1,721,052 research outputs found
Combinatorial high-throughput screening for highly active Pd-Ir-Ce based ternary catalysts in electrochemical oxygen reduction reaction
No full textA combinatorial library having 66 different ternary compositions of Pd-Ir-Ce was prepared via the impregnation method to find the optimum ternary composition with the highest performance toward oxygen reduction reaction (ORR) in acid media. Its performance in ORR activity of the combinatorial array was evaluated through two different combinatorial high-throughput screening methods to gain validity: (1) multielectrode half cell method and (2) optical screening method. From the combinatorial results, the spot at 79:12:9 for Pd-Ir-Ce (at.%) in the array showed the highest ORR activity. The electrochemical characterizations of the single catalyst demonstrates that the optimized Pd79Ir12Ce9/C catalyst shows 1.5 times the ORR activity compared to that of Pd/C catalyst at 0.85 V (vs. RHE). In the Pd-Ir-Ce based catalysts, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results reveal that Ir and Ce are present in the form of IrO2 and CeO2, respectively, and the electron configuration of Pd is effectively modified through the decoration with IrO2 and CeO2. From the results, we suggest that the electro-modification of Pd through strong metal-metal oxide interaction with IrO2-CeO2 was a reason for the enhanced ORR activity
Highly durable carbon nanotube composite support by pyrolysis of conductive polymer for polymer electrolyte fuel cell
No full textA Design of Cobalt and Nitrogen Doped Nanoporous Carbon Sphere Synthesis
No full textAs problems regarding the decline in available fossil fuels and climate change are on the rise, our societies strive to develop clean, sustainable, and efficient sources of energy. Many developments in such branches of research include energy conversion and storage, hence the importance of new technologies and their composing materials are attracting attention worldwide. On this basic premise, porous carbons are widely used as adsorbents, catalyst support materials, supercapacitors, batteries, and hydrogen storage due to its large specific surface areas, high conductivity, and exceptional chemical stability.
Herein, we present a nanoporous carbon material with unique hierarchical structures that are heteroatom doped, to enhance ORR performance. To date, hard templating is used to make various carbon structures, yet these methods are tedious and unflexible due to the limiting of the parent template. Yet soft templating is also limited to the few known precursors for synthesis due to its picky requirements for stable reactions. This research gives insight into a soft template-based silica-assisted method for the preparation of nitrogen-doped hollow nanoporous carbon spheres(N-HNCS). Nitrogen doping is accomplished during the reaction process, without need of after treatment, therefore enhancing electrocatalytical performance without more complication of the methodology.
After establishing a modified soft templating process, we introduced cobalt into the synthesis to boost ORR performance. With fine adjustment of the mechanism, we controlled the reaction to form well-dispersed cobalt particles with minimum agglomeration. This sheds light on the progress of new experimental procedures to develop more active and promising non-noble catalysts in large and stable batches.Maste
The research on separation of resistances in electrode of polymer electrolyte membrane fuel cell
No full textEnvironmental problems are getting worse because of the greenhouse effect from overuse of fossil fuels. The carbon dioxide from fossil fuels spreads into the atmosphere and acts as a greenhouse that covers the earth, raising the earth's temperature. Therefore, renewable energy has become essential to reduce the use of fossil fuels and carbon dioxide emissions. Hydrogen energy is also becoming very important because it has high chemical energy per mass, and only water comes out as a by-product when it is converted into electrical energy. The fuel cell is a device that converts the chemical energy of a reaction in which oxygen and hydrogen react to form water into electrical energy. When hydrogen is supplied from the fuel cell anode, it is spontaneously decomposed into hydrogen ions. Hydrogen ions move to the cathode through the electrolyte and react with supplied oxygen to produce water. However, in this process, there is resistance to the activation energy of the reaction and the movement of ions and gases, which leads to energy loss. Therefore, reducing this energy loss plays an important role in increasing fuel cell performance.
