Structure Of Pt Nanoparticles Research Articles

Valence-to-core X-ray emission spectroscopy to resolve the size-dependent valence electronic structure of Pt nanoparticles

X-ray characterization of catalyst materials using synchrotron radiation has become more widely available to the scientific community in recent decades.

Interfacial structures of Pt nanoparticles and transition-metal-oxide supports

Local structural properties at the interface of Pt nanoparticles (NPs) and transition−metal−oxide supports are examined using wavelet−transformed extended X−ray absorption fine structure (WT−EXAFS) with an enhanced resolution at Pt L3 edge. The Pt NPs with a mean size of ∼1 nm on TiO2 supports are synthesized using an incipient wetness method. EXAFS measurements are performed from the Pt NPs/TiO2 during heating from room temperature to 250 °C in an H2 environment. Fourier−transformed EXAFS (FT−EXAFS) shows an absence of oxygen atoms around Pt atoms at T = 250 °C; meanwhile, the WT−EXAFS reveals a weak but distinguishable oxygen signal around Pt atoms. Pt–O bonds likely exist at the interface of Pt/TiO2 because oxygens on the outer surfaces of Pt NPs should be dissociated at T = 250 °C under an H2 environment. This finding indicates that the combination of FT−EAXFS and WT−EXAFS can more accurately describe the heterogeneous interfaces of nanostructures.

Revealing opposite behaviors of catalyst for VOCs Oxidation: Modulating electronic structure of Pt nanoparticles by Mn doping

Revealing the role of Pt electronic structure in the catalytic degradation of VOCs is of great significance for developing efficient catalysts. Herein, the catalytic oxidation of acetone and benzene on the ZSM-5 confined Pt-based catalyst (Pt@Z) was investigated. Surprisingly, after introducing Mn to Pt@Z, the activity of the PtMn@Z catalyst for acetone was significantly increased, while the activity for benzene was decreased. It was found that Mn introduction led to electron transfer to Pt, which enhanced the adsorption of acetone and gaseous oxygen, and promoted acetone degradation. However, the high electron density of Pt inhibited the adsorption and degradation of benzene. Importantly, we used this phenomenon to regulate the electronic structure of Pt by simply adjusting the amount of Mn and achieving the synergistic removal of benzene and acetone. Therefore, this work provided an idea for the design of highly efficient catalytic materials with mixed VOCs.

Complex ligand adsorption on 3D atomic surfaces of synthesized nanoparticles investigated by machine-learning accelerated ab initio calculation.

Nanoparticle surfaces are passivated by surface-bound ligands, and their adsorption on synthesized nanoparticles is complicated because of the intricate and low-symmetry surface structures. Thus, it is challenging to precisely investigate ligand adsorption on synthesized nanoparticles. Here, we applied machine-learning-accelerated ab initio calculation to experimentally resolved 3D atomic structures of Pt nanoparticles to analyze the complex adsorption behavior of polyvinylpyrrolidone (PVP) ligands on synthesized nanoparticles. Different angular configurations of large-sized ligands are thoroughly investigated to understand the adsorption behavior on various surface-exposed atoms with intrinsic low-symmetry. It is revealed that the ligand binding energy (Eads) of the large-sized ligand shows a weak positive relationship with the generalized coordination number . This is because the strong positive relationship of short-range direct bonding (Ebind) is attenuated by the negative relationship of long-range van der Waals interaction (EvdW). In addition, it is demonstrated that the PVP ligands prefer to adsorb where the long-range vdW interaction with the surrounding surface structure is maximized. Our results highlight the significant contribution of vdW interactions and the importance of the local geometry of surface atoms to the adsorption behavior of large-sized ligands on synthesized nanoparticle surfaces.

A cobalt metalized polymer modulates the electronic structure of Pt nanoparticles to accelerate water dissociation kinetics.

