Nanostructured platinum based catalysts for electrooxidation of small organic molecules prepared by microemulsion method

Pronalazak novih materijala koji bi omogućili komercijalizaciju gorivnih spregova i doprineli smanjenju upotrebe fosilnih goriva u proizvodnji energije je od velikog značaja za razvoj savremenog društva. Zbog toga je broj naučnih radova posvećen ovom problemu u značajnom porastu tokom proteklih godina. Kada je u pitanju oksidacija malih organskih molekula kao potencijalnih goriva za gorivni spreg, pored problema visoke cene platine koja se koristi kao katalizator, prisutan je i problem trovanja površine platine ugljen-monoksidom koji se formira kao intermedijar anodne reakcije. U ovom radu nanočestice platine na ugljeničnom nosaču sintetizovane su mikroemulzionim postupkom. Dodatkom različitih količina aditiva HCl tokom sinteze (od 0 do 35 %) ispitan je uticaj dodatka aditiva na oblik nanočestica. Pri optimalnoj koncentraciji od 25% HCl sintetizovane su nanočestice kubnog oblika. Četiri sintetizovana katalizatora okarakterisana su termogravimetrijskom analizom (TGA), rendgenskom difrakcijom X-zraka (XRD), transmisionom elektronskom mikroskopijom (TEM) i transmisionom elektronskom mikroskopijom visoke rezolucije (HRTEM). Ovim metodama potvrđena je promena oblika nanočestica izazvana dodatkom aditiva, utvrđen je udeo metala u katalizatoru (20%) i određena je veličina čestica, koja raste sa porastom udela aditiva (od 4 do 8 nm prema TEM analizi). Elektrohemijskom karakterizacijom i ispitivanjem reakcija oksidacije mravlje kiseline i metanola na ovim katalizatorima, ustanovljeno je da katalizator sa nanočesticama kubnog oblika, i većim udelom preferencijalno orijentisanih ravni (100) pokazuje bolju aktivnost za ove reakcije od katalizatora Pt sa konvencionalnim kub-oktaedarskim česticama. Razlog tome leži u lakšem uklanjanju adsorbovanog CO sa površine nanočestica sa zastupljenim kubnim oblikom.Development of novel materials that would enable the commercialization of fuel cell technology and contribute to reduction of fossil fuel usage in energy production is of great importance for the progress of modern society. As a result, the number of scientific papers devoted to this problem is in a significant increase over the past years. When it comes to the oxidation of small organic molecules (SOM) as potential fuel for the fuel cells, in addition to the problem of the high price of platinum used as a catalyst, there is a problem of poisoning the platinum surface by carbon-monoxide formed as an intermediate in the anodic reaction. In this research carbon supported platinum nanoparticles were synthesized by a water-in-oil microemulsion synthesis procedure. The effect of HCl as a capping agent on nanoparticle shape was investigated by adding up to 35 % HCl in the water phase of the microemulsion. The optimal HCl amount was found to be 25%, in which case platinum was synthesized in the form of cubic-shaped nanoparticles. Four prepared catalysts were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD) and (high resolution) transmission electron microscopy (HR)TEM. These analyses confirmed the change in particle shape induced by the capping agent. Metal loading in catalyst powder was determined to be close to 20%, and the particle size calculated from TEM data went from 4 to 8 nm, with the increase of the HCl amount used. The electrochemical characterization and the investigation of these samples in the reactions of formic acid and methanol oxidation revealed improved catalytic performance of the sample that predominantly contained cubic-shaped nanoparticles compared to conventional cube-octahedron shaped particles. The reason of the improved activity and stability of this catalyst lies in the facilitated CO removal from the catalyst surface, and thus improved tolerance to surface poisoning

Electrochemical oxidation of methanol on Pt/(RuxSn1-x)O2 nanocatalyst

The Ru-doped SnO2 powder, (RuxSn1-x)O2, with the Sn:Ru atomic ratio of 9:1 was synthesized and used as a support for Pt nanoparticles (30 mass% loading). The (RuxSn1-x)O2 support and Pt/(RuxSn1-x)O2 catalyst were characterized by X-ray diffraction, energy dispersive X-ray spectroscopy and transmission electron microscopy (TEM). (RuxSn1-x)O2 was found to be two-phase material consisting of probably solid solution of RuO2 in SnO2 and pure RuO2. The average Pt particle size determined by TEM was 5.3 nm. Cyclic voltammetry of Pt/(RuxSn1-x)O2 indicated good conductivity of the sup-port and displayed usual features of Pt. The results of the electrochemical oxidation of COads and methanol on Pt/(RuxSn1-x)O2 were compared with those on commercial Pt/C and PtRu/C catalysts. Oxidation of COads on Pt/(RuxSn1-x)O2 starts at less positive potentials than on PtRu/C and Pt/C. Potentiodynamic polarization curves and chronoamperometric curves of methanol oxidation indicated higher initial activity of Pt/(RuxSn1-x)O2 catalyst compared to PtRu/C, but also a greater loss in the current density over time. Potentiodynamic stability test of the catalysts revealed that deactivation of the Pt/(RuxSn1-x)O2 and Pt/C was primarily caused by the poisoning of Pt surface by the methanol oxidation residues, which mostly occurred during the first potential cycle. In the case of PtRu/C the poisoning of the surface was minor and deactivation was caused by the PtRu surface area loss. [Projekat Ministarstva nauke Republike Srbije, br. ON-172054

