Identical Location Transmission Electron Microscopy Research Articles

Application of Hydrogenated Graphitic Supports in Electrocatalysts: Effects on Carbon Support Surface Chemistry, Nanoparticle Growth, and Electrocatalytic Activity.

One of the key technical challenges before the widespread adoption of proton exchange membrane fuel cells (PEMFCs) is increasing the durability of the platinum catalyst layer to meet a target of 8000 operating hours with only a 10% loss of performance. Carbon corrosion, one of the primary mechanisms of degradation in fuel cells, has attracted attention from researchers interested in solving the durability problem. As such, the development of catalyst supports to avoid this issue has been a focus in recent years, with interest in hydrophobic supports such as highly graphitized carbons. In this research, we propose a method to increase the durability of carbon supports by way of exploiting hydrogenated graphene's hydrophobic properties. By performing a Birch reduction on graphene nanoplatelets, we were able to synthesize hydrogenated graphene nanoplatelets which were used as support for hollow porous PtNi nanoparticles. The structure of these nanoparticle-carbon composites was characterized by transmission electron microscopy (TEM), energy dispersive spectroscopy coupled with scanning transmission electron microscopy (STEM-EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). We found that hydrogenation can strongly affect the morphology of nanoparticles formed as well as increase the electrochemical stability of the composites. Accelerated stress tests for 6000 cycles between 1.0 and 1.6 V vs RHE at 25 °C demonstrated that a hydrogenated support for PtNi increased the retained electrochemical surface from 36.8% to 61.9% when compared to the pristine graphene nanoplatelets. Moreover, the retained activity was increased from 26.6% to 53.0% by use of the hydrogenated carbon support. To confirm that hydrogenation enhanced durability, stress tests combined with Raman spectroscopy showed minimal change in the ID/IG ratio of the hydrogenated composite. Finally, identical location transmission electron microscopy (IL-TEM) was used to support the results of the electrochemical stress tests.

Differentiating PGM Ostwald Ripening from Catalyst Degradation Using Identical Location TEM and Controlled Potential Cycling

Nanoscale Platinum group metals (PGMs) over conductive supports with large specific area have been widely used as highly efficient catalysts for various reactions, including oxygen reduction reaction (ORR) (for fuel cells) and oxygen evolution reactions (OER) (for water electrolyers). However, these PGM nanoparticles (NPs) usually suffer from significant performance degradation over prolonged operation, primarily attributed to catalyst degradation, which remains a long-standing challenge. Two principal mechanisms, Ostwald ripening and particle migration, contribute to this degradation. Ostwald ripening is a process involves the first dissolution of smaller PGM NPs into PGM ions, followed by their diffusion and redeposition onto the surfaces of larger NP, where the driven force is surface energy. Particle migration, on the other hand, is a process of movement of PGM NPs leading to the formation of large agglomerates due to the weak interactions between NPs and supports. In general, both processes occurred simultaneously during catalyst degradation in the fuel cell/electrolyzer operation. However, addressing the PGM catalyst degradations caused by these mechanisms requires completely different strategies: enhancing intrinsic catalyst stability for overcoming Ostwald ripening and improving interactions between PGM NPs and supports for reducing particle migration. Hence, it is critically required to quantitatively differentiate between these two mechanisms during catalyst degradation. Here, we propose an innovative approach to distinguish the two mechanisms utilizing Identical Location Transmission Electron Microscope (IL-TEM) coupled with carefully designed experiments. Specifically, the IL-TEM grids with dispersed PGM catalysts, such as TKK 46%Pt/Kejten Black EC-300, would be imaged to characterized the particle geometry, size and interparticle distance of PGM NPs on before and after accelerated stress test (AST) for various cycles (i.e. 0, 5000, 10,000, 30,000 cycles, etc.) within an electrochemical cell. These PGM catalysts will undergo AST cycling among two potential regions: (1) 0.2 ~ 0.6V (vs. standard hydrogen electrode (SHE)) and (2) 0.6 ~ 0.95V (vs. SHE). PGM particles cycled within the potential region (1) should exhibit only particle migration, since potential below 0.6 V do not cause any oxidation of PGM, while those cycled within potential region (2) would experience both Ostwald ripening and particle migration. By comparing changes in particle geometry, size and interparticle distance for PGM NPs subjected to cycling within different potential regions, we could quantitively determine the contributive effect of each mechanism on the catalyst degradation. This study will shed the light on differentiation of these two different mechanisms and provide guidance for the design of highly active and stable PGM catalysts.