Herein, we construct a composite material of Pt-NPs@NPCNs-Co by anchoring Pt nanoparticles (Pt NPs) and Co-salen covalent organic polymer (Co-COP) onto N, P co-doped carbon nanotubes (NPCNs), thereby offering an integrated approach to enhance H2O dissociation. The bimetallic catalyst Pt-NPs@NPCNs-Co demonstrates exceptional HER performance, and the overpotential at 40 mA cm-2 is lower than that of 20% Pt/C. When the overpotential is 50 mV, the mass activity of Pt-NPs@NPCNs-Co is 2.8 times that of the commercial Pt/C catalyst. Experimental results reveal that the synergistic interplay between Pt NPs and Co contributes to the excellent electrocatalytic performance observed. Density function theory calculations found that Co effectively modulates the electronic structure of Pt NPs and lowers the activation energy of the Volmer step, thereby accelerating the water dissociation kinetics of Pt NPs. This research contributes to the advancement of knowledge regarding the development of more efficient bimetallic co-catalytic electrocatalysts in alkaline media.

Tailoring the surface structure of iron compounds to optimize the selectivity of 3-nitrostyrene hydrogenation reaction over Pt catalyst

Selective hydrogenation of substituted nitroarenes is an important reaction to obtain amines. Supported metal catalysts are wildly used in this reaction because the surface structure of supports can tune the properties of the supported metal nanoparticles (NPs) and promote the selectivity to amines. Herein, Pt NPs were immobilized on FeOOH, Fe3O4 and α-Fe2O3 nanorods to synthesize a series of iron compounds supported Pt catalysts by liquid phase reduction method. Chemoselective hydrogenation of 3-nitrostyrene to 3-aminostyrene was used as probe reaction to evaluate the performance of the catalysts. The results show that Pt/FeOOH exhibits the highest selectivity and activity. FeOOH support with pores and -OH groups can tune the electronic structure of Pt NPs. The positive charge of Pt NPs supported on FeOOH is key factor for improving the catalytic performance.

Changes of Oxygen Adsorption State of Pt Nanoparticle Catalyst on the Carbon Support By the Ion Irradiation

Pt nanoparticles (NPs) on an Ar+-irradiated glassy carbon (GC) substrate were recently found to show a higher oxygen reduction reaction (ORR) activity than those on the non-irradiated one [1]. This finding suggests that the Pt nanoparticles would be electronically modified by vacancy introduction due to the irradiation into GC. Our theoretical research revealed that vacancies in graphite would lower a d-band center of the Pt nanoparticles [2]. The downshift of d-band center of Pt 5d electrons leads to higher ORR activity because the downshift causes the downshift of the antibonding orbital level of the oxygen adsorbed states of Pt (Pt-O) closing to Fermi level and then results in weaker Pt-O bond [3]. However, it has not been revealed whether the Pt-O antibonding level of Pt NPs is downshifted by the ion irradiation into the carbon support. Therefore, we performed in situ x-ray absorption fine structure (XAFS) measurements, which can observe the unoccupied states of the Pt 5d orbital binding with the adsorbed oxygen, of Pt NPs on the irradiated GC and derived the oxygen adsorbed surface states.The GC substrates were irradiated with 380 keV Ar+ at the fluences of 7.5×1015 ions/cm2 in the Takasaki Ion Accelerators for Advanced Radiation Application (TIARA) facility of the Takasaki Advanced Radiation Research Institute. The Pt nanoparticles were then deposited by RF magnetron sputtering. The Pt deposition was also done on the non-irradiated GC substrates for comparison. The XAFS spectra were measured at BL14B1 in SPring-8. We first measured the XAFS spectra of the irradiated and non-irradiated samples reduced by 1 atm. 100 °C H2 (10%) + He (90%) gas flowing at 100 ml/min for 10min. Then the samples were exposed under mixed gas with O2 + He gas flowing at 100 ml/min at room temperature to adsorb the oxygen to Pt nanoparticles and were measured XAFS spectra. In order to observe the oxygen adsorbed surface states of Pt NPs, we derived the Dm spectra by the subtraction from the XANES spectra after the reduction from the those during the oxygen exposure.Figure 1 shows the Dμ spectra for the Pt/GC and Pt/irradiated GC together with the results of peak fitting. In the non-irradiated sample, we could fit using one peak at around 11562 eV (denoted as peak 1), whereas needed peak 1 in addition to peak 2 on the higher energy side. Since the Dμ spectra represent the change of the electronic state in Pt by oxygen adsorption, the convex peak means that new electronic states are formed at the energy position by the oxygen adsorption. The main peak (peak 1) is the antibonding level of the oxygen adsorbed Pt (Pt-O). On the other hand, the peak 2 is considered to be an oxide species that is more strongly bind to oxygen than Pt-O. It needs future study to elucidate its origin.Comparing the peak 1 of the non-irradiated and the irradiated sample, we found that the peak position for the irradiated sample is 0.7 eV lower than that for the non-irradiated one. This indicates that the Pt-O antibonding level shifts toward low energy and gets close to the Fermi level. Thus, the shift leads to easy electron filling to the antibonding level and thus to a weaker Pt-O bond. In this presentation, we will discuss the change of electronic structure of Pt nanoparticles by the ion irradiation in detail.

