전기화학적 기반 리튬 회수 및 수소 생산용 고기능성 소재 연구 = Advanced Materials for Electrochemical Lithium Sorption and Water Splitting: Enabling Sustainable Resource Utilization for Clean Energy

다국어 초록 (Multilingual Abstract)

The increasing global demand for lithium, driven by the rapid development of electric vehicles and renewable energy storage systems, necessitates efficient, selective, and sustainable extraction from natural resources such as brine and seawater. Membrane Capacitive Deionization (MCDI) has emerged as a low-energy, green electrochemical separation technology with the potential for selective ion removal. In a separate work, we prepared a novel rGO/H₂TiO₃ composite electrode where lithium titanate (Li₂TiO₃) was converted into hydrated titanium oxide (H₂TiO₃) and anchored onto a reduced graphene oxide (rGO) matrix. The 60 wt% H₂TiO₃-loaded composite displayed the highest lithium electrosorption capacity (13.67 mg g⁻¹), rapid diffusion kinetics, and excellent cyclic stability in 10 mM LiCl solution. The outstanding performance is attributed to synergistic effects such as ion-exchange mechanisms, narrowly defined lattice spacings for Li⁺ selectivity, and enhanced conductivity from the rGO framework. The electrode demonstrates how engineered nanocomposite materials can significantly enhance the selectivity and capacity of MCDI systems for the strategic recovery of ions. Another study explores the integration of Prussian Blue (PB), a Li⁺- intercalating redox-active substance, with a highly conductive activated carbon (AC) matrix for the fabrication of high-performance composite electrodes. The optimized AC/PB-20% composite exhibited superior electrochemical performance, such as high specific capacitance (159 F g⁻¹) and excellent Li⁺ electrosorption capacity (24.42 mg g⁻¹) at 1.4 V, with 95.11% capacity retention over 50 cycles. The PB's redox function and reversible intercalation/de-intercalation capacity significantly improved ion transport and electrosorption efficiency. The findings illustrate how the integration of faradaic and capacitive components can impart new function to MCDI by realizing both selectivity and durability. These hybrid materials expand the design paradigm for next-generation desalination and lithium recovery systems and offer scalable solutions for industrial applications. Other than lithium mining, green energy harvesting through water electrolysis is also crucial in addressing global energy issues. In a third article, a novel monoclinic-phase FeH(SeO₃)₂ electrocatalyst was synthesized on nickel foam through a redox reaction method with selenium introduction. The OER electrocatalyst exhibited a low overpotential of 185 ± 2 mV at 10 mA cm⁻², a low Tafel slope of 53.3 mV dec⁻¹, and long-term stability for over 100 hours. The catalyst's outstanding activity is attributed to synergistic electronic coupling between Se, Fe, and Ni atoms that optimizes oxygen intermediate (OH*, O*, OOH*) adsorption/desorption and minimizes kinetic barriers. Aside from creating a new class of nonprecious metal-based electrocatalysts, this work illustrates how fundamental insight into material electronic structure and interface chemistry can drive performance. Together, these studies present a compelling vision of connecting MCDI and water-splitting technologies through the assistance of advanced materials in the direction of facilitating circular systems for concurrent resource recovery and green hydrogen production. The logical design of new functional materials-rGO/H₂TiO₃ composites, Prussian, Blue-anchored activated carbon, and FeH(SeO₃)₂ electrocatalysts-demonstrates how designed nanostructures have the potential to revolutionize both lithium recovery and clean energy production. Collectively, these materials highlight the significance of interface engineering, electronic structure modulation, and synergistic composite architectures in addressing global challenges of sustainable lithium recovery, and water splitting.

목차 (Table of Contents)

