Size Of Platinum Nanoparticles Research Articles

Platinum-Catalyzed Silicon Nanowire Growth─Evidence for a Switch from Vapor–Liquid–Solid to Vapor–Solid–Solid Mechanism with Platinum Nanoparticle Size

Platinum-Catalyzed Silicon Nanowire Growth─Evidence for a Switch from Vapor–Liquid–Solid to Vapor–Solid–Solid Mechanism with Platinum Nanoparticle Size

Platinum Nanoparticles Supported by Carbon Nanotubes: Improvement in electrochemical sensor performance for caffeine determination.

Platinum nanoparticles supported by carbon nanotubes were obtained by a simple chemical route and used for preparation of electrochemical sensor towards caffeine determination. Carbon nanotubes were used before and after an acid treatment, yielding two different materials. Morphological and structural characterization of these materials showed platinum nanoparticles (size around 12 nm) distributed randomly along carbon nanotubes. Modified electrodes were directly prepared through a dispersion of these materials. Voltammetric studies in the presence of caffeine revealed an electrocatalytic effect of platinum oxides, electrochemically produced from the chemical oxidation of the platinum nanoparticles. This behavior was explored in the development a selective method for caffeine determination based on platinum oxide reduction at a lower potential value (+0.45 V vs. Ag/AgCl). Using the best set of experimental conditions, it was shown a linear relationship for the caffeine concentration ranging from 5.0 to 25 µmol L-1 with a sensitivity of 449 nA L µmol-1. Limits of detection and quantification of 0.54 and 1.80 µmol L-1 were calculated, respectively. Recovery values for real samples of caffeine pharmaceutical formulations between 98.6% and 101.0% (n = 3) were obtained using the proposed procedure. Statistical calculations showed good concordance (95% confidence level) between the added and recovery values.

Effect of Fuel Cell Electrode Fabrication on Ionomer Nanostructure in Correlation with Electrochemical Performances

Proton Exchange Membrane Fuel Cell (PEMFC) electrodes, seat of the electrochemical reactions, rule the whole operation and are critical components in terms of cost, performance and durability. Their improvement will monitor the large-scale commercialization of PEMFC.These porous electrodes are made of catalyst, composed by platinum nanoparticles (2-5 nm) supported on electrically conductive carbon particles (~30-50 nm) which are bound by an ionomer. The ionomer plays a crucial role as a binder and proton conductor upon its hydration. It can be in the form of aggregates within the electrode pores or of nanofilms on the surface of the catalyst as shown by Atomic Force Microscopy (AFM)1 and Small angle neutron scattering (SANS)2.The electrode is obtained by coating and drying an ink made of catalyst and ionomer dispersed in a solvent. Electrode performances depend on the ionomer content3 and on fabrication parameters such as the solvent4 as it can be seen in Figure 1(a). It was shown that the solvent changes the ionomer organization into the ink5. Thus, it will affect its nanostructure within the electrode. The distribution of the ionomer at the nanometer scale influences the water sorption and reactants (protons and gases) transport properties of the electrode6. However, little is known about the ionomer in the electrode because of the complexity of its characterization.SANS is used to characterize the ionomer within the electrode because its contribution is clearly visible2 but neutron sources are rarer and less available than X-ray sources. In addition, Small angle X-ray scattering (SAXS) can be performed with laboratory equipment and therefore does not necessarily require the use of synchrotron facilities. SAXS have already been performed on electrodes but rather to investigate the carbon or platinum nanoparticle size distributions7,8. The ionomer contribution in a SAXS profile of an electrode is hardly distinguishable because its contribution is hidden by the large scattering of the Pt nanoparticles due to its strong interaction with X-rays.In this work, SAXS is used to characterize the structure of the ionomer within the electrode that is crucial to a better understanding of the correlation between the electrodes fabrication and their electrochemical performances. The performance of the electrodes was characterized thanks to tests under H2/Air at 1.5 bara. Electrochemical tests and SAXS measurements were performed on electrodes equilibrated at several relative humidities. A data processing method for SAXS profile of electrode is proposed in order to subtract the platinum contribution and to highlight the contributions of carbon, ionomer and water. This method allows the extraction of information about the ionomer nanostructure and the hydration of the electrode. Figure 1(b) shows 1D SAXS profiles obtained for an electrode made from a water/ethanol mix based ink and another one made from a triethyl phosphate (TEP) based ink. After data processing, the curves show differences with increasing humidity. The electrode made with TEP shows a peak around 0.2 Å-1 (Figure 1(d)) which can be assimilated to an ionomer peak and therefore to aggregates. It has been shown using SANS that if the ionomer is in the form of aggregates within the electrode, it behaves as bulk ionomer, thus presents an ionomer peak2. The electrode made with water/ethanol mix does not show this peak (Figure 1(c)), thus the ionomer is more efficiently dispersed within it. The better dispersion of the ionomer seems to lead to better electrochemical performances compared to TEP as shown in Figure 1(a).(1) Morawietz, T. & al. Fuel Cells 2018, 18 (3), 239–250. https://doi.org/10.1002/fuce.201700113.(2) Chabot, F. & al. ACS Appl. Energy Mater. 2023, 6 (3), 1185–1196. https://doi.org/10.1021/acsaem.2c02384.(3) Suzuki, T. & al. International Journal of Hydrogen Energy 2011, 36 (19), 12361–12369. https://doi.org/10.1016/j.ijhydene.2011.06.090.(4) Kim, T. & al. International Journal of Hydrogen Energy 2017, 42 (1), 478–485. https://doi.org/10.1016/j.ijhydene.2016.12.015.(5) Tarokh, A. & al. Macromolecules 2020, 53 (1), 288–301. https://doi.org/10.1021/acs.macromol.9b01663.(6) Kobayashi, A. & al. ACS Appl. Energy Mater. 2021, 4 (3), 2307–2317. https://doi.org/10.1021/acsaem.0c02841.(7) Povia, M. & al. ACS Catal. 2018, 8 (8), 7000–7015. https://doi.org/10.1021/acscatal.8b01321.(8) Wang, M. & al. ACS Appl. Energy Mater. 2019, 2 (9), 6417–6427. https://doi.org/10.1021/acsaem.9b01037. Figure 1

