Novel Graphitised Carbonaceous Materials for Use as a Highly Corrosion‐Tolerant Catalyst Support in Polymer Electrolyte Fuel Cells

Cathode catalysts for polymer electrolyte fuel cells (PEFCs) are prepared by depositing Pt nanoparticles on carbon nanospheres (CNSs) and graphitised carbon nanospheres (GCNSs), and their corrosion‐tolerance and electrocatalytic activities for the oxygen reduction reaction are evaluated. Transmission electron micrographs show that the deposited Pt nanoparticles are well dispersed on CNSs. In Pt/GCNS, Pt nanoparticles accumulate selectively along the edges of GCNSs' polygonal surfaces. Electrochemical measurements with a rotating‐ring disk electrode in an O₂‐saturated H₂SO₄ solution show that Pt/GCNS and Pt/CNS produce less H₂O₂ during oxygen reduction, compared to that obtained with a Pt catalyst on carbon black (CB). Thermogravimetric analysis reveals that GCNSs show greater combustion‐tolerance than CNSs and CB. Furthermore, GCNSs show excellent electrochemical corrosion‐tolerance in a H₂SO₄ solution. These results indicate that GCNSs are superior for use as carbon supports, and can serve as cathode catalysts in PEFCs even under oxidative conditions.     

Nanosized Composite Pt‐Ru Catalysts for Production of Modern Modified Fuels

A Pt‐Ru/2 % Ce/(θ+α)‐Al₂O₃ nanosized catalyst was developed for selective catalytic oxidation of CH₄ to synthesis gas. The process was carried out entirely with the formation of synthesis gas at high selectivity by H₂ and CO with H₂:CO = 2.0 ratio only at Pt:Ru = 2:1 or 1:1 atomic ratio and short contact time on Pt‐, Ru‐, and Pt‐Ru low‐percentage catalysts. Samples, which were reduced by H₂ at high temperature, presented a mixture of Pt‐, Ru‐, and Pt‐Ru nanosized particles, its alloy in the mixed catalysts. The correlation between experimental results and data of physicochemical research was established. The activity together with physicochemical properties and quantum chemical calculations for the developed low‐percentage Pt‐Ru catalysts was investigated.     

Influence of Pyridine‐Polybenzimidazole Film Thickness of Carbon Nanotube Supported Platinum on Fuel Cell Applications

Pyridine‐polybenzimidazole (PyPBI) films of different thickness (∼1.0–2.4 nm) are wrapped on the surfaces of multi‐walled carbon nanotubes (CNTs). To prepare Pt on PyPBI/CNT (Pt‐PyPBI/CNT) catalysts, Pt⁴⁺ ions are immobilized on these PyPBI wrapped CNTs (PyPBI/CNTs) via Lewis acid‐base coordination between Pt⁴⁺ and :N‐ of imidazole groups, followed by reducing Pt⁴⁺ to Pt nanoparticles. The influence of PyPBI film thickness on the Pt particle size, loading and electrochemical surface area, respectively, of Pt‐PyPBI/CNTs is investigated. Fuel cell performances of the PBI/H₃PO₄ based membrane electrode assemblies (MEAs) prepared from these Pt‐PyPBI/CNT catalysts are also evaluated at 160 °C with unhumidified H₂/O₂ gases. Among the catalysts, the Pt‐PyPBI/CNT catalyst with a PyPBI film thickness of ∼1.6 nm (which is around half of the Pt particle size), a Pt loading of ∼44 wt.%, and a Pt particle size of ∼3.3 nm exhibits the best fuel cell performance.     

