Summary Achieving highly active and stable oxygen reduction reaction performance at low platinum-group-metal loadings remains one of the grand challenges in the proton-exchange membrane fuel cells community. Currently, state-of-the-art electrocatalysts are high-surface-area-carbon-supported nanoalloys of platinum with different transition metals (Cu, Ni, Fe, and Co). Despite years of focused research, the established structure-property relationships are not able to explain and predict the electrochemical performance and behavior of the real nanoparticulate systems. In the first part of this work, we reveal the complexity of commercially available platinum-based electrocatalysts and their electrochemical behavior. In the second part, we introduce a bottom-up approach where atomically resolved properties, structural changes, and strain analysis are recorded as well as analyzed on an individual nanoparticle before and after electrochemical conditions (e.g. high current density). Our methodology offers a new level of understanding of structure-stability relationships of practically viable nanoparticulate systems.

The present research provides a study of carbon-supported intermetallic Pt-alloy electrocatalysts and assesses their stability against metal dissolution in relation to the operating temperature and the potential window using two advanced electrochemical methodologies: (i) the in-house designed high-temperature disk electrode (HT-DE) methodology as well as (ii) a modification of the electrochemical flow cell coupled to an inductively coupled plasma mass spectrometer (EFC-ICP-MS) methodology, allowing for highly sensitive time- and potential-resolved measurements of metal dissolution. While the rate of carbon corrosion follows the Arrhenius law and increases exponentially with temperature, the findings of the present study contradict the generally accepted hypothesis that the kinetics of Pt and subsequently the less noble metal dissolution are supposed to be for the most part unaffected by temperature. On the contrary, clear evidence is presented that in addition to the importance of the voltage/potential window, the temperature is one of the most critical parameters governing the stability of Pt and thus, in the case of Pt-alloy electrocatalysts, also the ability of the nanoparticles (NPs) to retain the less noble metal. Lastly, but also very importantly, results indicate that the rate of Pt redeposition significantly increases with temperature, which has been the main reason why mechanistic interpretation of the temperature-dependent kinetics related to the stability of Pt remained highly speculative until now.

sales of light electric vehicles (battery electric vehicles and plug-in hybrid electric vehicles) are politically pushed and increasing exponentially. [1] Vehicles based on proton-exchange-membrane fuel cells (PEMFCs) have the potential to surpass the limitations of battery-based ones, especially, regarding the driving range. Unfortunately, the mass commercialization of this technology is hampered by the limited availability and high cost of Pt, which is required to speed up the anodic and cathodic reactions happening in a PEMFC. [2,3] Since ≈4 times more Pt is required on the cathode than at the anode side, the development of cathode materials containing low Pt amount is a promising way to reduce costs. Unfortunately, low-Pt cathode materials suffer from other limitations, such as losses due to mass transport; [4] also, when the Pt content is reduced below 100 µg cm −2 , the cost of other components rises. [3] For these reasons, completely replacing the Pt at the cathode side is a reasonable and promising way to go.In the last 10 years, platinum-group-metal-free (PGM-free) catalysts for the oxygen reduction reaction (ORR) have drawn the attention of many research groups all over the world. Since it has been shown that bioinspired metal-nitrogen-doped-carbon (M-N-C, M = Fe, Co) catalysts could meet the requirements for Atomically dispersed Fe-N-C catalysts are considered the most promising precious-metal-free alternative to state-of-the-art Pt-based oxygen reduction electrocatalysts for proton-exchange membrane fuel cells. The exceptional progress in the field of research in the last ≈30 years is currently limited by the moderate active site density that can be obtained. Behind this stands the dilemma of metastability of the desired FeN 4 sites at the high temperatures that are believed to be a requirement for their formation. It is herein shown that Zn 2+ ions can be utilized in the novel concept of active-site imprinting based on a pyrolytic template ion reaction throughout the formation of nitrogen-doped carbons. As obtained atomically dispersed Zn-N-Cs comprising ZnN 4 sites as well as metal-free N 4 sites can be utilized for the coordination of Fe 2+ and Fe 3+ ions to form atomically dispersed Fe-N-C with Fe loadings as high as 3.12 wt%. The Fe-N-Cs are active electocatalysts for the oxygen reduction reaction in acidic media with an onset potential of E 0 = 0.85 V versus RHE in 0.1 m HClO 4 . Identical location atomic resolution transmission electron microscopy imaging, as well as in situ electrochemical flow cell coupled to inductively coupled plasma mass spectrometry measurements, is employed to directly prove the concept of the active-site imprinting approach.