In-situ electrochemical reconstruction and modulation of adsorbed hydrogen coverage in cobalt/ruthenium-based catalyst boost electroreduction of nitrate to ammonia

The electroreduction of nitrate offers a promising, sustainable, and decentralized route to generate valuable ammonia. However, a key challenge in the nitrate reduction reaction is the energy efficiency of the reaction, which requires both a high ammonia yield rate and a high Faradaic efficiency of ammonia at a low working potential (≥−0.2 V versus reversible hydrogen electrode). We propose a bimetallic Co–B/Ru12 electrocatalyst which utilizes complementary effects of Co–B and Ru to modulate the quantity of adsorbed hydrogen and to favor the specific hydrogenation for initiating nitrate reduction reaction at a low overpotential. This effect enables the catalyst to achieve a Faradaic efficiency for ammonia of 90.4 ± 9.2% and a remarkable half-cell energy efficiency of 40.9 ± 4% at 0 V versus reversible hydrogen electrode. The in-situ electrochemical reconstruction of the catalyst contributes to boosting the ammonia yield rate to a high level of 15.0 ± 0.7 mg h−1 cm−2 at −0.2 V versus reversible hydrogen electrode. More importantly, by employing single-entity electrochemistry coupled with identical location transmission electron microscopy, we gain systematic insights into the correlation between the increase in the catalyst’s active sites and its structural transformations during the nitrate reduction reaction.

Morphology-dependent support effect of PdCu/alpha-Fe2O3 catalysts on Suzuki-Miyaura cross-coupling reaction

The palladium-catalyzed Suzuki-Miyaura cross-coupling (SMC) reaction has received worldwide attention as a powerful and convenient synthetic tool for the formation of biaryl compounds. However, these reactions are highly dependent on the activity and stable of catalysts. Herein, the support morphology-dependent catalytic performance of SMC reactions was investigated. The truncated hexagonal bipyramid (α-Fe2O3-O) and rod-shaped morphologies of alpha-Fe2O3 (α-Fe2O3-R) were used as support to prepare PdCu nanoparticles (NPs) catalysts by NaBH4 reduction method. For PdCu/α-Fe2O3-R catalysts, the smaller size of PdCu NPs and more low coordination Pd sites leading to its superior catalytic performance for SMC reactions. Furthermore, it can be easily recycled through centrifugation and reused several times without obvious loss on its catalytic performance. Identical location transmission electron microscopy method was used to investigate the structural evolution of PdCu/α-Fe2O3-R catalysts. The results found that its structure almost unchanged during the catalytic reaction.

Deciphering nanostructural evolution of PtCu/C–N electrocatalyst via identical location transmission electron microscopy imaging: Gram-scale synthesis and superior activity in oxygen reduction reaction

Electrocatalysts play a pivotal role in advancing proton-exchange membrane fuel cell (PEMFC) for hydrogen energy applications. In this study, we investigate a novel PtCu/CN electrocatalyst synthesized via a gram-scale synthesis approach, which demonstrates remarkable activity and stability in the oxygen reduction reaction (ORR). The catalyst's effectiveness stems from its unique structure, combining bimetallic nanoparticles (NPs) and an N-doped carbon support. Employing identical location transmission electron microscopy (IL-TEM) imaging, we observe significant NP structure reorganization upon activation influenced by the upper limiting potential. Notably, the PtCu/CN catalyst activated to 1.0 V surpasses the United States Department of Energy (DOE) target for ORR activity by 3.3-fold. These findings underscore the potential of this catalyst in enhancing the performance of PEMFCs, marking a significant advancement in hydrogen energy technology.