Influence of the Temperature for the Ethanol Oxidation Reaction (EOR) on Pt/C,Pt‐Rh/C and Pt‐Rh‐SnO2/C

The electrocatalytic activity of Pt/C, Pt‐Rh/C and Pt‐Rh‐SnO₂/C electrocatalysts toward the ethanol oxidation reaction (EOR) was investigated in a three‐electrode assembly at 25 °C, 40 °C and 70 °C in acidic medium. The 10 wt.% electrocatalysts were prepared with a modified polyol method and physically characterized by both X‐Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). The CO‐stripping study revealed that CO_ad oxidation initiates at lower potential on Pt‐Rh/C and Pt‐Rh‐SnO₂/C than on Pt/C and shifts negatively when the temperature increases. The positive effect of the temperature is maintained for the EOR: the three electrocatalysts exhibit a higher activity and a negative shift of the EOR wave at higher temperature. Pt‐Rh‐SnO₂/C demonstrates the lowest EOR onset potential of the three electrocatalysts. The steady‐state Tafel slopes and apparent activation energies E_a were determined in 0.5 M H₂SO₄ + 0.1 M EtOH between E = 0.4 and 0.7 V vs. RHE in the temperature range 25–70 °C. The results show rather comparable rate determining steps (rds) for the ethanol electrooxidation on Pt/C and Pt‐Rh/C in the ranges of potential and temperature studied. The EOR on Pt‐Rh‐SnO₂/C seems less influenced by the potential than on Pt/C and Pt‐Rh/C electrocatalysts, but is more temperature sensitive.     

Polyaniline‐supported platinum‐hydrous ruthenium oxide nanocomposite as electrocatalyst for methanol oxidation

A novel composite electrode is fabricated through the electrodeposition of hydrous ruthenium oxide (RuO₂·xH₂O) and platinum (Pt) particles into the matrix of polyaniline (PANI). Scanning electron microscopy reveals that RuO₂·xH₂O and Pt particles are homogeneously distributed into the matrix of PANI. A comparison of the sizes of Pt and RuO₂·xH₂O particles incorporated into the PANI film reveals that Pt particles are smaller in sizes as compared with the sizes of RuO₂·xH₂O particles. The catalytic activity of composite electrodes was evaluated for the oxidation of methanol by using cyclic voltammetry and chronoamperometry. A relatively high catalytic current was noticed for the oxidation of methanol (2.37 mA/cm²) at PANI‐Pt‐RuO₂·xH₂O electrode (+0.6 V (V vs. Ag/AgCl) in comparison to oxidation current at PAN‐Pt (1.27 mA/cm²) electrode. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Potent,Metabolically Stable 2‐Alkyl‐8‐(2H‐1,2,3‐triazol‐2‐yl)‐9H‐adenines as Adenosine A2A Receptor Ligands

Inhibition of adenosine A_2A receptors has been shown to elicit a therapeutic response in preclinical animal models of Parkinson’s disease (PD). We previously identified the triazolo‐9H‐purine, ST1535, as a potent A_2AR antagonist. Studies revealed that ST1535 is extensively hydroxylated at the ω‐1 position of the butyl side chain. Here, we describe the synthesis and evaluation of derivatives in which the ω‐1 position has been substituted (F, Me, OH) in order to block metabolism. The stability of the compounds was evaluated in human liver microsomes (HLM), and the affinity for A_2AR was determined. Two compounds, (2‐(3,3‐dimethylbutyl)‐9‐methyl‐8‐(2H‐1,2,3‐triazol‐2‐yl)‐9H‐purin‐6‐amine ( 3 b ) and 4‐(6‐amino‐9‐methyl‐8‐(2H‐1,2,3‐triazol‐2‐yl)‐9H‐purin‐2‐yl)‐2‐methylbutan‐2‐ol ( 3 c ), exhibited good affinity against A_2AR (K_i=0.4 nM and 2 nM , respectively) and high in vitro metabolic stability (89.5 % and 95.3 % recovery, respectively, after incubation with HLM for two hours).     

