Porous Platinum Nanoparticles Research Articles

Smartphone-enabled flow injection amperometric glucose monitoring based on a screen-printed carbon electrode modified with PEDOT@PB and a GOx@PPtNPs@MWCNTs nanocomposite

This study presents a modified screen-printed carbon electrode (SPCE) to determine glucose in a custom-built flow injection system. The biosensor was constructed by immobilizing glucose oxidase on porous platinum nanoparticles decorated on multi-walled carbon nanotubes (GOx@PPtNPs@MWCTNs). The fabrication of the biosensor was completed by coating the GOx@PPtNPs@MWCTNs nanocomposite on an SPCE modified with a nanocomposite of poly(3,4-ethylenedioxythiophene) and Prussian blue (GOx@PPtNPs@MWCTNs/PEDOT@PB/SPCE). The fabricated electrode accurately measured hydrogen peroxide (H2O2), the byproduct of the GOx-catalyzed oxidation of glucose, and was then applied as a glucose biosensor. The glucose response was amperometrically determined from the PB-mediated reduction of H2O2 at an applied potential of −0.10 V in a flow injection system. Under optimal conditions, the developed biosensor produced a linear range from 2.50 μM to 1.250 mM, a limit of detection of 2.50 μM, operational stability over 500 sample injections, and good selectivity. The proposed biosensor determined glucose in human plasma samples, achieving recoveries and results that agreed with the hexokinase-spectrophotometric method (P > 0.05). Combining the proposed biosensor with the custom-built sample feed, a portable potentiostat and a smartphone, enabled on-site glucose monitoring.

Self-enhanced nanohydrogel electrochemiluminescence biosensor based on CRISPR/Cas12a and gold platinum nanoparticles modification for high-sensitivity detection of Burkholderia pseudomallei

The simple, rapid, and accurate detection of highly lethal melioidosis is crucial for early clinical diagnosis and improving cure rates. Currently, due to time consumption, low sensitivity and detection rate the existing clinical detection methods cannot satisfy the needs of clinical diagnosis. Herein, a novel self-enhanced porous hydrogel material (Au@PEI-ABEI@Pt) for ultrasensitive ECL strategy of detection B. pseudomallei was report. The novel porous hydrogel material composed of PEI-ABEI porous hydrogel, gold nanoparticles (AuNP) and platinum nanoparticles (PtNP) have large specific surface area and porous structure, which not only fix more ABEI to realize self-enhanced ECL signal amplification, but also facilitate ion diffusion and efficient utilization of catalytic materials, realizing rapid electron transfer and zero-distance catalysis, significantly improving the initial signal of ECL sensor. Moreover, the most attractive aspect is that Au@PEI-ABEI@Pt hydrogels with good biocompatibility can achieve widespread application of CRISPR/Cas12a in solid-phase carriers without affecting the sensitivity, specificity and shearing activity of CRISPR/Cas12a. After coupling with the ECL system and CRISPR/Cas12a signal amplification strategy, the Au@PEI-ABEI@Pt can achieve an ultrasensitive ECL assay of B. pseudomallei with the LOD of 5 CFU mL−1 in complex samples, with high specificity and stability to effectively classify B. pseudomallei and other Gram-negative bacteria. This study shows that the developed porous hydrogel materials not only serve as an excellent ECL signal reporter to significantly improve the detection sensitivity of ECL biosensors, but also provide a new approach for the wide application of CRISPR/Cas systems in solid-phase carriers.