Combined approach of density functional theory and quantum Monte Carlo method to electron correlation in dilute magnetic semiconductors

We present a realistic study for electronic and magnetic properties in dilute magnetic semiconductor (Ga,Mn)As. A multi-orbital Haldane-Anderson model parameterized by density-functional calculations is presented and solved with the Hirsch-Fye quantum Monte Carlo algorithm. Results well reproduce experimental results in the dilute limit. When the chemical potential is located between the top of the valence band and an impurity bound state, a long-range ferromagnetic correlations between the impurities, mediated by antiferromagnetic impurity-host couplings, are drastically developed. We observe an anisotropic character in local density of states at the impurity-bound-state energy, which is consistent with the STM measurements. The presented combined approach thus offers a firm starting point for realistic calculations of the various family of dilute magnetic semiconductors.Comment: 5 pages, 4 figure

Sanitation of blackwater via sequential wetland and electrochemical treatment

The discharge of untreated septage is a major health hazard in countries that lack sewer systems and centralized sewage treatment. Small-scale, point-source treatment units are needed for water treatment and disinfection due to the distributed nature of this discharge, i.e., from single households or community toilets. In this study, a high-rate-wetland coupled with an electrochemical system was developed and demonstrated to treat septage at full scale. The full-scale wetland on average removed 79 +/- 2% chemical oxygen demand (COD), 30 +/- 5% total Kjeldahl nitrogen (TKN), 58 +/- 4% total ammoniacal nitrogen (TAN), and 78 +/- 4% orthophosphate. Pathogens such as coliforms were not fully removed after passage through the wetland. Therefore, the wetland effluent was subsequently treated with an electrochemical cell with a cation exchange membrane where the effluent first passed through the anodic chamber. This lead to in situ chlorine or other oxidant production under acidifying conditions. Upon a residence time of at least 6 h of this anodic effluent in a buffer tank, the fluid was sent through the cathodic chamber where pH neutralization occurred. Overall, the combined system removed 89 +/- 1% COD, 36 +/- 5% TKN, 70 +/- 2% TAN, and 87 +/- 2% ortho-phosphate. An average 5-log unit reduction in coliform was observed. The energy input for the integrated system was on average 16 +/- 3 kWh/m(3), and 11 kWh/m(3) under optimal conditions. Further research is required to optimize the system in terms of stability and energy consumption

Instrumentation for fluorescence lifetime measurement using photon counting

We describe the evolution of HORIBA Jobin Yvon IBH Ltd, and its time-correlated single-photon counting (TCSPC) products, from university research beginnings through to its present place as a market leader in fluorescence lifetime spectroscopy. The company philosophy is to ensure leading-edge research capabilities continue to be incorporated into instruments in order to meet the needs of the diverse range of customer applications, which span a multitude of scientific and engineering disciplines. We illustrate some of the range of activities of a scientific instrument company in meeting this goal and highlight by way of an exemplar the performance of the versatile DeltaFlex instrument in measuring fluorescence lifetimes. This includes resolving fluorescence lifetimes down to 5 ps, as frequently observed in energy transfer, nanoparticle metrology with sub-nanometre resolution and measuring a fluorescence lifetime in as little as 60 μs for the study of transient species and kinetics

Semiconductor Spintronics

Spintronics refers commonly to phenomena in which the spin of electrons in a solid state environment plays the determining role. In a more narrow sense spintronics is an emerging research field of electronics: spintronics devices are based on a spin control of electronics, or on an electrical and optical control of spin or magnetism. This review presents selected themes of semiconductor spintronics, introducing important concepts in spin transport, spin injection, Silsbee-Johnson spin-charge coupling, and spindependent tunneling, as well as spin relaxation and spin dynamics. The most fundamental spin-dependent nteraction in nonmagnetic semiconductors is spin-orbit coupling. Depending on the crystal symmetries of the material, as well as on the structural properties of semiconductor based heterostructures, the spin-orbit coupling takes on different functional forms, giving a nice playground of effective spin-orbit Hamiltonians. The effective Hamiltonians for the most relevant classes of materials and heterostructures are derived here from realistic electronic band structure descriptions. Most semiconductor device systems are still theoretical concepts, waiting for experimental demonstrations. A review of selected proposed, and a few demonstrated devices is presented, with detailed description of two important classes: magnetic resonant tunnel structures and bipolar magnetic diodes and transistors. In most cases the presentation is of tutorial style, introducing the essential theoretical formalism at an accessible level, with case-study-like illustrations of actual experimental results, as well as with brief reviews of relevant recent achievements in the field.Comment: tutorial review; 342 pages, 132 figure