Thin‐Film Catalytic Coating of a Microreactor for Preferential CO Oxidation over Pt Catalysts

Different Pt‐based catalyst layers have been prepared and tested in a stacked foil microreactor for CO oxidation and preferential oxidation of CO in presence of hydrogen. The reactions were performed on Pt without support by impregnation of a pre‐oxidized microstructured metal plate, Pt/Al₂O₃ and Pt/CeO₂ based on sol methods as well as Pt/nano‐Al₂O₃, a combined method of sol‐gel and nanoparticle slurry coating. The ceria based sol‐gel catalyst was much more active for CO oxidation than alumina based sol‐gel catalysts at low temperature. However, total oxidation was only obtained at higher temperature on the alumina based catalysts. The combined method seems to have advantages in terms of less internal mass transfer limitation when trying to increase the catalyst coating thickness based on sol‐gel approaches due to no reduction of CO selectivity up to 300 °C reaction temperature. Experiments on CO oxidation with the Pt/CeO₂ catalyst have been conducted in an oxygen supply microreactor to evaluate the catalyst performance under sequential oxygen supply to reaction zone (CO excess).     

Synergistic Effect of a Palladium‐on‐Carbon/Platinum‐on‐Carbon Mixed Catalyst in Hydrogen/Deuterium Exchange Reactions of Alkyl‐Substituted Aromatic Compounds

We have found a synergistic effect in the H‐D exchange reaction of alkyl‐substituted aromatic compounds using the Pd/C‐Pt/C‐D₂O‐H₂ system. This system would lead to fully H‐D exchange results even on the sterically hindered sites which were only low‐deuterium incorporated by Pd/C or Pt/C independently. Since the reaction was general for a variety of aromatic compounds, it could be applied to the deuteration of dianiline derivatives as raw materials for polyimides.     

Nanostructured membrane electrode assemblies from layer‐by‐layer composite/catalyst containing membranes and their fuel cell performances

In this study, two approaches are compared to develop nanostructured membrane electrode assemblies (MEA) using layer‐by‐layer (lbl) technique. The first is based on the direct deposition of polyallylamine hydrochloride (PAH) and sulfonated polyaniline (sPAni) on Nafion support to prepare lbl composite membrane. In the second approach, sPAni is coated on the support in the presence of platinum (Pt) salt, Nafion solution and Vulcan for obtaining catalyst containing membranes (CCMs). SEM and UV–vis analysis show that the multilayers are deposited on both sides of Nafion successfully. Although H₂/O₂ single cell performances of acid doped lbl composite membrane based MEA are found to be at the range of 126 and 160 mW cm^?2 depending on the number of deposited layers, the cell performance of MEA obtained from catalyst containing lbl self‐assembled thin membrane (PAH/sPAni‐H⁺)_10‐Pt is found to be 360 mW cm^?2 with a Pt utilization of 720 mW mgPt^?1. This performance is 82% higher as compared to original Nafion^®117 based MEA (198 mW cm^?2). From the cell performance evaluations for different structured MEAs, it is mainly found out that the use of lbl CCMs instead of composite membranes and fabrication of thinner electrolytes result in a higher H₂/O₂ cell activity due to significant reduction in ohmic resistivity. Also, it is observed that the use of sPAni slightly improves the cell performance due to an increased probability of the triple phase contact and it can lead to superior physicochemical properties such as conductivity and thermal stability. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40314.     

Graphite Electrodes Modified with Platinum‐Nickel Nano‐Particles for Methanol Oxidation

Methanol electro‐oxidation is investigated at graphite electrodes modified with various platinum and nickel nano‐particle deposits using cyclic voltammetry. The modified electrodes are prepared by the simultaneous electrodeposition of metals from their salt solutions using potentiostatic and galvanostatic techniques. They show enhanced catalytic activity towards methanol oxidation in KOH solution. The catalytic activity of platinum nano‐particles is found to be significantly affected by the presence of relatively small amounts of nickel deposits. A comparison is made between the electrocatalytic activity of Pt/C and (Pt‐Ni)/C electrodes. The results show that the methanol electro‐oxidation current increases with an increase in the nickel content. In particular, the highest catalytic activity is achieved for platinum to nickel deposits of 95%:5% (wt.‐%), in other cases the catalytic activity decreases. It is found that Ni enhances the catalytic activity of Pt by increasing the number of active sites, as well as through an electron donation process from Ni to Pt. This process takes place once the nickel hydroxide (Ni(OH)₂)/nickel oxy‐hydroxide (NiOOH) transformation begins. The effect of the methanol concentration on the methanol oxidation reaction is investigated. The order of reaction, with respect to methanol, at the modified (Pt‐Ni)/C electrode is found to be 0.5.     

