Investigating the presence of adsorbed species on Pt steps at low potentials

The study of the OH adsorption process on Pt single crystals is of paramount importance since this adsorbed species is considered the main intermediate in many electrochemical reactions of interest, in particular, those oxidation reactions that require a source of oxygen. So far, it is frequently assumed that the OH adsorption on Pt only takes place at potentials higher than 0.55 V (versus the reversible hydrogen electrode), regardless of the Pt surface structure. However, by CO displacement experiments, alternating current voltammetry, and Raman spectroscopy, we demonstrate here that OH is adsorbed at more negative potentials on the low coordinated Pt atoms, the Pt steps. This finding opens a new door in the mechanistic study of many relevant electrochemical reactions, leading to a better understanding that, ultimately, can be essential to reach the final goal of obtaining improved catalysts for electrochemical applications of technological interest.

Correlating Surface Structures and Electrochemical Activity Using Shape-Controlled Single-Pt Nanoparticles

We report a method for synthesizing and studying shape-controlled, single Pt nanoparticles (NPs) supported on carbon nanoelectrodes. The key advance is that the synthetic method makes it possible to produce single, electrochemically active NPs with a vast range of crystal structures and sizes. Equally important, the NPs can be fully characterized, and, therefore, the electrochemical properties of the NPs can be directly correlated to the size and structure of a single shape. This makes it possible to directly correlate experimental results to first-principles theory. Because just one well-characterized NP is analyzed at a time, the difficulty of applying a theoretical analysis to an ensemble of NPs having different sizes and structures is avoided. In this article, we report on two specific Pt NP shapes having sizes on the order of 200 nm: concave hexoctahedral (HOH) and concave trapezohedral (TPH). The former has {15 6 1} facets and the latter {10 1 1} facets. The electrochemical properties of these single NPs for the formic acid oxidation (FAO) reaction are compared to those of a single, spherical polycrystalline Pt NP of the same size. Finally, density functional theory, performed prior to the electrochemical studies, were used to interpret the experimental results of the FAO experiments.

Unveiling the Mechanisms Ruling the Efficient Hydrogen Evolution Reaction with Mitrofanovite Pt3Te4

By means of electrocatalytic tests, surface-science techniques and density functional theory, we unveil the physicochemical mechanisms ruling the electrocatalytic activity of recently discovered mitrofanovite (Pt₃Te₄) mineral. Mitrofanovite represents a very promising electrocatalyst candidate for energy-related applications, with a reduction of costs by 47% compared to pure Pt and superior robustness to CO poisoning. We show that Pt₃Te₄ is a weak topological metal with the Z2 invariant, exhibiting electrical conductivity (∼4 × 10⁶ S/m) comparable with pure Pt. In hydrogen evolution reaction (HER), the electrode based on bulk Pt₃Te₄ shows a very small overpotential of 46 mV at 10 mA cm^-2 and a Tafel slope of 36-49 mV dec^-1 associated with the Volmer-Heyrovsky mechanism. The outstanding ambient stability of Pt₃Te₄ also provides durability of the electrode and long-term stability of its efficient catalytic performances.

Electro-Oxidation of CO Saturated in 0.1 M HClO4 on Basal and Stepped Pt Single-Crystal Electrodes at Room Temperature Accompanied by Surface Reconstruction

The electro-oxidation of CO on Pt surface is not only fundamentally important in electrochemistry, but also practically important in residential fuel cells for avoiding the poisoning of Pt catalysts by CO. We carried out cyclic voltammetry on Pt(111), (110), (100), (10 10 9), (10 9 8), (10 2 1), (432), and (431) single-crystal surfaces using a three compartment cell to understand the activity and durability towards the electro-oxidation of CO saturated in 0.1 M HClO4. During the potential cycles between 0.07 and 0.95 V vs. the reversible hydrogen electrode, the current for the electro-oxidation of CO at potentials lower than 0.5 V disappeared, accompanied by surface reconstruction. Among the electrodes, the Pt(100) electrode showed the lowest onset potential of 0.29 V, but the activity abruptly disappeared after one potential cycle; the active sites were extremely unstable. In order to investigate the processes of the deactivation, potential-step measurements were also conducted on Pt(111) in a CO-saturated solution. Repeated cycles of the formations of Pt oxides at a high potential and Pt carbonyl species at a low potential on the surface were proposed as the deactivation process.

Unraveling the Nature of Active Sites in Ethanol Electro-oxidation by Site-Specific Marking of a Pt Catalyst with Isotope-Labeled 13CO

This works deals with the identification of preferential site-specific activation at a model Pt surface during a multiproduct reaction. The (110)-type steps of a Pt(332) surface were selectively marked by attaching isotope-labeled ¹³CO molecules to them, and ethanol oxidation was probed by in situ Foureir transfrom infrared spectroscopy in order to precisely determine the specific sites at which CO₂, acetic acid, and acetaldehyde were preferentially formed. The (110) steps were active for splitting the C-C bond, but unexpectedly, we provide evidence that the pathway of CO₂ formation was preferentially activated at (111) terraces, rather than at (110) steps. Acetaldehyde was formed at (111) terraces at potentials comparable to those for CO₂ formation also at (111) terraces, while the acetic acid formation pathway became active only when the (110) steps were released by the oxidation of adsorbed ¹³CO, at potentials higher than for the formation of CO₂ at (111) terraces of the stepped surface.

Nitrate Reduction on Platinum (111) Surfaces Modifiedl with Bi: Single Crystalsl and Nanoparticles

Nitrate reduction on well-oriented platinum surfaces modified with Bi adatoms has been studied. The quantification of the electrocatalytic enhancement of the reaction rate due to the presence of Bi at different coverages was made on Pt(111) and the vicinal surfaces Pt(554) and Pt(332). These contain 9 and 5 atoms-width (111) terraces, respectively, separated by (110) monoatomic steps. The study was then extended to preferentially {111}Pt oriented nanoparticles. In all cases, Bi catalyzes nitrate reduction at high potentials, but the catalytic current suddenly drops when Bi is reduced. The analysis of the variation of catalytic activity with Bi coverage reveals the participation of a third body effect, meaning that Bi impedes the NO formation on the surface that acts as a poison for the nitrate reduction.