Platinum Content Research Articles

Property-governed performance of platinum-modified titania photocatalysts.

Titania is probably the most widely investigated semiconductor photocatalyst because of various advantages, such as high activity, thermal and chemical stability, low price, abundance, and negligible toxicity. However, pristine titania is also characterized by charge carriers’ recombination, and thus lower quantum yields of photocatalytic reactions than theoretical 100%. Moreover, its wide bandgap, despite being recommended for excellent redox properties, means also inactivity under visible part of solar radiation. Accordingly, titania has been surface modified, doped and coupled with various elements/compounds. For example, platinum deposited on the surface of titania has shown to improve both UV activity and the performance under vis. Although the studies on titania modification with platinum started almost half a century ago, and huge number of papers have been published up to now, it is unclear which properties are the most crucial and recommended to obtain highly efficient photocatalyst. In the literature, the opposite findings could be found on the property-governed activities that could result from huge differences in the reaction systems, and also examined photocatalysts. Considering the platinum properties, its content, the size of nanoparticles and the oxidation state, must be examined. Obviously, the characteristics of titania also influence the resultant properties of deposited platinum, and thus the overall photocatalytic performance. Although so many reports on Pt/TiO2 have been published, it is hardly possible to give indispensable advice on the recommended properties. However, it might be concluded that usually fine platinum NPs uniformly deposited on the titania surface result in high photocatalytic activity, and thus in the low optimal content of necessary platinum. Moreover, the aggregation of titania particles might also help in the lowering the necessary platinum amount (even to 0.2 wt%) due to the interparticle electron transfer mechanism between titania particles in one aggregate. In respect of platinum state, it is thought that it is highly substrate-specific case, and thus either positively charged or zero valent platinum is the most recommended. It might be concluded that despite huge number of papers published on platinum-modified titania, there is still a lack of comprehensive study showing the direct correlation between only one property and the resultant photocatalytic activity.

Core‐shell nanocatalysts with reduced platinum content toward more cost‐effective proton exchange membrane fuel cells

AbstractProton exchange membrane fuel cells (PEMFCs) have become a major component of current clean energy technologies. Accounting for nearly half the cost of a commercial fuel cell stack, Pt‐based catalysts are the main choices for both anode and cathode in PEMFCs. However, catalytical activity and operating life of Pt‐based catalysts are still unsatisfactory. High cost and scarcity of Pt further hinder the development of PEMFCs. Constructing core‐shell structure for Pt‐based catalysts is a promising strategy to enhance the catalytic activity and reduce the cost. In this review, we overview recent advances in Pt‐based core‐shell catalysts according to catalytic reaction types involved in PEMFCs. Furthermore, we discuss the working principle of core‐shell catalysts from the perspective of coupling between core and shell. In the end, we conclude the recent progress and discuss the future developments and facing challenges.

Effect of the PtCu/C electrocatalysts initial composition on their activity in the de-alloyed state in the oxygen reduction reaction

The promising ORR electrocatalysts with the low platinum content have been obtained by a simple method in one pot. The morphology of Pt-based nanoparticles supported on carbon was controlled to enhance the catalytic performance in oxygen reduction reaction (ORR). A detailed study of the microstructural characteristics and electrochemical behavior of the de-alloyed electrocatalysts made it possible to obtain a correlation between the effect of PtCu/C materials initial composition and their ORR activity. It has been established that the initial content of the alloying component has a significant effect on the structural reorganization of bimetallic nanoparticles. Electrochemical study results showed that the ORR performance of de-alloyed PtCu/C catalyst with large Cu content in the initial structure was better than that of de-alloyed PtCu/C catalysts with low Cu content due to the morphology advantages. A successful reorganization of NPs structure increased the ORR activity of the de-alloyed catalysts by two times. A presented approach can be applied to design of different ORR electrocatalysts based on the PtM nanoparticles.

SSR-based genome-wide association study in turkish durum wheat germplasms revealed novel QTL of accumulated platinum.