Sensors based on iron phthalocyanine films decorated with platinum nanoparticles and carbon rods for electrochemical detection of nitrites

The iron phthalocyanine derivatives (FePc) are regarded as active layers of sensors. The films of iron phthalocyanines, viz. FePc, FePcF4, and FePcCl4 were deposited onto glassy carbon electrodes. Annealed film (a-FePc) were decorated with platinum nanoparticles (PtNPs) and carbon rods using facile metal organic chemical vapor deposition (MOCVD), resulting in a series of Pt/a-FePc heterostructures. The composition, distribution and sizes of PtNPs and carbon rods in the heterostructures were investigated. The electrochemical characteristics of the series of FePc, FePcF4, and FePcCl4 and Pt/a-FePc samples were determined in 0.1 M PBS solution using cyclic voltammetry (CV, 0.25–2.00 mM), amperometry (CA 0.5–30 μM), and impedance spectroscopy. The Pt/a-FePc heterostructures with a Pt content of 21–63 μM/cm2, which consisted of uniformly distributed PtNPs with a size of 9–12 nm and carbon rods up to 1 μm in length, demonstrated the excellent electron transfer characteristics Synergetic combination of the properties of 3 components (a-FePc, PtNPs or carbon rods) resulted in the improvement of the performance of Pt/a-FePc sensors. The Pt/a-FePc electrode demonstrated the lowest detection limit of 0.06 μM and high sensitivity to NO2−. This sensor had good selectivity in the presence of interfering analytes, repeatability and stability.

Preparation of boron-doped diamond microelectrodes to determine the distribution size of platinum nanoparticles using current transient method

Boron-doped diamond (BDD) microelectrodes were prepared to investigate the correlation of hydrazine oxidation current responses with Pt nanoparticle (Pt NP) size distribution. The BDD film was grown on the surface of a tungsten needle with a diameter of 25 µm. An average particle size of around 5 µm BDD crystalline was successfully synthesized using a microwave plasma-assisted chemical vapor deposition technique. The Raman spectrum confirmed the presence of diamond formation as indicated by peaks corresponding to C-C sp3 bonds, while X-ray photoelectron spectroscopy spectrum showed the presence of C-H and C-OH bonds on the surface of the BDD microelectrode. Meanwhile the Pt nanoparticles was synthesized through reduction reaction of PtCl62- solution using NaBH4 with citric acid as the capping agent. Particles size between 4.46 to 4.78 nm were observed by using TEM measurements. The BDD microelectrodes were utilized to investigate the relationship between Pt nanoparticle size distribution and the current generated from the oxidation reaction of 15 mM hydrazine in a 50 mM phosphate buffer solution pH 7.4 in the presence of 1.0 mL nanoparticle solutions. A current range of 5 and 6 nA with a noise level of 0.15 nA was observed showing a good correlation with the particle sizes of Pt NPs. Comparison was also performed with the measurements using Au microelectrodes, indicated that the prepared BDD microelectrodes is promising for the measurements of nanoparticle sizes distribution, especially Pt NPs.

