Surface Properties of Graphite for Efficient Electrocatalysis of Vanadium Redox Reactions

Die Ergebnisse dieser Arbeit tragen zu einem tieferen Verständnis der kinetischen Prozesse in Vanadium-Redox-Flow-Batterien bei. Dafür wurden die elektrokatalytischen und physikochemischen Eigenschaften von industriell relevantem Graphitfilz und verwandten kohlenstoffbasierten Materialien untersucht. Der Einsatz von mehrere spektroskopischen und mikroskopischen Methoden ermöglichte die Abbildung verschiedener Skalen der Mikrostruktur, die chemische Zusammensetzung, die elektronische Struktur und schließlich die kinetischen Vorgänge mittels theoretischen Berechnungen und spektro-elektrochemischen Untersuchungen. Aufgrund widersprüchlicher Ergebnisse in der Literatur im Themenkomplex funktionelle Sauerstoffgruppen hat sich die Arbeit zum Ziel gesetzt, eindeutige Zusammenhänge zwischen Oberflächenstruktur und Elektrokatalyse herzustellen. Die Analyse von Eigenschaften chemisch und strukturell modifizierter Elektroden vor und nach elektrochemischen Tests führte zur Identifizierung graphitischer Defekte als aktive Zentren. Nach der vollständigen Entfernung von Sauerstoff ergaben sich wasserstoffterminierte Defekte anstelle von Oberflächengruppen als Ursache für die katalytische Aktivität. Die Anbringung von Pyrenen mit unterschiedlichen Funktionalitäten auf der Graphitoberfläche diente zum Nachweis der Effekte einzelner Sauerstoffgruppen. Um die Auswirkung der verschiedenen Defekt-Geometrien zu spezifizieren, wurden durch thermochemische Aktivierungen Kohlenstoffatome in Modell- und realen Elektroden durch Phosphor substituiert. Unter gezielter Berücksichtigung aller dabei veränderten Elektrodeneigenschaften konnte so die elektrochemische Aktivität deutlich gesteigert werden. Die Untersuchung der elektronischen Struktur von polyzyklischen aromatischen Kohlenwasserstoffen verband die elektrokatalytische Aktivität mit der Elektrodenarchitektur und der Austrittsarbeit. Theoretische Modellierungen definierten Wechselwirkungen zwischen den solvatisierten Vanadium-Ionen und der Substrate durch verschiedene wasserstoff- und sauerstoffterminierte Kanten. Schließlich formuliert die Arbeit durch die Untersuchung der Elektrode–Elektrolyt-Grenzfläche bei angelegtem Potential einen experimentell und rechnerisch gestützten, innovativen Reaktionsmechanismus

2021: A Surface Odyssey. Role of Oxygen Functional Groups on Activated Carbon‐Based Electrodes in Vanadium Flow Batteries

The market breakthrough of vanadium flow batteries is hampered by their low power density, which depends heavily on the catalytic activity of the graphite-based electrodes used. Researchers try to increase their performance by thermal, chemical, or electrochemical treatments but find no common activity descriptors. No consistent results exist for the so-called oxygen functional groups, which seem to catalyze mainly the V$^{III}$/V$^{II}$ but rarely the V$^{V}$O$_{2}$$^{+}$/V$^{IV}$O$^{2+}$ redox reaction. Some studies suggest that the activity is related to graphitic lattice defects which often contain oxygen and are therefore held responsible for inconsistent conclusions. Activation of electrodes does not change one property at a time, but rather surface chemistry and microstructure simultaneously, and the choice of starting material is crucial for subsequent observations. In this contribution, the literature on the catalytic and physicochemical properties of activated carbon-based electrodes is analyzed and evaluated. In addition, an outlook on possible future investigations is given to avoid the propagation of contradictions

Edge Site Catalyzed Vanadyl Oxidation Elucidated by Operando Raman Spectroscopy

The kinetic processes responsible for the efficient oxidation of dissolved vanadyl oxide species in the positive half-cell of a vanadium flow battery are far from being understood. Despite recent evidence that the reaction is most strongly favored at hydrogen-terminated graphite edge sites, a mechanism involving oxygen-containing surface groups has still been frequently reproduced to date. In this work, operando Raman spectroscopy follows the reaction at the interface between graphite-based model electrodes and vanadium-containing sulfuric acid as the electrolyte. The potential-dependent growth of different vibrational modes is related to the electrocatalytic activity of the sample and allows to track the oxidation of the electrolyte species. Moreover, the results express vanadium reaction intermediates of dimeric origin only on the edge-exposed surface of graphite, which exhibits significantly higher electrochemical activity. No interaction with surface oxygen postulated before could be observed for the active electrodes at potentials relevant to the reaction. Instead, a new growing graphite-related feature shows direct electronic interactions between vanadium ions and carbon atoms during charge transfer

