Pt In Catalysts Research Articles

Indium oxide supported Pt–In alloy nanocluster catalysts with enhanced catalytic performance toward oxygen reduction reaction

Few currently applied carbon-supported metal cathode catalysts exhibit satisfactory durability under the harsh operation conditions of proton exchange membrane fuel cells. Herein we report for the first time a highly active In2O3 supported Pt–In alloy nanocluster (NC) catalyst (Pt–In/In2O3) toward oxygen reduction reaction, with small alloy NCs and a Pt content of 42 wt%, which exhibits obviously enhanced durability compared to currently applied carbon-supported Pt catalysts (Pt/C) and previously reported Pt NCs-based catalysts with a similar Pt content. The mass activity (MA) and specific activity (SA) over Pt–In/In2O3 are 0.32 A·mg−1Pt and 1.14 mA cm−2 at 0.9 V (vs. reversible hydrogen electrode (RHE)), respectively. Electron transfer from In to Pt in the alloy NCs occurs as confirmed by X-ray absorption measurements, which is an important cause of the high catalytic activity. After an accelerated aging test of 6000 potential cycles between 1.0 and 1.6 V, the MA loss over Pt–In/In2O3 is 3%, but that over Pt/C is 33%. The catalysts subjected to the aging test are characterized by transmission electron microscopy and X-ray diffraction to understand the extremely high durability.

Highlights of C (sp2 )-H hydrogen isotope exchange reactions.

The highlights of C (sp2 )-H hydrogen isotope exchange (HIE) methods developed over the past 10 years are summarized in this review. Major developments include improved Ir(I) catalysts with greater functional group and solvent compatibility and the development of novel base metal catalysts for HIE. In addition, a number of novel Ru-based catalysts have been developed with promising activity. In the area of Pt- and Pd-catalysed exchange, in addition to new advances on heterogeneous Pt- and Pd-catalysed HIE by Sajiki and Shevchenko, a number of groups have reported on homogenous catalysts of Pt and Pd that show an interesting activity and selectivity.

A highly durable N-enriched titanium nanotube suboxide fuel cell catalyst support

Reduced bandgap metal oxide materials are consider an alternative to carbon black supports for fuel cell catalysts. Here we report a unique N-enriched titanium nanotube suboxide doped with molybdenum (TNTS-Mo) fuel cell catalyst support. The support was prepared by the surface modification of a TNTS-Mo with a terpyridine (TPY) ligand, yielding TPY/TNTS-Mo. We have deposited Pt onto this support and evaluated its activity and stability. The Pt/TPY/TNTS-Mo catalyst was subjected to stringent accelerated stress tests (AST) designed to induce catalyst degradation similar to automotive operation and startup-shutdown conditions. The Pt/TPY/TNTS-Mo was compared with Pt/TNTS-Mo and a benchmark carbon supported Pt catalyst (Pt/C). These stability protocols confirmed that TPY modification greatly enhances the stability and durability of the Pt nanoparticles via strong metal support interaction (SMSI). In addition, the covalently attached TPY layer stabilizes the doped metal oxide supports itself, preventing changes in its surface state and composition at high potentials.

Effect of preparation method on the Pt-In modified Mg(Al)O catalysts over dehydrogenation of propane

The Pt-In modified Mg(Al)O catalysts were prepared by co-precipitation, co-impregnation, and successive impregnation methods with Pt and In loading at 0.3 and 0.6 wt.%, respectively. The catalysts were tested in the propane dehydrogenation at 550 °C and atmospheric pressure. Pt loading on In-modified Mg(Al)O support prepared by co-precipitation (Pt/Mg(In)(Al)O) exhibited the highest catalytic performances with initial propane conversion and propylene selectivity of 24.2%.and 98.2%, respectively. As revealed by the H2-TPR and XPS results, the Pt/Mg(In)(Al)O exhibited a stronger metal-support interaction and favorable led to more PtIn alloy formation compared to those obtained by the other methods, which greatly enhanced the catalytic performance and stability. Coke formation was significant reduced on all the prepared bimetallic PtIn catalysts, especially coke on the active metal, which diminished the catalytic deactivation. The catalysts were also characterized by CO chemisorption, transmission electron microscopy (TEM), NH3-temperature program desorption (NH3-TPD).

