Synthesis and characterisation of ternary Pt/Ru/Mo catalysts for the anode of the PEM fuel cell

Miscellaneous compositions of carbon-supported Pt/Ru/Mo catalysts were synthesised via reductive precipitation using hydrazine. The precipitation of the different Pt/Ru/Mo catalysts was carried out with H2PtCl6, RuCl3 and Mo(CO)6 as precursors for synthesis I and (NH4)6Mo7O24 for synthesis II. The home-made catalysts were structurally characterised with different methods before and after electrochemical investigation in a membrane fuel cell. Furthermore cyclic voltammetry was perfomed to determine the catalytic activity of the different Pt/Ru/Mo catalysts. X-ray fluorescence analysis (XFA), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDXS) demonstrate that the precursor used in synthesis I is not adequate for the preparation of ternary Pt/Ru/Mo catalysts. Transmission electron microscopy (TEM) images of the differently prepared catalysts show the formation of 20 nm agglomerates composed of 2-3 nm crystallites, which separate into individual nanoparticles during fuel cell operation. The particle size was determined with TEM and X-ray diffraction (XRD), and is independent of the Pt/Ru/Mo ratio. No significant particle growth is observed after operation

Electrochemical impedance and x-ray absorption spectroscopy (EXAFS) as in-situ methods to study the PEMFC anode

The effect of alloy formation on the performance of carbonsupported Pt and Ru fuel cell catalysts has been investigated by electrochemical impedance spectroscopy (EIS), X-ray absorption spectroscopy (EXAFS) and fuel cell tests. The CO tolerance of the respective anode electrocatalysts has been tested in both reformate and methanol operation. This paper describes results for mixtures of carbon-supported Pt and carbon-supported Ru catalysts. The particle sizes of the active metals have been modified by heat-treatment in nitrogen. It has been observed that the size of Pt and Ru particles has a significant influence on the electrochemical performance, the activity improving for smaller Ru particles. The performance of certain Pt-Ru mixtures in a single cell fuel cell is comparable with an alloy catalyst

Electron microscopy techniques for the analysis of the polymer electrolyte distribution in proton exchange membrane fuel cells

The polymer electrolyte distribution in PEMFC electrodes plays an important role for the catalyst utilization and various transport processes in the electrode. Moreover, its influence on the transport processes is not only limited to proton transport but it may also affect gas transport, electron conductivity and water management of the cell. However, experimental techniques to study the polymer electrolyte distribution are scarce. In this paper we present various approaches based on scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to characterize the polymer electrolyte distribution. The methods presented include staining of the polymer electrolyte with heavy metal ions, energy dispersive X-ray (EDX) mapping and energy filtered imaging (EFI). Their use for the analysis of the polymer electrolyte distribution and electrode structure will be presented and current limitations of these techniques will be discussed

How to Cope With Heavy Metal Ions: Cellular and Proteome-Level Stress Response to Divalent Copper and Nickel in Halobacterium salinarum R1 Planktonic and Biofilm Cells

Halobacterium salinarum R1 is an extremely halophilic archaeon capable of adhesion and forming biofilms, allowing it to adjust to a range of growth conditions. We have recently shown that living in biofilms facilitates its survival under Cu2+ and Ni2+ stress, with specific rearrangements of the biofilm architecture observed following exposition. In this study, quantitative analyses were performed by SWATH mass spectrometry to determine the respective proteomes of planktonic and biofilm cells after exposition to Cu2+ and Ni2+.Quantitative data for 1180 proteins were obtained, corresponding to 46% of the predicted proteome. In planktonic cells, 234 of 1180 proteins showed significant abundance changes after metal ion treatment, of which 47% occurred in Cu2+ and Ni2+ treated samples. In biofilms, significant changes were detected for 52 proteins. Only three proteins changed under both conditions, suggesting metal-specific stress responses in biofilms. Deletion strains were generated to assess the potential role of selected target genes. Strongest effects were observed for 1OE5245F and 1OE2816F strains which exhibited increased and decreased biofilm mass after Ni2+ exposure, respectively. Moreover, EPS obviously plays a crucial role in H. salinarum metal ion resistance. Further efforts are required to elucidate the molecular basis and interplay of additional resistance mechanisms