Impact of Surface Composition Changes on the CO2-Reduction Performance of Au-Cu Aerogels.

Over the past decades, the electrochemical CO2-reduction reaction (CO2RR) has emerged as a promising option for facilitating intermittent energy storage while generating industrial raw materials of economic relevance such as CO. Recent studies have reported that Au-Cu bimetallic nanocatalysts feature a superior CO2-to-CO conversion as compared with the monometallic components, thus improving the noble metal utilization. Under this premise and with the added advantage of a suppressed H2-evolution reaction due to absence of a carbon support, herein, we employ bimetallic Au3Cu and AuCu aerogels (with a web thickness ≈7 nm) as CO2-reduction electrocatalysts in 0.5 M KHCO3 and compare their performance with that of a monometallic Au aerogel. We supplement this by investigating how the CO2RR-performance of these materials is affected by their surface composition, which we modified by systematically dissolving a part of their Cu-content using cyclic voltammetry (CV). To this end, the effect of this CV-driven composition change on the electrochemical surface area is quantified via Pb underpotential deposition, and the local structural and compositional changes are visually assessed by employing identical-location transmission electron microscopy and energy-dispersive X-ray analyses. When compared to the pristine aerogels, the CV-treated samples displayed superior CO Faradaic efficiencies (≈68 vs ≈92% for Au3Cu and ≈34 vs ≈87% for AuCu) and CO partial currents, with the AuCu aerogel outperforming the Au3Cu and Au counterparts in terms of Au-mass normalized CO currents among the CV-treated samples.

Extrinsic hydrophobicity-controlled silver nanoparticles as efficient and stable catalysts for CO2 electrolysis.

To realize economically feasible electrochemical CO2 conversion, achieving a high partial current density for value-added products is particularly vital. However, acceleration of the hydrogen evolution reaction due to cathode flooding in a high-current-density region makes this challenging. Herein, we find that partially ligand-derived Ag nanoparticles (Ag-NPs) could prevent electrolyte flooding while maintaining catalytic activity for CO2 electroreduction. This results in a high Faradaic efficiency for CO (>90%) and high partial current density (298.39 mA cm‒2), even under harsh stability test conditions (3.4 V). The suppressed splitting/detachment of Ag particles, due to the lipid ligand, enhance the uniform hydrophobicity retention of the Ag-NP electrode at high cathodic overpotentials and prevent flooding and current fluctuations. The mass transfer of gaseous CO2 is maintained in the catalytic region of several hundred nanometers, with the smooth formation of a triple phase boundary, which facilitate the occurrence of CO2RR instead of HER. We analyze catalyst degradation and cathode flooding during CO2 electrolysis through identical-location transmission electron microscopy and operando synchrotron-based X-ray computed tomography. This study develops an efficient strategy for designing active and durable electrocatalysts for CO2 electrolysis.

One‐Pot Synthesis of Carbon‐Supported Pd Nanoparticles with Ni and Carbon Matrix Protection for Durable Alkaline Hydrogen Oxidation Reaction

