Origin of Multiple Peaks in the Potentiodynamic Oxidation of CO Adlayers on Pt and Ru-Modified Pt Electrodes

Identifying Adsorbed OH Species on Pt and Ru Electrodes with Surface-Enhanced Infrared Absorption Spectroscopy through CO Displacement

OH adspecies are involved in numerous electrocatalytic reactions, such as CO, H2, methanol, and ethanol oxidation and oxygen reduction reactions, as a reaction intermediate and/or reactant. In this work, we have, for the first time, identified the OH stretching band of OH adspecies on Pt, Ru, and Pt/Ru electrodes with surface-enhanced infrared absorption spectroscopy (SEIRAS) in a flow cell through potential modulation and CO displacement. We found that while Ru had a relatively constant OH coverage at potentials between 0.1 and 0.8 V, Pt had a maximum OH coverage at 0.6 V in 0.1 M HClO4 and 0.7 V in 0.1 M KOH. CO oxidation kinetics on Ru were sluggish, although adsorbed OH appeared on Ru at very low potentials. Binary Pt/Ru electrodes promote CO oxidation through a synergistic effect in which Ru promotes OH adsorption and Pt catalyzes the reaction between the CO and OH adspecies. In addition, water coadsorbed with CO at Ru sites of Pt/Ru also plays an important role. These new spectroscopic results about OH adspecies could advance the understanding of the mechanism of fuel cell related electrocatalysis.

Engineering the Near-Surface of PtRu3 Nanoparticles to Improve Hydrogen Oxidation Activity in Alkaline Electrolyte

Tailoring the near-surface composition of Pt-based alloy can optimize the surface chemical properties of a nanocatalyst and further improve the sluggish H₂ electrooxidation performance in an alkaline electrolyte. However, the construction of alloy nanomaterials with a precise near-surface composition and smaller particle size still needs to overcome huge obstacles. Herein, ultra-small PtRu₃ binary nanoparticles (<2 nm) evenly distributed on porous carbon (PtRu₃ /PC), with different near-surface atomic compositions (Pt-increased and Ru-increased), are successfully synthesized. XPS characterizations and electrochemical test confirm the transformation of a near-surface atomic composition after annealing PtRu₃ /PC-300 alloy; when annealing in CO atmosphere, forming the Pt-increased near-surface structure (500 °C), while the Ru-increased near-surface structure appears in an Ar heat treatment process (700 °C). Furthermore, three PtRu₃ /PC nanocatalysts all weaken the hydrogen binding strength relative to the Pt/PC. Remarkably, the Ru-increased nanocatalyst exhibits up to 38.8-fold and 9.2-fold HOR improvement in mass activity and exchange current density, compared with the Pt/PC counterpart, respectively. CO-stripping voltammetry tests demonstrate the anti-CO poisoning ability of nanocatalysts, in the sequence of Ru-increased ≥ PtRu₃ /PC-300 > Pt-increased > Pt/PC. From the perspective of engineering a near-surface structure, this study may open up a new route for the development of high-efficiency electrocatalysts with a strong electronic effect and oxophilic effect.

Understanding the Voltammetry of Bulk CO Electrooxidation in Neutral Media through Combined SECM Measurements

Recently, the bulk electrooxidation of CO on gold or platinum has been used to detect CO produced during CO₂ reduction in neutral media. The CO bulk oxidation voltammetry may show two distinct peaks depending on the reaction conditions, which up to now have not been understood. We have used scanning electrochemical microscopy (SECM) to probe CO oxidation and pH in the diffusion layer during CO₂ reduction. Our results show that the two different peaks are due to diffusion limitation by two different species, namely, CO and OH^-. We find that between pH 7 and 11, CO oxidation by water and OH^- gives rise to the first and second peak observed in the voltammetry, respectively. Additional rotating disc experiments showed that specifically in this pH range the current of the second peak is diffusion limited by the OH^- concentration, since it is lower than the CO concentration.

In Situ Raman Study of CO Electrooxidation on Pt(hkl) Single-Crystal Surfaces in Acidic Solution

The adsorption and electrooxidation of CO molecules at well-defined Pt(hkl) single-crystal electrode surfaces is a key step towards addressing catalyst poisoning mechanisms in fuel cells. Herein, we employed in situ electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) coupled with theoretical calculation to investigate CO electrooxidation on Pt(hkl) surfaces in acidic solution. We obtained the Raman signal of top- and bridge-site adsorbed CO* molecules on Pt(111) and Pt(100). In contrast, on Pt(110) surfaces only top-site adsorbed CO* was detected during the entire electrooxidation process. Direct spectroscopic evidence for OH* and COOH* species forming on Pt(100) and Pt(111) surfaces was afforded and confirmed subsequently via isotope substitution experiments and DFT calculations. In summary, the formation and adsorption of OH* and COOH* species plays a vital role in expediting the electrooxidation process, which relates with the pre-oxidation peak of CO electrooxidation. This work deepens knowledge of the CO electrooxidation process and provides new perspectives for the design of anti-poisoning and highly effective catalysts.

Surface sites assembled-strategy on Pt–Ru nanowires for accelerated methanol oxidation

Isolated Ru atoms activate more Pt atoms involved in the Langmuir–Hinshelwood (L–H) pathway, which collectively accelerate methanol oxidation.

Titrating Pt Surface with CO Molecules

Identification and quantification of the surface sites on Pt nanoparticles are essential for developing more active electrocatalysts for many practical devices such as fuel cells and electrochemical fuel generators. In this work, we studied CO adsorption from dissolved CO in an H₂SO₄ electrolyte solution on a polycrystalline Pt film electrode held at a constant potential in the underpotential hydrogen deposition region using in situ attenuated total reflectance-surface-enhanced IR absorption spectroscopy (ATR-SEIRAS). Slowing down the adsorption rate by limiting the CO addition rate to the solution allows the individual CO molecules arriving at the Pt surface to rearrange, move to, and occupy their most energetically favorable sites. By using ATR-SEIRAS spectroscopy to follow the stepwise CO adsorption process, one can identify and quantify the Pt surface sites along with uncovering the CO adsorption energetic sequence. This method of slow CO adsorption on the Pt surface is analogous to the chemical titrations used for quantitative chemical analyses.

Catalytic production of impurity-free V3.5+ electrolyte for vanadium redox flow batteries

The vanadium redox flow battery is considered one of the most promising candidates for use in large-scale energy storage systems. However, its commercialization has been hindered due to the high manufacturing cost of the vanadium electrolyte, which is currently prepared using a costly electrolysis method with limited productivity. In this work, we present a simpler method for chemical production of impurity-free V^3.5+ electrolyte by utilizing formic acid as a reducing agent and Pt/C as a catalyst. With the catalytic reduction of V⁴⁺ electrolyte, a high quality V^3.5+ electrolyte was successfully produced and excellent cell performance was achieved. Based on the result, a prototype catalytic reactor employing Pt/C-decorated carbon felt was designed, and high-speed, continuous production of V^3.5+ electrolyte in this manner was demonstrated with the reactor. This invention offers a simple but practical strategy to reduce the production cost of V^3.5+ electrolyte while retaining quality that is adequate for high-performance operations.

The vanadium redox flow battery is promising for commercial applications, but is hampered by high-cost electrolytes that are typically prepared via electrolysis. Here the authors demonstrate cost-effective chemical production of a high-quality vanadium electrolyte using platinum nanoparticles as a catalyst.