Durum wheat has a genetic capacity to accumulate toxic metals that can exceed the safety limit of the international standards, which may seriously affect human health. Identifying germplasms with low, nontoxic accumulated metal contents is important to select and develop new varieties. Thus, the objective of this study is to identify the levels of accumulated platinum in durum wheat and detect novel QTL. Platinum contents were determined using 130 durum genotypes. Results generally showed low values of accumulated Pt and significantly less than the maximum grain's Pt content determined by international standards. Pt contents among genotypes varied from ≤ 0.001 to 0.72µg/kg with an average of 0.02. Landraces showed the lowest average accumulated Pt. GWAS was then performed with 780 SSR markers. Five QTL were detected and explained 14.4-23.1% of the total phenotypic variation. Chromosomes 3A, 3B, and 5B appear to be hotspots and may play a crucial role in accumulated Pt and were harbored in 1, 3, and 1 QTL, respectively. This assessment of accumulated Pt within a unique panel included accessions mostly from Turkish regions, and GWAS used is the first study regarding accumulated Pt indices to reveal novel QTL. It will allow breeders to accelerate their selection of proper genotypes according to desired alleles and offer an opportunity to apply MAS to minimize Pt toxicity in durum wheat. Results indicated that the significance of genome (B) regions are likely related to the inheritance control of Pt content and may play a pivotal role regarding durum wheat's Pt contents. Nonetheless, these novel QTL should be validated in independent populations in numerous environments.

(Digital Presentation) New Trends in the Formation of Composites with Desired Functional Properties

The main requirements for anode materials can be divided into two groups: i) overall operating (satisfactory electrical conductivity, availability and reasonable cost, long service life, etc.); ii) specific, due to particular target process (high electrocatalytic activity and selectivity) [1]. The lack of universal anode material requires the creation of new approaches to managing the functional properties of the catalyst. In our opinion, the optimal strategy is to choose a base material that meets the general operational requirements, followed by the creation of an active layer on its basis in accordance with the requirements of particular target processes.The regularities of formation of composites of the TiOx-Pt and TiOx-Pt-Pd systems and their physicochemical properties were studied.Composites were obtained in two stages. First, a thin non-continuous layer of Pt or successive layers of Pt-Pd was applied to the substrate by electrodeposition. Nitrite electrolyte for platinating and phosphate palladation were used. The amount of Pt and Pd on the surface ranged from 0.1 to 2.0 mg cm-2. Then the resulting material was heat treated in an air atmosphere. The surface layers of the composites were formed due to the oxidation of the substrate and the encapsulation of platinum and palladium particles into titanium oxides during this stage. The chemical composition of the bulk and surface of the electrocatalytic coatings obtained was determined by XPS, SEM and EDAX.XPS showed that Pt exists in the metallic state, while Ti is in the form of both metal and intermetallic TixPty, with low Pt content, and in oxide form in Ti(IV) compounds on the surface of non-heat treated electrode As one can see, the coating is not uniform, and the platinum content is significantly reduced from the surface to the substrate (from 92 to 67 at.%), that indicates the local nature of the coating and confirmed by SEM data. As thermal treatment contributes to a more uniform distribution of Pt on the surface, as well as its diffusion in combination with oxygen in the coating bulk, it leads to the formation of a composite of titanium-platinum oxides.The semiconductor properties of such anodes are due to the presence of TiO2, which is an n-type semiconductor. As the temperature increases, the potentials of the flat zones and the carrier concentrations increase, which may be related to the interaction of platinum (electron donor) with TiO2. The use of titanium suboxides as a substrate and increasing the processing temperature also leads to an increase in the potential of flat zones. However, this reduces the number of carriers due to the increase in the degree of stoichiometry of titanium suboxides due to oxygen uptake. The electrodes obtained at 583 K do not correspond to the general dependence. It is likely that the new Ti-O phase formed under such conditions makes an individual contribution to the semiconductor properties of such materials.Palladation of platinum titanium does not lead to a significant change in surface morphology. Platinum, according to EDAX, is fairly evenly distributed on the surface of titanium, which is not observed for palladium. Unlike platinum, the maximum amount of palladium is observed in the protruding parts of the surface, and the minimum - in the hollows, due to the uneven distribution of current on the surface of Ti/Pt during the electrodeposition of palladium. The most noticeable change in morphology occurs at a surface Pd content of 1.0 mg cm-2. The oxygen concentration increases on the surface during heat treatment of Ti/Pt-Pd, there is oxidation of Pd, the surface becomes blue. The distribution of oxygen on the surface coincides with palladium, which indicates the formation of an oxide layer. The XRD method detected the PdO phase on the surface of heat-treated samples with a surface palladium content of 0.2 to 1.0 mg cm-2. At 2θ = 33.8°, the PdO-specific reflex is manifested, the area of which increases with increasing of surface palladium content.Thus, the use of the combined electrochemical-pyrolytic method of obtaining composite anode materials allows to create materials that differ significantly in their structural parameters, composition and physicochemical properties. The main factors influencing the properties of such materials are the nature of the substrate, the amount and nature of platinum and palladium in the surface layer, the temperature and duration of heat treatment in the air. Developed anode materials are characterized by long service life. References Walsh, F.C. Modern developments in electrodes for electrochemical technology and the role of surface finishing / F.C. Walsh // Trans. Inst. Met. Finish. – 2019. – Vol. 97(1). – P. 28-42