Protecting nanoparticles with a carbon matrix can enhance the durability of the catalysts in alkaline fuel cells (AFC) and is well‐documented. While others have tried complex syntheses to produce small nanoparticle catalysts, in this work, in order to scale‐up batches of 15 g or more, carbon‐cap (or carbon‐coating) protected Vulcan XC72‐supported Pd‐Ni (1‐2) nanoparticles (Pd‐Niacc/C) were successfully synthesized via a one‐step dry‐synthesis process. This catalyst was compared with a commercial Pd‐Ni/Vulcan XC72 material (PdNi/C, Premetek) in terms of hydrogen oxidation reaction (HOR) activity and stability. To produce less ordered carbon caps (versus graphite/graphene), a low‐temperature heat‐treatment (below 500°C) was used, resulting in Pd‐Niacc/C of unique electrochemical properties: easily electrochemically activated, this catalyst outperforms PdNi/C for alkaline HOR and proves more durable under highly oxidizing accelerated stress test (AST) conditions. Identical location transmission electron microscopy (ILTEM), X‐ray photoelectron spectroscopy (XPS) and rotating disk electrode (RDE) measurements demonstrate how the Ni‐rich surface plays an important role in HOR activity for both PdNi/C and PdNiacc/C and that the protective carbon‐coating of the latter ensures better durability of performance and better resistance to materials degradation.

Multiscale Regulation of Ordered PtCu Intermetallic Electrocatalyst for Highly Durable Oxygen Reduction Reaction.

Transforming the Pt-M alloy into an ordered intermetallic is an effective strategy to improve the electrocatalytic activity and stability toward the oxygen reduction reaction (ORR). However, the synthesis of nanosized intermetallics remains challenging. Herein, we report an efficient ORR electrocatalyst, consisting of a monodisperse nanosized PtCu intermetallic on hollow mesoporous carbon spheres (HMCS). As predicted by theoretical calculations, PtCu intermetallics exhibit beneficial electronic structure, with a low theoretical overpotential of 0.33 V and enhanced Cu stability. Resulting from the multiscale modulation of catalyst structure, the O-PtCu/HMCS catalyst delivers a high mass activity of 2.73 A cm-2Pt at 0.9 V and remarkable stability. Identical location transmission electron microscopy (IL-TEM) investigations demonstrate that the rate of carbon corrosion is alleviated on HMCS, which contributes to the long-term durability. This work provides a promising design strategy for an ORR electrocatalyst, and the IL-TEM investigations offer new perspectives for the performance enhancement mechanism.

Using the IL-TEM Technique to Understand the Mechanism and Improve the Durability of Platinum Cathode Catalysts for Proton-Exchange Membrane Fuel Cells.

Proton-exchange membrane fuel cells are one of the most promising energy conversion technologies for both automotive and stationary applications. Scientists are testing a number of solutions to increase the durability of cells, especially catalysts, which are the most expensive component. These solutions include, among others, the modification of the composition and morphology of supported nanoparticles, the platinum-support interface, and the support itself. A detailed understanding of the mechanism of platinum degradation and the subsequent improvement of the durability of the entire cell requires the development of methods for effectively monitoring the behavior of catalytic nanoparticles under various cell operating conditions. The Identical-Location Transmission Electron Microscopy (IL-TEM) method makes it possible to visually track structural and morphological changes in the catalyst directly. Because the tests are performed with a liquid electrolyte imitating a membrane, they provide better control of the degradation conditions and, consequently, facilitate the understanding of nanoparticle degradation processes in various operating conditions. This review is primarily intended to disseminate knowledge about this technique to scientists using electron microscopy in the study of energy materials and to draw attention to issues related to the characterization of the structure of carbon supports.

Resolving Nanoscale Processes during Carbon Mineralization Using Identical Location Transmission Electron Microscopy

Resolving Nanoscale Processes during Carbon Mineralization Using Identical Location Transmission Electron Microscopy

Stabilitätsuntersuchungen an einem Pt@HGS‐Katalysator als Modellmaterial für Brennstoffzellenanwendungen: Die Rolle des lokalen pH‐Wertes

