Markus Nesselberger

The Particle Size Effect on the Oxygen Reduction Reaction Activity of Pt Catalysts: Influence of Electrolyte and Relation to Single Crystal Models

The influence of particle size on the oxygen reduction reaction (ORR) activity of Pt was examined in three different electrolytes: two acidic solutions, with varying anionic adsorption strength (HClO(4) < H(2)SO(4)); and an alkaline solution (KOH). The experiments show that the absolute ORR rate is dependent on the supporting electrolyte; however, the relationship between activity and particle size is rather independent of the supporting electrolyte. The specific activity (SA) toward the ORR rapidly decreases in the order of polycrystalline Pt > unsupported Pt black particles (~30 nm) > high surface area (HSA) carbon supported Pt nanoparticle catalysts (of various size between 1 and 5 nm). In contrast to previous work, it is highlighted that the difference in SA between the individual HSA carbon supported catalysts (1 to 5 nm) is rather trivial and that the main challenge is to understand the significant differences in SA between the polycrystalline Pt, unsupported Pt particles, and HSA carbon supported Pt catalysts. Finally, a comparison between measured and modeled activities (based on the distribution of surface planes and their SAs) for different particle sizes indicates that such simple models do not capture all aspects of the behavior of HSA carbon supported catalysts.

The effect of particle proximity on the oxygen reduction rate of size-selected platinum clusters

The diminished surface-area-normalized catalytic activity of highly dispersed Pt nanoparticles compared with bulk Pt is particularly intricate, and not yet understood. Here we report on the oxygen reduction reaction (ORR) activity of well-defined, size-selected Pt nanoclusters; a unique approach that allows precise control of both the cluster size and coverage, independently. Our investigations reveal that size-selected Pt nanoclusters can reach extraordinarily high ORR activities, especially in terms of mass-normalized activity, if deposited at high coverage on a glassy carbon substrate. It is observed that the Pt cluster coverage, and hence the interparticle distance, decisively influence the observed catalytic activity and that closely packed assemblies of Pt clusters approach the surface activity of bulk Pt. Our results open up new strategies for the design of catalyst materials that circumvent the detrimental dispersion effect, and may eventually allow the full electrocatalytic potential of Pt nanoclusters to be realized.

Design, development, and demonstration of a fully LabVIEW controlled in situ electrochemical Fourier transform infrared setup combined with a wall-jet electrode to investigate the electrochemical interface of nanoparticulate electrocatalysts under reaction conditions

We present a detailed description of the construction of an in situ electrochemical ATR-FTIR setup combined with a wall-jet electrode to investigate the electrocatalytic properties of nanoparticulate catalysts in situ under controlled mass transport conditions. The presented setup allows the electrochemical interface to be probed in combination with the simultaneous determination of reaction rates. At the same time, the high level of automation allows it to be used as a standard tool in electrocatalysis research. The performance of the setup was demonstrated by probing the oxygen reduction reaction on a platinum black catalyst in sulfuric electrolyte.

1-Naphthylamine functionalized Pt nanoparticles: electrochemical activity and redox chemistry occurring on one surface

We present the preparation and electrochemical application of Pt nanoparticles (Pt NPs) functionalized with 1-naphthylamine. Under electrochemical conditions, Pt surface bound 1-naphthylamine (NA) can be reversibly switched (oxidized and reduced), while simultaneously electrocatalytic reactions (e.g. CO oxidation) can proceed on the Pt surface. While the redox activity of the ligand is established immediately after functionalization, the functionalized NPs have to be stored as a colloidal dispersion in tetrahydrofuran (THF) prior to deposition onto the support material in order to induce their catalytic activity. We interpret this catalytic activation due to partial desorption of ligands from the particle surface induced by storing the particles in THF. However, the experimental results do not indicate a loss of ligands from the ligand shell, but evidence that the ligands form oligomers when kept as colloids in THF. As a result the catalytic surface becomes partially available while the redox activity of the ligands is maintained.

In Situ FTIR Spectroscopy: Probing the Electrochemical Interface during the Oxygen Reduction Reaction on a Commercial Platinum High-Surface-Area Catalyst

In situ observation of anion adsorption on industrial high‐surface‐area catalysts is used for the first time under oxygen reduction reaction (ORR) conditions with a defined mass transport. For this purpose, a specially fabricated electrode is used for which the catalyst layer is spray‐coated on top of a structured Au contact layer and applied to our recently developed in situ attenuated total reflectance FTIR wall‐jet electrode. The designed interface allows us to track anion adsorption and measure the reaction rate simultaneously under mass controlled conditions. The observed absorption bands are caused by anion interaction with the active phase and also the carbon support. If we analyze the absorption band intensity of adsorbed anions as a function of the oxygen reduction reaction rate, the band intensity decreases with the onset of the ORR. This shows that ORR inhibition is a complex interplay between site blocking caused by anion adsorption and oxide formation.