Influence of Carbon Support Type, Presence of Platinum and Ionomer Content on Agglomeration in Catalyst Layers

Polymer electrolyte fuel cell (PEFC) energy conversion systems have found application in transportation applications due to their high power density, low operating temperature, high energy conversion efficiency, and speed of refueling.1 One of the key components of a PEFC is the membrane electrode assembly (MEA), which consists of a proton exchange membrane (PEM), such as a perfluorosulfonic acid (PFSA), sandwiched between two catalyst layers (CLs) serving as anode and cathode. Several studies of CL microstructure−performance relationships suggest that the electrode microstructure characteristics, such as the extent of the catalyst−ionomer interaction, continuity of the ionomer phase, and pore size distribution are critical for performance.2-4 However, successful implementation of novel materials for PEFC electrodes is hindered by the lack of a fundamental understanding of the complex, multicomponent nature of the CL, the interplay of its components, and their independent and cooperative effects on the effective properties and performance.In this work, ultra-small angle X-ray scattering (USAXS) was employed to investigate the effects of carbon support type, presence of platinum, and ionomer loading on catalyst agglomeration in CLs. Particle size distributions (PSDs), obtained from fitting the scattering data using the maximum entropy (MaxEnt) method, were used to determine the size of carbon aggregates and agglomerates from carbon-ionomer and platinum-carbon-ionomer CLs. Three types of carbon supports were chosen for the investigation: high surface area carbon (HSC), Vulcan XC-72, and graphitized Vulcan XC-72. CLs with a range of perfluorosulfonic acid (PFSA) ionomer loadings (0.2-1.0 ionomer to carbon ratio, I/C) were studied in order to evaluate the effect of ionomer on the CL agglomerate structure. The CL agglomerate structure will be correlated with electrochemical performance to reveal the interplay of the components, and their independent and cooperative effects on performance. References B.D. McNicol, D. A. J. Rand, K. R. Williams, J. Power Sources 100 (2001) 47–59.F. C. Cetinbas, X. Wang, R. K. Ahluwalia, N. N. Kariuki, R. P. Winarski, Z. Yang, J. Sharman, and D. J. Myers, J. Electrochem. Soc., 164, (2017) F1596–F1607.Y.-C. Park, H. Tokiwa, K. Kakinuma, M. Watanabe, M. Uchida, J. Power Sources 315 (2016) 179-191.S. Holdcroft, Chem. Mater., 26 (2014) 381−393. This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office under the auspices of the Fuel Cell Performance and Durability Consortium (FC-PAD). The Advanced Photon Source was supported by the U.S. Department of Energy, Office of Science User Facility. Argonne National Laboratory is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, also under contract DE-AC-02-06CH11357.