Assessment by a multi-technique approach of PtNPs' transformations in waters under relevant environmental concentrations and conditions

Once released to the environment, platinum nanoparticles (PtNPs) can undergo different transformations and are affected by several environmental conditions. An only analytical technique cannot provide all the information required to understand those complex processes, so new analytical developments are demanded. In the present work, the potential of asymmetric flow field flow fractionation hyphenated to inductively coupled plasma mass spectrometry (AF4-ICP-MS) for these studies, has been investigated, and classical dynamic and electrophoretic light scattering (DLS & ELS) have been used as complementary techniques. The role of ionic strength, ionic water composition, and natural organic matter (NOM) in the behaviour of PtNPs of different sizes (5 and 50 nm) has been specifically studied. Dynamic and electrophoretic light scattering have been used to track changes in the hydrodynamic diameters (dh) and polydispersity index (PdI) for 50 nm PtNPs (5 nm cannot be studied by DLS) and Z-potential values (for all sizes) to monitor aggregation. AF4-ICP-MS has been also employed to have a solid insight of aggregation at low environmental concentrations for different sizes of PtNPs simultaneously. The information gathered with those techniques was useful to observe changes as the ionic strength increases, which induces aggregation. Also, it was observed that this aggregation process was attenuated in the presence of organic matter. This approach, based on complementary analytical techniques, is needed for a comprehensive study of such complex interactions of NPs in the environment. AF4-ICP-MS is still under-exploited but shows a great potential for this purpose, especially low size NPs and concentrations.

Impact of platinum loading and dispersion on the catalytic activity of Pt/SnO2 and Pt/α-Fe2O3

The Pt/SnO2 (SP-samples) and Pt/α-Fe2O3 (FP-samples) with platinum loadings between 1 and 10 mol% were synthesized mechanochemically starting from platinum(II) acetylacetonate dissolved in toluene and from SnO2 and α-Fe2O3 powders obtained from tin(II) and iron(II) acetates. The STEM results show that the ultrasmall platinum nanoparticles (PtNPs) are well dispersed on the SnO2 and α-Fe2O3 supports. The PtNPs size distributions calculated with lognormal functions ranged from 1.0 to 1.3 nm. The results of temperature programmed reduction in hydrogen showed maxima at 120–160 °C due to the reduction of PtOx to Pt0. The Pt-4f-XPS results showed that the dispersed platinum on the SnO2 and α-Fe2O3 supports consisted of all three oxidation states of platinum: Pt4+, Pt2+ and Pt0. The average oxidation state of platinum as a function of molar fraction of Pt loading in the SP samples varies from 1.69 to 2.11, whereas the oxidation state of Pt in the FP samples varies more linearly and steeply from 1.42 to 2.58. The synthesized samples showed high catalytic activity for the reduction of 4-nitropenol (4-NP) to 4-aminophenol (4-AP), which can be explained by the high dispersion of non-aggregated ultrasmall PtNPs with a size of about 1 nm on the SnOx and FeOx supports.

Platinum-Based Nanoparticle Fuel Cell Catalysts Synthesized By Sputtering Onto Liquid Substrates

