Electrocatalysts for Fuel Cells and Water Electrolyzers: From Synthesis to Performance Evaluation at Realistic Reaction Conditions

Fuel cells and electrolyzers are key aspects for the storage and conversion of renewable energy. Due to the kinetic hindered oxygen reactions at the cathode or anode of fuel cells and electrolyzers, respectively, the improvement of those Pt and Ir based nanoparticle (NP) based catalysts is crucial for their application. In a first step an understanding of the NP synthesis including a size control is necessary, then the investigation of the activity and stability of the catalysts. Therefore, this dissertation deals with “Electrocatalysts for Fuel Cells and Water Electrolyzers: From Synthesis to Performance Evaluation at Realistic Reaction Conditions”. The polyol process enables the synthesis of “surfactant-free” NPs with tailored catalyst properties like the control of the particle size. A mechanistic investigation of the Pt NP synthesis in the polyol process can be achieved by slowing down the reduction process inducing the particle formation process by visible light. The particle size control by the OH-/Pt ratio as described previously in the polyol process can be confirmed in the visible-light-induced reduction. By systematically reducing different precursors in presence of the bases NaOH or Na(acac) it can be shown that the size of Pt NPs can be controlled additionally by the acac-/Pt ratio reaching a comparable size control at the respective OH-/Pt ratio. Besides the control by the anion/Pt ratio the character of the precursor seems to determine the particle size. The gas diffusion electrode (GDE) setup is presented as a straightforward testing device enabling the performance of accelerated stress tests (ASTs) of Pt/C catalysts under realistic conditions with respect to catalyst loading and temperature close to the conditions applied in fuel cells. The coupling to ex situ small angle X-ray scattering (SAXS) enables degradation studies comparing the change of the particle size and the electrochemically active surface area (ECSA) during the ASTs. Applying ASTs on catalysts with different initial particle sizes revealed similar end-of-treatment sizes. For a deeper understanding of the degradation mechanism, operando SAXS is performed during the application of ASTs. One of the main challenges in coupling SAXS to ASTs is the recording of a suitable background. In this work, the background measurement in transmission configuration is achieved by the vertical movement of the cell of the gas diffusion layer (GDL) experiencing the same electrochemical treatment. Thus, a bimodal catalyst consisting of two size populations, so that the electrochemical Ostwald ripening should be induced, could be studied. The same bimodal catalyst was investigated at a synchrotron in an operando SAXS study in grazing incidence configuration enabling the establishment of a depth profile of the degradation within the catalyst layer. Surprisingly, both studies are not clearly evidencing the expected electrochemical Ostwald ripening. “Surfactant-free” Ir NPs were synthesized with the colloidal so-called Co4Cat process performed in low boiling point solvents. These Ir NPs can be used as potential electrolyzer catalysts. Efforts to control the obtained particle size were performed by adjusting different synthesis parameters such as the temperature or water content. Furthermore, the GDE setup was adjusted to obtain a straightforward performance testing setup for electrolyzer catalysts reaching comparable results as compared to the rotating disk electrode (RDE) method, which is currently the standard testing device in basic research. It is shown that the used carbon based GDL is stable enough to perform performance tests. In addition, a straightforward way to prepare catalyst films on top of titanium based porous transport layers (PTLs) typically used in electrolyzers was developed. Using a simple hot-pressing of a Nafion membrane to the catalyst layer leads to comparable activity results as generated using a GDL. Kinetic studies assuming Arrhenius behavior enabled the determination of the electrochemical activation energy and the estimation of the exchange current density

Social Identities in the Policy Process of Authoritarian Systems.

The integration of the social-psychological social identity approach to policy process research has recently generated new insights on policy-making. Empirical applications for established democracies and multilevel settings such as the European Union have identified five general types of social identities that are relevant for the preferences and behavior of policy actors and their stability and change over time. Social identities are based on joint memberships in social groups, such as organizations, demographic/biographical identities, sectors, locations, and informal opportunities for exchange (which may result in programmatic groups and identities). Some of these social groups, above all pluralistic interest associations and political parties, are directly related to the settings of embedded democracies. This article sheds light on the traveling capacity of the Social Identities in the Policy Process (SIPP) perspective by applying it to the Russian political system. An analysis of policy actors' social identities in two federal ministries shows that in autocracies, interest intermediation, legitimacy, and influence on policy processes run through professional and informal groups when competing organizations and democratic institutions are absent. The results indicate that the SIPP perspective is adaptable to policy processes in different contexts but that the importance of identity types varies

Sexual and Reproductive Health during the COVID-19 Pandemic: Results from a Cross-Sectional Online Survey in Germany

The accumulated evidence maps the COVID-19 pandemic's diverse impacts on sexual and reproductive health (SRH);however, the precise changes in sexual behaviours and the underlying causes producing these changes are rarely considered. This study is aimed at assessing the changes in sexual behaviours during the COVID-19 pandemic in Germany, using quantitative methods, and it is also aimed at identifying the underlying reasons, using qualitative methods. It is a part of the broader I-SHARE project, which administered a cross-sectional online survey in 33 countries to describe the effects of the COVID-19 restrictions on different aspects of SRH. In the current study, a total of 611 adults from Germany are included. The findings demonstrate a decline in sexual satisfaction, as well as increases in sexual problems and partnership conflicts. Furthermore, the findings indicate an increase in pornography consumption and masturbation. Psychological stress, due to the pandemic, seemed to be the main reason for the changes in the participants' sexual behaviours, followed by a decrease in social contacts, and an increase in time resources. Thus, it is important to provide accessible clinical and psychosocial (online) interventions and services in order to maintain good sexual health in times of pandemic