The Electronic State of Pt Nanoparticles on an Ion-Beam-Irradiated Carbon Support

Pt nanoparticle electrocatalysts on an Ar+-irradiated glassy carbon (GC) substrate were recently found to show a higher oxygen reduction reaction (ORR) activity than those on the non-irradiated one [1]. This finding suggests that the Pt nanoparticles would be electronically modified by the lattice defects in irradiated GC. Our theoretical research previously revealed that vacancies in graphite would lower a d-band center of the supported Pt nanoparticles; this is probably the reason for the higher activity [2]. We investigated here the electronic states of the interface between the Pt nanoparticles and the irradiated carbon support by X-ray absorption fine structure (XAFS) measurements in order to get an insight into the mechanism of the activity enhancement.Highly oriented pyrolytic graphite (HOPG) and glassy carbon (GC) substrates were irradiated with 380 keV Ar+. The HOPG substrate was employed so that the electronic structure could be resolved into orbital components (σ and π bonds). The Pt nanoparticles were then deposited by RF magnetron sputtering. The Pt deposition was also done on the non-irradiated HOPG and GC substrates for comparison. The XAFS spectra were measured at BL14B1 in SPring-8 and at BL-8 of the SR Center, Ritsumeikan University.Figure 1 shows the C-K XAFS spectra for the pristine HOPG, the irradiated HOPG, Pt/non-irradiated HOPG, and Pt/irradiated HOPG. This spectral measurement was made at the X-ray incident angle of 30° to obtain the X-ray absorption due to C-C π* and s* orbitals with almost the same cross-section. The pristine and irradiated HOPG substrates exhibited three peaks from a C-C π* orbital (285.3 eV), C-C σ*, σ1 orbital (291.5 and 292.5 eV), and surface carbon with adsorbates (287.5 eV). The shoulder structure around 284 eV was observed for Pt/non-irradiated HOPG, indicating the occurrence of Pt-C interaction at the interface. The intensity of this shoulder increases for Pt/irradiated HOPG as shown by the arrow. Therefore, the vacancies in the irradiated carbon support would induce the change of Pt-C interaction, leading to the different electronic structure at the interface.Our previous paper reported that the Pt nanoparticles on the irradiated carbon support were distorted [3]. According to the result of Fig. 1, the Pt-C interaction could be an origin of the observed distortion of the Pt nanoparticles, which lowered the d band center and then improved their ORR activity. In this presentation, we will additionally clarify the electronic structure of Pt nanoparticles based on the XAFS results of Pt L edge.

Pt Nanoparticles with High Oxidase-Like Activity and Reusability for Detection of Ascorbic Acid.