Recent Mechanistic Understanding of Oxygen Reduction Reaction over Pt-Supported 3D Carbon Nanofiber Catalysts

For both proton exchange membrane and direct methanol fuel cells, oxygen reduction reaction (ORR) is a performance-determining step. While Pt has been established as a standard bearer in ORR catalyst development, practical long-term applications require continuing effort to pursue active, stable, as well as affordable materials as alternatives to precious metals. In this talk, carbon-based vertically aligned carbon nanofibers (VACNFs), essentially a stack of conical graphitic structures, will be discussed as highly promising ORR catalysts. In an alkaline medium, at -0.4 V applied potential, the current density measured on VACNF cathode is twice more than that measured with commercial Pt catalyst (Pt/C). Molecular insights have been gained through the use of Density functional theory (DFT) calculations to: (1) reveal interactions of ORR intermediate species at the catalytically active sites; and (2) elucidate the origin of catalytic activities of VACNF under reaction conditions. Specifically, semi-periodic fishbone-like stacked graphene sheets, bare or terminated with H and OH, have been employed to understand the impact on ORR mechanism and corresponding reactivities. Bindings of O2, O, and OH at various configurations obtained from DFT are then used as descriptors to assess catalyst performance against simple Pt (111) and Pt (211) surfaces. In addition, Pt nanocatalysts supported on VACNF (Pt/VACNF), which can push the ORR current density even higher, will be discussed as well. Again, with DFT, a model with Pt anchored at the VACNF edges was proposed to investigate the functionalities of Pt/VACNF for alkaline ORR reactions. In this talk, both associative and dissociative ORR pathways will be analyzed based on the established models. In particular, the overall computed ORR thermodynamics are shown to be favored toward Pt/VACNF than Pt (111), consistent with experimental results. Nevertheless, the unique interactions of ORR intermediates such as O*, OOH*, and OH* with catalytic active VACNF edge sites, revealed by DFT calculations, suggest intriguing but also complex electrochemistries.

Comparative Evaluation of Coated and Non-Coated Carbon Electrodes in a Microbial Fuel Cell for Treatment of Municipal Sludge

This study aims to provide insight into the cost-effective catalyst on power generation in a microbial fuel cell (MFC) for treatment of municipal sludge. Power production from MFCs with carbon, Fe2O3, and Pt electrodes were compared. The MFC with no coating on carbon generated the least power density (6.72 mW·m−2) while the MFC with Fe2O3-coating on carbon anodes and carbon cathodes generated a 78% higher power output (30.18 mW·m−2). The third MFC with Fe2O3-coated carbon anodes and Pt on carbon as the cathode catalyst generated the highest power density (73.16 mW·m−2) at room temperature. Although the power generated with a conventional Pt catalyst was more than two-fold higher than Fe2O3, this study suggests that Fe2O3 can be investigated further as an efficient, low-cost, and alternative catalyst of Pt, which can be optimized for improving performance of MFCs. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) results demonstrated reduced resistance of MFCs and better charge transfer between biofilm and electrodes containing coated anodes compared to non-coated anodes. Scanning electron microscopy (SEM) was used to analyze biofilm morphology and microbial community analysis was performed using 16S rRNA gene sequencing, which revealed the presence of known anaerobic fermenters and methanogens that may play a key role in energy generation in the MFCs.

Pt-Co Alloy Nanoparticles on a γ-Al2 O3 Support: Synergistic Effect between Isolated Electron-Rich Pt and Co for Automotive Exhaust Purification.