In this study, resistance analysis was conducted on changes in electrode properties and performance of high- and low-temperature fuel cells due to changes in materials. In the first chapter, the basic reaction mechanisms and materials of high- and low-temperature polymer membrane electrolyte fuel cells are introduced, and the basic concepts of electrochemical impedance spectroscopy (EIS) and distribution of relaxation time (DRT) resistance analysis are explained. In the second chapter, the physical properties were analyzed for four gas diffusion layers, and gas diffusion electrodes (GDEs) for the cathode of HT-PEMFC were fabricated through bar coating with three B/C (binder to carbon) ratios. Among them, The GDE from JNT30-A6P showed a significant change in secondary pore volume at a B/C ratio of 0.31, which had the largest pore volume among all GDEs. In the polarization curve, JNT30-A6P GDE showed the best membrane electrode assembly (MEA) performance with a peak power density of 384 mW cm-2 at a B/C ratio of 0.31. From the DRT, the peak 1 corresponding to the mass transfer resistance of oxygen reduction reaction (ORR) was significantly reduced in the JNT30-A6P GDE. In the third chapter, resistance analyses are conducted to elaborate on the performance and durability improvements induced by the adsorption of [MTBD][beti] ionic liquid (IL) on PtCo/C catalyst. The morphological changes caused by IL adsorption are observed on micro and macro scales via physicochemical methods. From the half-cell measurement, when the 4 wt.% IL was adsorbed, a 15 mVRHE improvement in ORR activity occurs; as the adsorption amount increases, the activity decreases, but the anion poisoning resistance increases. The single cell outperforms 1.3 times higher current density at 0.8 V and 40% decreased charge transfer resistance by 8 wt.% IL adsorption. DRT resistance analysis reveals that ORR charge transfer resistance (RORR) and proton charge transfer resistance (Rproton) decrease due to IL adsorption. During accelerated durability tests, 8 wt.% IL-loaded MEA showed a 20% increase in durability, and a lower degradation of RORR and Rproton encouraged improved durability.Maste
A study on solid state synthesis of electrocatalysts assisted by resonant acoustic mixing for electrochemical reactions
No full textGreen and scalable synthesis techniques for producing highly dispersed supported metal nanocatalysts (SMNCs) are essential for industrial heterogeneous catalysis. Traditional liquid-phase methods to create nanosized SMNCs often rely on organic capping agents and low metal loading to prevent nanoparticle aggregation, yet these requirements hinder practical, large-scale production. Supported metal nanoparticles are highly sought after for their exceptional activity, stability, and reusability in electrochemical applications, making it critical to develop more efficient and scalable synthesis methods. Conventional material synthesis processes tend to consume substantial time and energy and generate waste solvents, posing environmental challenges.
Mechanochemical synthesis provides a promising alternative as an environmentally friendly and scalable approach. This method, applied in fields such as metallurgy, mineral processing, and organic synthesis, has gained renewed interest in producing various nanomaterials, including organic, inorganic, and hybrid materials. Mechanochemistry proves particularly effective in creating highly porous carbons, metal-organic frameworks (MOFs), and covalent organic frameworks (COFs). Ball milling, a mechanochemical process, has also been used to produce ordered coordination polymers and mesoporous carbons. Today, mechanochemistry is recognized as a versatile and powerful tool for synthesizing a wide range of materials, particularly those used in adsorption, catalysis, and energy storage.
However, there are still challenges for synthesis of SMNCs in that they have limitations; possibility of oxidation, time-consuming, aggregation of particles and limited elements, etc. To solve those limitations, this study introduces an innovative solid-state synthesis method utilizing resonant acoustic mixing (RAM) with ball, a technique that enables easy, eco-friendly metal nanoparticle production without organic solvents. RAM employs acoustic energy to facilitate substance mixing, using ultrasound waves to increase particle movement and enhance blending efficiency. Known for its adaptability and energy efficiency, RAM supports improved product quality, operational efficiency, and reduced manufacturing costs, making it highly suitable for sustainable, large-scale applications.DoctorAbstract ⅴ
Contents ⅶ
List of tables ⅸ
List of figures ⅹ
Chapter I. INTRODUCTION 1
1.1. Background 1
1.2. Overview of the nanoparticle preparation methods 4
1.3. Recent developments of solid-state synthesis method 7
1.4. Resonant acoustic mixing 13
Chapter Ⅱ. PREPARATION OF THIOL-DECORATED Ag NANOPARTICLES ON N-DOPED CARBON THROUGH RESONANT ACOUSTIC MIXING FOR ELECTROCHEMICAL CO2 REDUCTION 19
2.1. Introduction 19
2.2. Experimental 24
2.3. Results and discussion 29
2.4. Conclusion 51
Chapter Ⅲ. FACILE PREPARATION OF CORE-SHELL Ru@Ir/C CATALYST AS A BIFUNCTIONAL ELECTROCATALYST FOR REVERSAL-TOLERANT ANODE IN POLYMER ELECTROLYTE MEMBRANE FUEL CELL 52
3.1. Introduction 52
3.2. Experimental 57
3.3. Results and discussion 63
3.4. Conclusion 93
Chapter Ⅳ. INVESTIGATION OF HIGH ENTROPY ALLOY NANOPARTICLES ASSISTED BY RESONANT ACOUSTIC MIXING FOR OXYGEN REDUCTION REACTION 94
4.1. Introduction 94
4.2. Experimental 98
4.3. Results and discussion 102
4.4. Conclusion 118
Chapter Ⅴ. SUMMARY 119
REFERENCES 123
Acknowledgement 132
CURRICULUM VITAE 133
Education 13