Noble metal nanoenzymes such as Pt, Au, Pd, etc. exhibit magnificent activity. However, due to the scarce reserves and expensive prices of precious metals, it is essential to investigate their enzyme-like activity and explore the possibility of their reuse. In this work, the oxidase-like activity and reusability of several Pt nanoparticles with different morphologies were detected. We compared the Pt nanoparticles (NPs) with a size of about 30 nm self-assembled by 5 nm Pt nanoparticles and Pt nanoparticles (Pt-0 HCl) with a diameter of about 5 nm, and found that their Michaelis−Menten constants (Km) were close and their initial performance similar, but the Pt NPs had better reusability. This was probably attributed to the stacked structure of Pt NPs, which was conducive to the substance transport and sufficient contact. At the same time, it was found that the size, dispersion, and organic substances adsorbed on the surface of Pt nanoparticles would have a significant impact on their reusability. A colorimetric detection method was designed using the oxidase-like activity of Pt NPs to detect ascorbic acid in triplicate. The limits of detection were 131 ± 15, 144 ± 14, and 152 ± 9 nM, with little difference. This research not only showed that the morphology of the catalyst could be changed and its catalytic performance could be controlled by a simple liquid phase synthesis method, but also that it had great significance for the reuse of Pt nanoenzymes in the field of bioanalysis.

Probing the performance of structurally controlled platinum-cobalt bimetallic catalysts for selective hydrogenation of cinnamaldehyde

The selective hydrogenation of cinnamaldehyde (CAL) is an extremely important transformation. Herein, oxygen functionalized carbon nanotubes (oCNTs) supported a series of PtxCoy bimetallic nanoparticles (NPs) with varied Pt to Co ratios were synthesized. The introduction of Co significantly affects the electronic structure of Pt NPs, which clearly promotes the selectivity to cinnamyl alcohol (COL). Among all PtxCoy-oCNTs catalysts, PtCo3-oCNTs exhibited the best catalytic performance and a selectivity of over 76% towards COL at a CAL conversion of 99% was obtained. Further characterization of the fresh, used and cycled catalysts revealed that the NP structures were stable and did no change. The structural evolutions during the catalytic reaction were also investigated by identical location transmission electron microscopy (IL-TEM) method in detail, which found that the deactivation of PtCo3-oCNTs catalyst during the cycle experiment results from the agglomeration and detachment of PtCo3 NPs.

Tuning the Structure of Pt Nanoparticles through Support Interactions: An in Situ Polarized X-ray Absorption Study Coupled with Atomistic Simulations.

Interactions of nanoparticles (NPs) with their environment may have a pronounced effect on their structure and shape as well as on their functionality in applications such as catalysis. It is therefore crucial to disentangle the particle–adsorbate and particle–support interaction effects on the particle shape, its local structure, atomic dynamics, and its possible anisotropies. In order to gain insight into the support effect, we carried out an X-ray absorption fine-structure spectroscopy (XAFS) investigation of adsorbate- and ligand-free size-selected Pt NPs deposited on two different supports in ultrahigh vacuum. Polarization-dependent XAFS measurements, neural network-based analysis of X-ray absorption near-edge structure data, and reverse Monte Carlo (RMC) simulations of extended X-ray absorption fine structure (EXAFS) were used to resolve the 3D shape of the NPs and details of their local structure. A synergetic combination of advanced in situ XAFS analysis with atomic force microscopy and scanning tunneling microscopy (STM) imaging provides uniquely detailed information about the particle–support interactions and the NP/support buried interface, not accessible to any experimental technique, when considered alone. In particular, our combined approach reveals differences in the structure of Pt NPs deposited on TiO2(110) and SiO2/Si(111). Pt NPs on SiO2 assume a spherical-like 3D shape and weakly interact with the support. In contrast, the effective shape of analogously synthesized Pt NPs on TiO2(110) after annealing at 600 °C is found to be a truncated octahedron with (100) top and interfacial facets that are encapsulated by the TiO2 support. Modeling disorder effects in these NPs using an RMC approach reveals differences in bond-length distributions for NPs on different supports and allows us to analyze their anisotropy, which may be crucial for the interpretation of support-dependent atomic dynamics and can have an impact on the understanding of the catalytic properties of these NPs.

