In-situ electrochemical quantification of active sites in Fe-N/C non-precious metal catalysts

The economic viability of low temperature fuel cells as clean energy devices is enhanced by the development of inexpensive oxygen reduction reaction catalysts. Heat treated iron and nitrogen containing carbon based materials (Fe–N/C) have shown potential to replace expensive precious metals. Although significant improvements have recently been made, their activity and durability is still unsatisfactory. The further development and a rational design of these materials has stalled due to the lack of an in situ methodology to easily probe and quantify the active site. Here we demonstrate a protocol that allows the quantification of active centres, which operate under acidic conditions, by means of nitrite adsorption followed by reductive stripping, and show direct correlation to the catalytic activity. The method is demonstrated for two differently prepared materials. This approach may allow researchers to easily assess the active site density and turnover frequency of Fe–N/C catalysts

A catalyst layer optimisation approach using electrochemical impedance spectroscopy for PEM fuel cells operated with pyrolysed transition metal-N-C catalysts

AbstractThe effect of the ionomer to carbon (I/C) ratio on the performance of single cell polymer electrolyte fuel cells is investigated for three different types of non-precious metal cathodic catalysts. Polarisation curves as well as impedance spectra are recorded at different potentials in the presence of argon or oxygen at the cathode and hydrogen at the anode. It is found that a optimised ionomer content is a key factor for improving the performance of the catalyst. Non-optimal ionomer loading can be assessed by two different factors from the impedance spectra. Hence this observation could be used as a diagnostic element to determine the ideal ionomer content and distribution in newly developed catalyst-electrodes. An electrode morphology based on the presence of inhomogeneous resistance distribution within the porous structure is suggested to explain the observed phenomena. The back-pressure and relative humidity effect on this feature is also investigated and supports the above hypothesis. We give a simple flowchart to aid optimisation of electrodes with the minimum number of trials

Laser-driven charged particle transport in warm dense matter and plasma

[EN]This thesis focuses on the physics of intense laser-generated charged particle beam transport. The two important applications related to inertial confinement fusion and particle acceleration: (i) the transport and collimation of fast electrons created in high intensity laser-matter interactions, and (ii) ion stopping power close to the Bragg peak in extreme states of matter. Both topics have been investigated in an integrated approach that combines experimental campaigns with detailed theoretical and numerical studies used to support the experiments both in the design prior to the experiments being carried out, and in the analysis of the experimental results afterwards. The experiments presented here are are the result of a long and extended collaboration with research institutions across the EU and abroad—without whom this work would not been possible. The most important results achieved in this work can be stated as following: • A first detailed parametric investigation of relativistic electron beam collimation as a controllable and reproducible technique by using the double pulse technique for fast Ignition and laser-particle and radiation sources acceleration. • The establishment of a dedicated workstation for laser-driven ion sources implementation for applications including generation, selection and transport of proton beams. • A first experimental measurement of proton stopping power close to the Bragg peak region in Warm Dense Matter for laser Inertial Confinement Fusion and proton particle applications using laser-driven ion sources

Ottimizzazione di codici di simulazione di esperimenti di mappatura di corrente in dispositivi nanoelettronici

Nella tesi vengono analizzati possibili metodi per l'utilizzo della tecnica delle funzioni di Green ricorsive al fine di implementare un programma per la simulazione di esperimenti di mappatura di corrente in dispositivi nanoelettronici. Gli algoritmi proposti sono analizzati e comparati, al fine di scegliere la soluzione più adatta per le esigenze presenti

Electrocatalytic and catalytic oxygen reduction utilising transition metal and heteroatom doped carbon materials

