Primož Jovanovič

New Insight into Platinum Dissolution from Nanoparticulate Platinum‐Based Electrocatalysts Using Highly Sensitive In Situ Concentration Measurements

Time‐ and potential‐resolved electrochemical Pt dissolution from commercial Pt and prepared PtCu alloy nanoparticulate catalysts have been studied under potentiodynamic conditions in 0.1 M HClO4 by using on‐line inductively coupled plasma mass spectrometry (ICP‐MS). For the first time the exact amount of dissolved Pt per cycle has been measured on real electrocatalysts. Results show clearly that Pt dissolution depends on the particle size: approximately seven times as much Pt is released into the solution from commercial 3 nm Pt particles as from a commercial 30 nm Pt sample. The stability of our prepared PtCu electrocatalyst is higher than that of a commercial 3 nm electrocatalyst, which is, however, still slightly lower than that of a commercial 30 nm Pt electrocatalyst.

Electrochemical Dissolution of Iridium and Iridium Oxide Particles in Acidic Media: Transmission Electron Microscopy, Electrochemical Flow Cell Coupled to Inductively Coupled Plasma Mass Spectrometry, and X-ray Absorption Spectroscopy Study

Iridium-based particles, regarded as the most promising proton exchange membrane electrolyzer electrocatalysts, were investigated by transmission electron microscopy and by coupling of an electrochemical flow cell (EFC) with online inductively coupled plasma mass spectrometry. Additionally, studies using a thin-film rotating disc electrode, identical location transmission and scanning electron microscopy, as well as X-ray absorption spectroscopy have been performed. Extremely sensitive online time-and potential-resolved electrochemical dissolution profiles revealed that Ir particles dissolve well below oxygen evolution reaction (OER) potentials, presumably induced by Ir surface oxidation and reduction processes, also referred to as transient dissolution. Overall, thermally prepared rutile-type IrO2 particles are substantially more stable and less active in comparison to as-prepared metallic and electrochemically pretreated (E-Ir) analogues. Interestingly, under OER-relevant conditions, E-Ir particles exhibit superior stability and activity owing to the altered corrosion mechanism, where the formation of unstable Ir(>IV) species is hindered. Due to the enhanced and lasting OER performance, electrochemically pre-oxidized E-Ir particles may be considered as the electrocatalyst of choice for an improved low-temperature electrochemical hydrogen production device, namely a proton exchange membrane electrolyzer.

In situ electrochemical dissolution of platinum and gold in organic-based solvent

In situ highly sensitive potential- and time-resolved monitoring of polycrystalline gold and platinum electrochemical dissolution in pure organic media is reported. This was achieved by successfully upgrading electrochemical flow cell coupled to inductively coupled plasma mass spectrometry. Similar to the aqueous media, aggressive transient dissolution takes place during oxide formation and reduction. In contrary to the aqueous electrolyte, both gold and platinum exhibit enhanced anodic compared to the cathodic oxide-assisted dissolution in organic media. This study intends to highlight the capabilities of the new methodology, which will expand the studies of metals dissolution to the fields like organic electrocatalysis, corrosion, battery research, and sensors among others.Metal corrosion: Going organicA technique to study the electrochemical dissolution of metals has been upgraded to enable insights into their dissolution in organic media. The ubiquitous use of metals means that understanding their stability in various environments is important. Techniques that involve the coupling of flow cells to mass spectrometers have been developed to monitor the dissolution of noble metals in situ. However, these techniques have been limited to aqueous electrolytes, even though components such as batteries and capacitors function in pure organic or mixed organic/aqueous phases. Now, a team led by Vid Simon Šelih and Nejc Hodnik from the National Institute of Chemistry, Ljubljana, Slovenia, have developed a technique based on the coupling of an electrochemical flow cell to inductively coupled plasma mass spectrometry that enables the in-situ monitoring of electrochemical metal dissolution in pure organic media.