There is interest in minimizing or eliminating the use of Pt in catalysts by replacing it with more widely abundant and cost-effective elements. The alloying of Pt with non-noble metals is a potential strategy for reducing Pt use because interactions between Pt and non-noble metals can modify the catalyst structure and electronic properties. Here, a γ-Al2 O3 -supported bimetallic catalyst [Pt(0.1)Co(1)/Al2 O3 ] was prepared which contained 0.1 wt % Pt and 1 wt % Co and thus featured an extremely low Pt : Co ratio (<1 : 30 mol/mol). The Pt and Co in this catalyst formed alloy nanoparticles in which isolated electron-rich Pt atoms were present on the nanoparticle surface. The activity of this Pt(0.1)Co(1)/Al2 O3 catalyst for the purification of automotive exhaust was comparable to the activities of 0.3 and 0.5 wt % Pt/γ-Al2 O3 catalysts. Electron-rich Pt and metallic Co promoted activation of NOx and oxidization of CO and hydrocarbons, respectively. This strategy of tuning the surrounding structure and electronic state of a noble metal by alloying it with an excess of a non-noble metal will enable reduced noble metal use in catalysts for exhaust purification and other environmentally important reactions.

The Role of Surface Functionalities in PtGe and PtIn Catalysts for Direct Methanol Fuel Cells

Bimetallic PtGe and PtIn catalysts were prepared over Vulcan carbon (VC) and multiwall carbon nanotubes (NT) by conventional impregnation method (CI). These supports were functionalized with citric or nitric acid. The structural and electrochemical characteristics of the different functionalized supported catalysts were analyzed in order to determine the influence of the functional groups. The methods applied were temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), cyclohexane dehydrogenation reaction (CHD), and CO stripping. The functionalization treatment with citric or nitric acid eases CO oxidation to CO2, decreasing poisoning effect of CO over Pt, due to the development of oxygenated groups on support surfaces and in the nearby Ge and In. Bimetallic catalysts supported on carbons functionalized with HNO3 present increasing electrochemical active surface values, indicating a better electrochemical behavior than the corresponding monometallic catalysts. DMFC experiments show a very good behavior of PtGe catalysts, mainly for those supported on HNO3-functionalized NT, reaching a maximum power density of 80 mW cm−2. Conversely, PtIn catalysts exhibit a very poor behavior.

Acceptorless Dehydrogenative Synthesis of Pyrimidines from Alcohols and Amidines Catalyzed by Supported Platinum Nanoparticles

A one-pot, acceptorless dehydrogenative method, using a carbon-supported Pt catalyst (Pt/C) along with KOtBu, has been developed for the synthesis of 2,4,6-trisubstituted pyrimidines from secondary and primary alcohols, and amidines. The reaction takes place efficiently using a wide range of substrate scopes (32 examples with isolated yields up to 92%). The Pt/C catalyst that promotes this process is reusable and has a higher turnover number (TON) than those employed in previously reported methods. The results of mechanistic studies suggest that the process takes place through a pathway that begins with Pt-catalyzed acceptorless dehydrogenation of the alcohol substrate, which is followed by sequential condensation, cyclization, and dehydrogenation. Measurements of the turnover frequency combined with the results of density functional theory calculations on different metal surfaces suggest that the adsorption energy of H on the Pt surface is optimal for the acceptorless dehydrogenation process, which cause...

Pt-Co and Pt-Ni Catalysts of Low Metal Content for H2 Production by Reforming of Oxygenated Hydrocarbons and Comparison with Reported Pt-Based Catalysts

New catalysts of Pt, PtNi, PtCo, and NiCo supported on Al2O3 were developed for producing hydrogen by aqueous phase reforming (APR) of oxygenated hydrocarbons. The urea matrix combustion technique was used for loading the metal on the support in order to improve several aspects: increase both the metal-support interaction and the metal dispersion and decrease the metal load. The catalysts were characterized by MS/ICP, N2 adsorption, XRD, TPR, CO chemisorption, and the test of cyclohexane dehydrogenation (CHD). The APR of a solution of 10% mass ethylene glycol (EG), performed in a tubular fixed bed reactor at 498 K, 22 bar, WHSV = 2.3 h−1, was used as the main reaction test. After 10 h on-stream, the catalysts prepared by UMC had better hydrogen yield and catalytic stability than common catalysts prepared by IWI. The UMC/IWI H2 yield ratio was 23.5/15.2 for Pt, 24.0/17.0 for PtCo, 26.6/21.0 for PtNi, and 8.0/3.9 for NiCo. Ni or Co addition to Pt increased the carbon conversion while keeping the H2 turnover high. Cobalt also improves stability. Reports of several authors were revised for a comparison. The analysis indicated that the developed catalysts are a viable and cheaper alternative for H2 production from a renewable resource.

