초록 ▼

개발 목적 및 필요성
본 연구는 태양광에너지 전환물질인 이종접합형 나노구조체 광전극 소재를 이용하여 석유정제 공정 내 폐가스(황화수소)처리와 동시에 청정에너지 회수를 위한 신공정 개발을 목적으로(태양에너지 전환효율 4%이상 달성) 한다. 기존에 개발된 광촉매 및 광전극 소재들은 주로 입자형태이거나 박막형 형태가 대부분을 차지한다. 그러므로, 입자간의 저항을 줄이고, 빛의 이용율을 향상시키기 위해 특정 기질 위에 한방향으로 직접 성장된 광전극 소재를 개발하고자 한다.

연구개발결과
1. 1차원 나노구조 광전극의

개발 목적 및 필요성
본 연구는 태양광에너지 전환물질인 이종접합형 나노구조체 광전극 소재를 이용하여 석유정제 공정 내 폐가스(황화수소)처리와 동시에 청정에너지 회수를 위한 신공정 개발을 목적으로(태양에너지 전환효율 4%이상 달성) 한다. 기존에 개발된 광촉매 및 광전극 소재들은 주로 입자형태이거나 박막형 형태가 대부분을 차지한다. 그러므로, 입자간의 저항을 줄이고, 빛의 이용율을 향상시키기 위해 특정 기질 위에 한방향으로 직접 성장된 광전극 소재를 개발하고자 한다.

연구개발결과
1. 1차원 나노구조 광전극의 합성
불소가 첨가된 산화 주석(FTO)을 코팅한 유리 위에 성장한 후 500°C에서 열처리한 TiO₂나노막대와 FTO 유리 위의 Fe₂O₃ 나노막대는 간단한 수열합성을 사용하여 성장시켰다.

2. 헤테로접합 광전극 물질들의 합성.
1) 본 연구그룹은 ZIS 전구체 농도를 조절하고 2단계 수열합성 방법을 사용하여 1차원 TiO₂ NR 위에 계면활성제가 없는 푹신한 2차원 ZIS NS을 성공적으로 합성하였다.
2) 간단한 2단계 수열합성 공정과 에틸렌디아민 (EDA)같은 용액과 주형 그리고 조정제를 응용하여 새로운 광전극 구조인 카드뮴 설파이드(CdS) 나노플라워/루타일(R)-TiO₂ 나노막대(NR) 헤테로접합을 성공적으로 합성하였다.
3) 새로운 3차원 구조의 CdS/ZnIn₂S₄/TiO₂ 헤테로접합은 3단계의 간단한 수열 합성 방법으로 만들어졌다. 삼차원 헤테로접합을 형성하기 위해서 TiO₂ 나노막대 위에 ZnIn₂S₄을 설계하고 CdS 나노 입자로 감광시켰다.
4) 수열합성 방법을 통한 FTO위에 향상된 광전기화학적 CdS/Zr:α-Fe₂O₃ 나노구조체 배열을 직접적으로 합성했다.

3. 보조 촉매의 개발/헤테로접합 광전극 물질
간단하고 효과적인 전략은 헤테로구조의 Ni(OH)₂/CdS/ZnIn₂S₄/TiO₂ 광전극의 성능을 근본적으로 향상시키기 위해 사용되었다.

4. Gradient Core/Shell Quantum Dot Photocatalyst의 합성
CdS 기반의 물질 연구들 중에 4번 코팅된 CdS/ZnS는 CdS와 3번 코팅된 CdS/ZnS에 비해 눈에 띄게 전체적으로 향상된 광전류를 나타내었다.

5. 대면적 광전기화학 전극으로 구성된 시스템 개발
(1) 대면적 광전극 제작 (10x10cm²):
(a) CdS 나노플라워/TiO₂ 나노로드
(b) Al₂O₃/CdS/Zr:Fe₂O₃ 나노로드
(2) 옥내외에서 평가가 가능한 광전기화학적 시스템 설계 및 제작
광전극 셀을 설치한 광전기화학 시스템을 구축하였다. 10x10cm²으로 제작된 광전극 (working electrode)와 상대전극(Pt 전극)을 광전극 셀에 고정화하였으며, 이를 활용하여 광전기화학 시스템과 연결하였다.