EGFR-antagonistic affibody-functionalized Pt-based nanozyme for enhanced tumor radiotherapy

Clinical radiotherapy (RT) is severely limited by hypoxic tumor microenvironment and a lack of targeting precision. Therefore, it is crucial to develop highly efficient radiosensitizers to enhance RT efficacy. Herein, a novel kind of epidermal growth factor receptor (EGFR)-antagonistic affibody-functionalized Pt-based nanozyme for RT sensitization to EGFR-positive tumors was developed. In this study, porous platinum nanoparticles (pPt NPs) featuring catalase (CAT)-like activity and strong radiation energy absorption ability were first synthesized. Then, a thin biomimetic polydopamine (PDA) layer was coated on pPt NPs to optimize its biocompatibility as well as provide a reactive surface. Finally, a dimeric EGFR-antagonistic affibody called ZEGFR expressed by the Escherichia coli (E. coli), was conjugated to pPt@PDA NPs (termed pPt@PDA-ZEGFR NPs) to precisely recognize EGFR-positive A431 tumors. Under the navigation of ZEGFR, superior tumor homing was achieved with these Pt-based nanozymes, which was ascribed to EGFR receptor-mediated endocytosis. As high-Z metal NPs exhibit an inherently strong ability to absorb radiation energy and catalyze endogenous H2O2 in tumors, the pPt@PDA-ZEGFR NPs demonstrated superb therapeutic efficacy; specifically, the NPs significantly inhibited HIF-1α expression and increased RT-induced DNA damage. Furthermore, the biosafety of these Pt-based nanozymes was good during short-term treatment. In summary, EGFR-antagonistic affibody-functionalized Pt-based nanozymes are promising radiosensitizers for the precise therapy of EGFR-positive tumors.

Electrochemical decarboxylation of acetic acid on boron-doped diamond and platinum-functionalised electrodes for pyrolysis-oil treatment.

Electrochemical decarboxylation of acetic acid on boron-doped-diamond (BDD) electrodes was studied as a possible means to decrease the acidity of pyrolysis oil. It is shown that decarboxylation occurs without the competitive oxygen evolution reaction (OER) on BDD electrodes to form methanol and methyl acetate by consecutive reaction of hydroxyl radicals with acetic acid. The performance is little affected by the applied current density (and associated potential), concentration, and the pH of the solution. At current densities above 50 mA cm-2, faradaic efficiencies (FEs) of 90% towards the decarboxylation products are obtained, confirmed by in situ electrochemical mass spectrometry (ECMS) investigation showing only small amounts of oxygen formed by water oxidation. Using platinum-modified BDD electrodes, it is shown that selectivity to ethane, the Kolbe product, strongly depends on the shape and geometry of the platinum particles. Using nano-thorn-like Pt particles, a faradaic efficiency of approx. 40% towards ethane can be obtained, whereas 3D porous platinum nanoparticles showed high selectivity towards the OER. Using thin platinum layers, a high FE of >70% towards ethane was obtained, which is thickness-independent at layer thicknesses above 20 nm. Comparison with other substrates revealed that BDD is an ideal support for Pt functionalisation, giving advantages of stability and high-value-product formation (ethane and methanol). In short, this work provides guidelines for electrode fabrication in the context of the electrochemical upgrading of biomass feedstocks by acid decarboxylation.

Wet-Chemical Synthesis of Porous Multifaceted Platinum Nanoparticles for Oxygen Reduction and Methanol Oxidation Reactions

Herein, we report a facile and flexible synthesis of porous and highly faceted platinum nanoparticles (NPs) performed in the liquid phase. The synthesis is performed by reduction of platinum 2,4-pentantedionate in the presence of oleylamine and oleic acid in dibenzyl ether at 200 °C. The growth process was monitored by time-course transmission electron microscopy (TEM), revealing a peculiar progressive evolution that, in comparison with previous methodologies, is quite unusual. In fact, the morphology evolves first through nanocubes, nanostars, and dendrites to arrive at porous multifaceted NPs. This offers the possibility to selectively obtain materials with different degrees of complexity at a different time of reaction with one synthetic approach. Moreover, fine tuning of the reaction conditions was achieved by assessing, in dedicated experiments, the effects of temperature, surfactant concentration, and surfactant ratio, allowing control on NPs’ dispersity and shape reproducibility. The dimensionally monodispersed NPs have a mean diameter of 52 ± 2 nm and display small regular crystallites with uniform facets exposed on the surface as evinced by high-resolution-TEM analysis. The as-prepared multifaceted platinum NPs were tested for oxygen reduction and methanol oxidation reactions exhibiting improved catalytic activity with respect to conventional Pt-based nanomaterials.

