Synthesis of Heteroatom-Doped Porous Carbons for Next-Generation Energy Applications

다국어 초록 (Multilingual Abstract)

The growing demand for sustainable energy storage and resource-circulation technologies has increased the importance of carbon materials for electrochemical systems. Vanadium redox flow batteries （VRFBs） and supercapacitors （SCs） are regarded as promising systems for large-scale energy storage and high-power applications, while electrochemical lithium recycling with hydrogen generation offers a sustainable route for resource recovery and clean energy production. However, the electrochemical performance of these systems is strongly governed by the properties of carbon-based electrodes or catalysts, particularly their electrical conductivity, pore structure, and surface chemistry. This work presents a sustainable and rapid microwave-assisted route to synthesize tannic acid （TA）-derived carbon materials with specific structures for diverse electrochemical systems.
First, edge-dominant pyridinic nitrogen-doped graphitic carbon was synthesized from TA and tris（2-aminoethyl）amine （TAEA） through a rapid two-step microwave process for VRFB applications. TAEA acted as both a condensing agent and a nitrogen source, inducing enhanced graphitic features, fewer defects, and abundant edge pyridinic-N sites. The catalyst enabled stable VRFB operation up to 500 mA cm-2, and the catalyst-loaded graphite felt retained 94.12% of its initial discharge capacity after 1,000 cycles at 400 mA cm-2.
Second, a microwave-assisted KOH post-treatment was introduced to modify TA- derived carbon for SC applications. This treatment increased the surface hydroxyl content while maintaining the porous carbon framework and improving graphitic ordering. As a result, the optimized carbon showed a 3.1-fold increase in electrical conductivity and delivered 313.5 F g-1 at 1 A g-1 in a three-electrode system and 95 F g-1 at 10 A g-1 in symmetric coin cells, together with an energy density of 14.75 Wh kg-1 and 99.6% capacitance retention after 5000 cycles.
Third, TA/TAEA-derived N-doped carbon catalysts were applied to a Fe（CN）6- mediated electrochemical lithium recycling system coupled with hydrogen production. The porous pyridinic-N carbon structure, obtained through short-time microwave treatment, provided active sites, favorable surface charge, and improved electrical conductivity for the Fe（CN）6 3-/4- redox reaction. These features enhanced mediator redox kinetics and interfacial charge-transfer behavior, thereby promoting LiOH recovery and H2 generation during flow-cell operation. These results demonstrate that TA/TAEA-derived carbon catalysts can serve as effective electrode platforms for integrated lithium resource recovery and clean energy production.
The synthesis strategies for TA-derived carbon materials presented in this work provide an efficient and sustainable route to functional carbon materials for multiple electrochemical systems. By controlling surface chemistry and structural features, TA- based carbons were developed for VRFBs, SCs, and electrochemical lithium recycling with hydrogen generation. These findings provide a useful basis for the development of next-generation energy storage and resource-recovery technologies. Keywords: Tannic acid-derived carbon, Vanadium redox flow batteries, Supercapacitors, Electrochemical lithium recycling, Hydrogen generation, Microwave-assisted synthesis

목차 (Table of Contents)

• Chapter Ⅰ. Overall Introduction 1
• 1.1. Overall introduction 2
• 1.2. References 6
• Chapter Ⅱ. Theoretical Backgrounds 11
• 2.1. Fundamentals of electrochemistry 12
• 2.2. Vanadium redox flow batteries 17
• 2.3. Supercapacitors 23
• 2.4. Electrochemical Lithium Recycling 30
• 2.5. Tannic acid-derived carbon materials 36
• 2.6. References 39
• Chapter Ⅲ. Sustainable Synthesis of Edge-Dominant Pyridinic Nitrogen-
• Doped Carbon from Tannic Acid for High-Performance Vanadium Redox
• Flow Batteries 54
• 3.1. Introduction 55
• 3.2. Experimental section 60
• 3.2.1. Materials 60
• 3.2.2. Catalyst synthesis 60
• 3.2.3. Electrode fabrication 61
• 3.2.4. Characterizations 61
• 3.2.5. Density functional theory calculations 62
• 3.2.6. Evaluation of the performance of the VRFB single cells ·· 63
• 3.3. Results and discussion 64
• 3.3.1. Chemical and optical evaluations 64
• 3.3.2. Electrochemical behaviors of TA-based carbons 91
• 3.3.3. Performances of the prepared electrodes in VRFB operations
• 100
• 3.4. Conclusion 111
• 3.5. References 114
• Chapter Ⅳ. Rapid Microwave-Assisted Selective Hydroxylation of Tannic
• Acid-Derived Carbon for High-Performance Supercapacitors
• 124
• 4.1. Introduction 125
• 4.2. Experimental section 129
• 4.2.1. Materials 129
• 4.2.2. Synthesis 129
• 4.2.3. Characterizations 129
• 4.2.4. Electrochemical test 130
• 4.2.5. Computational methods 131
• 4.3. Results and discussion 133
• 4.3.1. Chemical and optical evaluations 133
• 4.3.2. Performance as supercapacitor electrode 157
• 4.3.3. Symmetric cell test 163
• 4.4. Conclusion 174
• 4.5. References 176
• Chapter Ⅴ. Pyridinic-N Carbon Catalyst for Enhanced Fe（CN）6-Mediated
• Electrochemical Lithium Recycling and H2 Evolution 184
• 5.1. Introduction 185
• 5.2. Experimental section 189
• 5.2.1. Materials 189
• 5.2.2. Synthesis 189
• 5.2.3. Characterizations 190
• 5.2.4. Preparation of LFP black powder and electrolytes 190
• 5.2.5. Fabrication of the electrodes 191
• 5.2.6. Electrochemical test 191
• 5.3. Results and discussion 193
• 5.3.1. Reaction mechanism and chemical characterization
• 193
• 5.3.2. Electrochemical behavior toward Fe（CN） 6206
• 5.3.3. Performance of Li recycling cell 216
• 5.3.4. Characterization of produced LiOH and FP 221
• 5.4. Conclusion 225
• 5.5. References 226
• Chapter Ⅵ. Overall Conclusion 231
• 6.1. Overall Conclusion 231
• 국문초록 234
• Acknowledgments 236