Platinum-based nanostructured materials: synthesis, properties, and applications.

To increase their electrochemically active surface area, catalysts supported on high surface area materials, commonly carbons, are widely used in low-temperature fuel cells. Recent studies have revealed that the physical properties of the carbon support can greatly affect the electrochemical properties of the fuel cell catalyst. It has been reported that carbon materials with both high surface area and good crystallinity can not only provide a high dispersion of Pt nanoparticles, but also facilitate electron transfer, resulting in better device performance. On this basis, novel non-conventional carbon materials have attracted much interest as electrocatalyst support because of their good electrical and mechanical properties and their versatility in pore size and pore distribution tailoring. These materials present a different morphology than carbon blacks both at the nanoscopic level in terms of their pore texture (for example mesopore carbon) and at the macroscopic level in terms of their form (for example microsphere). The examples are supports produced from ordered mesoporous carbons, carbon aerogels, carbon nanotubes, carbon nanohorns, carbon nanocoils and carbon nanofibers. The challenge is to develop carbon supports with high surface area, good electrical conductivity, suitable porosity to allow good reactant flux, and high stability in fuel cell environment, utilizing synthesis methods simple and not too expensive. This paper presents an overview of carbon supports for Pt-based catalysts, with particular attention on new carbon materials. The effect of substrate characteristics on catalyst properties, as electrocatalytic activity and stability in fuel cell environment, is discussed.

Carbon supports for low-temperature fuel cell catalysts

Of the many important reactions that are known to be catalysed by gold particles supported on transition metal oxides, the oxidation of carbon monoxide is of outstanding significance: the current state of understanding of its mechanism is reviewed, and discordant observations reported in the literature are noted and analysed. A general mechanism involving reaction at the edge of a particle containing both gold atoms and ions, and involving the support, is suggested, although not all features of it are necessarily always operative. Possible practical uses for gold in catalysing this reaction include pollution control, fuel cells, and gas sensing.

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Gold-catalysed oxidation of carbon monoxide

Oxidation into CO2 is a major solution to CO abatement in air depollution treatments. The development of catalytic converters led to an extraordinary high number of publications on metal catalysts during the last fifty years. Due to the increasing price of noble metals and to remarkable progresses in oxide syntheses, catalytic oxidation of carbon monoxide over oxide catalysts has recently gained in interest, even if some oxides are known to present remarkable activity since the beginning of the 20th century. In this Review, the kinetics and mechanism of CO oxidation on single and mixed oxides are examined, alongside the catalyst structures

Catalytic Oxidation of Carbon Monoxide over Transition Metal Oxides

The recently published points of zero charge of metal oxides and related materials are compiled to update the previous compilation. The purity of materials is the most important factor responsible for discrepancies in the literature data. In contrast to the success of new spectroscopic methods in the studies of specific adsorption, the progress in studies of primary surface charging of oxides over recent years is less spectacular.

The pH-dependent surface charging and the points of zero charge.

An effective method is developed for preparing highly dispersed and nano-sized PtSn/C electrocatalysts synthesized by borohydride reduction and subsequent hydrothermal treatment. From the XRD patterns, the Pt(2 2 0) peak of the PtSn/C catalysts shift slightly to lower 2θ values with increasing Sn content, compared with that of the Pt/C catalyst, suggesting the alloy formation. Based on the HR-TEM, the PtSn nanoparticles show average particle sizes of approximately 2.3 nm on the carbon surface, which is consistent with XRD data. The XPS result shows that the slight shift in the bulk metallic Pt(0) to higher binding energies is attributed to a significant contribution from the metal-support interaction and the nano-size effect. The methanol and CO oxidations on the PtSn/C catalysts occur at lower potentials as compared to the commercial Pt/C catalyst. This result suggests that Sn has the ability to promote the oxidation of adsorbed CO at lower potentials. In the single-cell and accelerated durability tests, the 3Pt1Sn/C catalyst shows higher performance under a pure H2 and CO-containing H2 gases and better durability under a 0.5 M H2SO4 solution than the commercial Pt/C catalyst, due to the coexistence of PtSn alloys and Sn oxides.

A new synthesis of a highly dispersed and CO tolerant PtSn/C electrocatalyst for low-temperature fuel cell; its electrocatalytic activity and long-term durability

An effective method is developed for preparing highly dispersed CeO 2 nanoparticles on a Pt/C catalyst synthesized by a continuous two-step process as a cathode material in low-temperature fuel cell. The XRD patterns of the 20Pt–10CeO 2 /C catalyst reveal that both crystalline Pt and CeO 2 phases coexist. The HR-TEM images show that Pt and CeO 2 nanoparticles have average particle sizes of approximately 3.4 nm and 4.2 nm, respectively, with quite a narrow distribution between 3 nm and 5 nm. Based on the analysis of the polarization curves for the ORR, the optimum proportion of CeO 2 into the 20Pt/C catalyst is 10 wt%. In the ORR and single cell tests, the 20Pt–10CeO 2 /C catalyst shows higher performance than the commercial 20Pt/C catalyst, owing to the oxygen storage capacity of CeO 2 and its ability to exchange oxygen rapidly with oxygen in the buffer. In the accelerated stability tests, the 20Pt–10CeO 2 /C catalyst has a better durability compared to the commercial 20Pt/C catalyst due to the existence of CeO 2 , which prevents the agglomeration and dissolution of Pt nanoparticles on the carbon support, extending the life of the catalyst.

Effect of ceria nanoparticles into the Pt/C catalyst as cathode material on the electrocatalytic activity and durability for low-temperature fuel cell

Granulosa cell tumor (GCT) of the ovary is a very rare neoplasm, which is characterized by an indolent clinical course. Thus, the clinical characteristics, optimal treatment, and follow-up protocols are not well established. The goal of this study is to evaluate clinical findings, prognostic factors, and recurrent features of GCT in Korean patients. Between 1987 and 2005, 42 cases of GCT were diagnosed in our institution. There were 35 cases showing adult-type GCT, which were available for evaluation. All charts were reviewed, and the clinical data along with treatment results were retrospectively studied. Statistical analyses were performed for risk factors of recurrence and disease-free survival. GCT accounted for 3% of all ovarian malignancies in our institution during the study period. The median age was 45 years (range, 24–68 years). Abdominal and hormone-related symptoms were the main causes of first presentation. There were eight cases of recurrence including two cases of disease-related deaths during the median follow-up period of 177 months (range, 8–212 months). Factors affecting the recurrence involved residual tumor and stage, but residual tumor was the only significant factor of recurrence in multivariate analysis. The median time to relapse was 75 months (range, 55–137 months), and the liver was the most common extra-pelvic metastatic site followed by the intestine. Continuous long-term follow-up with pelvic and whole-abdominal surveillance is absolutely required. Active management including complete tumorectomy is the most important treatment modality in both primary surgeries and recurrent cases.

https://ijgc.bmj.com/content/ijgc/18/4/642.full.pdf

Ho-In Lee

Papers

A new synthesis of a highly dispersed and CO tolerant PtSn/C electrocatalyst for low-temperature fuel cell; its electrocatalytic activity and long-term durability

Effect of ceria nanoparticles into the Pt/C catalyst as cathode material on the electrocatalytic activity and durability for low-temperature fuel cell

Characteristics of recurrence in adult-type granulosa cell tumor.

The effect of cerium oxide nanoparticles on a Pt/C electrocatalyst synthesized by a continuous two-step process for low-temperature fuel cell

Nano-structured Pt–Cr anode catalyst over carbon support, for direct methanol fuel cell