Fabrication of porous noble metal nanoparticles based on laser ablation toward water and dealloying for biosensing

Porous noble metal nanoparticles (NPs) have been widely applied in biosensing owing to the excellent properties of the localized surface plasmon resonance (LSPR), catalytic and large surface-to-volume ratio. A fabrication strategy combining laser ablation toward water (LATW) with dealloying was developed for easy preparation of porous noble metal NPs, especially porous gold NPs (pAu NPs) and porous platinum NPs (pPt NPs) for biosensing. pAu NPs were explored for the surface-enhanced Raman scattering (SERS) detection of rhodamine 6G, achieving a detection limit of 10-8 M rhodamine 6G and the enhancement factor of 4.3 × 105. Moreover, based on the azo reaction between 4-aminothiophenol with nitrite, nitrite in the concentration range of 20 ∼ 100 μM was precisely detected by SERS of pAu NPs. pPt NPs were modified on the working electrode for the electrochemical sensing. Compared with Pt NPs and Pt/Ag NPs, pPt NPs modified electrode exhibited the best H2O2 detection performance with a good linear range of 0 ∼ 52.5 mM H2O2 and a good stability for one month. The well integration of LATW with dealloying provides an effective strategy for fabrication of various porous metal NPs, which are potentially applied in imaging, photothermal, drug delivery, molecular sensing and so on.

Converting polyethylene to valuable alkanes

A catalytic system consisting of porous silica and platinum nanoparticles can convert high-density polyethylene to compounds used for making diesel fuel and lubricants ( Nat. Catal. 2020, DOI: 10.1038/s41929-020-00519-4 ). The synthetic system mimics natural enzymes that digest proteins by repeatedly snipping the molecular chains. It could provide a way to turn plastic waste into products that are more valuable than those made via melt-processing and other methods for recycling plastics . To make the catalyst, researchers led by Wenyu Huang, Aaron D. Sadow, and Frédéric A. Perras of Ames Laboratory deposited roughly 3 nm diameter platinum nanoparticles on larger amine-functionalized silica spheres. Then they grew a shell of silica riddled with nanometer-sized pores around the silica spheres. NMR spectroscopy and other types of analyses show that the structure of the catalyst, the length and width of its pores, and polymer-surface interactions drive polyethylene chains to snake their way into

Porous Pt nanoparticles loaded with doxorubicin to enable synergistic Chemo-/Electrodynamic Therapy

Overexpression of P-glycoprotein (P-gp), which is responsible for pumping chemotherapeutic drugs out of tumor cells, has been recognized as an important cause of drug resistance in conventional chemotherapy. Herein, porous platinum nanoparticles (pPt NPs) are developed to enable the combined electrodynamic therapy (EDT) with chemotherapy. With polyethylene glycol (PEG) coating, the obtained pPt-PEG NPs could be loaded with anticancer drug doxorubicin (DOX) by utilizing the porous structure of pPt NPs. Those pPt-PEG NPs are able to produce reactive oxygen species (ROS) by triggering water decomposition under electric field, independent of O2 and H2O2 contents in the tumor. Furthermore, the ROS generated during EDT could induce the inhibition of P-glycoprotein (P-gp), in turn enhancing the efficacy of chemotherapeutic agents by facilitating intracellular accumulation of drugs. As the results, excellent synergetic therapeutic effects were observed by combining chemotherapy with EDT using DOX-loaded pPt (DOX@pPt-PEG) NPs, as demonstrated by both in vitro and in vivo experiments. This study demonstrates a new concept of combinational cancer therapy with superior therapeutic efficacy.