Methodology of the PEM FC Gas Diffusion Layer Permeability Determination and Its Description Related to the Fuel Cell Flow Field Design

Hydrogen fuel cells represent an important part of the new energy scheme for low emission society. Development of the more efficient, durable and energy dense systems requires precise information on the numerous aspects, especially on the local distribution of physio-chemical quantities inside the fuel cells stacks. It is extremely difficult to obtain such information experimentally. Therefore, the mathematical modelling represents a feasible alternative. It offers an efficient and versatile way for the acquisition of required information. Accuracy of mathematical model, however, is primarily determined by the accuracy and reliability of the experimental data available. In this particular case, permeability of gas diffusion layer for reactants and products is of interest. Permeability values in porous environment are available experimentally. It is, however, important to keep in mind that permeability value is strongly dependent on the material porosity and thus on a degree of its compression inside the stack. Therefore, permeability value is varying with position over the electrode. Suitable approach, making possible to describe smoothly variation of the gas diffusion layer permeability with degree of its compression, is desirable. Traditional approach is to use corresponding semi-empirical equations. It is a purpose of this work to verify applicability of the Kozeny-Carman equation for this particular case and thus to fill in this gap in the current knowledge.Prior the experimental validation of the Kozeny-Carman equation accuracy, methodology of obtaining sufficiently accurate permeability data needs to be developed. In the first step of this process, permeability cells were designed, characterized by the homogeneous gas flow distribution in the channel, used for positioning of the gas diffusion layer sample, to be characterized. A special attention was paid to the absence of any turbulence domains close to the pressure reading ports, which could cause potential error in the observed pressure values. The figure provided documents results of the cell geometry optimization. Mathematical model calculated gas stream lines shown document fulfilling above stated conditions and thus ensuring reliability of the experimental data obtained. The cell lid determined the channel height itself. A series of lids was produced, allowing study of gas diffusion layers permeability at the different degrees of compression, i.e. porosities. The channel depth accuracy was required to be within tolerance of 2 mm. Pressure drop on the channel was determined by varying the streaming gas flow rate. Hydrogen and nitrogen (simulating air) were used as a test gasses. Permeability of gas diffusion layers were determined based on pressure drops using Darcy’s law. This set of data allowed comparing experimental data with Kozeny-Carman equation behavior. The agreement obtained was sufficient to justify the usage of this type of semi-empirical equation for the flow field mathematical modelling. Corresponding conclusion was in the last step of the study verified by means of the model serpentine flow field attached at the gas diffusion layer at the different degrees of compression. Experimental data obtained have shown very good agreement with the model calculations. It can thus be concluded, that Kozeny-Carman provides sufficient approximation of the gas diffusion permeability values to be used in the mathematical models for design of fuel cells and fuel cells stacks for geometry optimization.The work was supported from European Regional Development Fund-Project "Fuel Cells with Low Platinum Content" (No. CZ.02.1.01/0.0/0.0/16_025/0007414). Figure 1

Gas Diffusion Layer: The Critical Player in Gases Distribution in the Proton Exchange Membrane Fuel Cell