Nitrogen-doped graphene aerogel with an open structure assisted by in-situ hydrothermal restructuring of ZIF-8 as excellent Pt catalyst support for methanol electro-oxidation

We report an innovative strategy to prepare the porous N-doped graphene aerogel with an open structure and abundant defects by hydrothermal self-assembly of zeolitic imidazolate framework (ZIF)-8 and graphene oxide. The in-situ hydrothermal restructuring of ZIF-8 on graphene sheets plays a key role in the synthesis of the open structure and the uniform N-doping. The dissolution and restructuring of ZIF-8 on graphene oxide obviously suppress the stacking and reunion of graphene sheets to obtain the continuous macroporous structure. Moreover, the introduction of N and Zn creates the abundant N-doped sites and microporous structure. Its unique structure and composition improve the accessible surface area, the mass transfer diffusion, the dispersion and electronic structure of Pt nanoparticles, further resulting in the high catalytic performance of Pt-based catalyst for methanol oxidation reaction (MOR). Its MOR activity is about 1.8 times of commercial Pt/C, and its long cycling durability is improved by about 18.7% compared with commercial Pt/C. This work renders a promising method by utilizing ZIF-8 derivatives to synthesize the excellent N-doped carbon materials for electrochemical applications.

(Invited) Facets of Nanocrystal: A Knob to Tune Electrocatalytic Activity

The electrocatalytic reactions strongly depend on the surface atomic structures of the electrocatalysts. Thus, tuning the surface facets of the nanoparticles can be a powerful tool to control the activity for a specific electrocatalytic reaction. In previous studies, we employed high-resolution transmission electron microscopy to reveal the surface atomic structure of Pt nanoparticles, where the amount of high-index surface facets on Pt nanoparticles was quantified.1,2 Correlating the surface steps on Pt nanoparticles with the electrochemical activity and stability clearly showed the significant role of surface steps in enhancing intrinsic activity for CO and methanol electro-oxidation.1 On the other hand, the oxygen reduction reaction (ORR) activity of Pt nanoparticles is not influenced by surface steps in contrast to methanol oxidation reaction (MOR) activity.2 More recently, we demonstrate the synthesis of Pd@Ir core−shell concave nanocubes as an advanced electrocatalyst for acidic oxygen evolution reaction (OER). The Pd@Ir core−shell concave nanocubes were successfully prepared by atomic layer-by-layer deposition of Ir atoms on the surface of free-standing Pd nanocubes in a liquid phase. Using X-ray photoelectron spectroscopy (XPS), the right composition and oxidation states of these nanocubes are confirmed. In the 0.1 M HClO4 electrolyte, the synthesized Pd@Ir concave nanocubes showed significantly increased activity compared to the IrO2 nanoparticles. The improved activity is mainly due to well-controlled surface structures based on high-index facets. We also observed that the specific activity of Pd@Ir concave nanocubes increased after the chronoamperometry test for 10 hours. S. W. Lee, S. Chen, W. Sheng, N. Yabuuchi, Y.-T. Kim, T. Mitani, E. Vescovo, and Y. Shao-Horn, Roles of surface steps on Pt nanoparticles in electro-oxidation of carbon monoxide and methanol, Journal of the American Chemical Society, 2009; 131(43): p. 15669-15677.S. W. Lee, S. Chen, J. Suntivich, K. Sasaki, R. R. Adzic, and Y. Shao-Horn, Role of surface steps of Pt nanoparticles on the electrochemical activity for oxygen reduction, The Journal of Physical Chemistry Letters, 2010; 1(9): p. 1316-1320.