Revealing Anomalous High Capacitance of Individual Porous Nanoparticles Employing Nano-Impact Electrochemistry

As a class of promising energy storage devices, supercapacitors have attracted great attention, regarding the deployment of high-power output in renewable energy technologies. The electrification of transportation and the dramatic increase of using portable electronic devices, require significant improvement in this field. Electric double-layer capacitors (EDLCs) are an important class of supercapacitors, in which the electrochemical double layer formed at the electrode/electrolyte interface is used to store energy. However, despite their high power density and remarkable cycle life, the prevalent application of EDLCs is limited because of their still insufficient energy density. Therefore, increasing the capacitance of EDLC electrodes is of great interest. One emerging approach for enhancing energy density has been employment of porous structures as novel electrodes for EDLCs [1].From a theoretical point of view, a conventional EDLC electrode can be considered as a parallel-plate capacitor that delivers a capacitance (C) according to C = ε A / d, where ε is the permittivity of the electrolyte, A is the electrode surface area, and d is the thickness of EDL. Consequently, increasing A of the EDLC electrodes using meso- or nanostructured materials is a classic approach toward realizing large specific capacitance and high energy density. Alternatively, it was experimentally proved that confinement effect on d in microporous EDLCs (pore size < 1 nm) leads to an anomalous increase in the specific capacitance as the pore width decreases. These findings suggest non-classical behaviors of EDLs emerged in sub nanometer pores. However, except for a few theoretical simulation results [2], there has been very limited research carried out on the application of the confinement effect in two-dimensional materials as an additional strategy toward high-energy density capacitors [3]. Herein, we propose single particle electrochemistry to study capacitive properties of individual porous nanoparticles, as an ideal candidate for fabrication of EDLCs.Employing “nano-impact” electrochemistry, an enhanced current is measured, which is caused by randomly colliding nanoparticles with a microelectrode [4,5]. In capacitive nano-impacts, the colliding particle causes the perturbation of a portion of the EDL with the subsequent charging-discharging processes which give rise to transient current-time events. This can be related to the electronic properties/capacitance of the particles [6]. Potentially this method will provide a powerful tool to study the properties of individual nanoparticles without any ensemble effects and overlaying effects of neighboring particles. In the present study, capacitance of individual porous platinum nanoparticles is investigated, by using PtNP impacts at platinum microelectrode in aqueous solution. These experiments are exploited to extract physico-chemical information about the structural effects on the energy density of EDLCs. The gained insights will help to improve our fundamental understanding of the EDL formation and will, thus, provide guidance towards the development of new and improved EDLCs.

Detection of Free Oxygen Reduction Reaction Intermediates Generated at Pt Nanoparticles By Electron Paramagnetic Resonance Spectroscopy

In the search for clean energy conversion systems, PEM fuel cells have attracted a lot of attention over the last decades. Nanostructured electrocatalysts such as porous platinum nanoparticles (NPs) are considered one of the most promising advances to lower the cost of these fuel cells and make them more commercially attractive. The efficiency of these catalysts is limited by their activity towards the oxygen reduction reaction (ORR), and most research is thus focused on understanding reaction mechanisms and improving the activity. The mechanism is well understood for alkaline conditions, but there is still some debate for that under acidic conditions. It has been shown indirectly[1],[2] that radical intermediates formed during the reaction can desorb from the catalyst surface, but direct proof is still absent. More importantly, these free radicals are suspected to be responsible for the degradation of the carbon support, leading to the deactivation of the electrocatalyst NPs[3]. We propose an approach to detect and identify the free radicals produced during the ORR using electron paramagnetic resonance (EPR) spectroscopy. EPR spectroscopy combined with spin trapping has been shown to be useful for detecting radicals produced in electrochemical reactions[4],[5]. This method relies on binding the free oxygen radicals to the spin trap DMPO, forming the stable radical complex DMPO-OH•. The DMPO-OH complex can be detected using an EPR spectrometer. Custom-made glassy carbon RDE’s with a large geometrical surface area have been designed and were loaded with Pt nanoparticles via double pulse electrodeposition. The large surface area is necessary in order to produce sufficiently large amounts of free radicals to be detectable in the EPR spectrometer. A DMPO-OH• signal is formed and increases in strength for the duration of the ORR experiments. Furthermore, we observe a direct correlation between the charge produced during the experiment and the strength of the DMPO-OH• signal. This approach, capable of detecting the free oxygen radicals produced during the ORR, is employed to shed light on the ORR mechanism at carbon electrodes loaded with Pt NPs in acidic conditions.