Insights into electrochemical dealloying of Cu out of Au-doped Pt-alloy nanoparticles at the sub-nano-scale

Pt alloy nanoparticles present the most probable candidate to be used as the cathode cathodic oxygen reduction reaction electrocatalyst for achieving commercialization targets of the low-temperature fuel cells. It is therefore very important to understand its activation and degradation processes. Besides the ones known from the pure Pt electrocatalysts, the dealloying phenomena possess a great threat since the leached less-noble metal can interact with the polymer membrane or even poison the electrocatalyst. In this study, we present a solution, supported by in-depth advance electrochemical characterization, on how to suppress the removal of Cu from the Pt alloy nanoparticles.

Gold Doping in PtCu3/HSAC Nanoparticles and its Morphological, Structural and Compositional Changes During ORR Electrochemical Cycling

Pt‐based nanoparticles supported on high‐surface‐area carbon (HSAC) show very good properties as catalysts in polymer electrolyte membrane fuel cells (PEMFC). In many cases, however, the initial high activity of such catalysts rapidly drops as caused by various detrimental phenomena occurring in a typical electrochemical environment. In this work, a detailed study of a highly active system composed of PtCu3/HSAC nanoparticles with partially ordered structure and Pt skin with the addition of Au is performed. By using aberration‐corrected scanning transmission electron microscopy, the effects of adding small amounts of gold compared to the nonmodified sample are followed through the different stages of an electrochemical cycling degradation protocol. Various morphological changes such as faceting, reshaping, and thickening of the Pt skin are investigated for both sets of samples on the atomic level. Interesting features such as well‐defined shapes and surface defects are observed after degradation. However, the most important differences in terms of durability seem related to particle porosity. Finally, the experimental morphological observations are successfully reproduced by dealloying simulation with kinetic Monte Carlo modeling.

Quantitative HAADF Study of Twin Boundaries in Cu3Pt Nanoparticles

The properties of Pt-based intermetallic nanoparticles, used as a cathode catalyst for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFC) strongly depend on their size, shape and the crystal structure [1]. Imperfections of the crystal structure, such as partial ordering, formation of core-shell and Pt rich skin improve the electrocatalytic activity [2]. Controlling the lattice strain was found to be an efficient way of tuning the Pt-based catalyst activity because lattice strain can have an impact on surface reactivity, even if the source of strain is more than a few atomic layers away [3]. Strasser et al. reported an enhanced ORR activity of CuPt core–shell nanostructures, owing to the compressive strain that was induced on the Pt shell by the PtCu core [4]. In the case of twinned structure, the induced lattice strain caused by planar defects significantly influences the interatomic distances and consequently the energy levels of bonding electrons, which determines the catalytic, electrical and optical properties [5].

In-situ TEM and Atomic-Resolution STEM Study of Highly Active Partially Ordered Cu 3 Pt Nanoparticles used as PEM-Fuel Cells Catalyst

The efficiency of harvesting the energy in proton exchange membrane fuel cells (PEM-FC), like in all other types of fuel-cells, is mainly limited by the activity of the cathode catalyst for oxygen reducing reaction (ORR). Various catalysts, such as noble metals, intermetallic alloys, carbon-based supports, metal chalcogenides and carbides, are used to reduce the ORR temperature and achieve maximum reaction efficiency [1]. The main problem is slow adsorption and reaction kinetics, so searching for more efficient catalysts is one of the main challenges in the field of fuel cells. Among the most promising materials are C-supported Pt-based catalysts [2, 3]. In order to reduce the price of the material, Pt has been alloyed with various transition metal elements. In many cases not only the expected mass activity of the catalyst is improved, but also its specific activity is enhanced due to crystal lattice strains and the ligand effects through the d-band center shift induced by the transition elements [4, 5]. In the case of C-supported CoPt3 particles it has been recently shown that the electrocatalytic activity can be radically increased through core-shell structural ordering of intermetallic nanoparticles [5].