(Invite) Prospective Investigations of Tungsten and Molybdenum Carbide-Containing Materials As Catalysts for Electrochemical Energy Conversion Processes: Proton, Oxygen, and CO/CO2 Reduction Reaction

In the last decade, transition metal carbides, particularly based of molybdenum and tungsten, have emerged as novel materials with promising catalytic properties toward several important practical electrochemical reactions. In this presentation, the activity of such materials will be discussed for the following electrochemical approaches/reactions: i) the electrocatalysis of oxygen reduction reaction (ORR) in acid media on Pt- and Pt2Ni-nanoparticles supported on carbon forming composites with tungsten and molybdenum carbides with cubic (α) and hexagonal (β) structures; ii) the hydrogen evolution reaction (HER) in acid and alkaline media on TM-modified molybdenum carbide (TM-Mo2C) catalysts, where TM is a transition metal, such as, Fe, Co, Ni and Cu; iii) the CO2 and CO electro-reduction reactions in 0.1 M NaClO4 and 0.5 and 1 M KHCO3 solutions on carbon supported tungsten and molybdenum carbides. Syntheses of the carbide-based catalysts have been conducted employing different procedures, after which the produced material are characterized by X-Ray diffraction (XRD), energy dispersive X-ray spectroscopy, (EDS), X-ray photoelectron spectroscopy (XPS), in situ X-ray absorption near edge structure (XANES), and transmission electron microscopy (TEM). Cyclic voltammetry and polarization measurements on stationary and rotation disk electrodes have been employed for the electrochemical investigations. For the CO/CO2 reduction, reaction products were analyzed by differential electrochemical mass spectrometry (DEMS) and high performance liquid chromatography (HPLC) analyses. Enhanced mass and specific ORR activities are seen for Pt–molybdenum carbide-derived composites compared to Pt-α-WC/C, which in turn presents specific activity for the ORR similar to that of a standard carbon supported Pt catalyst (Pt/C). For Pt-β-WC1-x/C composites, the specific activity is also higher than that of Pt/C when a carbide-to carbon load of 40 wt.% is used. In the case of the HER, high activities are observed for all TM-Mo2C catalysts in acid and alkaline media. Nonetheless, while in acid there is a decrease in the activity upon metal doping, with an activity trend of α-Mo2C > Fe-Mo2C > Co-Mo2C > Ni-Mo2C > Cu-Mo2C, the opposite tendency is found in alkaline solutions. In situ near-edge X-ray adsorption analysis reveals different oxidation states of the TM inside the carbide in both solutions. In acid, a positive charge of the TM in the materials in the electrochemical environment is possibly at the origin of the deleterious effect of Fe, Co, Ni and Cu. In addition, catalysts stability against dissolution in acid media is increased by doping of molybdenum carbide with TM. Regarding of CO and CO2 electro-reductions in 0.1 M NaClO4 and 0.5 and 1 M KHCO3 solutions, results suggest that neither molybdenum nor tungsten carbides can be considered as active catalysts, in contrast to reported results in gas phase. It appears that both the aqueous environment and their activity toward the HER surpass the reactivity toward these latter reactions. Acknowledgements: Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP - Procs. 2013/16930-7 and 2014/23486-9) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) (Procs. 1423454), Brazil, for financial supports.