Learn to crawl, learn to walk, learn the structures on which society is based on! : about how teenagers use of public space through the impact of gender roles

Arbetet söker svar på hur 12-16 åringars rumsanvändning i offentliga rum påverkas av könsroller utifrån konstruktivismens perspektiv på könet som en konstruktion av miljön vi lever i. Syftet med arbetet är att skapa underlag för fortsatt forskning kring genusmedveten planering och gestaltning av landskapsrummet. För att besvara frågeställningen har flera metoder, litteraturstudier, observationer och enkätsvar. Grundpelare för arbetet är filosofiteoretiska perspektiv på könsskapandet, utvecklingspsykologi utifrån målgruppen 12-16 år samt könsnormativt rumsanvändande. Avslutningsvis har slutsatsen dragits att 12-16 åringens rumsanvändande på många sätt är påverkade av könsnormer, men också som anledning till fortsatt könsnormativ rumsanvändning.The essay seeks answers to how 12-16 year olds is influenced by gender roles in their use of public spaces. This based on the perspective of constructivism on the sex as a social construction of society. The purpose of the work is to provide a foundation for further research on gender conscious planning and landscaping. To answer the question, several methods as literature studies, observations and questionnaire answers are used. Fundamentals for the work are philosophytheoretical perspectives on gender roles, developmental psychology based on the target group 12-16 years, as well as gender normative use of space. In conclusion, it has been concluded that the use of space in the 12-16 years is in many ways affected by gender norms, but also as a reason for continued gender-normative using of space

Youthground : a Design Proposal for the Youthcenter Tegelhuset in Rosengård, Malmö

Examensarbetet Ungdomsplats - Ett gestaltningsförslag för fritidsgården Tegelhuset i Rosengård, Malmö är ett gestaltningsförslag framtaget genom metoden Research-for-design, utifrån konceptet forskningsbaserad landskapsarkitektur. Arbetet grundar sig i författarens intresse för ungdomars rätt till staden och behov av utemiljöer som utvecklats under landskapsarkitektutbildningen. I arbetet trianguleras praktisk kunskap, litteraturstudier och det specifika uppdraget - för att sammanföra det vetenskapliga arbetssättet och designprocessen inom landskapsarkitekturkontexten. Målet med det framtagna gestaltningsförslaget var att, genom research-for-design, ta fram ett socialt hållbart gestaltningsförslag utifrån platsens unika förutsättningar med fokus på att försöka exemplifiera hur en plats kan göras välkomnande och trygg för ungdomarna som besöker platsen. Slutsatserna är av dels av generell karaktär kring hur ungomsplatser kan utformas och, dels platsspecifika för just fritidsgårdens utemiljö. Detta beror på examensarbetets två syften; Det första syftet avser att bidra till att utveckla kunskapen kring gestaltad utemiljö och stadsplanering med ungdomars behov i fokus, generellt, och det andra att genom ett gestaltningsförslag exemplifiera och inspirera fastighetsägare, Malmö stad och fritidsgårdens verksamhet att utveckla fritidsgårdens utemiljö, specifikt. Gestaltningsförslaget är, av den anledningen, också en del av slutsatserna som presenteras i arbetet.The master thesis Youthground - A Design Proposal for the Youthcenter Tegelhuset in Rosengård, Malmö is a landcape design project, produced based on the method Research-for-design from the concept of Landscape design based on research. The thesis is based on the writers intrest in youths right to the city and their needs av outdoor environments, that have been developed during her education in landskape architecture. From the metod of Research-for-design, the three concepts practical knowledge, litterature studies and the specific project is trangulated as a way to intertwine the scientific field of work with the landscape arkitect's design process. And aims, with the choosed method, to present a design proposal based on the specific site's preconditions with a focus on trying to state an example on how a site can be designed to become an attractive and comfortable place for youths visiting the youthcenter. The conlusion is divided in to two different level of detail that are evaluated in the thesis; one of the conclusion subsumes how sites for youths can be designed in a generall way, and the second one embraces the site specific solutions for the specific site in the proposal. In short, this is due to the two purpose of the thesis. The general purpose of the thesis is to contribute with knowledge about outdoor environments for youths, and lastly, the second purpose is to inspire the municipality Malmö stad, the property owner, and the youthcenter to evolve the specific site. By that, the design proposal is both an example of, and a conclusion, in itself