성능사양 및 기술개발 수준
본 연구에서는 다양한 광전극 소재들이 개발되었으며, 가장 우수한 성능을 보이는 두 물질로는 태양광전환(STH(%)) 효율이 3.95%인 CdS NF/R-TiO₂ NR 소재와 효율이 6.22%인 Al₂O₃/CdS/Zr:Fe₂O₃ 광전극 소재를 확보할 수 있었다.

활용계획
- H₂S 광분해용 광전극 소재 개발에 대한 유용한 기술적 정보 제공
- 유해성 환경 오염물질분야(수질정화, 살균/항균, 공기정화, 악취제거)에 활용
- 태양전지의 전극소재 개발에 대한 합성기술 제공

(출처 : 요약서 3p)

Abstract ▼

Ⅳ. Results
1. Synthesis of one-dimensional nanostructure photoanode
1) TiO₂ Nanorod/FTO Substrate
TiO₂ nanorods grown hydrothermally on fluorine-doped tin oxide (FTO) and annealed at 500 °C yielded an optimal photocurrent density of ~988 μA cm^-2 at 0.1 V vs.

Ⅳ. Results
1. Synthesis of one-dimensional nanostructure photoanode
1) TiO₂ Nanorod/FTO Substrate
TiO₂ nanorods grown hydrothermally on fluorine-doped tin oxide (FTO) and annealed at 500 °C yielded an optimal photocurrent density of ~988 μA cm^-2 at 0.1 V vs. Ag/AgCl under simulated illumination conditions. The annealing process minimized the defects in TiO₂ and assisted in the formation of close contacts between the FTO and TiO₂ nanorods, which allowed for efficient electron transport.

2) Zr:Fe₂O₃ Nanorod/FTO Substrate
Hematite nanorods on FTO glass were deposited on FTO substrate by using a simple hydrothermal method as previously reported. the photocurrent density of the pristine 1D Zr:α-Fe₂O₃ is ca. 0.75 mA cm^-2 at -0.3 V Ag/AgCl. In the next work, Metal oxides formed a perfectly uniform shell layer on the outside of the 1D Zr:Fe₂O₃. That is, the 1D Zr:Fe₂O₃ nanorod will play a role of buliding block structure as well as visible active materials.

2. Synthesis of heterojunction photoanode materials
1) ZnIn₂S₄ Nanosheet/TiO₂ Nanorod
We have successfully prepared the surfactant free fluffy 2D ZIS NS’s onto the 1D TNR’s using conventional two step hydrothermal method by controlling the concentration of ZIS precursor. The empirical measurements were used to confirm that the manifold concentration of ZIS precursor is one of the crucial factor to determining the morphologies, wavelength, and crystal phase. The PEC performance for the entire samples attained manifold enhancement due to the effect of concentration of the ZIS precursor. The optimized heterojunction photoanode reveal higher photocurrent density is 1600 μA/Cm² at an applied potential of –0.5V vs .Ag/AgCl under the BSI, which is 3 fold higher than the bare 1D TNR’s.

2) CdS Nanoflower/TiO₂ Nanorod
With the application of ethylenediamine (EDA) as a solvent, a template, and co-ordination agents, novel photoanode architecture of the cadmium sulfide (CdS) nanoflower (NF)/rutile(R)-TiO₂ nanorod(NR) heterojunction is successfully synthesized using a facile two-step hydrothermal process.The optimized CdS(medium concentration; MC)NF/R-TiO₂ NR heterojunction exhibited agreatly enhanced visible-light photoelectrochemical (PEC) performance, whereby the highest photocurrent density of 3.23 mA cm^-2 at 0.1V versus Ag/AgCl and a photoconversion efficiency(PCE) of 0.46% were achieved under solar light irradiation. The optimal photocurrent density of the CdS (MC) NF/R-TiO2 NR heterojunction, photoanode is 2.54 times(60.68%) higher than that of the pristine R-TiO₂ NR. this surface modification reveals the synergistic effect. The optimal CdS(MC)NF/R-TiO₂ NR heterojunction showed a PEC hydrogen (H₂) generation of 1007.98 μmol after 3hr. The design of the novel heterojunction photoanode that is proposed in the present strategy canshed light on the fabrication of new,cheap photocatalysts for an effective H₂generation.