Nanostructured porous coatings via electrospray atomization and deposition of nanoparticle suspensions

The controlled deposition of aerosols is shown to be a valuable tool to prepare nanostructured porous coatings as required in many applications. Experiments were conducted to prepare nanostructured materials from the electrohydrodynamic atomization of liquid suspensions. The charged droplets generated by the electrospray are driven by the electric field, the liquid evaporates along the droplet path leaving a dry residue of nanoparticles that deposit on a substrate. The range of parameters leading to a stable cone-jet was studied for two different suspensions; carbon nanoparticles in ethanol and catalytic inks formed by Pt supported on carbon nanoparticles and Nafion® in ethanol. The morphology of the deposits was examined by means of digital scanning electron microscope (SEM) images. Upper views of the deposit show a structure based on clusters of nanoparticle aggregates formed by the attachment at the deposit of nanoparticle aggregates coming from several electrospray droplets, with the cluster size (of the order of 10 µm) increasing with the flow rate. Lateral SEM images of the deposits cross-sections were processed to calculate the deposit mean density and porosity. The porosity is rather high (always larger than 90%) decreasing as the electrospray flow rate increases. Coatings prepared from catalytic inks were tested as electrodes in a fuel cell. These electrodes have shown extremely large specific power (reaching a power of 21 kW per gram of Pt in the cell) due to the outstanding properties of the electrosprayed catalytic layer: large porosity, uniform distribution of the catalyst and high density of (Pt) active sites.

Pt/C containing different platinum loadings for use as electrocatalysts in alkaline PBI-based direct glycerol fuel cells

This study shows the influence of the Pt percentage in Pt catalysts (Pt/C) on their application in Direct Glycerol Fuel Cells (DGFC). Catalysts with 20, 30, 40 and 60% Pt were prepared by formic acid reduction. X-Ray Diffraction (XRD) confirmed the formation of Pt fcc nanocrystals (with average sizes between 3 and 4 nm). Thermogravimetric analysis (TGA) corroborated the Pt loadings and the Transmission Electron Microscopy (TEM) images show a homogeneous distribution of the Pt nanoparticles, with larger particles at higher Pt percentages. Electrochemical measurements reveal that higher Pt percentages promote the activity of the glycerol electroxidation reaction, resulting in lower onset potentials, higher current densities and reduced poisoning of the Pt surface. Single cell tests confirm these results, with greater maximum power density at higher Pt percentages, although the glycerol crossover effect starts to become significant in the 60% Pt/C catalyst, owing to the reduced thickness of this catalytic layer. A final product selectivity analysis indicates that tartronate is the preferential glycerol electroxidation product, along with glycerate and oxalate in lower proportions, with minor amounts of glycolate and mesoxalate. In general, a thicker catalytic layer is associated with the formation of more oxidized products.

Electrocatalytic activity of platinum nanoparticles supported on different phases of tungsten carbides for the oxygen reduction reaction

Carbon-supported tungsten carbides with cubic (β-WC1-x/C) and hexagonal (α-WC/C) are evaluated as support materials of Pt-nanoparticles, to be used as electrocatalysts for the oxygen reduction reaction (ORR) in acid media. The produced materials are characterized by X-Ray diffraction (XRD), energy dispersive X-ray spectroscopy, (EDS), X-ray photoelectron spectroscopy (XPS), in situ X-ray absorption near edge structure (XANES), and transmission electron microscopy (TEM). Cyclic voltammetry and polarization measurements on stationary and rotation disk electrodes are employed for the electrochemical investigations. It is seen that all Pt-α-WC/C catalysts present specific activity for the ORR similar to that of a standard carbon supported Pt catalyst (Pt/C), while for the Pt-β-WC1-x/C composites the specific activitiy is 3.6 times higher than that of Pt/C, when a carbide-to-carbon load of 40 wt% is used. These differences in reactivity for the ORR may be associated to differences in the binding energy of adsorbed oxygen on Pt, introduced by the tungsten carbide substrates. Pt XANES results for the β-WC/C1-x materials evidence a small increase in the Pt 5d band occupancy, which may lead to a weaker Pt-OHx interaction, increasing the ORR kinetics.

