Interactions Of Pt Nanoparticles Research Articles

Characterization of Fuel Cell Catalyst Layers in a Gas Diffusion Electrode Setup (GDE)

Although the performance of new catalyst materials for proton exchange membrane fuel cells (PEMFC) often show very promising results in ideal rotating disc electrode (RDE) environment, these results cannot always be transferred to applicable conditions in membrane electrode assemblies (MEAs). This is mainly attributed to differences in the catalyst layer (CL) structure, which hinders the transport of reactants and products for the oxygen reduction reaction (ORR). Therefore, the chemical structure and morphology of the CL have to be considered to improve the performance of these systems in fuel cells. However, due to the various possibilities in producing CLs, many experiments must be carried out until the optimum is reached. The interaction of Pt nanoparticles, carbon support, and ionomer creates a complex triple phase interface dependent on numerous parameters. Characteristics of the carbon support,[1] the Pt loading[2] or the ionomer content[3-5] leads to intensive research efforts and a considerable amount of time as many MEA experiments have to be performed for such studies.[6] To accelerate the screening of catalyst layers, the gas diffusion electrode (GDE) was recently proposed as a half-cell to study real catalyst layers.[7] As a proof of concept study, our group recently shown that catalyst layers with different Pt loading in GDE demonstrate similar ORR trends to MEA experiments.[7] Subsequently, GDEs from different laboratories were benchmarked with standardized electrochemical protocols obtaining reproducible results.[8] Most recently, advanced electrochemical characterization methods developed for MEA technique were established as a GDE method.[9] In the present work, we focus on main aspects of catalyst development, such as the morphology of catalyst layer formation and different catalyst materials, to gain fundamental insights into catalyst layer development. We tuned the porosity of real catalyst layers using different solvent compositions. The results show that low macroporosity leads to severe O2 mass transport limitations, whereas a better performance could be achieved for higher porosity. This allows a critical consideration of key parameters in MEA manufacturing, which has hot pressing as an indispensable step.This work demonstrates the importance of morphology and treatment of the catalyst layer and how substantially it affects the performance and mass transport in GDE setups to elucidate the optimal conditions for the accessibility of the triple phase interface.Literature[1] V. Yarlagadda, M. K. Carpenter, T. E. Moylan, R. S. Kukreja, R. Koestner, W. Gu, L. Thompson and A. Kongkanand, ACS Energy Lett. 2018, 3, 618-621.[2] J. P. Owejan, J. E. Owejan and W. Gu, J. Electrochem. Soc. 2013, 160, F824.[3] E. Antolini, L. Giorgi, A. Pozio and E. Passalacqua, J. Power Sources 1999, 77, 136-142.[4] K.-H. Kim, K.-Y. Lee, H.-J. Kim, E. Cho, S.-Y. Lee, T.-H. Lim, S. P. Yoon, I. C. Hwang and J. H. Jang, Int. J. Hydrogen Energy 2010, 35, 2119-2126.[5] G. Sasikumar, J. W. Ihm and H. Ryu, J. Power Sources 2004, 132, 11-17.[6] K. Ehelebe, D. Escalera-López and S. Cherevko, Current Opinion in Electrochemistry 2021, 29, 100832.[7] K. Ehelebe, D. Seeberger, M. T. Y. Paul, S. Thiele, K. J. J. Mayrhofer and S. Cherevko, J. Electrochem. Soc. 2019, 166, F1259-F1268.[8] K. Ehelebe, N. Schmitt, G. Sievers, A. W. Jensen, A. Hrnjić, P. Collantes Jiménez, P. Kaiser, M. Geuß, Y.-P. Ku, P. Jovanovič, K. J. J. Mayrhofer, B. Etzold, N. Hodnik, M. Escudero-Escribano, M. Arenz and S. Cherevko, ACS Energy Lett. 2022, 7, 816-826.[9] P. Kaiser, V. Lloret Segura, K. Ehelebe and S. Cherevko, ECS Meeting s 2022, MA2022-01, 2071.

Molecular Insights into the Ligand‐Reactant Interactions of Pt Nanoparticles Functionalized with α‐Amino Acids as Asymmetric Catalysts for β‐Keto Esters

AbstractThe asymmetric hydrogenation of ß‐keto esters over α‐amino acid‐functionalized Pt nanoparticles was explored in order to expand our understanding of ligand‐reactant interactions underlying the chiral induction. A comprehensive investigation aimed at the quantification of the nonlinear effects demonstrated that for most of the ligands and reactants enantiodifferentiation is determined by 1 : 1 ligand‐reactant interaction. However, attachment of phenyl substituents to the ligands or reactants likely involves the formation of more intricate intermediate complexes. We have shown that the asymmetric bias is sensitive to even small changes in the geometry of the ligand. Additionally, we have found that alkali metal cations, which balance the negative charge of the ligand's carboxyl group and originate from the metal hydroxide used for ligand functionalization, play a key role in the process of chiral induction. As the nature of the cation can be varied by simply changing the metal hydroxide used during functionalization, this finding opens an additional possibility to control the stereoselectivity by tuning the ligand‐reactant interaction.