The quest of finding cheaper and better fuel cell catalyst materials has been long ongoing and remains a crucial step in making fuel cells a commercially viable technology. Platinum (Pt) is still the conventional catalyst used in proton exchange membrane (PEM) fuel cells, however, with slow cathode kinetics and high material cost. Platinum-rare earth (RE) and lanthanide alloys have been found to greatly enhance the catalytic activity towards the oxygen reduction reaction (ORR).1 Increases in ORR activity of up to one order of magnitude compared to pure platinum has been observed for these alloys, but high oxygen affinity of the RE alloying agents considerably complicates their synthesis. Sputter deposition into low vapor pressure liquid substrates, such as ionic liquids and certain polymers enables fabrication of clean nanoparticles, without the presence of air and other contaminates, making it a potential technique for Pt-RE nanoparticle synthesis.Here, we will present our recent work on magnetron sputtering of Pt 2 and Pt-alloys into different liquid substrates, including polyethylene glycol and three imidazolium-based ionic liquids. We have investigated the influence of substrate temperature on Pt nanoparticle growth during sputtering, and in post-sputtering heat treatment.2 We show that whilst substrate temperature influences the Pt nanoparticle size, the effect is not as great as for other materials. Better understanding the growth processes of Pt nanoparticles sputtered into liquids is an important step towards tunable sizes and catalytic activities of Pt-RE nanocatalysts. Escudero-Escribano, María, et al. "Tuning the activity of Pt alloy electrocatalysts by means of the lanthanide contraction." Science 352.6281 (2016): 73-76.Brown, Rosemary, et al. "Plasma-Induced Heating Effects on Platinum Nanoparticle Size During Sputter Deposition Synthesis in Polymer and Ionic Liquid Substrates." Langmuir 37.29 (2021): 8821-8828.

Biosynthesis of Platinum Nanoparticles with Cordyceps Flower Extract: Characterization, Antioxidant Activity and Antibacterial Activity.

The aim of this work is to develop a green route for platinum nanoparticles (PtNPs) biosynthesized using Cordyceps flower extract and to evaluate their antioxidant activity and antibacterial activity. Different characterization techniques were utilized to characterize the biosynthetic PtNPs. The results showed that PtNPs were spherical particles covered with Cordyceps flower extract. The average particle size of PtNPs in Dynamic Light Scattering was 84.67 ± 5.28 nm, while that of PtNPs in Transmission Electron Microscope was 13.34 ± 4.06 nm. Antioxidant activity of PtNPs was evaluated by DPPH free radical scavenging ability test. The results showed that the antioxidant activity was positively correlated with the concentration of PtNPs, the DPPH scavenging efficiency of PtNPs (0.50–125.00 μg/mL) was 27.77–44.00%. In addition, the morphological changes of four kinds of bacteria (Escherichia coli, Salmonella typhimurium, Bacillus subtilis, Staphylococcus aureus) exposed to PtNPs were observed by scanning electron microscope. The results showed that the antibacterial activity of PtNPs against Gram-negative bacteria was stronger than that of Gram-positive bacteria.

Reaction pathway of nitric oxide oxidation on nano-sized Pt/SiO2 catalysts for diesel exhaust purification

Catalytic NO oxidation on the diesel oxidation catalyst is of great significance for the low-temperature abatement of diesel soot and NOx pollutants. Here, a series of Pt/SiO2 catalysts with different particle sizes (2.78–13.94 nm) were prepared and their effects on NO oxidation activity and reaction pathway were investigated. The results show that the size of platinum nanoparticles is a relevant factor for NO oxidation activity by influencing platinum chemical states during the reaction. Furthermore, NO catalytic oxidation on Pt/SiO2 catalysts are primarily through the bidentate nitrite and bridged nitrate intermediates pathways. Relatively larger platinum nanoparticles (∼13.94 nm) will lead to the generation of nitrates between layers that are difficult to decompose and desorb from catalyst surface, and thereby adverse to NO oxidation activity. Thus, this work suggests that the size of Pt nanoparticles do not only influence the catalytic NO oxidation activity, but also the reaction pathway on the catalyst.

Doped graphene/carbon black hybrid catalyst giving enhanced oxygen reduction reaction activity with high resistance to corrosion in proton exchange membrane fuel cells

Nitrogen doping of the carbon is an important method to improve the performance and durability of catalysts for proton exchange membrane fuel cells by platinum–nitrogen and carbon–nitrogen bonds. This study shows that p−phenyl groups and graphitic N acting bridges linking platinum and the graphene/carbon black (the ratio graphene/carbon black = 2/3) hybrid support materials achieved the average size of platinum nanoparticles with (4.88 ± 1.79) nm. It improved the performance of the lower-temperature hydrogen fuel cell up to 0.934 W cm−2 at 0.60 V, which is 1.55 times greater than that of commercial Pt/C. Doping also enhanced the interaction between Pt and the support materials, and the resistance to corrosion, thus improving the durability of the low-temperature hydrogen fuel cell with a much lower decay of 10 mV at 0.80 A cm−2 after 30 k cycles of an in−situ accelerated stress test of catalyst degradation than that of 92 mV in Pt/C, which achieves the target of Department of Energy (<30 mV). Meanwhile, Pt/NrEGO2−CB3 remains 78% of initial power density at 1.5 A cm−2 after 5 k cycles of in−situ accelerated stress test of carbon corrosion, which is more stable than the power density of commercial Pt/C, keeping only 54% after accelerated stress test.

