Gustav K. H. Wiberg

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.

Impact of Glass Corrosion on the Electrocatalysis on Pt Electrodes in Alkaline Electrolyte

The influence of glass corrosion on the electrocatalytic activity of fuel cell catalysts was studied. A Teflon electrochem. cell was designed for measurements in alk. electrolyte. The cell performance was tested and compared to a std. electrochem. glass cell by measuring the O redn. reaction and the H oxidn. reaction on polycryst. Pt in 0.1M KOH. In the Teflon cell the shape of the cyclic voltammogram as well as the activity for the reactions are reproducible and do not alter over a long period of time. By comparison, using the std. electrochem. cell made out of Duran glass, the expts. on polycryst. Pt electrodes in alk. electrolyte are insufficiently reproducible. The cyclic voltammograms alter over time, and the activities for H oxidn. as well as O redn. depend on the applied potential scan limits. This is due to the contamination of the electrolyte because of the etching of glass by KOH - anal. of the alk. electrolyte after usage in the resp. cell types by ICP-OES confirmed this suggestion. [on SciFinder(R)]

Analysis of the Impact of Individual Glass Constituents on Electrocatalysis on Pt Electrodes in Alkaline Solution

In the previous paper [ibid., P1 (2008)] the authors reported on the impact of glass corrosion on establishing the electrocatalytic activity of fuel cell catalysts. The leaching of glass constituents into the electrolyte is responsible for insufficiently reproducible measurements of the oxygen redn. reaction as well as the hydrogen oxidn. reaction on polycryst. Pt. The authors elucidate which glass constituents are leached into the electrolyte through the anal. of alk. electrolytes in contact with Duran glass by inductively coupled plasma optical emission spectroscopy. By adding these constituents, i.e., silicates, borates, aluminates, and lead, sep. to the electrolyte, the authors evaluate their individual impact on electrocatalytic measurements. The results presented in this study help to explain the effects seen in measurements in alk. electrolyte with glass cells. [on SciFinder(R)]

Rotating disk electrode system for elevated pressures and temperatures

We describe the development and test of an elevated pressure and temperature rotating disk electrode (RDE) system that allows measurements under well-defined mass transport conditions. As demonstrated for the oxygen reduction reaction on polycrystalline platinum (Pt) in 0.5M H2SO4, the setup can easily be operated in a pressure range of 1-101 bar oxygen, and temperature of 140 °C. Under such conditions, diffusion limited current densities increase by almost two orders of magnitude as compared to conventional RDE setups allowing, for example, fuel cell catalyst studies under more realistic conditions. Levich plots demonstrate that the mass transport is indeed well-defined, i.e., at low electrode potentials, the measured current densities are fully diffusion controlled, while at higher potentials, a mixed kinetic-diffusion controlled regime is observed. Therefore, the setup opens up a new field for RDE investigations under temperature and current density conditions relevant for low and high temperature proton exchange membrane fuel cells.

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.

Design and test of a flexible electrochemical setup for measurements in aqueous electrolyte solutions at elevated temperature and pressure

We present a detailed description of the construction and testing of an electrochemical cell allowing measurements at elevated temperature and pressure. The cell consists of a stainless steel pressure vessel containing the electrochemical glass cell exhibiting a three electrode configuration. The design of the working electrode is inspired by conventional rotating disk electrode setups. As demonstrated, the setup can be used to investigate temperature dependent electrochemical processes on polycrystalline platinum and also high surface area type electrocatalysts.

Gas diffusion electrode setup for catalyst testing in concentrated phosphoric acid at elevated temperatures

We present a detailed description of the construction and testing of an electrochemical cell setup allowing the investigation of a gas diffusion electrode containing carbon supported high surface area catalysts. The setup is designed for measurements in concentrated phosphoric acid at elevated temperature, i.e., very close to the actual conditions in high temperature proton exchange membrane fuel cells (HT-PEMFCs). The cell consists of a stainless steel flow field and a PEEK plastic cell body comprising the electrochemical cell, which exhibits a three electrode configuration. The cell body and flow field are braced using a KF-25 vacuum flange clamp, which allows an easy assembly of the setup. As demonstrated, the setup can be used to investigate temperature dependent electrochemical processes on high surface area type electrocatalysts, but it also enables quick screening tests of HT-PEMFC catalysts under realistic conditions.

Accessing the Inaccessible: Analyzing the Oxygen Reduction Reaction in the Diffusion Limit

The oxygen reduction reaction (ORR) is one of the key processes in electrocatalysis. In this communication, the ORR is studied using a rotating disk electrode (RDE). In conventional work, this method limits the potential region where kinetic (mass transport free) reaction rates can be determined to a narrow range. Here, we applied a new approach, which allows us to analyze the ORR rates in the diffusion-limited potential region of high mass transport. Thus, for the first time, the effect of anion adsorption on the ORR can be studied at such potentials.

Levich Analysis and the Apparent Potential Dependency of the Levich B Factor

ABSTRACT Levich analysis is a frequently used method for extraction of diffusional properties of electrochemical active species. The analysis is based on plotting current versus the square root of the rotation rate of a rotating disc electrode. From the slope of this plot, the Levich B factor and the diffusional parameters may be obtained. In this article, we focus on issues related to the extraction of the B factor from experimental measurements. We show that the plot does not fully linearize the data: a prerequisite for the slope extraction. Furthermore, analyzing data at various potentials results in varying values of the B factor, contrary to predictions by theory. Thus, as an alternative, we introduce a ω½-normalized Levich plot. This plot linearized the data and the resulting B factor was potential-independent. The difference between the two methods is ascribed to the consideration that the electrolyte–electrode interface current may be limited. We conclude that the potential-dependent B factor based on the standard Levich analysis is an artifact and the resulting values are systematically underestimated in comparison to results from the ω½-normalized Levich analysis.