Suchergebnisse

Catalysts and electmcatalysts are crucial for energy production and storage. To develop cost-efficient systems taking advantage of functionalized surfaces, the catalysts can be synthesized as nanomaterials or thin films. In this work, cobalt thin films were deposited on low-alloyed steel using magnetron sputtering. The films are uniform with a smooth surface and a thickness of similar to 400 nm. The films were electrochemically oxidized via anodization to a mix of cobalt oxides, one of them being Co3O4, at room temperature in an alkaline solution. The electrocatalytic performances of the anodized films were evaluated in 1 M KOH electrolyte saturated with oxygen. Cathodic currents in -0.5 mA/cm(2) range, corresponding to oxygen reduction reaction (ORR) activity, were measured with cyclic voltammetry. The catalytic activity of the films was evaluated as a function of time. The anodized Co coating exhibited three times higher activity than the steel substrate. The kinetics for the ORR were evaluated through Tafel plots and a slope of 226 mV/decade was found. Post-ORR characterization of the films revealed hexagonal plate-like oxide particles on the surface. After 50 cyclic voltammograms, the film was further oxidized, indicating that the ORR activity also affects the overall surface state of the film. This study demonstrates that thin films, after electrochemical modification, can be electrocatalysts for the oxygen reduction reaction and potentially used for applications in energy production and storage. ; Funding Agencies|competence center FunMat-II - Swedish Agency for Innovation Systems (VINNOVA)Vinnova [2016-05156]; VINNOVAVinnova [2018-04291]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]

With the current global greenhouse gas emissions, our remaining carbon budget is depleted in only 7 years. After that, several biophysical systems are predicted to collapse such as the arctic ice, coral reefs and the permafrost, leading to potentially irreversible consequences. Our emissions are strongly correlated to access of energy and even if we are aware of the planetary emergency today, our emissions still continue to grow. Electrical vehicles have the possibility to reduce the emissions in the transportation sector significantly. However, these vehicles are still expensive and impractical for long-distance or heavy transportation. While political actions and technological development are essential to keep prices down, the driving dis- tance can be increased by replacing the batteries for onboard electricity production. In hydrogen fuel cells, electricity is produced by combining hydrogen gas (H2) and oxygen with only water as the by-product and if employed in electrical vehicles, distances of 500 km are enabled with a refueling time in 5 minutes. For other uses than in vehicles, H2 is also promising for large-scale electricity storage and for several industrial processes such as manufacturing CO2-free steel, ammonia and synthetic fuels. However, today most H2 production methods relies on fossil fuels and releases huge amounts of CO2. Electrolysis of water is an alternative production method where H2, along with oxygen are produced from water. To split the water, electricity has to be added and if renewable energy sources are used, the method has zero emissions and is considered most promising for a sustainable hydrogen energy economy. The tech- nique is relatively expensive compared to the fossil fuel-based methods and relies on rare noble metals such as platinum as catalysts for decreasing the required energy to split water. For large scale productions, these metals need to be replaced by more sustainable and abundant catalysts to lower the cost and minimize the environmental impacts. In this thesis we have investigated such candidates for the water splitting reaction but also to some extent for the oxygen reduction reaction in fuel cells. By combining theory and experiments we hope to aid in the development and facilitate a transition to clean hydrogen energy. We find among other things that i) defects in catalytic materials plays a significant role the performance and efficiency, and that ii) heterogeneity influence the adsorption energies of reaction intermediates and hence the catalytic efficiency and iii) while defects are not often studied for electrocatalytic reactions, these may inspire for novel materials in the future.

This is the final version. Available on open access from Wiley via the DOI in this record ; Simple, yet versatile, methods to functionalize graphene flakes with metal (oxide) nanoparticles are in demand, particularly for the development of advanced catalysts. Herein, we report a laserassisted, continuous, solution route for the simultaneous reduction and modification of graphene oxide with catalytic nanoparticles. Electrochemical graphene oxide (EGO) was used as both the starting material and electron-hole pair source due to its low degree of oxidation, which imparts structural integrity and an ability to withstand photo-degradation. Simply illuminating a stream containing EGO and metal salt precursor solutions(e.g. H2PtCl6 or RuCl3) with a 248 nm wavelength laser produced reduced EGO (rEGO, oxygen content 4.0 at.%) flakes decorated with Pt (~2.0 nm) or RuO2 (~2.8 nm) nanoparticles. The RuO2-rEGO flakes exhibited superior catalytic activity for the oxygen evolution reaction, requiring a small overpotential of 225 mV to reach a current density of 10 mA cm−2 . Whereas, the Pt-rEGO flakes shows significantly enhanced mass activity for the hydrogen evolution reaction and a similar performance for oxygen reduction reaction compared to a commercial 20% Pt/C catalyst. This simple production method was also used to deposit PtPd alloy and MnOx nanoparticles on rEGO , demonstrating its versatility in synthesizing functional nanoparticle-modified graphene materials. ; University of Manchester ; Engineering and Physical Sciences Research Council (EPSRC) ; European Union Horizon 2020