Supra‐monolayer coverages on small metal clusters and their effects on H2 chemisorption particle size estimates

H₂ chemisorption measurements are used to estimate the size of supported metal particles, often using a hydrogen‐to‐surface‐metal stoichiometry of unity. This technique is most useful for small particles whose sizes are difficult to estimate through electron microscopy or X‐ray diffraction. Undercoordinated metal atoms at the edges and corners of particles, however, make up large fractions of small metal clusters, and can accommodate multiple hydrogen atoms leading to coverages which exceed 1 ML (supra‐monolayer). Density functional theory was used to calculate hydrogen adsorption energies on Pt and Ir particles (38–586 atoms, 0.8–2.4 nm) at high coverages (≤3.63 ML). Calculated differential binding energies confirm that Pt and Ir (111) single‐crystal surfaces saturate at 1 ML; however, Pt and Ir clusters saturate at supra‐monolayer coverages as large as 2.9 ML. Correlations between particle size and saturation coverage are provided that improve particle size estimates from H₂ chemisorption for Pt‐group metals. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3109–3120, 2018     

BODIPY‐Appended 2‐(2‐Pyridyl)benzimidazole Platinum(II) Catecholates for Mitochondria‐Targeted Photocytotoxicity

Platinum(II) complexes of the type [Pt(L)(cat)] ( 1 and 2 ), in which H₂cat is catechol and L represents two 2‐(2‐pyridyl)benzimidazole ligands with 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) pendants, were synthesized to achieve mitochondria‐targeted photocytotoxicity. The complexes showed strong absorptions in the range λ=510–540 nm. Complex 1 exhibited intense emission at λ=525 nm in 1 % DMSO/water solution (fluorescence quantum yield of 0.06). Nanosecond transient absorption spectral features indicated an enhanced population of the triplet excited state in di‐iodinated complex 2 . The generation of singlet oxygen by complex 2 upon exposure to visible light, as evidenced from experiments with 1,3‐diphenylisobenzofuran, is suitable for photodynamic therapy because of the remarkable photosensitizing ability. The complexes resulted in excellent photocytotoxicity in HaCaT cells (half maximal inhibitory concentration IC₅₀≈3 μm , λ=400–700 nm, light dose=10 J cm^?2), but they remained non‐toxic in the dark (IC₅₀>100 μm ). Confocal microscopy images of 1 and Pt estimation from isolated mitochondria showed colocalization of the complexes in the mitochondria. Complex 2 displayed generation of reactive oxygen species induced by visible light, disruption of the mitochondrial membrane potential, and apoptosis.     

Effect of Catalyst Supports on Water‐Gas Shift Reaction at Ultrahigh Temperatures Using Syngas

Monometallic and bimetallic catalysts (Pt, Ni, and Pt‐Ni) with single support (Al₂O₃, TiO₂) and composite support (CeO₂/Al₂O₃, CeO₂/TiO₂) were prepared and tested for water‐gas shift reaction in a tubular quartz reactor. Syngas and steam with different steam‐to‐carbon ratios served as feedstock. The operating pressure was fixed while the reaction temperature was varied. The measured results indicated that the monometallic Ni/Al₂O₃ catalyst exhibits the lowest CO conversion and H₂ yield as compared with other catalysts. About the same CO conversion can be obtained from Pt and Pt‐Ni catalysts with single or composite support. However, higher H₂ yield can be achieved from the TiO₂‐supported catalyst compared with those supported by Al₂O₃. The experimental data also indicated that good thermal stability can be reached for the Pt‐based catalysts studied.     