A surrogate model for data-driven magnetic stray field calculations

In this contribution we propose a data-driven surrogate model for the prediction of magnetic stray fields in two-dimensional random micro-heterogeneous materials. Since data driven models require thousands of training data sets, FEM simulations appear to be too time consuming. Hence, a stochastic model based on Brownian motion, which utilizes an efficient evaluation of stochastic transition matrices, is applied for the training data generation. For the encoding of the microstructure and the optimization of the surrogate model, two architectures are compared, i.e. the so-called UResNet model and the Fourier Convolutional neural network (FCNN). Here we analyze two FCNNs, one based on the discrete cosine transformation and one based on the complex-valued discrete Fourier transformation. Finally, we compare the magnetic stray fields for independent microstructures (not used in the training set) with results from the FE$^2$ method, a numerical homogenization scheme, to demonstrate the efficiency of the proposed surrogate model

Health-related quality of life in adolescents and young adults with high functioning autism-spectrum disorder

Aim: Over the last years, health-related quality of life (HRQOL) has emerged as an important measure not only in somatic medicine but also in psychiatry. To date, there are only few reports on HRQOL in patients with autism-spectrum disorder (ASD). This study aimed at studying HRQOL in ASD patients with an IQ >70, using a self-report HRQOL questionnaire with cross-cultural validity

A randomized controlled trial on a smartphone self-help application (Be Good to Yourself) to reduce depressive symptoms

Accepted manuscript version, licensed CC BY-NC-ND 4.0. Published version available at https://doi.org/10.1016/j.psychres.2018.08.113.Depressive symptoms are common, yet only a subgroup of individuals receive adequate treatment. To reduce the treatment gap, several online self-help programs have been developed, yielding small to moderate effects. We developed a smartphone self-help application addressing depressive symptoms. We sought to evaluate its feasibility and efficacy in participants reporting a subjective need for help (a diagnosis of depression was not mandatory). We conducted a randomized controlled trial (N = 90). The primary outcome was a reduction of depressive symptoms measured with the Patient Health Questionnaire-9 (PHQ-9). Secondary outcomes included improved self-esteem (Rosenberg Self-Esteem Scale) and quality of life (WHOQOL-BREF). The intervention group obtained access to the application for four weeks, the wait-list group received access after the post assessment. No group differences emerged in either outcome in intention-to-treat analyses. Per protocol analyses with frequent users (i.e., several times a week or more) yielded a small effect size (η2p = 0.049) at trend level on the reduction of depressive symptoms in favor of the treatment group. However, 39% of the participants did not use the application frequently. Mobile self-help applications represent a promising addition to existing treatments, but it is important to increase patients’ motivation to use them

Investigating the Particle Growth in Bimodal Pt/C Catalysts by In-Situ Small-Angle X-ray Scattering: Challenges in the Evaluation of Stress Test Protocol-Dependent Degradation Mechanisms

The influence of different combinations of accelerated stress test (AST) protocols simulating load-cycle and start/stop conditions of a proton exchange membrane fuel cell (PEMFC) vehicle is investigated on a bimodal Pt/C catalyst. The bimodal Pt/C catalyst, prepared by mixing two commercial catalysts, serves as a model system and consists of two distinguishable size populations. The change in mean particle size was investigated by in situ small-angle X-ray scattering (SAXS). The comparison to the reference catalysts, i.e., the two single-size population catalysts, uncovers the presence of electrochemical Ostwald ripening as a degradation mechanism in the bimodal catalyst. Increasing the harshness of the applied AST protocol combinations by faster changing between load-cycle or start/stop conditions, the particle size of the larger population of the bimodal catalyst increases faster than expected. Surprisingly, the change in mean particle size of the smaller size population indicates a smaller increase for harsher AST protocols, which might be explained by a substantial electrochemical Ostwald ripening

Politikwissenschaftsstudierende und der 1. Mai 2004:Eine empirische Untersuchung zu Informiertheit, Wissen und Meinung von Hochschülern der Westfälischen Wilhelms-Universität Münster zur Osterweiterung der Europäischen Union

Seminar: Am Anfang steht das Problem: Einführung in die Durchführung empirischer Studien. Sommersemester 2004Dozentin: Susanne in der Smitten Forschungsprojekt im Rahmen der empirischen Sozialforschung Erstellungszeitraum: 19. April 2004 - 04. August 2004 Durchgeführt von: Martin Biederstedt, Dominik Bulla, Johanna Keifenheim, Maria Schröder, David Schulke</div

UV-induced syntheses of surfactant-free precious metal nanoparticles in alkaline methanol and ethanol

Surfactant-free UV-induced syntheses of Pt and Ir nanoparticles in alkaline methanol and ethanol are presented. Small size nanoparticles ca. 2 nm in diameter are obtained without surfactants in a wide range of base concentration

Vegetationsbrände Bayern : Projektbericht

In der vorliegenden Studie werden verschieden Waldbrandszenarien für Bayern vorgestellt und diskutiert