HIPE 기반 전이금속/이종원자 개질 탄소 발포체 제조 및 슈퍼커패시터 전극재 응용 = Fabrication of heteroatom-modified carbon foams via HIPE templates and their application as supercapacitor electrode materials

다국어 초록 (Multilingual Abstract)

The high internal phase emulsion (HIPE) technique using monomers is a useful technology for synthesizing microporous polymer foams. Carbon foams obtained by heat-treating these foams at high temperatures exhibit high electrical conductivity and specific surface area, making them promising candidates for use as electrode materials for electrical storage. In this study, polyHIPE was synthesized by polymerizing HIPE, primarily composed of divinylbenzene and water. This was then carbonized to produce hierarchically porous carbon foams. The electrochemical properties of these carbon foams as supercapacitor electrodes were then investigated. After various modifications, the resulting carbon foams stably maintained a hierarchical porous structure with micro-/meso-/macro-pores. This structure shortens electrolyte ion diffusion paths and maximizes the active surface area, playing a crucial role in enhancing supercapacitor electrode performance. To enhance the electrochemical properties of CF, four functionalization strategies were applied. First, KOH activation created micropores and mesopores, enabling the fabrication of carbon foams with a hierarchical pore structure, thereby significantly increasing the specific surface area. Second, sulfonation treatment not only enhanced hydrophilicity but also improved electrical conductivity through heteroatom (S) doping and formed thioether crosslinks, which suppressed structural collapse during the carbonization process and enhanced morphology preservation. Third, urea treatment enhanced conductivity by increasing the electrically active sites within the carbon skeleton through heteroatom N-doping. Finally, the addition of TiO2 nanoparticles induced catalytic graphitization during the carbonization process in samples containing TiO2 nanoparticles, which enhanced the rearrangement of sp2 networks and structural stability, thereby facilitating electron transfer. The electrochemical performance was evaluated by cyclic voltametry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) using a three-electrode system. KOH-activated carbon foam (CF) had a surface area of 1837 m2g-1, a specific capacitance of 233 F g-1 at 1 A g-1, and a capacitance retention of 93% after 5000 cycles at 5 A g-1. Sulfonated CF (SCF) had a surface area of 2305 m2g-1, a specific capacitance of 250 F g-1, and a very high capacitance retention of 99% due to the enhanced hydrophilicity based on -SO₃H, which facilitated the reversible adsorption–desorption of ions. TiO₂-introduced and N–, S–doped TNSCF had an increased surface area of 3318 m2g-1, a specific capacitance of 253 F g-1, and capacitance retension of over 97%. To evaluate practical performance, SCF and NSCF were evaluated in symmetric two-electrode coin cells, respectively, and the results showed stable CV and GCD behaviors, confirming the possibility of supercapacitor electrode materials with both power density and energy density. In summary, this study effectively realized high-performance hierarchical porous carbon by integrating KOH activation, heteroatom doping, and TiO2 catalytic graphitization with the structural advantages of polyHIPE template, an emulsion-based foam. The fabricated carbon foam is expected to have high potential as a next-generation supercapacitor electrode material based on high capacitance, improved conductivity, excellent cycle stability, and outstanding practical performance.

목차 (Table of Contents)

• I. 서론 1
• 1. 연구 배경 1
• 1) 고내상 에멀션 3
• 2) 이산화 티타늄의 구조 및 특성 4
• 3) 이종원자 도핑의 전자구조와 표면특성 6
• 4) KOH활성화 7
• 5) 슈퍼커패시터 8
• 2. 연구 목적 11
• II. 실험 13
• 1. 시약 및 재료 13
• 2. 고내상 에멀션 템플릿을 이용한 미세기공 발포체 제조 15
• 3. 미세기공 발포체의 설폰화 17
• 4. KOH 활성화 및 N 도핑 19
• 5. CF 제조 20
• 6. 슈퍼커패시터용 대칭 셀 전극 제조 22
• 7. 3전극 측정용 전극 제조 24
• 8. 분석 26
• 1) PF 및 CF의 구조 분석 26
• 2) 비표면적 측정 및 열 안정성 분석 26
• 3) 전기화학적 특성 분석 27
• III. 결과 및 고찰 28
• 1. PF의 설폰화와 TiO2 첨가에 따른 특성 분석 28
• 1) TGA분석을 이용한 PF의 열 안정성 평가 28
• 2) XPS분석을 이용한 PF의 기능화 평가 30
• 3) SEM분석을 이용한 PF의 표면 및 기공형상 평가 33
• 4) BET분석을 이용한 PF의 비표면적 및 기공구조 평가 35
• 2. 이종원자 도핑과 TiO2 첨가에 따른 CF의 특성 분석 39
• 1) SEM분석을 이용한 CF의 미세구조 및 기공 형상 평가 39
• 2) XPS분석을 이용한 CF의 기능화 평가 41
• 3) Raman분석을 이용한 CF의 구조적 결함 및그래파이트화 평가 45
• 4) XRD분석을 이용한 CF의 결정구조 평가 47
• 5) BET분석을 이용한 CF의 비표면적 및 기공구조평가 49
• 3. 3전극계로 평가한 전극재의 전기화학적 특성 53
• 1) 전기화학 측정 조건의 최적화 및 측정 변수 설정 53
• 2) CF의 이종원자 도핑과 TiO2 첨가에 따른 전기화학적 특성 56
• (1) CV 특성 56
• (2) GCD 특성 59
• (3) EIS 특성 62
• (4) 사이클 안정성 특성 64
• 4. 슈퍼커패시터용 대칭 셀의 전기화학적 특성 67
• 1) 이종원자 도핑에 따른 전기화학적 특과 조건 설정 67
• 2) Ragone plot 70
• IV. 결론 73
• V. 참고문헌 76