Polyaniline and Perfluorosulfonic Acid Co-Stabilized Metal Catalysts for Oxygen Reduction Reaction.

A proton (perfluorosulfonic acid, PFSA) and electron (polyaniline, PANI) conductor polymer costabilized Pt catalyst (Pt-PFSA/C@PANI) is synthesized to improve the long-term stability of polymer electrolyte membrane fuel cells (PEMFCs). The prepared catalyst not only displays comparable oxygen reduction reaction (ORR) activity, but significantly higher electrochemical stability than commercial porous carbon nanosphere supported Pt catalysts (Pt/C). This robust electrochemical property can be due to the result of PFSA and PANI. PANI as protector inhibits carbon nanospheres from corrosion of carbon supports in harsh chemical and electrochemical conditions. Meanwhile, PFSA wrapped Pt NPs (Pt@PFSA) can also anchor Pt NPs on C@PANI to avoid aggregation and detachment of Pt NPs, due to the increased metal-support interaction caused by the strong electrostatic attraction between PANI and PFSA with corresponding positive and negative charges. Significantly, after coating PANI on carbon supports (C@PANI), almost all micropores in the surface of carbon disappear, effectively avoiding the embedding of Pt nanopaticles into micropores. Furthermore, the triple-phase boundary toward ORR catalysis can be facilitated by PFSA as proton conductor (solid electrolyte). These are of benefit to increase utilization of Pt noble metals and ORR activity of our new catalysts.

ChemInform Abstract: Synthesis of 2,5‐Disubstituted Pyrroles via Dehydrogenative Condensation of Secondary Alcohols and 1,2‐Amino Alcohols by Supported Platinum Catalysts.

Direct synthesis of 2,5-disubstituted pyrroles has been achieved via acceptorless dehydrogenative heterocyclization of 1,2-aminoalcohols and secondary alcohols by utilizing a heterogeneous carbon-supported Pt catalyst (Pt/C). The optimized method gave 92% yield of 2-ethyl-5-phenyl-1H-pyrrole as a desired product from 2-amino-1-butanol and 1-phenylethanol in the presence of 0.1 mol% of Pt/C and 1.1 equiv. of KOtBu. It has been revealed that Pt/C demonstrates superior catalytic activity to a number of catalysts tested in this study including other transition metal-loaded carbon and various metal-oxide-supported Pt catalysts. In addition, the turnover number (TON) obtained in the present system was found to be higher than those obtained in previously-reported catalytic systems. It is significant that the Pt/C catalyst could be recycled as a heterogeneous catalyst without significant loss in the activity and showed a wide substrate scope for the 2,5-disubstituted pyrrole forming process.

Lamellar structured CoSe2 nanosheets directly arrayed on Ti plate as an efficient electrochemical catalyst for hydrogen evolution

Splitting water by electrochemical reactions is considered to be the most promising strategy to create hydrogen. Herein, an efficient hydrogen evolution cathode was developed by in-situ growth of lamellar structured cobalt diselenide (CoSe2) nanosheets on the surface of commercial titanium (Ti) plate (CoSe2NS@Ti) in the first time. Both SEM images and XRD data confirmed that the Ti plate is homogeneously coated by few stacking layers of lamellar structured CoSe2, which could provide more active sites for hydrogen evolution reaction (HER) with the thickness about 20nm. This catalytic cathode shows exceptionally high activity for hydrogen evolution with 152mV overpotential to afford a current density of 10mAcm−2 and a high exchange current density of 5.01×10−3mAcm−2, as well as high cyclic stability with negligible decrease of cathodic current after 500 cycles. Remarkably, the CoSe2NS@Ti catalyst exhibits fast hydrogen evolution kinetics with Tafel slope of 38.5mV per decade, which approaches the state-of-art Pt catalyst (Pt/C) in 0.5M H2SO4. This CoSe2NS@Ti material is easily prepared with excellent electrocatalytic performance, thus could be a promising earth-abundant electrocatalyst for the HER and other renewable energy applications.