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The rational design of electrochemical oxygen evolution reaction (OER) electrocatalyst is essential for the development of efficient and sustainable electrochemical energy conversion, storage and electrolysis applications. One of the remaining limitations of the low‐temperature electrolyzers is the large amounts of highly scarce and expensive iridium used as the OER electrocatalysts. This could be solved by applying much smaller amounts of iridium on efficient and stable support. Here we present a very promising functionality of titanium oxynitride (TiONx) high‐surface‐area support that effectively disperses the iridium nanoparticles, exhibits good intrinsic electrical conductivity and stability and thus promises efficient reduction of the noble‐metal loading in electrolyzers gas diffusion electrodes. The new nanocomposite made of approximately 3 nm‐sized iridium nanoparticles finely dispersed on TiONx support is produced using a novel synthetic route. Extensive characterization shows that the new composites exhibit an electronic interaction with the support and, ultimately, a high OER performance in acidic media.

The development of affordable, low-iridium-loading, scalable, active, and stable catalysts for the oxygen-evolution reaction (OER) is a requirement for the commercialization of proton-exchange membrane water electrolyzers (PEMWEs). However, the synthesis of high-performance OER catalysts with minimal use of the rare and expensive element Ir is very challenging and requires the identification of electrically conductive and stable high-surface-area support materials. We developed a synthesis procedure for the production of large quantities of a nanocomposite powder containing titanium oxynitride (TiON x ) and Ir. The catalysts were synthesized with an anodic oxidation process followed by detachment, milling, thermal treatment, and the deposition of Ir nanoparticles. The anodization time was varied to grow three different types of nanotubular structures exhibiting different lengths and wall thicknesses and thus a variety of properties. A comparison of milled samples with different degrees of nanotubular clustering and morphology retention, but with identical chemical compositions and Ir nanoparticle size distributions and dispersions, revealed that the nanotubular support morphology is the determining factor governing the catalyst's OER activity and stability. Our study is supported by various state-of-the-art materials' characterization techniques, like X-ray photoelectron spectroscopy, scanning and transmission electron microscopies, Xray powder diffraction and absorption spectroscopy, and electrochemical cyclic voltammetry. Anodic oxidation proved to be a very suitable way to produce high-surface-area powder-type catalysts as the produced material greatly outperformed the IrO 2 benchmarks as well as the Ir-supported samples on morphologically different TiON x from previous studies. The highest activity was achieved for the sample prepared with 3 h of anodization, which had the most appropriate morphology for the effective removal of oxygen bubbles.

Pt-alloy (Pt–M) nanoparticles (NPs) with less-expensive 3d transition metals (M = Ni, Cu, Co) supported on high-surface-area carbon supports are currently the state-of-the-art (SoA) solution to reach the production phase in proton exchange membrane fuel cells (PEMFCs). However, while Pt–M electrocatalysts show promise in terms of increased activity for oxygen reduction reaction (ORR) and, thus, cost reductions from the significantly lower use of expensive and rare Pt, key challenges in terms of synthesis, activation, and stability remain to unlock their true potential. This work systematically tackles them with a combination of electrocatalyst synthesis and characterization methodologies including thin-film rotating disc electrodes (TF-RDEs), an electrochemical flow cell linked to an inductively coupled plasma mass spectrometer (EFC-ICP-MS), and testing in 50 cm 2 membrane electrode assemblies (MEAs). In the first part of the present work, we highlight the crucial importance of the chemical activation (dealloying) step on the performance of Pt–M electrocatalysts in the MEA at high current densities (HCDs). In addition, we provide the scientific community with a preliminary and facile method of distinguishing between a “poorly” and “adequately” dealloyed (activated) Pt-alloy electrocatalyst using a much simpler and affordable TF-RDE methodology using the well-known CO-stripping process. Since the transition-metal cations can also be introduced in a PEMFC due to the degradation of the Pt–M NPs, the second part of the work focuses on presenting clear evidence on the direct impact of the lower voltage limit (LVL) on the stability of Pt–M electrocatalysts. The data suggests that in addition to intrinsic improvements in stability, significant improvements in the PEMFC lifetime can also be obtained via the correct MEA design and applied limits of operation, namely, restricting not just the upper but equally important also the lower operation voltage.

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