The commercialisation of polymer electrolyte fuel cells (PEFCs) is partly delayed due to the use of expensive and scarce precious metal catalysts for the oxygen reduction reaction (ORR). Transition metal and nitrogen containing carbon materials (M-N/C) could potentially replace Pt. However, the activity and stability is still too low. This is due to a lack in the understanding of the active site, a difficulty in determining intrinsic catalyst parameters and the challenges posed by the higher catalyst loading in fuel cells. A new precursor was identified. It can be doped with different metal centres and readily forms self-supporting ORR active carbon catalysts upon pyrolysis. Physicochemical characterisations of the Fe-N/C material suggests atomic metal centres as active sites. A proton coupled electron transfer is presumably the rate determining step. The catalyst is exceptionally poison tolerant against a wide range of compounds that affect Pt based materials. It was found that nitrite and nitric oxide interact with the active site(s). Fundamental insight was gained and it seems that two different types of metal centred active sites are present within Fe-N/C catalysts. A methodology was developed to electrochemically count one type of those active sites by means of reductive nitrite stripping in a conventional rotating disk electrode (RDE) setup. It is possible to estimate the turnover frequency and active site density. The material also catalyses the epoxidation of alkenes at room temperature and ambient pressure, suggesting a similar working principle as transition metal macrocycles. A study of M-N/C catalysts in operating PEFCs has been conducted. The catalyst layer was investigated by means of impedance spectroscopy. The peculiar 45 degree feature and its deviation in the impedance spectrum can be used to determine the optimal ionomer content in the catalyst layer and therefore speed up the investigation in single cells.Open Acces

Judicial acts and judicial life in modern society

Artykuł ten przedstawia problem określania kategorii aktów prawnych w prawie procesowym. Autorki sugerują, że przyjęte akty prawne są sposobami realizacji życia sądowego w nowoczesnym społeczeństwie. Aktywność sądowa jest spójna i logiczna, ze względu na przyjęte przez sądy wyższej instancji orzeczenia sądowe. Autorki zapewniają w artykule przegląd danych statystycznych na temat wydajności Sądu Najwyższego Federacji Rosyjskiej do spraw cywilnych, spraw do rozstrzygania sporów gospodarczych, spraw wykroczeń administracyjnych i innych.This article discusses the problem of determining the categories of judicial acts in procedural law. The authors suggest that the adopted legal acts are the means of implementation of the judicial life in modern society. Judicial life takes consistent and logical due to adopted by higher courts enforcement of judicial decisions. Authors provide an overview of statistical data on the performance of the Supreme Court of the Russian Federation for civil affairs, affairs of for settling economic disputes, cases of administrative offenses and others

Kinetic isotope effect in the oxygen reduction reaction (ORR) over Fe-N/C catalysts under acidic and alkaline conditions.

Heat treated Fe-N/C materials which are highly effective oxygen reduction catalysts in alkaline and acid, show a significant kinetic isotope effect (KIE). The values in acid (~3.4) and alkaline (~2.5) are much larger than the value for the metal free catalyst in acid (~1.8) suggesting that the rate determining step (RDS) is a proton coupled electron transfer in acid with a significant pathway involving a proton independent step under an alkaline environmen

Krylov Methods for Large Sparse Systems: A Comprehensive Overview

In this paper are analyzed behavior and properties for different Krylov methods applied in different categories of problems. These categories often include PDEs, econometrics and network models, which are represented by large sparse systems. For our empirical analysis are taken into consideration size, the density of non-zero elements, symmetry/un-symmetry, eigenvalue distribution, also well/ill-conditioned and random systems. Convergence, approximation error and residuals are compared for the full version of methods, some restarted methods and preconditioned methods. Two preconditioners are considered respectively, ILU(0) and IC(0) by using at least five preconditioning techniques. In each case, empirical results show which technique is best to use based on properties of the system and are backed up by general theoretical information already found on Krylov space methods

Regional legal policy: a comparative analysis of information resources

Artykuł bazuje na analizie porównawczej informacji krajowych zasobów regionalnej polityki prawnej. Zawiera sugestie na temat optymalizacji informacji w celu zwiększenia (poprawy) efektywności wykorzystania zasobów prawa i norm prawnych dla poprawy jakości życiaThis article on the basis of a comparative analysis of national information resources regional legal policy suggestions on optimizing this information file in order to improve the efficiency of resource use legal, legal standards and quality of lif

Alternative uses of shipbuilding and ship repair facilities of Sevastopol

У статті розглядається досвід альтернативного використання суднобудівно-судноремонтних потужностей міста Севастополя, причини перепрофілювання підприємств галузі та можливі варіанти допомоги існуючим заводам м. Севастополя і України в цілому. Крім того, в статті коротко розглянуто відповідний міжнародний досвід диверсифікації та розвитку підприємств судноремонтно-суднобудівної галузі