AbstractDie Erhöhung der Widerstandsfähigkeit von Katalysatoren gegen elektrochemische Degradation ist eine der wichtigsten Voraussetzungen für den breiteren Einsatz von Protonenaustausch‐Membran‐Brennstoffzellen (PEMFCs). Hier untersuchen wir die Degradation eines einzelnen Partikels eines hochstabilen Katalysators, Pt@HGS auf einer Nanoelektrode unter nicht‐limitierenden Massentransportbedingungen. Wir stellen fest, dass der Katalysator schneller degradiert als aufgrund früherer Ensemblemessungen erwartet wird. Auf Basis von Transmissionselektronenmikroskopie (TEM) an identischen Stellen nach elektrochemischer Belastung und Experimenten mit einer Katalysatorschicht auf einem TEM‐Träger schließen wir, dass lokal unterschiedliche pH‐Werte wahrscheinlich der Grund für diesen Stabilitätsunterschied sind. Letztendlich bietet diese Arbeit Einblicke in die tatsächlichen Bedingungen in einer PEMFC und wirft Fragen zur Anwendbarkeit von beschleunigten Belastungstests auf, die normalerweise zur Bewertung der Katalysatorstabilität durchgeführt werden, insbesondere wenn sie in Halbzellenaufbauten unter Inertgas durchgeführt werden.

Stability Investigations on a Pt@HGS Catalyst as a Model Material for Fuel Cell Applications: The Role of the Local pH.

Increasing the resistance of catalysts against electrochemical degradation is one of the key requirements for the wider use of Proton Exchange Membrane Fuel Cells (PEMFCs). Here, we study the degradation of one entity of a highly stable catalyst, Pt@HGS, on a nanoelectrode under accelerated mass transport conditions. We find that the catalyst degrades more rapidly than expected based on previous ensemble measurements. Corroborated by identical location transmission electron microscopy and catalyst layer experiments, we deduce that locally different pH values are likely the reason for this difference in stability. Ultimately, this work provides insights into the actual conditions present in a PEMFC and raises questions about the applicability of accelerated stress tests usually performed to evaluate catalyst stability, particularly when they are performed in half-cell setups under inert gas.

Stability of Carbon Supported Silver Electrocatalysts for Alkaline Oxygen Reduction and Evolution Reactions.

Ag-based electrocatalysts are promising candidates to catalyze the sluggish oxygen reduction reaction (ORR) in anion exchange membrane fuel cells (AEMFC) and oxygen evolution reaction (OER) in unitized regenerative fuel cells. However, to be competitive with existing technologies, the AEMFC with Ag electrocatalyst must demonstrate superior performance and long-term durability. The latter implies that the catalyst must be stable, withstanding harsh oxidizing conditions. Moreover, since Ag is typically supported by carbon, the strict stability requirements extend to the whole Ag/C catalyst. In this work, Ag supported on Vulcan carbon (Ag/VC) and mesoporous carbon (Ag/MC) materials is synthesized, and their electrochemical stability is studied using a family of complementary techniques. We first employ an online scanning flow cell combined with inductively coupled plasma mass spectrometry (SFC-ICP-MS) to estimate the kinetic dissolution stability window of Ag. Strong correlations between voltammetric features and the dissolution processes are discovered. Very high silver dissolution during the OER renders this material impractical for regenerative fuel cell applications. To address Ag stability during AEMFC load cycles, accelerated stress tests (ASTs) in O2-saturated solutions are carried out in rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) setups. Besides tracking the ORR performance evolution, an ex situ long-term Ag dissolution study is performed. Moreover, morphological changes in the catalyst/support are tracked by identical-location transmission electron microscopy (RDE-IL-TEM). Voltammetry analysis before and after AST reveals a smaller change in ORR activity for Ag/MC, confirming its higher stability. RRDE results reveal a higher increase in the H2O2 yield for Ag/VC after the ASTs. The RDE-IL-TEM measurements demonstrate different degradation processes that can explain the changes in the long term performance. The results in this work point out that the stability of carbon-supported Ag catalysts depends strongly on the morphology of the Ag nanoparticles, which, in turn, can be tuned depending on the chosen carbon support and synthesis method.

Electrochemical Behavior and Shape Evolution of Structured Pd Nanoparticles in Alkaline Media─Influence of Electrochemically Absorbed Hydrogen.