Development of Highly Active and Durable Pt-Pd System Catalysts for PEFCs

Introduction Carbon supported Pd core-Pt shell catalyst (Pt/Pd/C) and Pt-Pd alloy catalyst (PtPd/C) are attractive alternatives to a carbon supported Pt catalyst (Pt/C) because their ORR specific activities are enhanced with an accelerated durability test (ADT) performed at 80°C [1, 2]. However, ECSA of the catalysts drastically decreased with the ADT, resulting in slight increase of ORR mass activities. We explored the ADT protocol and developed a high activation protocol (HAP) to mitigate the ECSA decay and enhance the ORR mass activities. Furthermore, we developed a Cu-O2 treatment which mimics the HAP carried out on GC electrode and is suitable for mass-production of highly activated catalysts. We also applied SiO2 coating technique [3, 4] to prevent agglomeration of the catalyst particles with the ADT and improve durability of the catalysts. Experimental Pt/Pd/C was synthesized with a modified Cu-UPD/Pt replacement process [1]. A carbon supported Pd core (Pd/C, Pd size: 4.6 nm, Pd loading: 30 wt.%, Ishifuku Metal Industry) was dispersed in 50 mM H2SO4 containing 10 mM CuSO4 and the solution was stirred with co-existence of a metallic Cu sheet at 5°C under Ar atmosphere. After stirring for 5 h, the Cu sheet was removed and K2PtCl4 was added to replace under potentially deposited Cu shell on the Pd core surface with Pt shell. PtPd/C alloy catalyst was synthesized with an impregnation method. Pt(acac)2 and Pd(acac)2 were impregnated onto a carbon support using t-butylamine as a solvent (Pt20Pd80 in at.%), followed by reduction under 15% H2/Ar atmosphere at 600°C for 4 h. The catalysts were characterized by TG, XRF, XRD, TEM, CV and XAFS techniques. ORR activity of the catalysts was evaluated with RDE technique in O2 saturated 0.1 M HClO4 at 25°C. ADT was conducted using rectangular wave potential cycling of 0.6 V (3 s)-1.0 V (3 s) vs. RHE in Ar saturated 0.1 M HClO4 at 80°C for 10,000 cycles. Results and Discussion Changes in ECSA and ORR mass activity of the Pt/Pd/C and PtPd/C catalysts with ADT, HAP and Cu-O2 treatment are summarized in Fig. 1 (dotted black lines show Pt/C catalyst; Pt size: 2.8 nm, Pt loading: 46 wt.%, TEC10E50E, TKK). The ECSA of the catalysts drastically decreased with the ADT, by which the ORR mass activity showed slight increases. On the contrary, the ECSA decay was mitigated with the HAP (rectangular wave potential cycling of 0.4V (300 s)-1.0 V (300 s) vs. RHE in Ar saturated 0.1 M HClO4 at 80°C for 30-40 cycles) and the ORR mass activity was highly enhanced, showing ca. 3-fold values of the Pt/C catalyst. Since the HAP is performed on the GC electrode, treated amount of the catalysts is extremely small (ca. 30 µg), we developed a Cu-O2 treatment (Fig. 2) to scale-up the HAP. In the Cu-O2 treatment, the catalyst powders are stirred for 300 s in 2 M H2SO4 containing 0.1 M CuSO4 at 80°C under an inert atmosphere (N2) with co-existence of a metallic Cu sheet, where the equilibrium potential of Cu2+/Cu (ca. 0.3 V) is applied to the catalysts when they contact with the Cu sheet. Next, the Cu sheet is removed and O2 gas is introduced in the solution, where the equilibrium potential of the ORR (ca. 1.0 V) is applied to the catalysts. As shown in Fig. 1, the ECSA decay by the Cu-O2 treatment is equivalent to that by the HAP and the ORR mass activity of the catalysts were equivalently enhanced, indicating that the Cu-O2 treatment mimics the HAP on the GC electrode and is suitable for mass-production of highly activated Pt/Pd/C and PtPd/C catalysts. However, the highly activated Pd@Pt NPs were severely agglomerated with the ADT and the ORR mass activity was decayed. In order to prevent the NPs agglomeration with the ADT, we applied SiO2 coating onto the Pd@Pt NPs [3, 4]. The SiO2 coating suppressed the NPs agglomeration and the ECSA decay was mitigated (Fig. 3), which highly enhanced the ORR mass activity of the Pt/Pd/C catalyst even after the ADT (Fig. 4). Acknowledgement This work was supported by NEDO, Japan.

