 0.05 M NaOH is investigated. The qualitative picture of both metals' dissolution is pH-independent. Oxidation/reduction of the metal's surface leads to the transient dissolution peaks which we label A 1 and C 1 on the dissolution profiles. Commencement of the oxygen evolution reaction (OER) results in the additional dissolution peak A 2 . Quantitatively, there are important differences. The amount of gold transiently dissolved in alkaline medium is more than an order of magnitude higher in comparison to that in acidic medium. Oppositely, steady-state gold dissolution in base in the potential region of OER is hindered. The transient dissolution of platinum is by a factor of two higher in base. It is suggested that variation of the pH does not change the mechanism of the OER on platinum. Consequently, the dissolution rate of platinum is equal in acidic and alkaline electrolytes. As an explanation of the observed difference in gold dissolution, a difference in the thickness of compact oxide formed in acid and base is suggested. Growth of a thicker compact oxide in the alkaline medium explains the increased transient and the decreased steady-state dissolution of gold. Platinum and gold are perhaps the most frequently studied metals in electrochemistry. In particular, they constitute important model systems in the context of fundamental investigations of the mechanism and kinetics of the initial stages of metal oxidation. Surface processes during transition of adsorbed hydroxyl groups to, initially, compact couple of monolayers thickness and, later, relatively thick bulk phase oxides have occupied electrochemists for many decades. In the earliest works, investigations were directed toward the general problem of metal passivity, hotly debated at the beginning of the twentieth century. [1][2][3] In the 1960s and 1970s, the rapid development of fuel cells and application of platinum as a catalyst for the hydrogen oxidation and the oxygen reduction reactions (HOR and ORR) re-stimulated research efforts on noble metal oxidation. As adsorbed intermediates and other oxygenated species present on the catalyst surface were believed to have a poisoning effect on the rate of the ORR, understanding of the oxygen-platinum interaction was of substantial importance. The great progress in the development of electrochemical experimental techniques and surface analytics in these years significantly contributed to new insights of electrocatalysis at the solid-liquid interface. The understanding of noble metal oxidation is, however, not only crucial for these reactions but also the essential step in the comprehension of dissolution. Despite its importance in general and as a basis for the current work, the description of the theories and models for noble metal oxidation over the last century is beyond the scope of the present article. The interested reader is therefore referred to a comprehensive work published by Conway, and references therein. Plat...

One of the most important practical issues in low‐temperature fuel‐cell catalyst degradation is platinum dissolution. According to the literature, it initiates at 0.6–0.9 VRHE, whereas previous time‐ and potential‐resolved inductively coupled plasma mass spectrometry (ICP–MS) experiments, however, revealed dissolution onset at only 1.05 VRHE. In this manuscript, the apparent discrepancy is addressed by investigating bulk and nanoparticulated catalysts. It is shown that, given enough time for accumulation, traces of platinum can be detected at potentials as low as 0.85 VRHE. At these low potentials, anodic dissolution is the dominant process, whereas, at more positive potentials, more platinum dissolves during the oxide reduction after accumulation. Interestingly, the potential and time dissolution dependence is similar for both types of electrode. Dissolution processes are discussed with relevance to fuel‐cell operation and plausible dissolution mechanisms are considered.

We provide a comprehensive durability assessment dedicated to a promising class of electrocatalysts for the oxygen reduction reaction (i.e., porous platinum nanoparticles). The stability of these nanoengineered open structures is tested under two accelerated degradation test conditions (ADT), particularly selected to mimic the potential regimes experienced by the catalyst during the operative life of a fuel cell (i.e., load cycles (up to 1.0 V RHE ) and start-up cycles (up to 1.4 V RHE )). To understand the evolution of the electrochemical performance, the catalyst properties are investigated by means of fundamental rotating disc electrode studies, identical location-transmission electron microscopy (IL-TEM) coupled with electron energy loss spectroscopy chemical mapping (IL-EELS), and post-use chemical analysis and online highly sensitive potential resolved dissolution concentration monitoring by scanning flow cell inductively coupled plasma-mass spectrometry (SFC-ICP-MS). The experimental results on the nanoporous Pt revealed distinctive degradation mechanisms that could potentially affect a wide range of other nanoengineered open structures. The study concludes that, although providing promising activity performance, under the relevant operational conditions of fuel cells, the nanoporosity is only metastable and subjected to a progressive reorganization toward the minimization of the nanoscale curvature. The rate and pathways of this specific degradation mechanism together with other well-known degradation mechanisms like carbon corrosion and platinum dissolution are strongly dependent on the selected upper limit potential, leading to distinctly different durability performance.

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We report on an adjustable process for chemical vapour deposition of thin films of pyrolytic carbon on inert substrates using an acetylene feedstock. Through modification of the reaction parameters control over film thickness and roughness is attained. These conducting films can be deposited in a conformal fashion, with thicknesses as low as 5 nm and a surface roughness of less than 1 nm. The highly reliable, cost effective and scalable synthesis may have a range of applications in information and communications technology and other areas. Raman and X-ray photoelectron spectroscopies, as well as high resolution transmission electron microscopy are used to investigate the composition and crystallinity of these films. The suitability of these films as electrodes in transparent conductors is assessed through a combination of absorbance and sheet resistance measurements. The films have a resistivity of ~ 2 × 10-5 m but absorb strongly in the visible range. The electrochemical properties of the films are investigated and are seen to undergo a marked improvement following exposure to O 2 or N 2 plasmas, making them of interest as electrochemical electrodes.