Highly efficient Pt/NaNbO3 nanowire photocatalyst: Its morphology effect and application in water purification and H2 production

Pt nanoparticles (NPs) supported on wire- and cube- like NaNbO3 were successfully synthesized by a facile hydrothermal route combined with in situ photodeposition method. Photocatalytic performances towards photocatalytic H2 production and organic-pollutant degradation of NaNbO3 with morphology of nanowire and nanocube, with or without support of Pt NPs were comparatively investigated. In addition, special attention was paid to investigate the influence of the morphologies on the photocatalytic performance of Pt/NaNbO3 systems. It was found that, by incorporation of Pt NPs, Pt/NaNbO3 systems show much higher activity than their counterparts. Moreover, by contrast with Pt/NaNbO3 nanocube, the Pt NPs tend to be better uniformly dispersed on NaNbO3 nanowire while prefer to agglomerate on NaNbO3 nanocube, resulting in more direct contact between Pt NPs and NaNbO3 nanowire. Meanwhile, it was found that the stronger interaction of Pt NPs and NaNbO3 nanowire, confirmed by XRD, Raman spectroscopy and XPS, significantly enhanced the electron transfer between NaNbO3 nanowire and Pt NPs, and hence further increased the separation efficiency of electron-hole pairs. Thus, a remarkably more enhanced photocatalytic activity of Pt/NaNbO3 nanowire than other materials has been realized, and this catalyst presented super stability as well. A deep insight into the underlying of the photocatalytic reaction mechanism was also proposed.

A comparative investigation of metal-support interactions on the catalytic activity of Pt nanoparticles for ethanol oxidation in alkaline medium

The effects of interactions of Pt nanoparticles with hybrid supports on reactivity towards ethanol oxidation in alkaline solution are investigated. Studies involve catalysts with identical Pt nanoparticles on six hybrid supports containing carbon powder and transition metal oxides (TiO2, ZrO2, SnO2, CeO2, MoO3 and WO3). In situ X-ray absorption spectroscopy (XAS) results evidence that metal-support interactions produce changes in the Pt 5d band vacancy, which appears to determine the catalytic activity. The highest and lowest activities are observed for Pt nanoparticles on hybrid supports containing TiO2 and CeO2, respectively. Further studies are presented for these two catalysts. In situ FTIR reflection spectroscopy measurements, taken using both multi-stepped FTIR spectroscopy (MS-FTIR) and single potential alteration FTIR spectroscopy (SPA-FTIR), evidence that the main product of ethanol oxidation is acetate, although signals attributed to carbonate and CO2 indicate some differences in CO2 production. Fuel cell performances of these catalysts, tested in a 4.5 cm2 single cell at different temperatures (40–90 °C) show good agreement with data obtained by electrochemical techniques. Results of this comprehensive study point out the possibility of compensating a reduction of noble metal load with an increase in activity promoted by interactions between metallic nanoparticles and a support.

Interactions of Pt nanoparticles with molecular components in polymer electrolyte membrane fuel cells: multi-scale modeling approach

Three phase model consists of Pt nanoparticles, Nafion, and graphite with oxygen, water, and hydronium.

Synthesis of ultrafine Pt nanoparticles stabilized by pristine graphene nanosheets for electro-oxidation of methanol.

In this study, the pristine graphene nanosheets (GNS) derived from chemical vapor deposition process were employed as catalyst support. In spite of the extremely hydrophobic GNS surface, ultrafine Pt nanoparticles (NPs) were successfully assembled on the GNS through a surfactant-free solution process. The evolution of Pt NPs in the GNS support was studied using transmission electron microscopy. It was found that the high-energy surface sites in the GNS, such as edges and defects, played a critical role on anchoring and stabilizing Pt nuclei, leading to the formation of Pt NPs on the GNS support. The concentration of the Pt precursor, i.e., H2PtCl6 solution had significant effects on the morphology of Pt/GNS hybrids. The resulting Pt/GNS hybrids were examined as catalysts for methanol electro-oxidation. It was indicated that the electrochemical active surface area and catalytic activity of the Pt/GNS hybrids were highly dependent on Pt loadings. The superior activity of the catalysts with low Pt loadings was attributed to the presence of Pt subnanoclusters as well as the strong chemical interaction of Pt NPs with the GNS support.