Plasma-Induced Heating Effects on Platinum Nanoparticle Size During Sputter Deposition Synthesis in Polymer and Ionic Liquid Substrates

Nanoparticle catalyst materials are becoming ever more important in a sustainable future. Specifically, platinum (Pt) nanoparticles have relevance in catalysis, in particular, fuel cell technologies. Sputter deposition into liquid substrates has been shown to produce nanoparticles without the presence of air and other contaminants and the need for precursors. Here, we produce Pt nanoparticles in three imidazolium-based ionic liquids and PEG 600. All Pt nanoparticles are crystalline and around 2 nm in diameter. We show that while temperature has an effect on particle size for Pt, it is not as great as for other materials. Sputtering power, time, and postheat treatment all show slight influence on the particle size, indicating the importance of temperature during sputtering. The temperature of the liquid substrate is measured and reaches over 150 °C during deposition which is found to increase the particle size by less than 20%, which is small compared to the effect of temperature on Au nanoparticles presented in the literature. High temperatures during Pt sputtering are beneficial for increasing Pt nanoparticle size beyond 2 nm. Better temperature control would allow for more control over the particle size in the future.

One-Pot Synthesis of Ultra-Small Pt Dispersed on Hierarchical Zeolite Nanosheet Surfaces for Mild Hydrodeoxygenation of 4-Propylphenol

The rational design of ultra-small metal clusters dispersed on a solid is of crucial importance in modern nanotechnology and catalysis. In this contribution, the concept of catalyst fabrication with a very ultra-small size of platinum nanoparticles supported on a hierarchical zeolite surface via a one-pot hydrothermal system was demonstrated. Combining the zeolite gel with ethylenediaminetetraacetic acid (EDTA) as a ligand precursor during the crystallization process, it allows significant improvement of the metal dispersion on a zeolite support. To illustrate the beneficial effect of ultra-small metal nanoparticles on a hierarchical zeolite surface as a bifunctional catalyst, a very high catalytic performance of almost 100% of cycloalkane product yield can be achieved in the consecutive mild hydrodeoxygenation of 4-propylphenol, which is a lignin-derived model molecule. This instance opens up perspectives to improve the efficiency of a catalyst for the sustainable conversion of biomass-derived compounds to fuels.

Effect of Nanoparticle Size in Pt/SiO2 Catalyzed Nitrate Reduction in Liquid Phase

Effect of platinum nanoparticle size on catalytic reduction of nitrate in liquid phase was examined under ambient conditions by using hydrogen as a reducing agent. For the size effect study, Pt nanoparticles with sizes of 2, 4 and 8 nm were loaded silica support. TEM images of Pt nanoparticles showed that homogeneous morphologies as well as narrow size distributions were achieved during the preparation. All three catalysts showed high activity and were able to reduce nitrate below the recommended limit of 50 mg/L in drinking water. The highest catalytic activity was seen with 8 nm platinum; however, the product selectivity for N2 was highest with 4 nm platinum. In addition, the possibility of PVP capping agent acting as a promoter in the reaction is highlighted.