Porous platinum nanoparticles as a high-Z and oxygen generating nanozyme for enhanced radiotherapy in vivo

Radiotherapy (RT), along with surgery and chemotherapy, is a major modality of cancer therapy. Nevertheless, insufficient deposition of radiation energy in tumors and hypoxia-associated radioresistance remain the greatest challenges in RT. Here, we propose porous platinum nanoparticles as a new nanomedicine platform for solving these two problems at the same time using a single agent. Because of the combined advantages of a high-Z element and oxygen generation capability, porous platinum nanoparticles can significantly increase radiation-induced DNA damage, ROS stress, and cell cycle arrest by effectively depositing X-ray radiation energy within the cancer cells. Further, porous platinum nanoparticles increase tumor oxygenation by converting endogenic H2O2 to O2, thus greatly enhancing RT with no apparent in vivo toxicity to animals. This study presents a new nanomedicine strategy based on the use of porous high-Z metal nanoparticles with oxygen generation function for the synergistic enhancement of RT in cancer treatment.

Stability of Dealloyed Porous Pt/Ni Nanoparticles

We provide a comprehensive durability assessment dedicated to a promising class of electrocatalysts for the oxygen reduction reaction (i.e., porous platinum nanoparticles). The stability of these nanoengineered open structures is tested under two accelerated degradation test conditions (ADT), particularly selected to mimic the potential regimes experienced by the catalyst during the operative life of a fuel cell (i.e., load cycles (up to 1.0 VRHE) and start-up cycles (up to 1.4 VRHE)). To understand the evolution of the electrochemical performance, the catalyst properties are investigated by means of fundamental rotating disc electrode studies, identical location-transmission electron microscopy (IL-TEM) coupled with electron energy loss spectroscopy chemical mapping (IL-EELS), and post-use chemical analysis and online highly sensitive potential resolved dissolution concentration monitoring by scanning flow cell inductively coupled plasma-mass spectrometry (SFC-ICP-MS). The experimental results on the nan...

Porous platinum nanoparticles and PdPt nanocages for use in an ultrasensitive immunoelectrode for the simultaneous determination of the tumor markers CEA and AFP

We describe the use of porous platinum nanoparticles (pPt NPs) and PdPt nanocages (PdPt NCs) in an electrochemical immunoassay for two tumor markers (CEA and AFP) directly in serum and with enhanced detection performance. The pPt NPs possess a high specific surface area and electrical conductivity, while the PdPt NCs display excellent catalytic property and high loading capacity. The PdPt NCs were labeled with anti-CEA and thionine, and the PdPt NCs were labeled with anti-AFP and ferrocene. The resulting electrode displayed a large decrease of the anodic peak current and an increase of cathodic peak current for hydrogen peroxide (H2O2). The dual square wave voltammetric immunoassay was performed at −0.1 V (for CEA) and +0.6 V (for AFP) after exposure to a sample containing CEA and AFP and in the presence of H2O2. CEA can be detected in the 0.05 to 200 ng mL−1 concentration range and AFP between 0.03 and 100 ng mL−1. The limits of detection are 1.4 pg mL−1 for CEA and 1 pg mL−1 for AFP (at an SNR of 3). The sensitivity of the method (expressed as slope vs. concentration) is better by a factor of 4.6 to 100 compared to conventional electrochemical immunoassays. Analytical data obtained with diluted serum samples were in good agreement with reference values obtained via a standard ELISA. Negligible cross-reactivity is found between CEA and AFP. In our opinion, this approach paves the way for developing other kinds of electrochemical immunosensors based on the use of pPt NPs and PdPt NCs as materials for designing new electrode interfaces.