The effect of Pt characteristics on the photoactivity of Pt/TiO2 for hydrogen production from ethanol

Pt/TiO2 photo-catalysts prepared by different methodologies (deposition–precipitation and wet impregnation using various Pt precursors) are investigated for the photo-production of hydrogen from aqueous solutions of ethanol. Textural, structural and surface catalyst properties are determined by N2 adsorption isotherms, UV–vis spectroscopy, XRD and XPS and related to the photo-activity results. Physicochemical characterization of Pt/TiO2 samples revealed differences in the electronic state and surface concentration of Pt nanoparticles depending on the method of preparation. Stronger interaction of Pt nanoparticles with TiO2 support that leads to some partially charged Pt particles was observed in the samples prepared by the deposition–precipitation (Ptδ−) and by impregnation (Ptδ+) using neutral Pt acetylacetonate precursor. It is found that H2 production rates on Pt/TiO2 photo-catalysts depend on the characteristics of Pt particles showing the partially charged Pt particles (Ptδ−and Ptδ+) better intrinsic photoactivity than that observed for metallic Pt counterpart. The improvement in the intrinsic activity observed for the partially charged Pt particles is attributed to a better e-conductivity (in the case of Ptδ− particles) and an increase in the adsorption of surface molecules (in the case of Ptδ+) extending the e-/hole carrier separation of TiO2 photo-catalyst.

Metal-Support Interaction of Pt Nanoparticles with Ionically and Non-Ionically Conductive Supports for CO Oxidation

Platinum nanoparticles of narrow size distribution (similar to 2.5 nm) were synthesized using a modified polyol method and deposited on yttria-stabilized zirconia (Pt/YSZ), carbon (Pt/C) and gamma-alumina (Pt/gamma-Al2O3) supports, resulting in 1 wt % of Pt loading. Pt/YSZ has the highest catalytic activity toward CO oxidation among the studied catalysts. Decrease in the average particle size of Pt/YSZ led to the increase in CO conversion at low temperatures. Enhanced performances can be explained by the thermally induced O2- backspillover from YSZ over Pt nanoparticles in agreement with the electrochemical promotion mechanism. Observed effect becomes more pronounced with decreasing the particle size. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.024203esl] All rights reserved.

Pt Nanoparticles Supported on Highly Dispersed Alumina Coated inside SBA‐15 for Enantioselective Hydrogenation

AbstractA series of Al2O3@SBA‐15 composites with different alumina loadings have been prepared using a solid‐state grinding method. Various techniques, such as X‐ray diffraction, N2 sorption, FT‐IR spectroscopy, and NMR spectroscopy, are used to characterize their structures and acidity. The Al2O3@SBA‐15 composites retain the mesostructure of the SBA‐15 host and the alumina is highly dispersed and uniformly coated inside the mesopores. The Al2O3@SBA‐15 composites serve as remarkable supports for Pt nanoparticles, which can be used as catalysts in the enantioselective hydrogenation of ethyl pyruvate. Both the Brønsted acid sites that originate from the interface of Al2O3 and SBA‐15 in the Al2O3@SBA‐15 composites and the appropriate interaction of Pt nanoparticles with alumina coated inside the mesopores of SBA‐15 can improve the catalytic behavior of Pt/Al2O3@SBA‐15 catalysts.

Probing metal substrate interaction of Pt nanoparticles: Structural XRD analysis and oxygen reduction reaction

Platinum nanoparticles were selectively deposited on titania via a facile photochemical method. The anatase-type TiO 2 nanostructure, prepared by sol-gel, is in intimate contact with the carbon (Vulcan XC-72) used as supporting material. The structural studies via XRD in the as prepared and heat-treated samples were evaluated and compared to the substrate without oxide. The lattice constant of platinum was found 0.6% less than the value in the bulk. This observation is accompanied by high internal strains, which are not present on the Pt/C system. A healing of such defects is achieved by the thermal treatment. The consequence of such observations is discussed in terms of a strong-metal nanoparticle oxide interaction, which is favorable for electrocatalysis. These studies suggest that Pt–TiO 2–C might serve as an element of response to lower the amount of utilized platinum in low temperature H 2/O 2 fuel cells cathodes.

