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In this work, we have synthesized tetrahexahedral (THH) Pt nanoparticles (NPs) enclosed with {730} high-index facets using a one-step square wave potential procedure. The catalytic activity of the THH NPs toward the oxygen reduction reaction (ORR) is studied under both transient and steady-state conditions. As a benchmark, the ORR activity is compared with those of polycrystalline Pt and a commercial Pt/C catalyst. The results show that, under transient conditions, the catalytic performance of the THH Pt NPs and Pt/C are approximately the same and about 2 times lower than that of polycrystalline Pt. However, under steady-state conditions the THH Pt NPs perform considerably better than Pt/C. Under steady-state conditions THH Pt NPs are even slightly more active than polycrystalline Pt

We employ a recently developed stripping protocol to examine the equilibrium coverage of oxygenated species and their influence on the oxygen reduction reaction (ORR) and the hydrogen oxidation reaction (HOR). In particular we aim to distinguish between dynamic and steady state conditions and establish if distinctive potential regions exist where the different respective oxygenated species OHad, Oad and Pt-oxide dominate.

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.

The objectives of this work can be separated into three different topics: the design and development of a state-of-the art electrochemical experiment setup, which is then followed by two separate experimental studies in alkaline electrolyte. These studies demonstrate the capabilities of the experimental setup, and each focus on separate model catalysts. The first study investigated the influence of Pt oxide formation on the measured catalytic activity of fuel cell relevant reactions on polycrystalline Pt in alkaline electrolyte. The second study focused on the characterisation of the oxygen reduction reaction for a non-platinum catalyst, in this case Ag, by adapting the established thin-film RDE methodology employed for characterising Pt based electrocatalysts., Das Ziel dieser Arbeit kann in drei verschiedene Bereiche unterteilt werden: die Entwicklung eines state-of-the-art elektrochemischen Versuchsaufbaus und zwei separater nachfolgender experimenteller Studien im alkalischen Elektrolyt. Diese Studien zeigen die Leistungsfähigkeit des experimentellen Aufbaus und fokussieren auf unterschiedlichen Modellkatalysatoren. Die erste Studie untersucht den Einfluss der Bildung von Pt-Oxid auf die gemessene katalytische Aktivität, der für die Brennstoffzelle relevanten Reaktionen des polykristallinen Pt in alkalischem Elektrolyt. Die zweite Studie legt ihren Schwerpunkt auf die Charakterisierung der Sauerstoffreduktion eines platinfreien Katalysators, in diesem Falle Ag, durch die Anpassung der etablierten thin-film RDE Methode die zu Charakterisierung von Pt-basierten Elektrokatalysatoren angewandt wird.

The objectives of this work can be separated into three different topics: the design and development of a state-of-the art electrochemical experiment setup, which is then followed by two separate experimental studies in alkaline electrolyte. These studies demonstrate the capabilities of the experimental setup, and each focus on separate model catalysts. The first study investigated the influence of Pt oxide formation on the measured catalytic activity of fuel cell relevant reactions on polycrystalline Pt in alkaline electrolyte. The second study focused on the characterisation of the oxygen reduction reaction for a non-platinum catalyst, in this case Ag, by adapting the established thin-film RDE methodology employed for characterising Pt based electrocatalysts., Das Ziel dieser Arbeit kann in drei verschiedene Bereiche unterteilt werden: die Entwicklung eines state-of-the-art elektrochemischen Versuchsaufbaus und zwei separater nachfolgender experimenteller Studien im alkalischen Elektrolyt. Diese Studien zeigen die Leistungsfähigkeit des experimentellen Aufbaus und fokussieren auf unterschiedlichen Modellkatalysatoren. Die erste Studie untersucht den Einfluss der Bildung von Pt-Oxid auf die gemessene katalytische Aktivität, der für die Brennstoffzelle relevanten Reaktionen des polykristallinen Pt in alkalischem Elektrolyt. Die zweite Studie legt ihren Schwerpunkt auf die Charakterisierung der Sauerstoffreduktion eines platinfreien Katalysators, in diesem Falle Ag, durch die Anpassung der etablierten thin-film RDE Methode die zu Charakterisierung von Pt-basierten Elektrokatalysatoren angewandt wird.