Within the last decades, fuel cells have become the center of attention of research community, industry, and the general public. This is due to the emphasis on the sustainability of the society and the emerging concept of a hydrogen economy. Proton exchange membrane fuel cells (PEM FCs) represent a mature and established fuel cell technology. The flexibility of operation, the high degree of fuel utilization, and the output power density make them suitable for mobile applications such as hydrogen-fueled vehicles or on-site energy generation. Membrane electrode assembly (MEA) is the mainstay of the PEM FCs. The MEA consists of the proton exchange membrane, catalytic layers, and gas diffusion layers (GDLs). Single MEAs are interconnected by bipolar plates with flow field channels homogenously distributing reactants and realizing easy removal of the generated water. Individual cells are compressed together, forming the fuel cell stack. The GDL plays a three-fold role in the performance of PEM fuel cells. It has to offer good electrical conductivity, ensure good reactant distribution along the reaction zone, and facilitate the removal of the water produced by the fuel cell operation. The optimal combination of these three aspects of GDL allows the FC to achieve high performance. Furthermore, the homogeneous distribution of the reactants is crucial for the durability and lifespan of the FC. The inhomogeneous reactants distribution leads to a local starvation of the electrode, leading to high local overvoltage and thus shortening the lifespan of overloaded parts. Although GDLs play a crucial role in the operation of PEM fuel cells, so far, they have received little attention. Hence, the objective of our study is to compare commercially available GDLs with respect to their properties, namely permeability under conditions close to the operating fuel cell.The approach of combining advanced mathematical modeling with extensive experimental characterization was used to achieve this task. Testing cells allowing precise determination of the in-plane permeability of various GDLs were designed based on the computational fluid dynamics modeling. According to the contemporary literature, two different carbon based GDLs were examined, namely carbon-cloth and carbon-paper, which principally differ in the carbon-fiber orientation in their internal structure. The investigated properties of GDLs thus include thickness, porosity, internal structure, and the presence or absence of microporous layer.The achieved experimental results show that at given compression, thicker carbon paper GDLs are superior to carbon cloth samples in terms of permeability and deformation resistance. The obtained permeability values of GLDs at different degrees of compression were compared with predictions based on the Carman-Kozeny equation to assess the accuracy of this semi-empirical prediction. Finally, the importance of the optimal flow field and GDL combination in terms of reactant distribution in the fuel cell stack of industrial conditions is documented via mathematical modelling based on the obtained experimental data.This work was supported by the European Regional Development Fund-Project “Fuel Cells with Low Platinum Content” (No. CZ.02.1.01/0.0/0.0/16_025/0007414).

Recovery and Enrichment of Platinum from Spent Al2O3 Carrier Catalysts by Matte Smelting-Acid Leaching Process

Recovery of platinum from spent catalysts can meet the comprehensive recycling of secondary resources. Recovery and enrichment of platinum from the spent Al2O3 carrier catalyst using matte smelting for the pyrite-acid leaching process were studied. In melting process, the effects of pyrite, CaO, quartz sand, and Na2B4O7 dosage on the recovery rate of Pt were investigated. In leaching process, the effect of H2SO4 concentration, temperature, time, and liquid/solid (L/S) ratio on Pt enriching efficiency was also investigated. The slag, iron matte, and leaching residue were analyzed using XRD. The molten platinum content in the slag was measured using an atomic absorption spectrometer. The experimental results showed that 98% recovery of platinum was obtained under the following optimum conditions: 1400°C temperature, 50 min smelting time, 1 : 2 mass ratio of pyrite to spent catalysts, 0.5 : 1 ratio of CaO to spent catalysts, and 2 : 1 ratio of quartz sand to the raw material with optimum conditions, which include 15% dosage of Na2B4O7. Moreover, the acid leaching was more efficient under the following optimum conditions: H2SO4 concentration of 1.8 mol/L, time of 70 min, temperature of 60°C, and L/S ratio of 10 : 1. The enrichment and recovery of Pt were achieved at the disappearance of FeS during the acid-leaching process.

Use of PtC Nanotips for Low-Voltage Quantum Tunneling Applications.