Designed synthesis of thin CeO2 nanowires-supported Pt electrocatalysts with pore-interconnected structure and its high catalytic activity for methanol oxidation

A strong local coordination structure of Pt nanoparticles (NPs) over ultra-thin CeO2 nanowires (NWS) has been synthesized to investigate the role of CeO2 NWS on the enhancement of methanol oxidation activity. The Pt/CeO2 NWS catalyst was characterized by X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy and electrochemical tests. The results showed that Pt/CeO2 NWS exhibited 1.23 times higher activity and 1.22 times longer-time durability over a commercial 20 wt% Pt/XC-72 catalyst. To further enhance the activity of Pt/CeO2 NWS catalyst and mass transfer ability, the in situ carbonization of urea had been adopted to provide N-doped carbon doping layer and porous interconnection between CeO2 NWS network, and the resulted catalyst showed 1.38 times greater activity than undoped Pt/CeO2 NWS. It was ascribed to the pyridine-like and pyrrole-like nitrogen in N-doped carbon layers, which greatly increased the electrical conductivity of CeO2 NWS and decreased the loss of electron transfer energy, as well as the strong interaction between Pt NPs and CeO2 NWS with their anisotropy and unique pore-interconnected structure.

Electrocatalytic performance of Pt nanoparticles sputter-deposited on indium tin oxide toward methanol oxidation reaction: The particle size effect

We sputter-deposited Pt nanoparticles with an average size ranging from 2.0nm to 8.5nm on the indium-tin oxide (ITO) glass substrate, and studied the effect of the size of Pt nanoparticles on electrocatalytic activity of the Pt/ITO electrode toward methanol oxidation reaction (MOR) in acidic solution. X-ray photoelectron spectroscopy (XPS) reveals an interfacial oxidized Pt layer present between Pt nanoparticles and the ITO substrate, which may modify the surface electronic structure of Pt nanoparticles and thus influences the electrocatalytic properties of the Pt catalyst toward MOR. According to electrochemical analyses, smaller Pt nanoparticles exhibit slower kinetics for CO electrooxidation and MOR. However, a smaller particle size enables better CO tolerance because the bifunctional mechanism is more effective on smaller Pt nanoparticles. The electrocatalytic activity decays rapidly for Pt nanoparticles with a size smaller than 3nm and larger than 8nm. The rapid activity decay is attributed to Pt dissolution for smaller nanoparticles and to CO poisoning for larger ones. Pt nanoparticles of 5–6nm in size loaded on ITO demonstrate a greatly improved electrocatalytic activity and stability compared with those deposited on different substrates in our previous studies.

Methanol dehydrogenation and oxidation on Pt1–XNiX/CNTs at low temperature: Effect of Ni addition

This study reports the effect on catalytic activity resulting from Ni incorporation in Pt nanoparticles supported on carbon nanotubes (CNTs) for electrochemical methanol oxidation at low temperature in acidic conditions. Chemical composition, morphology and structure of the Pt1–XNiX/CNTs (X = 0, 0.1, 0.2, 0.3, 0.4, 0.5) catalysts were studied by EDS, SEM, XRD, TEM and TGA. The catalytic activity of the prepared materials in methanol electro-oxidation reaction was investigated by cyclic voltammetry (CV) and chronoamperometry (CA). The results of catalytic activity of the nanostructured materials showed a volcano-type relationship between the Ni relative concentration current density. The enhancement of catalytic activity was attributed to changes in surface electronic structure of Pt nanoparticles that impacted in an increment of active sites for methanol dehydrogenation and oxidation processes. On the other hand, high concentration of Ni (concentration ≥ 30 at.%) in Pt nanoparticles caused a substantial decrease of the catalytic activity due to a depletion of active sites for the methanol dehydrogenation process. The highest catalytic activity was observed when the Ni relative concentration reaches 30 at.%.