Improving the Stability and Ethanol Electro‐Oxidation Activity of Pt Catalysts by Selectively Anchoring Pt Particles on Carbon‐Nanotubes‐Supported‐SnO2

To improve the stability and activity of Pt catalysts for ethanol electro‐oxidation, Pt nanoparticles were selectively deposited on carbon‐nanotubes (CNTs)‐supported‐SnO₂ to prepare Pt/SnO₂/CNTs and Pt/CNTs was prepared by impregnation method for reference study. X‐ray diffraction (XRD) was used to confirm the crystalline structures of Pt/SnO₂/CNTs and Pt/CNTs. The stabilities of Pt/SnO₂/CNTs and Pt/CNTs were compared by analyzing the Pt size increase amplitude using transmission electron microscopy (TEM) images recorded before and after cyclic voltammetry (CV) sweeping. The results showed that the Pt size increase amplitude is evidently smaller for Pt/SnO₂/CNTs, indicating the higher stability of Pt/SnO₂/CNTs. Although both catalysts exhibit degradation of electrochemical active surface area (EAS) after CV sweeping, the EAS degradation for the former is lower, further confirming the higher stability of Pt/SnO₂/CNTs. CV and potentiostatic current–time curves were recorded for ethanol electro‐oxidation on both catalysts before and after CV sweeping and the results showed that the mass specific activity of Pt/CNTs increases more than that of Pt/SnO₂/CNTs, indicating that Pt/CNTs experiences more severe evolution and is less stable. The calculated area specific activity of Pt/SnO₂/CNTs is larger than that of Pt/CNTs, indicating SnO₂ can co‐catalyze Pt due to plenty of interfaces between SnO₂ and Pt.     

One‐Step Preparation of Pt on Pretreated Multiwalled Carbon Nanotubes for Methanol Electrooxidation

For the first time, intermittent microwave heating (IMH) is a one‐step technique applied to pretreat the multiwalled carbon nanotubes (MWCNTs) in H₂O₂ solution. The approach does not require washing and filtration of the sample, thus significantly reducing the loss of the material and treatment time. The IMH associated with H₂O₂ treatment, is optimised to fabricate efficient support for Pt electrocatalyst. Both as‐received and treated MWCNTs are used as Pt electrocatalyst supports, respectively. It demonstrates that the treated MWCNTs supported Pt has much better electrocatalytic performance than that of untreated MWCNTs supported Pt. The Pt on MWCNTs treated with an IMH irradiation mode in 10 s on and 20 s off for 5 times, shows the best performance for methanol oxidation. This work provides a novel approach to simply and economically fabricate an efficient MWCNT support at a large scale, for high performance Pt electrocatalysts.     

Preparation of Platinum‐Poly(O‐dihydroxybenzene) Composite Catalyst and Its Electrocatalytic Activity Toward Methanol and Formic Acid Oxidation

A composite catalyst has been successfully prepared by dispersing Pt nanoparticles on a poly(o‐dihydroxybenzene) (PoDHB) modified glassy carbon (GC) electrode and characterized by SEM, EDX, and electrochemical analysis. Compared with Pt nanoparticles deposited on the bare GC, the Pt/PoDHB/GC exhibits higher catalytic activity and stronger poisoning tolerance for electro‐oxidation of methanol and formic acid. The enhanced performance could be attributed to the increase of electrochemical active surface area (EASA) arisen from the PoDHB modification. Furthermore, performance limiting factors such as platinum loading, polymer mass, H₂SO₄, methanol, and formic acid concentrations have been evaluated for optimizing the electrocatalytic activities.     

8‐Benzyltetrahydropyrazino[2,1‐f]purinediones: Water‐Soluble Tricyclic Xanthine Derivatives as Multitarget Drugs for Neurodegenerative Diseases

