Electrochemical measurement of intrinsic oxygen reduction reaction activity at high current densities as a function of particle size for Pt4–xCox/C (x = 0, 1, 3) catalysts

While extensive literature shows Pt alloy catalysts are a more active substitute for pure Pt catalysts at 0.9 V, high activity is also needed at high current densities if they are to be adopted for fuel cell application. We use a newly developed electrochemical technique to compare the performance of a range of catalysts with initial composition Pt4–xCox/C of different particle sizes at high current densities (∼0.65 V vs RHE) as well as the typical ∼0.9 V vs RHE. Moving from 0.9 to 0.65 V, the current densities were found to increase by up to 80-fold for the Pt/C catalysts, with this factor decreasing as the amount of Co in the PtCo alloy increases. A kinetic model incorporating site blocking species at both high and low potentials has been used to explain this change. While the dealloyed catalysts were found to have a greater mass activity at low current densities (∼0.9 V vs RHE), they were no longer as active as 2.1 nm Pt particle catalyst at high current densities (∼0.65 V vs RHE). However, for equivalent particle sizes, the mass activity of the dealloyed Co-containing catalysts remains higher across the normal operating potentials of a fuel cell. Using this insight, we predict that at 0.65 V a catalyst composed of 3.8 nm CoPt@Pt1ML particles would give optimum mass activity performance. In addition, two peaks were observed during the cyclic voltammetry (CV) of the oxygen reduction reaction (ORR) on pure Pt nanoparticles in the hydrogen adsorption region (0–0.4 V vs RHE). These peaks are associated with surface sites with different reactivities toward the ORR

Fishing on Silba

From olden times fishermen from Silba have used different techniques of fishing, depending on weather conditions and season: nets, hooks, tridents and traps. Men matted traps from thatch and used them in the summertime. Hooks, tied on a line and a cane stick, are used when fishing on the shore, or from a boat on the sea. Several hooks on a line (parangal) are used for fishing from a boat in motion, and so is the trident, but in the night-time. The most significant is fish hunting with nets of different forms and names. The catch is sorted according to quality and size, and then better fish is taken to the market of Zadar, and the other is consumed or sold on the island and the neighboring island of Olib

Effects of fertilization on Picea abies stands situated on drained peat soils

ArticleNorway spruce used for afforestation of drained peat soils frequently has low productivity and decay in a long - term, which could be related to soil chemical composition and nutrient status. The research aim was to elucidate the effect of PSM on new Norway spruce plantings (1st experiment) and 20 - year - old spruce stands (2nd experiment) on drained peat soils by evaluating: (1) nutrient accumulation in soil - plant system, (2) soil microbiological activity, (3) health status of spruce individuals, (4) growth int ensity and productivity of spruce, (5) changes in composition of vascular plant and moss species. The study was conducted at two forest ( Myrtillosa turf.mel .) sites in Latvia, each consisting of two plots: control and treated with PMS (100 g m - 2 in Septemb er 2007, 50 g m - 2 in April 2008). During 2008 – 2016, regular analysis of soil, spruce needles, soil microbiology, assessment of tree crown vitality, stand productivity, inventory of vascular plant and moss species were done. The results showed that the fert ilization with PMS resulted in a significantly improved K, Ca, Zn, and N status of trees, crown vitality and up to three times increased tree growth parameters at both experiments during the study period. The average count of bacteria and fungi in soil of fertilized plots, accompanied by a remarkable variability in the study years, was significantly higher only for the 1 st experiment. Fungi : bacteria ratio for the fertilized and control plots differed significantly only for the 1 st experiment. Significant i ncrease of cover with nitrophilic plant ( Urtica dioica, Antriscus sylvestris, Rubus idaeus ) and moss ( Plagiomnium cuspidatum , P. ellipticum ) species at both fertilized sites were stated

(M,Ru)O2 (M = Mg, Zn, Cu, Ni, Co) rutiles and their use as oxygen evolution electrocatalysts in membrane electrode assemblies under acidic conditions

The rutiles (M,Ru)O2 (M = Mg, Zn, Co, Ni, Cu) are formed directly under hydrothermal conditions at 240 °C from potassium perruthenate and either peroxides of zinc or magnesium, or poorly crystalline oxides of cobalt, nickel or copper. The polycrystalline powders consist of lath-shaped crystallites, tens of nanometres in maximum dimension. Powder neutron diffraction shows that the materials have expanded a axis and contracted c axis compared to the parent RuO2, but there is no evidence of lowering of symmetry to other AO2-type structures, supported by Raman spectroscopy. Rietveld refinement shows no evidence for oxide non-stoichiometry and provides a formula (MxRu1-x)O2 with 0.14 < x < 0.2, depending on the substituent metal. This is supported by energy-dispersive X-ray analysis on the transmission electron microscope, while Ru K-edge XANES spectroscopy shows that upon inclusion of the substituent the average Ru oxidation state is increased to balance charge. Variable temperature magnetic measurements provide evidence for atomic homogeneity of the mixed metal materials, with suppression of the high temperature antiferromagnetism of RuO2 and increased magnetic moment. The new rutiles all show enhanced electrocatalysis compared to reference RuO2 materials for oxygen evolution in 1 M H2SO4 electrolyte at 60 °C, with higher specific and mass activity (per Ru) than a low surface area crystalline RuO2, and with less Ru dissolution over 1000 cycles compared to an RuO2 with a similar surface area. Magnesium substitution provides the optimum balance between stability and activity, despite leaching of the Mg2+ into solution, and this was proved in membrane electrode assemblies

Properties of the hydrogen oxidation reaction on Pt/C catalysts at optimised high mass transport conditions and its relevance to the anode reaction in PEFCs and cathode reactions in electrolysers