How to Cope With Heavy Metal Ions: Cellular and Proteome-Level Stress Response to Divalent Copper and Nickel in Halobacterium salinarum R1 Planktonic and Biofilm Cells

Halobacterium salinarum R1 is an extremely halophilic archaeon capable of adhesion and forming biofilms, allowing it to adjust to a range of growth conditions. We have recently shown that living in biofilms facilitates its survival under Cu2+ and Ni2+ stress, with specific rearrangements of the biofilm architecture observed following exposition. In this study, quantitative analyses were performed by SWATH mass spectrometry to determine the respective proteomes of planktonic and biofilm cells after exposition to Cu2+ and Ni2+.Quantitative data for 1180 proteins were obtained, corresponding to 46% of the predicted proteome. In planktonic cells, 234 of 1180 proteins showed significant abundance changes after metal ion treatment, of which 47% occurred in Cu2+ and Ni2+ treated samples. In biofilms, significant changes were detected for 52 proteins. Only three proteins changed under both conditions, suggesting metal-specific stress responses in biofilms. Deletion strains were generated to assess the potential role of selected target genes. Strongest effects were observed for 1OE5245F and 1OE2816F strains which exhibited increased and decreased biofilm mass after Ni2+ exposure, respectively. Moreover, EPS obviously plays a crucial role in H. salinarum metal ion resistance. Further efforts are required to elucidate the molecular basis and interplay of additional resistance mechanisms

Sub 500nm refractory carbonaceous particles in the polar stratosphere

Eleven particle samples collected in the polar stratosphere during SOLVE (SAGE III Ozone loss and validation experiment) from January until March 2000 were characterized in detail by high-resolution transmission and scanning electron microscopy (TEM/SEM) combined with energy-dispersive X-ray microanalysis. A total number of 4175 particles (TEM = 3845; SEM = 330) was analyzed from these samples which were collected mostly inside the polar vortex in the altitude range between 17.3 and 19.9 km. By particle volume, all samples are dominated by volatile particles (ammonium sulfates/hydrogen sulfates). By number, approximately 28–82 % of the particles are refractory carbonaceous with sizes between 20–830 nm. Internal mixtures of refractory carbonaceous and volatile particles comprise up to 16 %, individual volatile particles about 9 to 72 %.Most of the refractory carbonaceous particles are completely amorphous, a few of the particles are partly ordered with a graphene sheet separation distance of 0.37 ± 0.06 nm (mean value ± standard deviation). Carbon and oxygen are the only detected major elements with an atomic O / C ratio of 0.11 ± 0.07. Minor elements observed include Si, S, Fe, Cr and Ni with the following atomic ratios relative to C: Si / C: 0.010 ± 0.011; S / C: 0.0007 ± 0.0015; Fe / C: 0.0052 ± 0.0074; Cr / C: 0.0012 ± 0.0017; Ni / C: 0.0006 ± 0.0011 (all mean values ± standard deviation).High resolution element distribution images reveal that the minor elements are distributed within the carbonaceous matrix, i.e., heterogeneous inclusions are not observed. No difference in size, nanostructure and elemental composition was found between particles collected inside and outside the polar vortex.Based on chemistry and nanostructure, aircraft exhaust, volcanic emissions and biomass burning can certainly be excluded as source. The same is true for the less probable, but globally important sources: wood burning, coal burning, diesel engines and ship emissions.Rocket exhaust and carbonaceous material from interplanetary dust particles remain as possible sources of the refractory carbonaceous particles studied. However, additional work is required in order to identify the sources unequivocally