Colloidal platinum nanoparticles are obtained via a surfactant-free polyol process in alkaline ethylene glycol. In this popular synthesis, ethylene glycol functions as solvent and reducing agent. The preparation procedure is known for its reproducibility to obtain 1-2 nm nanoparticles, but at the same time the controlled preparation of larger nanoparticles is challenging. A reliable size control without the use of surfactants is a fundamental yet missing achievement for systematic investigations. In this work it is demonstrated how the molar ratio between NaOH and the platinum precursor determines the final particle size and how this knowledge can be used to prepare and study in a systematic way supported catalysts with defined size and Pt to carbon ratio. Using small-angle X-ray scattering, transmission electron microscopy, infrared spectroscopy, X-ray absorption spectroscopy, pair distribution function and electrochemical analysis it is shown that changing the NaOH/Pt molar ratio from 25 to 3, the Pt nanoparticle size is tuned from 1 to 5 nm. This size range is of interest for various catalytic applications, such as the oxygen reduction reaction (ORR). Supporting the nanoparticles onto a high surface area carbon, we demonstrate how the particle size effect can be studied keeping the Pt to carbon ratio constant, an important aspect that in previous studies could not be accomplished.

Compared to conventional preparation methods for supported heterogeneous catalysts, the use of colloidal nanoparticles (NPs) allows for a precise control over size, size distribution, and distribution/location of the NPs on the support. However, common colloidal syntheses have restrictions that limit their applicability for industrial catalyst preparation. We present a simple, surfactant‐free, and scalable preparation method for colloidal NPs to overcome these restrictions. We demonstrate how precious‐metal NPs are prepared in alkaline methanol, how the particle size can be tuned, and how supported catalysts are obtained. The potential of these colloids in the preparation of improved catalysts is demonstrated by two examples from heterogeneous catalysis and electrocatalysis.

In this work, we present a facile and straightforward approach to synthesize, activate and benchmark small, i.e. 1.6 nm in diameter, Ir nanoparticles (NP) as oxygen evolution reaction (OER) catalysts.

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We present a step-by-step tutorial to prepare proton exchange membrane fuel cell (PEMFC) catalysts, consisting of Pt nanoparticles (NPs) supported on a high surface area carbon, and to test their performance in thin film rotating disk electrode (TF-RDE) measurements. The TF-RDE methodology is widely used for catalyst screening; nevertheless, the measured performance sometimes considerably differs among research groups. These uncertainties impede the advancement of new catalyst materials and, consequently, several authors discussed possible best practice methods and the importance of benchmarking.The visual tutorial highlights possible pitfalls in the TF-RDE testing of Pt/C catalysts. A synthesis and testing protocol to assess standard Pt/C catalysts is introduced that can be used together with polycrystalline Pt disks as benchmark catalysts. In particular, this study highlights how the properties of the catalyst film on the glassy carbon (GC) electrode influence the measured performance in TF-RDE testing. To obtain thin, homogeneous catalyst films, not only the catalyst preparation, but also the ink deposition and drying procedures are essential. It is demonstrated that an adjustment of the ink's pH might be necessary, and how simple control measurements can be used to check film quality. Once reproducible TF-RDE measurements are obtained, determining the Pt loading on the catalyst support (expressed as Pt wt%) and the electrochemical surface area is necessary to normalize the determined reaction rates to either surface area or Pt mass. For the surface area determination, so-called CO stripping, or the determination of the hydrogen underpotential deposition (Hupd) charge, are standard. For the determination of the Pt loading, a straightforward and cheap procedure using digestion in aqua regia with subsequent conversion of Pt(IV) to Pt(II) and UV-vis measurements is introduced.

Gas diffusion electrode (GDE) setups have very recently received increasing attention as a fast and straightforward tool for testing the oxygen reduction reaction (ORR) activity of surface area proton exchange membrane fuel cell (PEMFC) catalysts under more realistic reaction conditions. In the work presented here, we demonstrate that our recently introduced GDE setup is suitable for benchmarking the stability of PEMFC catalysts as well. Based on the obtained results, it is argued that the GDE setup offers inherent advantages for accelerated degradation tests (ADT) over classical three-electrode setups using liquid electrolytes. Instead of the solid-liquid electrolyte interface in classical electrochemical cells, in the GDE setup a realistic three-phase boundary of (humidified) reactant gas, proton exchange polymer (e.g. Nafion) and the electrocatalyst is formed. Therefore, the GDE setup not only allows accurate potential control but also independent control over the reactant atmosphere, humidity and temperature. In addition, the identical location transmission electron microscopy (IL-TEM) technique can easily be adopted into the setup, enabling a combination of benchmarking with mechanistic studies.

We investigated the influence of the ink properties of proton exchange membrane fuel cell (PEMFC) catalysts on the oxygen reduction reaction (ORR) activity determined in thin film rotating disk electrode (TF-RDE) measurements. It was found that the adaption of a previously reported ink recipe to home-made catalysts does not lead to satisfying results, although reported work could be reproduced using commercial catalyst samples. It is demonstrated that the pH of the catalyst ink, which has not been addressed in previous TF-RDE studies, is an important parameter that needs to be carefully controlled to determine the intrinsic ORR activity of high surface area catalysts.

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