The use of focused ion and focused electron beam (FIB/FEB) technology permits the fabrication of micro- and nanometer scale geometries. Therefore, FIB/FEB technology is a favorable technique for preparing TEM lamellae, nanocontacts, or nanowires and repairing electronic circuits. This work investigates FIB/FEB technology as a tool for nanotip fabrication and quantum mechanical tunneling applications at a low tunneling voltage. Using a gas injection system (GIS), the Ga-FIB and FEB technology allows both additive and subtractive fabrication of arbitrary structures. Using energy dispersive X-ray spectroscopy (EDX), resistance measurement (RM), and scanning tunneling microscope (STM)/spectroscopy (STS) methods, the tunneling suitability of the utilized metal–organic material–platinum carbon (PtC) is investigated. Thus, to create electrode tips with radii down to 15 nm, a stable and reproducible process has to be developed. The metal–organic microstructure analysis shows suitable FIB parameters for the tunneling effect at high aperture currents (260 pA, 30 kV). These are required to ensure the suitability of the electrodes for the tunneling effect by an increased platinum content (EDX), a low resistivity (RM), and a small band gap (STM). The STM application allows the imaging of highly oriented pyrolytic graphite (HOPG) layers and demonstrates the tunneling suitability of PtC electrodes based on high FIB aperture currents and a low tunneling voltage.

Platinum containing semiconductor nanomaterials based on SnO2 with Pt-additives to analyze concentration of CH4 in air

Nanosized semiconductor gas sensitive materials Pt/SnO2 were obtained by using sol-gel route, and sensors on their base were created. The nanoscale nature of semiconductor particles in Pt/SnO2 materials and aggregation of platinum clusters for the Pt/SnO2 materials with large platinum loading were confirmed by the x-ray diffraction method (XRD) and transmission electron microscopy (TEM) data. It was found that gas sensitive and catalytic properties to methane oxidation depend on the platinum content. The catalytic activity increases with an increase in the amount of introduced Pt, but the response dependence on the platinum content is extremal. The highest response to methane was found to be 9.7 for the sensors based on 1.76 wt.% Pt/SnO2 at operation temperature 325 °C. This inconsistence was explained by the role of Pt–SnO2 interface in the process of the sensor signal formation.

Understanding Platinum Ionomer Interface Properties of Polymer Electrolyte Fuel Cells

A well-designed cathode catalyst layer with optimal ionomer distribution is critical to minimizing amount of Platinum (Pt) content in polymer electrolyte fuel cells (PEFCs). The impact of Pt loading, ionomer content and carbon support types on the catalyst/ionomer interface were also investigated at dry and wet conditions. Higher Pt loadings resulted in higher double layer capacity (Cdl) and similar electrochemical surface area (ECSA) due to well dispersed ionic phase material. Higher ionomer content resulted in higher ionic conductivity but also showed similar group coverage. High surface area (HSA) carbon support had larger ECSA and Cdl at both dry and wet conditions, as less agglomerated Pt was well dispersed in the meso-pores of the support. Lower group coverages were observed for HSA carbon than for Vulcan carbon due to Pt particles being buried within the porous HSA carbon support. The effect of cell conditioning and voltage recovery on the PEFC cathode catalyst layer was shown to have minimal impact on group coverage despite a decrease in Cdl and ECSA due to the size increase of Pt particles. At dry condition, a significant increases in group coverage were observed for all MEAs due to higher adsorptivity of ionomer in dry conditions.

Degradation Analysis of Pt/Nb–Ti<sub>4</sub>O<sub>7</sub> as PEFC Cathode Catalysts with Controlled Arc Plasma-deposited Platinum Content

Degradation Analysis of Pt/Nb–Ti<sub>4</sub>O<sub>7</sub> as PEFC Cathode Catalysts with Controlled Arc Plasma-deposited Platinum Content

Highly efficient hydrogen production under visible light over g-C3N4-based photocatalysts with low platinum content