In Situ Growth of Porous Platinum Nanoparticles on Graphene Oxide for Colorimetric Detection of Cancer Cells

A green approach is proposed for in situ growth of porous platinum nanoparticles on graphene oxide (PtNPs/GO). The resulting nanocomposite has been proven to function as peroxidase mimetics that can catalyze the reaction of peroxidase substrate in the presence of hydrogen peroxide. On the basis of the peroxidase-like activity, we used the PtNPs/GO as a signal transducer to develop a colorimetric assay for the direct detection of cancer cells. By using folic acid as a recognition element, a total of 125 cancer cells (MCF-7) can be distinguished by naked-eye observation. We envision that this nanomaterial could be used as a power tool for a wide range of potential applications in biotechnology and medicine.

Electrochemical determination of cefotaxime based on a three-dimensional molecularly imprinted film sensor

A novel electrochemical sensor is presented for the determination of cefotaxime (CEF), which is constructed by molecularly imprinted polymer (MIP), gold networks@IL (IL, 1-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF4]) (GNWs@IL), porous platinum nanoparticles (PPNPs) and carboxyl graphene (COOH-r-GO). The GNWs@IL is prepared by directly reducing HAuCl4 with sodium citrate in [BMIM][BF4] aqueous solution. The PPNPs are well embedded in GNWs@IL due to the adhesion of IL to form GNWs@IL-PPNPs suspension, which is coated on a COOH-r-GO modified glassy carbon electrode to construct a porous three-dimensional networks modified electrode. Then, MIP is prepared by cyclic voltammetry at the modified electrode, using CEF as template and o-phenylenediamine as monomer. The factors concerning this assay strategy are carefully investigated. Under the optimal conditions, the electrochemical sensor offers an excellent response for CEF, the linear response range is 3.9×10−9~8.9×10−6molL−1 and the detection limit is 1.0×10−10molL−1. The electrochemical sensor has been applied to the determination of CEF in real samples with satisfactory results.

A Highly Efficient, Clean‐Surface, Porous Platinum Electrocatalyst and the Inhibition Effect of Surfactants on Catalytic Activity

Herein we report a gentle seedless and surfactant-free method for the preparation of clean-surface porous platinum nanoparticles. In terms of electrocatalytic CH(3)OH oxidation, the clean-surface porous platinum exhibited better performance than platinum nanoparticles and a commercial Pt/C catalyst. The porous nanostructures exhibited 2.26-fold higher mass activity and 2.8-fold greater specific activity than the Pt/C catalyst. More importantly, three typical surfactants, cetyltrimethylammonium bromide/chloride (CTAB/C), poly(vinylpyrrolidone), and sodium dodecyl sulfate, were chosen to study the inhibition effect of surfactants on electrocatalytic performance. It was observed that the surfactants led to a clear selective decrease in electrocatalytic performance. CTAB/C inhibited the catalytic activity the most due to the stronger interaction between the OH-enriched platinum surface and the positively charged molecules. Thus, this work indicates that these clean-surface porous platinum nanoparticles may be used as efficient catalysts for direct methanol fuel cells and provides a greater understanding of the inhibition effects of surfactants on catalytic activity.

Stability of Porous Platinum Nanoparticles: Combined In Situ TEM and Theoretical Study.

Porous platinum nanoparticles provide a route for the development of catalysts that use less platinum without sacrificing catalytic performance. Here, we examine porous platinum nanoparticles using a combination of in situ transmission electron microscopy and calculations based on a first-principles-parametrized thermodynamic model. Our experimental observations show that the initially irregular morphologies of the as-sythesized porous nanoparticles undergo changes at high temperatures to morphologies having faceted external surfaces with voids present in the interior of the particles. The increasing size of stable voids with increasing temperature, as predicted by the theoretical calculations, shows excellent agreement with the experimental findings. The results indicate that hollow-structured nanoparticles with an appropriate void-to-total-volume ratio can be stable at high temperatures.