Effect of Temperature on Platinum Dissolution from PEFC Catalysts

The durability of polymer electrolyte fuel cells (PEFCs) is a big concern for its applications like FCVs to be commercialized on a large scale. In particular, the instability of Pt-based cathode catalyst has been discussed intensively. Platinum (Pt) dissolution is recognized as one of the degradation mechanisms for carbon supported Pt catalysts (Pt/C) in PEFCs. It has been found that repeated potential cycles accelerate Pt dissolution.[1-3] Fundamental studies in aqueous media revealed preliminary behaviors of Pt dissolution during one potential cycle. The up-to-date data were mostly obtained near room temperature, and a dominant cathodic dissolution during reduction of Pt oxide was understood. As reported by Fuller et al.,[4] however, degradation of Pt/Cs at an elevated temperature near 60 to 80 °C, whereat a PEFC normally operates, was severer than that at room temperatures. Thus, it is necessary to evaluate Pt dissolution from Pt/Cs at such temperatures. In prior studies,[5-6] we compared Pt dissolution at 25 °C and 65 °C by inductively coupled plasma mass spectrometry (ICP-MS) and a channel flow double electrode (CFDE). The experiments had some difficulties, but the results showed a ca. 5-time enhancement from 25 to 65 °C. The cathodic dissolution was enhanced because larger amount of Pt oxide was formed at 65 °C. The effect of temperature on the anodic dissolutions and the place exchange process remains unclear yet. In this study, we evaluate Pt dissolution under temperatures ranging from 20 to 80 °C. We test a series of commercial Pt/C catalysts produced by TKK that have Pt loadings from 20 to 70 wt% and average Pt particle size from ca. 1.5 to 5 nm. We limited the potential region between 0.6 and 1.4 V, which is closely related to the operation region of a PEFC cathode. We use ICP-MS to evaluate to overall dissolutions and a CFDE to analyze the dissolution behavior in one potential cycle. The attached Figure showed a typical CFDE data presenting the current on a working electrode loading a 30wt% Pt/C (TEC10E30A) under potential cycling (I WE) and the current recorded on a collector electrode (I CE) at 80 °C in 0.5 M H2SO4. The I CE helps to understand the dissolution of Pt4+ and Pt2+ complex during one potential cycle. Similar analysis will be discussed at other temperatures like 20, 40, and 80 °C in the presentation. Reference Z. Wang, E. Tada, and A. Nishikata, J. Electrochem. Soc., 161, F380 (2014).A.A. Topalov, S. Cherevko, A.R. Zeradjanin, J.C. Meier, I. Katsounaros, and K.J.J. Mayrhofer, Chem. Sci., 5, 631 (2014).P. Jovanovič, A. Pavlišič, V.S. Šelih, M. Šala, N. Hodnik, M. Bele, S. Hočevar, and M. Gaberšček, ChemCatChem, 6, 449 (2014).W. Bi and T.F. Fuller, J. Electrochem. Soc., 155, B215 (2008).Z. Wang, E. Tada, and A. Nishikata, J. Electrochem. Soc., 163, F1-F3 (2016).Z. Wang, E. Tada, and A. Nishikata, ECS Trans., 69, 255 (2015). Figure 1

ChemInform Abstract: Some of Tomorrow′s Catalysts for Processing Renewable and Non‐Renewable Feedstocks, Diminishing Anthropogenic Carbon Dioxide and Increasing the Production of Energy

AbstractReview: 144 refs.