The successive combination including thermolysis of melamine cyanurate complex, chemisorption of platinum from the solution of the labile nitratocomplex and, finally, reductive treatment with hydrogen was implemented to obtain highly active Pt/g-C3N4 photocatalysts (0.01–0.5 wt% of Pt). The prepared in this way materials evinces photocatalytic activity in hydrogen evolution reaction from TEOA/water solutions with the superb rate of H2 evolution per platinum atom loaded (1560 h−1) and the net rates being among the highest reported to date values (11 mmol·g−1·h−1). Such a remarkable performance correlates with the structure of these materials where the branchy net of the pores provides easy access of reagents to and ejection of products from the nanoparticulated Pt co-catalysts. A crucial contribution to the formation of the noted Pt/g-C3N4 morphology ascribed to the self-catalyzed hydrogenation of the Pt/g-C3N4 composites resulting in “scarifying” of the g-C3N4 particles preferentially at the surface layer where Pt species are located. Taking into account the high productivity of the synthesized Pt/C3N4 materials and robustness of the preparation method this approach can be convenient for the large-scale applications that were successfully demonstrated under pilot installation (total volume 1 l) with the fuel cell (PEMFC with max output 1 W) as a hydrogen consumer. Evaluation of the productivity of the large-scale reactor for hydrogen production with a scaled-up installation was carried out. This study also grants a new vision on developing expandable synthetic approaches to enhance the performance of carbon nitride-based photocatalysts and at the same time mitigate the noble metal co-catalysts usage.

Recovery of platinum and rhenium using selective precipitation induced by two-stage photochemical treatment

Platinum(IV) and rhenium(VII) can be selectively recovered as precipitates from aqueous solution by means of UV–Visible light irradiation in the presence of 2-propanol and acetone. When an aqueous solution (pH 13.2) containing platinum(IV) (10.9 mM) and rhenium(VII) (11.5 mM) was irradiated with 60 mW cm−2 light for 3 h, 95% of initial platinum content was recovered in the precipitate in its zerovalent state with high selectivity (the recovery efficiency was 24 times that of rhenium), while 96% of the initial rhenium content remained in the reaction solution. To recover the rhenium in the remaining solution, the platinum-containing precipitate was removed, and the collected solution was further irradiated in another photochemical cell. After 12 h of the second irradiation, 82% of the rhenium content in the initial solution (before the first irradiation) was recovered as a precipitate with a recovery efficiency that was 16 times that of platinum. Using this two-stage photochemical treatment, both the platinum and rhenium in the aqueous solutions were successfully recovered as precipitates with high selectivity.

Contribution of dissolved platinum ions to heat dissipation in ytterbium–erbium glass under lamp pumping

Subject of study. The contribution of platinum ions dissolved in ytterbium–erbium phosphate glasses to the heating of active elements under lamp pumping is investigated in this study. Laser-quality glasses are synthesized in platinum crucibles; therefore, they always contain a certain amount of platinum depending on many factors. One of these factors is the duration of the melting process, which for erbium glasses is two or more times longer than that for neodymium glasses. This results in an elevated platinum content in the former. Methodand brief description of the experiement. Heat dissipation in an active element was determined using its relative elongation during the propagation of a pumping pulse. The elongation was obtained using an interferometric method. Glasses with different platinum contents were melted to determine the contribution of platinum ions to the overall heat dissipation of the active element. Experimental dependences of the platinum ion contribution to the overall heat dissipation on the concentration of platinum ions in LGS-KhCh glass (V. A. Kotel’nikov FIRE RAS) were obtained for active elements with sizes of ∅4×80mm. We established that up to 10% of the overall heat is generated in the absorption bands of the platinum ions in the active elements made of glass with a passive loss level corresponding to laser applications. The obtained data made it possible to explain the previously observed discrepancies between experimental data and the calculation results using a model of ytterbium–erbium and chromium–ytterbium–erbium active media proposed by the authors. The practical significance of this study is a recommendation of additional filtering of the pumping lamp radiation to reduce the heating of active elements formed of ytterbium–erbium glasses.

Secondary Dispersion Halos of Platinum and Palladium in the Shorzha Dunite-Peridotite Massif of the Sevan Ophiolite Belt of Armenia

Distribution of platinoids within the massifs of Sevan ophiolitic belt has been very poorly studied. As a result of the research implemented, a negative assessment of the prospects for platinum content of dunite-harzburgite massifs of Sevan ophiolitic zone was given [1,2].