• CHAPTER 1. Introduction 1
• 1.1 Background and Motivation 2
• 1.2 Lithium Extraction for Sustainable Future 3
• 1.3 Conventional Lithium Extraction Technologies 8
• 1.3.1 Extraction from Solid Sources (Ores, Clays) 8
• 1.3.1.1 Hydrometallurgical and Pyrometallurgical Routes 8
• 1.3.1.2 Pressure Leaching Methods 14
• 1.3.1.3 Bioleaching Technique 14
• 1.3.2 Extraction from Brine Sources 15
• 1.3.2.1 Precipitation-Based Method 17
• 1.3.2.2 Ion-Exchange Method 19
• 1.3.2.3 Liquid-Liquid Extraction Method 20
• 1.3.2.4 Membrane-Based Process 20
• 1.4 Emerging Technologies for Lithium Recovery 21
• 1.5 Principle of Capacitive Deionization (CDI) 23
• 1.6 Capacitive Deionization for Lithium Extraction 25
• 1.7 Aims of Research 26
• 1.8 Water Splitting - A Green Route for Energy Generation 29
• 1.8.1 Fundamentals of Electrochemical Water Splitting 30
• 1.8.2 Hydrogen Evolution Reaction (HER) 32
• 1.8.3 Oxygen Evolution Reaction (OER) 33
• 1.8.3.1 Adsorbate Evolution Mechanism (AEM) 35
• 1.8.3.2 Lattice Oxygen Mechanism (LOM) 36
• 1.9 Challenges of OER 37
• 1.10 Aims of Research 39
• CHAPTER 2. Layered H₂TiO₃/rGO Composite for High Performance Lithium Recovery via Membrane Capacitive Deionization 41
• 2.1 Introduction 42
• 2.2 Materials 44
• 2.3 Synthesis of Lithium Titanate (Li₂TiO₃) 45
• 2.4 Synthesis of Hydrogenated Titanium Oxide (H₂TiO₃) 45
• 2.5 Synthesis of Reduced Graphene Oxide (rGO) 46
• 2.6 Synthesis of rGO/H₂TiO₃ Composites 46
• 2.7 Material Characterization 47
• 2.8 Electrode Fabrication 48
• 2.9 Electrochemical Measurements 48
• 2.10 MCDI Set-up and Electrosorption Measurements 49
• 2.11 Results and Discussions 53
• 2.11.1 Physical Characterization 53
• 2.11.2 Electrochemical Analysis 65
• 2.11.2.1 Cyclic Voltammetry 65
• 2.11.2.2 Galvanostatic Charge-Discharge (GCD) Analysis 70
• 2.11.2.3 Electrochemical Impedance Spectroscopy (EIS) 72
• 2.11.3 Membrane Capacitive Deionization (MCDI) 73
• 2.11.4 Ragone Plot 76
• 2.11.5 Selectivity and Stability Investigations 77
• 2.11.6 Mechanism of Li⁺ Adsorption in H₂TiO₃ 81
• 2.12 Conclusions 85
• CHAPTER 3. Sustainable Lithium Recovery via Membrane Capacitive Deionization Using Redox-Active Prussian Blue/Activated Carbon Electrodes 87
• 3.1 Introduction 88
• 3.2 Materials 90
• 3.3 Preparation of AC/PB Composites 91
• 3.4 Material Characterization 92
• 3.5 Electrode Fabrication 93
• 3.6 Electrochemical Measurements 93
• 3.7 MCDI Set-up and Electrosorption Measurement 94
• 3.8 Results and Discussion 98
• 3.8.1 Physical Characterization 98
• 3.8.2 Electrochemical Analysis 107
• 3.8.2.1 Cyclic Voltammetry 107
• 3.8.2.2 Galvanostatic Charge-Discharge (GCD) Analysis 113
• 3.8.2.3 Electrochemical Impedance Spectroscopy (EIS) 114
• 3.8.2.4 Analysis 116
• 3.8.3 Membrane Capacitive Deionization (MCDI) Studies 121
• 3.8.3.1 Ragone Plot 121
• 3.8.4 Selectivity and Stability Investigations 124
• 3.8.5 Mechanism of Li⁺ Extraction by the AC/PB-20% Composite 127
• 3.9 Conclusions 128
• CHAPTER 4. Monoclinic Iron(III) Hydrogen Biselenite as an Efficient OER Catalyst for Efficient Water Oxidation 132
• 4.1 Introduction 133
• 4.2 Materials and Chemicals 135
• 4.3 Preparation of FeH(SeO₃)₂/NF Electrode 135
• 4.4 Preparation of FeO(OH)/NF Electrode 140
• 4.5 Synthesis of RuO₂/NF Electrode 140
• 4.6 Characterizations 141
• 4.6.1 Ultraviolet-Diffuse Reflectance Spectroscopy (UVDRS) 142
• 4.7 Electrocatalytic Measurements 142
• 4.7.1 Electrochemically Active Surface Area (ECSA) Calculation 144
• 4.7.2 Turnover Frequency (TOF) Calculation 145
• 4.7.3 Stability Number 147
• 4.7.4 In-situ Electrochemical Impedance (EIS) Spectroscopy 148
• 4.7.5 In-situ Raman Spectra Set-up 148
• 4.8 Computational Methods 149
• 4.9 Results and Discussion 151
• 4.9.1 Synthesis, Morphology, and Characterization 151
• 4.9.2 Oxygen Evolution Reaction Performance 163
• 4.9.3 Work Function and Mott-Schottky Effect on the OER Performance 183
• 4.9.4 Catalytic Mechanism Analysis 187
• 4.10 Conclusions 199
• CHAPTER 5. Conclusions & Perspectives 201
• 5.1 Conclusions 202
• 5.2 Future Directions 205