8‐Benzyl‐substituted tetrahydropyrazino[2,1‐f]purinediones were designed as tricyclic xanthine derivatives containing a basic nitrogen atom in the tetrahydropyrazine ring to improve water solubility. A library of 69 derivatives was prepared and evaluated in radioligand binding studies at adenosine receptor (AR) subtypes and for their ability to inhibit monoamine oxidases (MAO). Potent dual‐target‐directed A₁/A_2A adenosine receptor antagonists were identified. Several compounds showed triple‐target inhibition; one of the best compounds was 8‐(2,4‐dichloro‐5‐fluorobenzyl)‐1,3‐dimethyl‐6,7,8,9‐tetrahydropyrazino[2,1‐f]purine‐2,4(1H,3H)‐dione ( 72 ) (human AR: K_i A₁ 217 nM , A_2A 233 nM ; IC₅₀ MAO‐B: 508 nM ). Dichlorinated compound 36 [8‐(3,4‐dichlorobenzyl)‐1,3‐dimethyl‐6,7,8,9‐tetrahydropyrazino[2,1‐f]purine‐2,4(1H,3H)‐dione] was found to be the best triple‐target drug in rat (K_i A₁ 351 nM , A_2A 322 nm; IC₅₀ MAO‐B: 260 nM ), and may serve as a useful tool for preclinical proof‐of‐principle studies. Compounds that act at multiple targets relevant for symptomatic as well as disease‐modifying treatment of neurodegenerative diseases are expected to show advantages over single‐target therapeutics.     

Catalytic Combustion‐Type Hydrogen Sensor Using BaTiO3‐based PTC Thermistor

A catalytic combustion‐type gas sensor using a positive temperature coefficient (PTC) thermistor, which shows a sharp resistance change around Curie temperature, was developed for the detection of hydrogen. La‐doped BaTiO₃ (Ba_0.998 La_0.002 TiO₃) was prepared through a solid‐state method and an oxalic acid method. La‐doped BaTiO₃ obtained by the oxalic acid method showed improved PTC properties, due to the formation of fine particles, as compared to that prepared with the solid‐state method. The resulting sensor device showed a fairly high H₂ sensitivity in the range of 100–1000 ppm. In addition, the H₂ sensitivity and response speed were improved by coating a Pt/SiO₂ catalyst on the sensor device because the catalytic combustion efficiency of H₂ was improved by the catalyst coating.     

Partial hydrogenation of benzene catalyzed by Pt/N‐n‐propyl chitosan hybrid membrane

The partial hydrogenation of benzene by a Pt nano‐cluster/N‐n‐propyl chitosan hybrid membrane was investigated in this article. Monodispersed Pt nano‐clusters were prepared by the reduction of H₂PtCl₆ with ethylene glycol under microwave conditions. TEM, FTIR, XRD, ¹H‐NMR, and XPS were used to characterize the structure of Pt nano‐particles, N‐n‐propyl chitosan and Pt/N‐n‐propyl chitosan hybrid membrane, respectively. Experimental results showed that Pt/N‐n‐propyl chitosan hybrid membrane catalyst gave a high selectivity for cyclohexene of 85.2% in the liquid phase hydrogenation of benzene, while the selectivity of cyclohexene was only 58.2% over the Pt/chitosan hybrid membrane catalyst. It was worth noting that there was no cyclohexene in the product when the catalyst was only Pt nano‐particles without chitosan hybrid membrane. So the chitosan or modified‐chitosan membranes played an important role in the controlling to the hydrogenation of benzene, and the relationship of the swelling degree and the catalytic activity was discussed in detail. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Suppression of Potential Oscillations in PEFCs by Using Anode Catalyst Prepared by Polygonal Barrel‐Sputtering Method

In this study, we investigated the suppression of potential oscillations that occur while feeding H₂ gas including a large amount of CO to polymer electrolyte fuel cells. A carbon‐supported Pt–Ru alloy (Pt–Ru/C) sample was prepared by the polygonal barrel‐sputtering method. Electrochemical measurement was conducted in 1 N H₂SO₄ electrolyte solution saturated with H₂ gas including CO of 1,000 ppm. From the measurement, it was found that the prepared Pt–Ru/C sample showed higher CO tolerance than a commercially available sample, and therefore, potential oscillations in the case of the prepared sample occurred for slightly longer intervals. Additional samples were prepared by sputtering different amounts of Ru on the prepared Pt–Ru/C sample, and it was observed that the average interval of potential oscillations increased with the amount of Ru. This result suggests that in the case of the polygonal barrel‐sputtering method, Ru plays an important role in suppressing potential oscillations and influences the CO tolerance of Pt–Ru/C.