Pyrolysis of Tibetan Yak Dung for Producing Biochar Pertinent to Agro-environmental Application

ABSTRACT The study was investigated the influence of pyrolysis conditions on the yield and nutrient properties of yak dung-based biochar and its potential of agro-environmental applications. A series of biochars were made by hydrothermal carbonization (HTC) under the different atmospheres, such as Nitrogen (N2) and carbon dioxide (CO2), processing temperatures (200-300 °C) and residence times (1-2 h). The results showed the yield of yak dung-based biochar ranges from 35.33 wt% to 58.29 wt%. The concentration of nitrogen (N), phosphorus (P) and potassium (K) in biochar varied from 28.18 mg·g−1 to 15.54 mg·g−1, 16.23 mg·g−1 to 25.31 mg·g−1 and 0.59 mg·g−1 to 1.02 mg·g−1, respectively. And the contents of micronutrients Zn and Fe varied from 4.6 mg·g−1 to 17.42 mg·g−1, and 15.28 mg·g−1 to 29.22 mg·g−1, respectively. The yield, total carbon (C), N, hydrogen (H) and oxygen (O) content of biochar decreased with increasing processing temperature, while the total P and K content, pH and Brunauer-Emmett-Teller (BET) surface area increased; moreover, the P and K content of biochar produced in N2 increased more compared with CO2. The heavy metal contents of copper (Cu), cadmium (Cd), chromium (Cr), platinum (Pb) and arsenic (As) all were lower in yak dung-based biochar compare with other manures or sewage sludge-based biochar. Biochar produced in N2 had higher nutrient content indicating the potential of application for fertilizer compared with it in CO2; while the biochar produced in CO2 with larger surface area characteristic and more abundant functional groups showing higher potential of application for the soil amendments and nutrient control materials. Our study provides some new insights for biochar production according to its application.

Preparation and Electrochemical Performance of a Graphene Cathode Catalyst Decorated With Pt by Prolysis

For fuel cells, to produce high-quality and low-platinum catalyst is a pressing technical problem. In this study, graphene cathode catalysts with controllable platinum content were decorated by pyrolyzing chloroplatinic acid under various process parameters to obtain a high catalytic activity and durability. The results show that platinum particles generated by pyrolyzing chloroplatinic acid are uniformly loaded on graphene without agglomeration. The average particle size of platinum particles is about 2.12 nm. The oxygen reduction reaction catalytic activity of catalyst samples first increases, then decreases with increasing platinum loading in cyclic voltammetry and LSV. Compared with the commercial Pt/C (20 wt% Pt) catalyst, the initial potential and the current density retention rate of the catalyst decorated with 8% platinum are 55 mV and 23.7% higher, respectively. From i-t curves, it was found that the stability of the catalyst prepared in this paper was improved compared with the commercial Pt/C catalyst. The catalysts prepared in the present research exhibits superior catalytic activity and stability.

Синтез германата висмута с кристаллической структурой эвлитина методом литья

The conditions for the preparation of a compound with an eulithine crystal structure (ESS) during the crystallization of a stoichiometric melt in the Bi2O3 – GeO2 system by casting have been investigated. The initial components (Bi2O3 and GeO2) were placed in a platinum crucible and heated to a temperature in zone C at a rate of ~ 20 °C/min, with holding under isothermal conditions for 1 h. Then, the melt was poured from the crucible onto a heated platinum plate. The macrostructure of the surface of the crystallized samples was observed using a Stemi 2000 stereoscope (Carl Zeiss), the microstructure was observed using a Carl Zeiss Axio Observer A1m optical microscope on microsections. X-ray phase analysis (XRD) of the powder was performed on a Shimadzu XRD 6000 diffractometer (Cu Kα radiation). Atomic absorption spectrometry was carried out on a SOLAAR M device. For the first time, the possibility of obtaining Bi4Ge3O12 with the eulithine crystal structure (ESS) by fusing a stoichiometric mixture of initial oxides and subsequent cooling of the melt by casting was experimentally shown. It is shown that when using this method, it is possible not only to achieve record rates of synthesis, but also to reduce the content of platinum (which is a harmful impurity) in the resulting material by 2 times.