Origin of the catalytic activity at graphite electrodes in vanadium flow batteries

For many electrochemical devices that use carbon-based materials such as electrolyzers, supercapacitors, and batteries, oxygen functional groups (OFGs) are considered essential to facilitate electron transfer. Researchers implement surface-active OFGs to improve the electrocatalytic properties of graphite felt electrodes in vanadium flow batteries. Herein, we show that graphitic defects and not OFGs are responsible for lowering the activation energy barrier and thus enhance the charge transfer properties. This is proven by a thermal deoxygenation procedure, in which specific OFGs are removed before electrochemical cycling. The electronic and microstructural changes associated with deoxygenation are studied by quasi in situ X-ray photoelectron and Raman spectroscopy. The removal of oxygen groups at basal and edge planes improves the activity by introducing new active edge sites and carbon vacancies. OFGs hinder the charge transfer at the graphite–electrolyte interface. This is further proven by modifying the sp2 plane of graphite felt electrodes with oxygen-containing pyrene derivatives. The electrochemical evolution of OFGs and graphitic defects are studied during polarization and long-term cycling conditions. The hypothesis of increased activity caused by OFGs was refuted and hydrogenated graphitic edge sites were identified as the true reason for this increase

Work Function Describes the Electrocatalytic Activity of Graphite for Vanadium Oxidation

In many applications such as vanadium flow batteries, graphite acts as an electrocatalyst and its surface structure therefore determines the efficiency of energy conversion. Due to the heterogeneity of the material, activity descriptors cannot always be evaluated with certainty because the introduction of defects is accompanied by a change in surface chemistry. Moreover, surface defects occur in multiple dimensions, and their occurrence and influence on catalysis must be separated. In this work, we have studied the surface of graphite felt electrodes by different methods in terms of morphology and chemistry to understand the electrocatalytic activity. We then defined the interaction between the surface and the electronic structure with particular emphasis on the work function and valence band. Using model catalysts with different architectures, we established correlations between the electrocatalytic activity and the size of the conjugation and the orientation of the edges. Finally, it was possible to link the level of the work function to the electrocatalytic activity

Structure–activity correlation of thermally activated graphite electrodes for vanadium flow batteries

Thermal activation of graphite felts has proven to be a valuable technique for electrodes in vanadium flow batteries to improve their sluggish reaction kinetics. In the underlying work, a novel approach is presented to describe the morphological, microstructural, and chemical changes that occur as a result of the activation process. All surface properties were monitored at different stages of thermal activation and correlated with the electrocatalytic activity. The subsequently developed model consists of a combined ablation and damaging process observed by Raman spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. Initially, the outermost layer of adventitious carbon is removed and sp(2) layers of graphite are damaged in the oxidative atmosphere, which enhances the electrocatalytic activity by introducing small pores with sharp edges. In later stages, the concentration of reaction sites does not increase further, but the defect geometry changes significantly, leading to lower activity. This new perspective on thermal activation allows several correlations between structural and functional properties of graphite for the vanadium redox couple, describing the importance of structural defects over surface chemistry

Establishing the regional sustainable developmental role of universities—from the multilevel-perspective (Mlp) and beyond

This article establishes the multilevel perspective (MLP) as one of the main research approaches in transition research to study complex systemic change processes in socio-technical systems at different structural levels. The application of the MLP to the higher education system, especially to conceptualize the transition of universities towards a sustainable (regional) developmental role, is still in its infancy. Through using a descriptive narrative analysis of seminal articles, the results of the four-years cooperation within an expert working group, and own empirical findings, the present paper investigates the suitability of the MLP to study the transition of universities and university systems towards a sustainable developmental role in the regional context. Based on these investiga-tions, three further perspectives (which must be considered for establishing a more comprehensive understanding of the universities’ sustainable developmental role) are identified and conceptualized: (a) The target dimension of sustainable regional development, (b) the role of agency, and (c) the introduction of space and place to multiscalar regional transitions. Based on these perspectives, a future research agenda beyond the MLP is developed. © 2021 by the authors. Licensee MDPI, Basel, Switzerland