Synthesis, characterization and electrocatalytical behavior of Nb–TiO 2/Pt nanocatalyst for oxygen reduction reaction

In order to point out the effect of the support to the catalyst for oxygen reduction reaction nano-crystalline Nb-doped TiO 2 was synthesized through a modified sol–gel route procedure. The specific surface area of the support, S BET, and pore size distribution, were calculated from the adsorption isotherms using the gravimetric McBain method. The support was characterized by X-ray diffraction (XRD) technique. The borohydride reduction method was used to prepare Nb–TiO 2 supported Pt (20 wt.%) catalyst. The synthesized catalyst was analyzed by TEM technique. Finally, the catalytic activity of this new catalyst for oxygen reduction reaction was investigated in acid solution, in the absence and the presence of methanol, and its activity was compared towards the results on C/Pt catalysts. Kinetic analysis reveals that the oxygen reduction reaction on Nb–TiO 2/Pt catalyst follows four-electron process leading to water, as in the case of C/Pt electrode, but the Tafel plots normalized to the electrochemically active surface area show very remarkable enhancement in activity of Nb–TiO 2/Pt expressed through the value of the current density at the constant potential. Moreover, Nb–TiO 2/Pt catalyst exhibits higher methanol tolerance during the oxygen reduction reaction than the C/Pt catalyst. The enhancement in the activity of Nb–TiO 2/Pt is consequence of both: the interactions of Pt nanoparticles with the support and the energy shift of the surface d-states with respect to the Fermi level what changes the surface reactivity.

Strongly Enhanced Interaction between Evaporated Pt Nanoparticles and Functionalized Multiwalled Carbon Nanotubes via Plasma Surface Modifications: Effects of Physical and Chemical Defects

Oxygen and argon plasmas were used to modify multiwalled carbon nanotubes (CNTs) to improve their interfacial interaction with subsequently deposited Pt nanoparticles. In contradistinction to what was found in the case of highly oriented pyrolytic graphite (HOPG), X-ray photoelectron spectroscopy (XPS) confirms the introduction of chemical functionalizations by oxygen plasma treatment; however, as in the case of HOPG, argon plasma treatment produced physical defects. Transmission electron microscopy (TEM) provided visual evidence of the interaction of subsequently evaporated Pt with treated CNTs, showing it to have been enhanced by both plasma treatments. XPS and TEM analyses demonstrate that the enhancement is due to similar interactions of Pt nanoparticles with both types of treated CNTs, although not to the same extent: X-ray photoelectron spectroscopy gives no evidence of chemical bonds formed for either plasma treatment. The morphology of the Pt nanoparticles changes with the deposition rate, which may be influenced by the limited availability of the CNT surface.

Evidence of the Interaction of Evaporated Pt Nanoparticles with Variously Treated Surfaces of Highly Oriented Pyrolytic Graphite

The interactions of Pt nanoparticles, deposited by evaporation onto highly oriented pyrolytic graphite surfaces modified by kiloelectronvolt Ar+ beam treatment, have been studied by X-ray photoelectron spectroscopy core-level line shape analysis. The C1s and Pt4f7/2 peaks were each considered to be composed of one asymmetric peak, and changes in their asymmetry parameters were used to study their interfacial interactions. In addition to these changes, strong signal intensity changes with time were found for both the C1s and Pt4f peaks, indicating an initial crystalline orientational instability of the Pt nanoparticles, which is supported by time-dependent high-resolution electron microscopy studies at elevated temperatures.

Electrocatalysis by nanoparticles – oxygen reduction on Ebonex/Pt electrode

Abstract The oxygen reduction reaction was studied in 0.5 mol dm −3 HClO 4 solution on an electrode based on Ebonex-supported platinum electrocatalyst applied on rotation Au disk electrode (Au/Ebonex/Pt). Pt catalyst was prepared by impregnation method from 2-propanol solution of Pt(NH 3 ) 2 (NO 2 ) 2 and Ebonex powder. Ebonex support (non-stoichiometric mixture of titanium oxides) was characterized by: X-ray diffraction, energy dispersive X-ray spectroscopy and BET techniques. The synthesized catalyst was analysed by TEM technique. The kinetics of oxygen reduction reaction on the Ebonex/Pt catalyst shows a significant enhancement in comparison with the same on polycrystalline Pt. Only a single Tafel slope of −0.106 V dec −1 is observed and the first-rate determining step in direct four-electron reduction is proposed as a main partway in the whole range of potential. The absence of PtOH layer, that inhibits oxygen reduction on polycrystalline Pt, was discussed through synergetic effect into the catalyst as a consequence of the interactions of Pt nanoparticles with Ebonex, on one hand, and, through the d-band coupling model where the surface reactivity is given by the energy shift of the surface d-states with respect to the Fermi level, on the other hand.