We report on the electrochemical behavior and shape evolution of Pd nanocubes (Pd NCs) and Pd nanooctahedrons (Pd NOs) with an average size of 9.8 and 6.9 nm, respectively, in aqueous alkaline medium in the potential range of the underpotential deposition of H (UPD H) and H absorption. While the Pd NCs and Pd NOs remain stable in the potential region of the UPD H, H absorption and desorption of absorbed H (Habs) induce structural changes to the Pd NPs, as indicated by the results of electrochemical measurements and identical location-transmission electron microscopy (IL-TEM) analyses. Because both Pd NCs and Pd NOs are known to be stable in the potential region of H absorption and Habs desorption in acidic medium and maintain their structure, the irreversible structural changes are attributed to their interfacial interaction with the aqueous alkaline medium. In the alkaline medium, the nanoparticle surface/electrolyte interfacial structure plays an essential role in the mechanism of Habs desorption that is observed at higher potentials than that in the acidic medium. Hydrogen desorption is substantially hindered due to the structure of the water network adjacent to the Pd nanoparticles or the interaction between hydrated cations and adsorbed OH on the nanoparticle surface, resulting in the trapping of a small amount of H (incomplete Habs desorption). It is proposed that H trapping and associated structural strain lead to the deformation of the Pd nanoparticles and the loss of their initial structure.

Expanding the Potential of Identical Location Scanning Transmission Electron Microscopy for Gas Evolving Reactions: Stability of Rhenium Molybdenum Disulfide Nanocatalysts for Hydrogen Evolution Reaction.

Identical location (scanning) transmission electron microscopy provides valuable insights into the mechanisms of the activity and degradation of nanocatalysts during electrochemical reactions. However, the technique suffers from limitations that hinder its widespread use for nanocatalysts of gas evolving reactions, e.g., the hydrogen evolution reaction (HER). The main issue is the production of bubbles that cause the loss of electric contact in identical location measurements, which is critical for the correct cycling of the nanocatalysts and interpretation of the electron microscopy results. Herein, we systematically evaluate different set-ups, materials, and tools to allow the facile and reliable study of the stability of HER nanocatalysts. The optimized conditions are applied for the study of layered rhenium molybdenum disulfide (Re0.2Mo0.8S2) nanocatalysts, a relevant alternative to Pt catalysts for the HER. With our approach, we demonstrate that although the morphology of the Re0.2Mo0.8S2 catalyst is maintained during HER, chemical composition changes could be correlated to the electrochemical reaction. This study expands the potential of the IL(S)TEM technique for the construction of structure-property relationships of nanocatalysts of gas evolving reactions.

Monolayer supertubes of Carbon-Armored platinum nanocrystals enabling robust oxygen reduction electrocatalysis

Self-assembled superstructures composed of nanocrystals (NCs) have shown immense potential for enhancing the performance in electrocatalytic applications. However, there has been limited research on the self-assembly of platinum (Pt) into low-dimensional superstructures as efficient electrocatalysts for oxygen reduction reaction (ORR). In this study, we designed a unique tubular superstructure composed of monolayer or sub-monolayer carbon-armored platinum nanocrystals (Pt NCs) using a template-assisted epitaxial assembly approach. The organic ligands on the surface of Pt NCs were in situ carbonized, resulting in few-layer graphitic carbon shells that encapsulate Pt NCs. Due to their monolayer assembly and tubular geometry, the Pt utilization of the supertubes was 1.5 times higher than that of conventional carbon-supported Pt NCs. As a result, such Pt supertubes exhibit remarkable electrocatalytic performance for the ORR in acidic media, with a high half-wave potential of 0.918 V and a high mass activity of 181 A g-1Pt at 0.9 V, which are comparable to commercial carbon-supported Pt (Pt/C) catalysts. Furthermore, the Pt supertubes demonstrate robust catalytic stability, as confirmed by long-term accelerated durability tests and identical-location transmission electron microscopy. This study presents a new approach to designing Pt superstructures for highly efficient and stable electrocatalysis.