The comparison of activation methods for the PEMFC MEA with PtCo/C catalyst in cathode
No full textto its various advantages. Before starting the fuel cell, the activ ation process is necessary to improve the performance of PEMFC, however, there are few studies on whether the conventional activation protocol can activate the membrane electrode assembly MEA with Pt alloy catalyst normally. In this study , two different MEAs with PtCo/C catalyst in the cathode electrode were activated by three different activation methods (constant voltage control, current cycling control, and hydrogen pumping control). All the protocols fully activated the MEAs showing th eir performances and resistances were saturated. However, the electrochemically active surface area wasn’t change d after activation for all MEAs and protocols, suggesting that the performance improvement is due to other reasons like hydration or pore openi ng rather than the change of catalyst surface. The hydrogen pumping protocol took the longest activation time (5h) because of the absence of an oxygen reduction reaction. The current cycling protocol took the shortest time (2h~3h), but the performance afte r activation was lower than that one of the other protocols. The constant voltage protocol needed a shorter time (3h) than the hydrogen pumping and the performance was higher than current cycling protocol,
implying that constant voltage is most appropriate to activate MEA with a PtCo/C catalyst.Maste
A Design of Mesoporous Nitrogen-Doped Carbon Support Derived from ZIF-8 for Oxygen Reduction Reaction
No full textZeolitic imidazolate framework-8 (ZIF-8) has been extensively studied as a precursor for nitrogen-doped carbon (NC) materials due to its high surface area, tunable porosity, and adjustable nitrogen content. However, the intrinsic microporous structure of the ZIF-8 limits mass transport and accessibility of reactants to active sites, reducing its usefulness in electrochemical applications. In this thesis, a soft templating approach using a triblock copolymer was used to prepare mesoporous ZIF-8-derived NC (Meso-ZIF-NC) samples. The hierarchical porous structure was investigated by varying the ratios of Pluronic F-127, NaClO₄, and toluene. The resulting Meso-ZIF- NC exhibited a widespread pore size distribution with an enhanced mesopore volume (2–50 nm), corresponding to the composition of the reaction mixtures. Pt nanoparticles were uniformly dispersed on the Meso-ZIF-NC to form Pt/Meso-ZIF-NC catalysts, which presented a high electrochemical surface area and improved oxygen reduction reaction activity. This study highlights the mesoporous structure of the support and the important role of nitrogen-doped support in improving catalytic activity, providing valuable insights into the design of supports for catalysts and catalyst layers.MasterCHAPTER I. INTRODUCTION 1
1.1 Research background 1
1.1.1 Environmental issues 1
1.1.2 Overview of the PEMFC system 6
1.1.3 Catalysts for oxygen reduction reaction 8
1.2 Objectives and organization of the thesis 13
CHAPTER II. ENGINEERING PORE STRUCTURE IN MESOPOROUS NITROGEN-DOPED
CARBON SUPPORT DERIVED FROM ZIF-8 USING SOFT TEMPLATE FOR PROTON
EXCHANGE MEMBRANE FUEL CELL 14
2.1 Introduction 14
2.2 Experimental Methods 17
2.2.1 Synthesis of Mesoporous ZIF-8 based nitrogen-doped carbon 17
2.2.2 Preparation of ORR catalysts 18
2.2.3 Characterization of materials 18
2.2.4 Electrochemical catalyst measurements 19
2.2.5 Electrochemical catalyst layer measurements 20
2.3 Results and Discussions 22
2.3.1 Synthesis of Mesoporous ZIF-8 based nitrogen-doped carbon 22
2.3.2 Physicochemical characterizations of ORR catalysts 29
2.3.3 Electrochemical catalyst characterization 41
2.3.4 Electrochemical catalyst layer characterization 46
2.4. Conclusion 56
CHAPTER III. CONCLUSIONS 57
Summary 59
References 61
Acknowledgement 6
Investigation of Carbon-Based Materials Synthesized by Nano-Replication Method for Li-ion Battery and Non-Precious Metal Catalyst
No full textAs a result of climate change caused by human activities such as fossil fuel use, people have begun research to solve environmental pollution. Many scientists are focusing on and studying alternative energy sources to reduce the use of fossil fuels. The strong candidates are batteries and fuel cells because batteries are already familiar and easy to apply. Fuel cells have additional functions such as eco-friendly final products and fine dust purification. In this study, the effect of the type of dopant and the length of pores of the carbon support of the lithium-ion battery was investigated. In addition, this study contributed to optimizing the non-precious metal catalyst conditions such as catalyst particle size, post-treatment, precursor composite ratio, and synthesis temperature. The both of carbon-based materials were synthesized by the nano-replication method to control particle size and pore structure. This method helped find factors related to battery and catalyst performance. As a result, N-doped carbon showed a better cycle life of Li-Se battery in case of battery and higher N content provide interaction between N doped carbon and Se. The small catalyst particle without agglomeration and impurities were excellent in performance because of electrolyte accessibility and the post-treatment catalyst showed the best performance because the post-treatment reduced 2-electron reaction site and promoted 4-electron reaction that is more effective and profer for fuel cell systems. The higher Fe content and optimized temperature enhanced the catalytic activity under the alkaline condition of ORR because the catalytic active site and conductivity.Maste
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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