Nitrogen Doped Reduced Electrochemically Exfoliated Graphene Oxide Inserted Carbon Black As Novel Catalyst Support for the Hydrogen Fuel Cell

Graphene, a two-dimensional (2D) structure of honeycomb lattice material with long-range π-conjugation, is an ideal catalyst support material due to its large surface area, excellent electrical conductivity, good mechanical and electrochemical stability [1]. It has already been reported that platinum nanoparticles (PtNPs) supported on reduced graphene oxide (rGO), is limited by van der Waals force resulting in the restacked rGO flakes during the reduction process, thereby hindering the transport of fuel gas to approach Pt active sites [2, 3].To overcome this issue, several publications have successfully developed PtNPs catalyst supported on rGO and carbon black (CB) hybrid supporting materials [4]. The synergistic effect between rGO and CB could enhance its activity for oxygen reduction reaction through controlling PtNPs size as well as improve its durability by preventing the agglomeration and corrosion of supporting materials [3]. However, Hummers GO leads to environmental and safety issues (use KMnO4, strong oxidizing agents and concentrated H2SO4) as well as a long-time preparation with high cost [2].Our previous research has already developed a novel graphene-based material prepared by electrochemical exfoliation of graphite, which is faster, more environmentally friendly and has a high yield, intercalated by CB as a bi-support and achieved 50% improvement performance compared with Pt/CB.To further improve catalyst activity, some research proposed that the introduction of nitrogen, especially graphitic N and pyridinic N, on the surface of carbon materials could improve ORR activity and electronic conductivity by changing the local electronic structure as well as polarization of the graphene network with smaller energy band gap [3, 5]. However, the effect and comparation of nitrogen doped rEGO intercalated by CB (NrEGO-CB) and nitrogen doped both EGO and CB (NrEGO-NCB) as bi-support materials to improve the performance of the hydrogen fuel cell have not been studied.In this work, EGO and EGO-CB was doped with nitrogen by hydrothermal treatment with urea as a nitrogen precursor in a Teflon-steel autoclave. Pt catalysts were synthesized by a modified polyol reduction method. Successful preliminary results can be observed in Fig 1, which shows that PtNPs supported on NrEGO-CB with ratio of 2 to 3 has a maximum power density of 1.2 W cm-2. It is more than 4 times compared with that 0.3 W cm-2 of Pt/CB.

The role of surface chemistry of modified MWCNT on the development and characteristics of Pt supported catalysts

The performance and stability of electrocatalysts strongly depend on the physicochemical characteristics, such as the surface area, the crystalline structure, size and shape of the particles and the interactions with the support. Platinum (Pt) is one of the most versatile elements in catalysis, efficiently mediating a multitude of chemical reactions. Reducing the demand for expensive Pt is a major driving force in catalysis research. The objective of the present study is the development of electrocatalysts with innovative features and focuses on the synthesis and characterization of highly dispersed Pt supported catalysts using functionalized Multi-Wall Carbon Nanotubes (f-MWCNT) as the substrate. The choice of the substrate was based on the unique properties of carbon nanotubes that generate strong interest for their use in many nano-material devices in catalysis, batteries, optics, gas storage, electronics, sensors and others. Various chemical pathways were used to modify the sidewalls of MWCNT and introduce several covalently attached groups like pyridine, sulfonic acid, carboxyl, benzene or zwitterion type moieties. Using these substrates, deposition of Pt nanoparticles was realized by means of the polyol synthetic procedure. The parameters of the synthetic procedure differentiate the reduction/deposition mechanism. The surface chemistry and functionalities of the support and the diverse reaction conditions resulted in differentiations of the properties, not only in terms of quantitative deposition, but also with respect to platinum oxidation state, nanoparticle size and dispersion and overall catalyst morphology. The combined characterization techniques used shed light into the fundamental understanding of the support effect on the final properties, while metal-support interactions are intensely discussed.

Optimization of Transports in a PEMFC Catalyst Layer at High Current Densities: Coupled Modeling/Imaging Approach