"Nano Lab" Advanced Characterization Platform for Studying Electrocatalytic Iridium Nanoparticles Dispersed on TiOxNy Supports Prepared on Ti Transmission Electron Microscopy Grids.

Aiming at speeding up the discovery and understanding of promising electrocatalysts, a novel experimental platform, i.e., the Nano Lab, is introduced. It is based on state-of-the-art physicochemical characterization and atomic-scale tracking of individual synthesis steps as well as subsequent electrochemical treatments targeting nanostructured composites. This is provided by having the entire experimental setup on a transmission electron microscopy (TEM) grid. Herein, the oxygen evolution reaction nanocomposite electrocatalyst, i.e., iridium nanoparticles dispersed on a high-surface-area TiOxNy support prepared on the Ti TEM grid, is investigated. By combining electrochemical concepts such as anodic oxidation of TEM grids, floating electrode-based electrochemical characterization, and identical location TEM analysis, relevant information from the entire composite's cycle, i.e., from the initial synthesis step to electrochemical operation, can be studied. We reveal that Ir nanoparticles as well as the TiOxNy support undergo dynamic changes during all steps. The most interesting findings made possible by the Nano Lab concept are the formation of Ir single atoms and only a small decrease in the N/O ratio of the TiOxNy-Ir catalyst during the electrochemical treatment. In this way, we show that the precise influence of the nanoscale structure, composition, morphology, and electrocatalyst's locally resolved surface sites can be deciphered on the atomic level. Furthermore, the Nano Lab's experimental setup is compatible with ex situ characterization and other analytical methods, such as Raman spectroscopy, X-ray photoelectron spectroscopy, and identical location scanning electron microscopy, hence providing a comprehensive understanding of structural changes and their effects. Overall, an experimental toolbox for the systematic development of supported electrocatalysts is now at hand.

Understanding the Degradation Mechanisms of Pt Electrocatalysts in PEMFCs by Combining 2D and 3D Identical Location TEM.

The evolution of Pt nanoparticles in proton-exchanged membrane fuel cells is monitored before and after electrochemical potential cycling, using 2D and 3D identical location aberration-corrected transmission electron microscopy. This work demonstrates that 2D images might be a challenge to interpret due to the 3D nature of the carbon support. Thus, it is critical to combine both 2D and 3D observations to be able to fully understand the mechanisms associated with the durability of Pt catalyst nanoparticles. In particular, this investigation reveals that the mechanism of particle migration followed by coalescence is operative mainly across short distances (<0.5 nm). This work also shows that new Pt particles appear on the carbon support, as the result of Pt dissolution, followed by the formation of clusters, which grow by Ostwald ripening. This mechanism of Ostwald ripening is also responsible for changes in shape and particle growth, which later may result in coalescence.

Multiple‐length scale investigation of Pt/C degradation by identical‐location transmission electron microscopy

AbstractPt‐based electrocatalysts on the cathode side of proton exchange membrane fuel cells (PEMFCs) generally undergo severe degradation, which contributes to the short life span of PEMFCs. Thus, it is crucial to understand the structural degradation of Pt‐based electrocatalysts. Here, various degradation mechanisms of individual Pt nanoparticles supported on Vulcan carbon during load‐cycle accelerated stress tests were investigated and quantified by identical‐location transmission electron microscopy (IL‐TEM). The atomic‐scale IL‐STEM imaging revealed the formation of Pt single atoms on the carbon support, which resulted from the dissolution of nanoparticles, and the following pathway change in the oxygen reduction reaction (ORR) was analyzed by rotating ring‐disk electrode tests. Our study provides new insight for understanding the relationship between the decline in the ORR activity and the formation of Pt atomic species resulting from the electrochemical degradation of Pt/C.