The activity degradation of hydrogen-fed proton exchange membrane fuel cells (H2-PEMFCs) in the presence of even trace amounts of carbon monoxide (CO) in the H2 fuel is among the major drawbacks currently hindering their commercialization. Although significant progress has been made, the development of a practical anode electrocatalyst with both high CO tolerance and stability has still not occurred. Currently, efforts are being devoted to Pt-based electrocatalysts, including (i) alloys developed via novel synthesis methods, (ii) Pt combinations with metal oxides, (iii) core–shell structures, and (iv) surface-modified Pt/C catalysts. Additionally, the prospect of substituting the conventional carbon black support with advanced carbonaceous materials or metal oxides and carbides has been widely explored. In the present review, we provide a brief introduction to the fundamental aspects of CO tolerance, followed by a comprehensive presentation and thorough discussion of the recent strategies applied to enhance the CO tolerance and stability of anode electrocatalysts. The aim is to determine the progress made so far, highlight the most promising state-of-the-art CO-tolerant electrocatalysts, and identify the contributions of the novel strategies and the future challenges. © 2021 by the authors. Licensee MDPI, Basel, Switzerland. ; The authors thankfully acknowledge co-financing from the European Union and Greek national funds through the Operational Program for Competitiveness, Entrepreneurship, and Innovation, under the program RESEARCH-CREATE-INNOVATE (Project code: T1EDK-02442).

Complex solid solutions ("high entropy alloys"), comprising five or more principal elements, promise a paradigm change in electrocatalysis due to the availability of millions of different active sites with unique arrangements of multiple elements directly neighbouring a binding site. Thus, strong electronic and geometric effects are induced, which are known as effective tools to tune activity. With the example of the oxygen reduction reaction, we show that by utilising a data‐driven discovery cycle, the multidimensionality challenge raised by this catalyst class can be mastered. Iteratively refined computational models predict activity trends around which continuous composition‐spread thin‐film libraries are synthesised. High‐throughput characterisation datasets are then used as input for refinement of the model. The refined model correctly predicts activity maxima of the exemplary model system Ag‐Ir‐Pd‐Pt‐Ru. The method can identify optimal complex‐solid‐solution materials for electrocatalytic reactions in an unprecedented manner. ; ZGH is acknowledged for using XRD, AFM, EDX and APT. W.S. acknowledges funding from Deutsche Forschungsgemeinschaft (DFG) under Germany's Excellence Strategy (EXC 2033‐390677874–RESOLV) and from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement CasCat.[833408] A.L., A.S., and B.X. acknowledge funding from DFG projects LU1175/22‐1 and LU1175/26‐1, V.S. acknowledges a scholarship from IMPRS SurMAT. J.P. acknowledges support from the Danish Ministry of Higher Education and Science (Structure of Materials in Real Time (SMART) grant). T.B., J.P, C.C., and J.R. thank the Danish National Research Foundation Center for High‐Entropy Alloy Catalysis (CHEAC) DNRF‐149, and from research grant 9455 from the VILLUM FONDEN. Open access funding enabled and organized by Projekt DEAL.

[EN] In this work, we report the synthesis of Fe/N/C electrocatalysts using triazine based porous organic polymers as precursors. Iron-doped triazine porous organic polymers were obtained by in situ polymerization of iron pre- cursor and 1,2- or 1,4- dicyanobenzene (DCB). In order to obtain the actual catalyst, the polymer obtained was subjected to thermal treatment under NH3. The catalysts obtained exhibit activity and durability for the oxygen reduction reaction in acid electrolyte. Thorough characterization of the catalysts reveal the formation of several types of iron species, including metallic iron, iron carbides and Fe-Nx moieties. The latter species is the main responsible for the high activity measured for the oxygen reduction reaction in acid electrolyte. 1,2-DCB results in more active catalysts than 1,4-DCB due to the higher fraction of FeNx ensembles in the former, probably because vicinal positions of N-bearing groups are more prone to coordinate Fe atoms. ; This work was supported by PEGASUS project, funded by the European Union's Horizon 2020 Programme (call JTI-FCH-2017-1) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement n° 779550, and by project ENE2016-77055-C3-3-R from the Spanish Ministry of Economy and Competitiveness (MINECO). We acknowledge the Spanish CRG BM25-SpLine, MINECO, The Spanish National Research Council (CSIC) and The European Synchrotron (The ESRF) for provision of synchrotron radiation facilities.