Adsorption/oxidation of CO on highly dispersed Pt catalyst studied by combined electrochemical and ATR-FTIRAS methods: oxidation of CO adsorbed on carbon-supported Pt catalyst and unsupported Pt black

Surface coverage control for dramatic enhancement of thermal CO oxidation by precise potential tuning of metal supported catalysts

External potential control allows reactant coverage control on the catalyst, in this case to suppress excessive CO adsorption, leading to improved thermal CO oxidation performance.

The Role of Tungsten Oxide in Enhancing the Carbon Monoxide Tolerance of Platinum-Based Hydrogen Oxidation Catalysts

Significant reductions in total cost of ownership can be realized by engineering PEM fuel cells to run on low-purity hydrogen. One of the main drawbacks of low-purity hydrogen fuels is the carbon monoxide fraction, which poisons platinum electrocatalysts and reduces the power output below useful levels. Platinum-tungsten oxide catalyst systems have previously shown high levels of CO tolerance during both ex situ and in situ investigations. In this work, we explore the mechanism of enhanced tolerance using in situ electrochemical attenuated total reflection-infrared (ATR-IR) and Raman spectroscopy methods and investigate, using a mixture of Pt/C and WO₃ powders, the role of the W^V/W^VI redox couple in the oxidation of adsorbed CO.

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.

Enhancement of Electrocatalytic Oxygen Reduction Activity and Durability of Pt-Ni Rhombic Dodecahedral Nanoframes by Anchoring to Nitrogen-Doped Carbon Support

Pt-based nanostructured electrocatalysts supported on carbon black have been widely studied for the oxygen reduction reaction (ORR), which occurs at the cathode in polymer electrolyte fuel cells. Because sluggish ORR kinetics are known to govern the cell performance, there is a need to develop highly active and durable electrocatalysts. The ORR activity of Pt-based electrocatalysts can be improved by controlling their morphology and alloying Pt with transition metals such as Ni. Improving the catalyst durability remains challenging and there is a lack of catalyst design concepts and synthetic strategies. We report the enhancement of the ORR activity and durability of a nanostructured Pt-Ni electrocatalyst by strong metal/support interactions with a nitrogen-doped carbon (NC) support. Pt-Ni rhombic dodecahedral nanoframes (NFs) were immobilized on the NC support and showed higher ORR electrocatalytic activity and durability in acidic media than that supported on a nondoped carbon black. Durability tests demonstrated that NF/NC showed almost no activity loss even after 50 000 potential cycles under catalytic conditions, and the Ni dissolution from the NFs was suppressed at the NC support, as confirmed by energy dispersive X-ray spectroscopy analysis. Physicochemical measurements including surface-enhanced infrared absorption spectroscopy of surface-adsorbed CO revealed that the strong metal/support interactions of the NF with the NC support caused the downshift of the d-band center position of the surface Pt. Our findings demonstrate that tuning the electronic structure of nanostructured Pt alloy electrocatalysts via the strong metal/support interactions with heteroatom-doped carbon supports will allow the development of highly active and robust electrocatalysts.

Surface enhanced spectroscopic investigations of adsorption of cations on electrochemical interfaces

The adsorption of alkali and tetraalkylammonium cations on Pt is investigated using surface enhanced infrared absorption spectroscopy and carbon monoxide as a probe molecule. Alkali cations exhibit a stronger adsorption than organic cations, with potassium showing the strongest effect, followed by sodium and lithium.

Electrochemical CO Oxidation at Platinum on Carbon Studied through Analysis of Anomalous in Situ IR Spectra

The oxidation of adsorbed CO is a key reaction in electrocatalysis. It has been studied extensively on both extended model surfaces and on nanoparticles; however, correlation between the two is far from simple. Molecular insight into the reaction is often provided using in situ IR spectroscopy; however, practical challenges mean in situ studies on nanoparticles have yet to provide the same level of detail as those on model surfaces. Here we use a new approach to in situ IR spectroscopy to study the mechanism of CO adlayer oxidation on a commercial carbon-supported Pt catalyst. We observe bipolar IR absorption bands but develop a simple model to enable fitting. Quantitative analysis of band behavior during the oxidation prepeak using the model agrees well with previous analysis based on conventional absorption bands. A second linear CO band is observed during the main oxidation region and is assigned to the distinct contribution of CO on step as opposed to terrace sites. Analysis of the step and terrace CO bands during oxidation shows that oxidation begins on the terraces of the nanoparticles before CO on steps is removed. Further correlation of this behavior with the current shows that step CO is only lost in the first of the two main oxidation peaks.

Formate adsorption on Pt nanoparticles during formic acid electro-oxidation: insights from in situ infrared spectroscopy

Adsorbed formate is observed on a supported Pt nanoparticle for the first time during formic acid electro-oxidation. Bands assigned to OCO stretching and CH bending reveal some OCO but little CH bond weakening on adsorption compared to the free anion. The formate potential dependence is similar to polycrystalline electrodes while adsorbed CO persists up to +1.2 V, 0.5 V higher than on polycrystalline Pt.

Control of particle size of pt and pt alloy electrocatalysts supported on carbon black by the nanocapsule method

Monodisperse Pt and Pt-M (M = Co, Ru) alloy nanoparticles supported on carbon black (Pt/CB, Pt(2)Ru(3)/CB, Pt(3)Co/CB) were prepared by the nanocapsule method. We have succeeded in controlling the particle size simply by changing the molar ratio of metal precursor(s) to surfactant (M/S) in the preparation, with the other conditions being identical. The particle size was well-controlled between 2.0 and 4.5 nm with a metal loading level of 50 wt % for all catalysts. The compositions of the alloy particles were close to the projected values, with a small standard deviation, i.e., <3.1 atom % for Pt(2)Ru(3) and 1.4 atom % for Pt(3)Co. It was also found that these alloys were in the form of the corresponding solid solutions with the fcc structure.