Electrochemical characterization of a porous Pt nanoparticle “Nanocube-Mosaic” prepared by a modified polyol method with HCl addition

Porous and single crystalline platinum (Pt) nanoparticles (NPs) have been successfully synthesized by reduction of H2PtCl6·6H2O and then investigated by optical spectroscopy and transmission electron microscopy. H2PtCl6·6H2O was reduced using ethylene glycol in the presence of polyvinylpyrrolidone under highly acidic conditions (pH < 1) to form single crystalline Pt particles about 5 nm in size. These particles were then stacked via {100} facets, forming 50-nm length porous nanocubes with a mosaic structure. The porous Pt NPs exhibited excellent catalytic properties for methanol oxidation. In particular, the electrochemical surface area was ∼63 m2/g, five times higher than that for non-porous Pt NPs prepared using a conventional method. We suggest that the high catalytic activity of porous Pt NPs is due to a combination of the crystalline structure having exposed {100} facets and a porous morphology. Open image in new window

Preparation and activity of carbon-supported porous platinum as electrocatalyst for methanol oxidation

In this paper, we reported a novel electrocatalyst, Vulcan XC-72-supported porous platinum nano-particles (Pt p/C) for methanol oxidation. In the preparation of Pt p/C, platinum precursor was first adsorbed on carbon and then reduced by l-ascorbic acid in ethylene glycol solution. The structure and morphology of Pt p/C and its activity toward methanol oxidation were characterized by transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) measurement, X-ray diffraction (XRD), energy-dispersion spectrometer (EDS), cyclic voltammetry (CV), and chronoamperometry (CA), with a comparison of the electrocatalyst prepared with sodium borohydride as reducer (Pt s/C). It is found that both electrocatalysts have similar particle size but have different surface morphology of platinum and thus exhibit different electrocatalytic activity toward methanol oxidation. The platinum particle size of both electrocatalysts is 3–5 nm, but the corresponding BET surface areas are different significantly, 131.6 m 2 g −1 and 87.7 m 2 g −1 for Pt p/C and Pt s/C, respectively, indicative of the porous structure of platinum particles in Pt p/C. The peak current for methanol oxidation on CV is 167 mA mg −1 and 44 mA mg −1 for Pt p/C and Pt s/C, respectively, indicative of the high electrocataytic activity of Pt p/C toward methanol oxidation. The result from CA shows that Pt p/C has good stability as the electrocatalyst for methanol oxidation.

Origin of the High Activity of Porous Carbon-Coated Platinum Nanoparticles for Aerobic Oxidation of Alcohols

In an attempt to clarify the origin of the high activity and durability for aerobic oxidation of alcohols over a platinum (Pt)−carbon composite, i.e., Pt nanoparticles embedded in microporous carbon (nPt@hC), the catalytic reaction mechanism and microstructure of Pt nanoparticles were investigated in detail. By means of kinetic analyses, catalytic oxidation on nPt@hC was found to proceed through the formation of Pt-alcoholates, the β-hydride elimination to form Pt-hydride species (Pt−H), and oxidation of Pt−H with molecular oxygen. It was also revealed that the β-hydride elimination step was a rate-determining step in this reaction. These findings and results of structural studies indicate that the achievement of high catalytic activity on nPt@hC is due to stabilization of its transition state of a positively charged carbocationic component by the electron-rich carbon matrix surrounding Pt nanoparticles, leading to lowering activation energy. Moreover, detailed investigation of the surface characteristics of Pt nanoparticles in nPt@hC after catalytic reactions by using various analytical methods revealed that the durability of nPt@hC for aerobic oxidation of alcohols is due to the suppression of aggregation of Pt nanoparticles and prevention of chemical poisoning of Pt surfaces.