Facet-Dependent Activity of Pt Nanoparticles as Cocatalyst on TiO2Photocatalyst for Dye-Sensitized Visible-Light Hydrogen Generation

The photocatalytic activities of polyoriented and preferential Pt(111) nanoparticles supported on TiO2(Pt(poly)/TiO2and Pt(111)/TiO2) were investigated by the photocatalytic hydrogen generation from water under visible-light irradiation. The photocatalytic hydrogen production rate of Pt(111)/TiO2was 1.6 times higher than that of Pt(poly)/TiO2. The corresponding apparent activation energy on Pt(111)/TiO2was about 2.39 KJ/mol, while on Pt(poly)/TiO2, it was about 4.83 KJ/mol. The difference in the apparent activation energies was probably due to the diversity in the number of surface atoms at corners and edges between the Pt(poly) and Pt(111) nanoparticles. The photocurrent of Pt(111)/TiO2was also bigger than that of Pt(poly)/TiO2, implying that the surface structure of Pt(111) nanoparticles can improve the transfer efficiency of photo-induced electrons from the conduction band of TiO2to Pt nanoparticles. As a result, the surface structure of Pt nanoparticles played an important role in the reactivity and kinetics performance of hydrogen evolution. Therefore, the photocatalytic properties of Pt/TiO2strongly depended on the surface structure of Pt nanoparticles.

Rod-shaped Au@PtCu nanostructures with enhanced peroxidase-like activity and their ELISA application

Pt and its based alloy nanoparticles (NPs) have been reported to demonstrate novel enzyme-like activities. Varying composition is very important to realize the optimization of their functions through the tuning of electronic structure. In this paper, our effort is focused in this direction by tailoring the electronic structure of Pt NPs via alloying with copper. Using gold nanorod (Au NR) as core, a simple method to prepare PtCu alloy shell is developed (termed as Au@PtCu NR). The introduction of copper could result in endcap-preferred growth mode owing to the lattice mismatch between alloy shell and the Au core. The variation in the electronic structure changes the substrate affinity, and enhanced affinity was found for H2O2. Besides, the designed Au@PtCu nanostructures have realized spatial separation of catalytic and recognition sites. Binding of recognition antibodies had negligible effect on their catalytic activity. Based on their peroxidase-like activity, a highly sensitive detection of human immunoglobulin G (IgG) was demonstrated in a direct enzyme-linked immunosorbent assay (ELISA) mode. The detection limit can be as low as 90 pg/mL.

Structural change of carbon supported Pt nanocatalyst subjected to a step-like potential cycling in PEM FC

In this paper we present detailed X-ray absorption fine structure (XAFS), X-ray diffraction (XRD) and transmission electron microscopy (TEM) investigations of the changes in the local geometric and electronic structure of Pt nanoparticles used as a cathode catalyst in proton exchange membrane fuel cell (PEMFC), working under controlled potential cycling conditions. The body of the results obtained suggests that in the first stage of PEMFC operation, small particle dissolution was a dominant process. Subsequent 100h of work led to the progressive agglomeration of nanoparticles followed by a pronounced growth of the mean nanoparticle size. At the same time, high-quality XAFS spectra analysis demonstrated that negligible changes in structural local ordering and a slight increase in Pt 5d-electron density occurred during the whole FC operation period under consideration.

Au@PtAg core/shell nanorods: tailoring enzyme-like activities via alloying

Pt nanoparticles (NPs) have been reported to demonstrate four kinds of enzyme-like activity including superoxide dismutase (SOD), catalase, oxidase and peroxidase. Some of these activities interfere with each other. For instance, as antioxidant enzyme mimics, their SOD and catalase activities are very helpful in scavenging related reactive oxygen species (ROSs). However, their oxidase-like and/or peroxidase-like activities may simultaneously oxidize some natural antioxidants, thus compromising the final anti-oxidation efficacy. Fine tuning different enzyme-like activities is therefore very important to realize the optimization of their functions. In this paper, our effort is focused in this direction by tailoring the electronic structure of Pt NPs via alloying with Ag. All four enzyme-like activities are found to be weakened by an increased Ag percentage in the alloy, as witnessed by decreased values of Kcat. The variation in the electronic structure also changes the substrate affinity. Introducing silver into Pt weakens the affinity for H2O2, which affects the limit of detection (LOD) for H2O2 and products with H2O2 involved. In contrast to Fe3O4 MNPs, for peroxidase-like activity, hydroxyl radicals are not involved in the oxidation of chromogenic substrates for the alloy nanostructures.