AbstractUsing a high mass transport floating electrode technique with an ultra-low catalyst loading (0.84–3.5μgPtcm−2) of commonly used Pt/C catalyst (HiSPEC 9100, Johnson Matthey), features in the hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) were resolved and defined, which have rarely been previously observed. These features include fine structure in the hydrogen adsorption region between 0.18<V vs. RHE<0.36V vs. RHE consisting of two peaks, an asymptotic decrease at potentials greater than 0.36V vs. RHE, and a hysteresis above 0.1V vs. RHE which corresponded to a decrease in the cathodic scan current by up to 50% of the anodic scan. These features are examined as a function of hydrogen and proton concentration, anion type and concentration, potential scan limit, and temperature. We provide an analytical solution to the Heyrovsky–Volmer equation and use it to analyse our results. Using this model we are able to extract catalytic properties (without mass transport corrections; a possible source of error) by simultaneously fitting the model to HOR curves in a variety of conditions including temperature, hydrogen partial pressure and anion/H+ concentration. Using our model we are able to rationalise the pH and hydrogen concentration dependence of the hydrogen reaction. This model may be useful in application to fuel cell and electrolyser simulation studies

Electrocatalyst performance at the gas/electrolyte interface under high mass transport conditions: optimization of the "floating electrode" method.

The thin-film rotating disk electrode (TF-RDE) is a well-developed, conventional ex-situ electrochemical method which is limited by poor mass transport in the dissolved phase and hence can only measure the kinetic response for Pt-based catalysts in a narrow overpotential range. Thus, the applicability of TF-RDE results in assessing how catalysts perform in fuel cells has been questioned. To address this problem, we use the floating electrode (FE) technique which can facilitate high mass transport to a catalyst layer composed of an ultra-low loading of catalyst (1-15 μgPt cmgeo-2) at the gas/electrolyte interface. In this paper, the aspects which have critical effects on the performance of the FE system are measured and parameterised. We find that in order to obtain reproducible results with high performance the following factors need to be taken into account: system cleanliness, break-in procedure, hydrophobic agent, ionomer type and the measurements of catalyst surface area and loading. For some of these parameters, we examined a range of different approaches/materials and determined the optimum configuration. We find that the gas permeability of the hydrophobic agent is an important factor for improving the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) performance. We provide evidence that the suppression of the HOR and ORR introduced by the Nafion ionomers is more than a local mass transport barrier but that a mechanism involving the adsorption of the sulfonate on Pt also plays a significant role. The work provides intriguing insights into how to manufacture and optimize electrocatalyst systems which must function at the gas/electrolyte interface

Service provider perceptions of transitioning from audio to video capability in a telehealth system

Background Telephone consultation and triage services are increasingly being used to deliver health advice. Availability of high speed internet services in remote areas allows healthcare providers to move from telephone to video telehealth services. Current approaches for assessing video services have limitations. This study aimed to identify the challenges for service providers associated with transitioning from audio to video technology. Methods Using a mixed-method, qualitative approach, we observed training of service providers who were required to switch from telephone to video, and conducted pre- and post-training interviews with 15 service providers and their trainers on the challenges associated with transitioning to video. Two full days of simulation training were observed. Data were transcribed and analysed using an inductive approach; a modified constant comparative method was employed to identify common themes. Results We found three broad categories of issues likely to affect implementation of the video service: social, professional, and technical. Within these categories, eight sub-themes were identified; they were: enhanced delivery of the health service, improved health advice for people living in remote areas, safety concerns, professional risks, poor uptake of video service, system design issues, use of simulation for system testing, and use of simulation for system training. Conclusions This study identified a number of unexpected potential barriers to successful transition from telephone to the video system. Most prominent were technical and training issues, and personal safety concerns about transitioning from telephone to video media. Addressing identified issues prior to implementation of a new video telehealth system is likely to improve effectiveness and uptake

Data for (M,Ru)O2 (M = Mg, Zn, Cu, Ni, Co) Rutiles and their use as Oxygen evolution electrocatalysts in membrane electrode assemblies under acidic conditions

The rutiles (M,Ru)O2 (M = Mg, Zn, Co, Ni, Cu) are formed directly under hydrothermal conditions at 240 °C from potassium perruthenate and either peroxides of zinc or magnesium, or poorly crystalline oxides of cobalt, nickel or copper. The polycrystalline powders consist of lath-shaped crystallites, tens of nanometres in maximum dimension. Powder neutron diffraction shows that the materials have expanded a axis and contracted c axis compared to the parent RuO2, but there is no evidence of lowering of symmetry to other AO2-type structures, supported by Raman spectroscopy. Rietveld refinement shows no evidence for oxide non-stoichiometry and provides a formula (MxRu1-x)O2 with 0.14 < x < 0.2, depending on the substituent metal. This is supported by energy-dispersive X-ray analysis on the transmission electron microscope, while Ru K-edge XANES spectroscopy shows that upon inclusion of the substituent the average Ru oxidation state is increased to balance charge. Variable temperature magnetic measurements provide evidence for atomic homogeneity of the mixed metal materials, with suppression of the high temperature antiferromagnetism of RuO2 and increased magnetic moment. The new rutiles all show enhanced electrocatalysis compared to reference RuO2 materials for oxygen evolution in 1 M H2SO4 electrolyte at 60 °C, with higher specific and mass activity (per Ru) than a low surface area crystalline RuO2, and with less Ru dissolution over 1000 cycles compared to an RuO2 with a similar surface area. Magnesium substitution provides the optimum balance between stability and activity, despite leaching of the Mg2+ into solution, and this was proved in membrane electrode assemblies