Decreasing the cost of proton exchange membrane fuel cells (PEMFC) is vital for the realization of the fuel cell vehicle market. For this challenge, it is essential not only to still reduce the electrode platinum loading but also to maintain a high performance at high current density. However, even for electrodes made with the most performant catalysts, a large performance loss is observed at high current density and this loss becomes larger as the Pt loading is lower. In operating conditions, recent work has shown that this performance loss was predominantly limited by oxygen [1] and proton transport to the catalytic surface. In order to quantify and link both effects to real active layer structural aspects a coupled modeling/imaging approach is performed. The microstructure of a real electrode is reconstructed in 3D using FIB-SEM (Fig.1a), STEM (Fig.1b) and HRTEM (Fig.1c). The first technique provides the carbon grain arrangement, whereas from the second one platinum nanoparticle size distribution is extracted. With HRTEM, an averaged-thickness is extracted for the ionomer thin layer. The raw imaging data acquired (Fig.1a) is then post-treated using a defined procedure. From the post-treated stack, certain portions that can be representative are selected according to [2]. An example is illustrated in Fig.1e with the respective raw portion in Fig.1d. From this portion, a statistically/imaging-based structure is then built in COMSOL ® Multiphysics software (Figs.1f-1h). The agglomerate 3D model is coupled with a 2D MEA model [3] – a model that allows computing local operating conditions. Studies on volume elements [2] of the catalyst layer are performed with physical input parameters as relative humidity, O2 concentration on the pore, among others, taken from the 2D MEA model.The following set of physics are included in the 3D agglomerate model: the Fickian diffusion for oxygen transport in the ionomer film – accounting for deviations of ionomer’s thin layer behaviour from bulk [4] – and in the pore phase – accounting for Knudsen effects; the ionic transport, through charge conservation equation; a kinetic model assuming a 4-step ORR reaction [5].From the studies performed, simulation results show that the catalyst layer performance is mainly limited by oxygen diffusion in the ionomer phase and ionic transport in the primary pores [6].Figs. 1a to 1k – Process from a raw image to numerical modeling : raw image stack (Fig.1a), platinum particle distribution from STEM acquisition (Fig.1b), HRTEM where Nafion layer can be observed (Fig.1c), portion of the image stack (Fig.1d) and the respective segmented portion (Fig.1e) ; carbon phase (brown), platinum phase (yellow), ionomer and pore phase (green and gray respectively) (Figs.1f-1h). Simulated oxygen concentration profile on Nafion (Fig.1i) and pore (Fig.1j) phases, ionic potential distribution (Fig.1k).

Atomic Scale Insight into the Formation, Size, and Location of Platinum Nanoparticles Supported on γ-Alumina

A clear description of the morphology and location, with respect to the support, of metallic subnanometric particles remains a current strenuous experimental challenge in numerous catalytic applica...

Using DMH as a complexing agent for pulse electrodeposition of platinum nanoparticles towards oxygen reduction reaction

Due to the excellent intrinsic activity of platinum, developing a Pt-based oxygen reduction catalyst with both high performance and low loading is highly desirable but still challenging. How to improve the utilization of platinum-based materials has become one of the most critical issues. Herein, a synthesis strategy using the 5,5-dimethylhydantoin (DMH) as complexing agent is designed to synthesize the Pt catalyst via pulse electrodeposition. On the one hand, the platinum nanoparticles prepared by electrodeposition are exposed on the surface of support materials, which effectively avoids performance degradation caused by the coverage of binder and support. On the other hand, the strong coordination affinity between DMH and platinum ions significantly inhibits the electrodeposition process, resulting in a smaller size of platinum nanoparticles. The effect of plating composition and pulse plating parameters on the Pt/KB catalyst activity for oxygen reduction reaction (ORR) has been investigated. The deposited Pt nanoparticles show a face-centered cubic (fcc) crystal structure with a size ranging from 3 to 10 nm. The optimized Pt/KB catalyst exhibits an enhanced activity (i.e., a half-wave potential of 0.906 V) and stability in the acidic media, even with lower loading of platinum. Moreover, the vital role of the DMH in the pulse electrodeposition process is further verified by using linear sweep voltammetry and cyclic voltammetry.

Oxygen Reduction Reaction Catalyzed by Carbon-Supported Platinum Few-Atom Clusters: Significant Enhancement by Doping of Atomic Cobalt.

Oxygen reduction reaction (ORR) plays an important role in dictating the performance of various electrochemical energy technologies. As platinum nanoparticles have served as the catalysts of choice towards ORR, minimizing the cost of the catalysts by diminishing the platinum nanoparticle size has become a critical route to advancing the technological development. Herein, first-principle calculations show that carbon-supported Pt9 clusters represent the threshold domain size, and the ORR activity can be significantly improved by doping of adjacent cobalt atoms. This is confirmed experimentally, where platinum and cobalt are dispersed in nitrogen-doped carbon nanowires in varied forms, single atoms, few-atom clusters, and nanoparticles, depending on the initial feeds. The sample consisting primarily of Pt2~7 clusters doped with atomic Co species exhibits the best mass activity among the series, with a current density of 4.16 A mgPt−1 at +0.85 V vs. RHE that is almost 50 times higher than that of commercial Pt/C.