3) CdS/ZnIn₂S₄/TiO₂ Heterojunction
A novel, three-dimensional, ternary CdS/ZnIn₂S₄/TiO₂ heterojunction has been fabricated via a three-step facile hydrothermal method. In this structure, one-dimensional TiO₂ nanorods were directly grown on conductive fluorine-doped tin oxide (FTO) substrates. Next, to form a ternary heterojunction of CdS/ZnIn₂S₄/TiO₂, ZnIn₂S₄ nanosheets were designed on the TiO₂ nanorods and sensitized by CdS nanograins. A systematic photoelectrochemical study shows that the photocurrent density of the ternary heterojunction architecture is as high as 1.4 mA cm^-2 at a potential of 0.1 V versus Ag/AgCl (under optimized conditions). A more detailed study shows that the photocurrent density is more than two times higher than that of a single CdS/TiO₂ heterojunction (0.615 mA cm^-2) and three times higher than that of ZnIn₂S₄/TiO₂ (at 0.1 V vs. Ag/AgCl). This excellent photoelectrochemical performance is ascribed to the way that the band structure of TiO₂ nanorods synergistically cascades with ZnIn₂S₄ and CdS, which allows for the absorption of a wider portion of the solar spectrum and improves the effective separation of the generated electron–hole pairs. Electrochemical impedance spectroscopy (EIS) studies also reveal the significant changes in both the interface resistance and the charge transfer resistance of the CdS/ZnIn₂S₄/TiO₂ heterostructure. This can be attributed to the efficient hierarchical cascading that occurs during the electron–hole transfer from the excited CdS to TiO₂ through the enlarged interface of ZnIn₂S₄ upon visible light illumination.

4) CdS/Zr:Fe₂O₃ Nanorod
Well-defined CdS nanograin-sensitized one-dimensional (1D) Zr:α-Fe₂O₃ nanostructured arrays with enhanced photoelectrochemical performance are synthesized directly on F-doped SnO₂ (FTO) using the hydrothermal method. Owing predominantly to the appropriate photogenerated electron–hole separation and charge collection in 1D Zr:α-Fe₂O₃ nanorods, hydrothermally deposited CdS/1D Zr:α-Fe₂O₃ samples exhibit improved photocurrent density over CdS/Fe₂O₃ nanosheets prepared by other methods. In our work, compared with 1D Zr:α-Fe₂O₃, the CdS-sensitized 1D Zr:α-Fe₂O₃ nanorod arrays show 1.9 times improved photoelectrochemical performance. Unfortunately, CdS nanograin-sensitized 1D Zr:α-Fe₂O₃ nanorod arrays suffer from instability problem. Nickel hydroxide loading, however, can boost the photoelectrochemical performance of the heterojunction and also act as a protective layer that improves the stability of the Ni(OH)₂/CdS/1D Zr:α-Fe₂O₃ electrode compared to CdS/1D Zr:α-Fe₂O₃.

3. Development of Cocatalyst/Heterojunction photoanode materials
1) Ni(OH)₂/CdS/ZnIn₂S₄/TiO₂ Heterojunction
A simple and effective strategy was used to fundamentally improve the performance of a heterostructured Ni(OH)₂/CdS/ZnIn₂S₄/TiO₂ photoanode. TiO₂ nanorods grown hydrothermally on fluorine-doped tin oxide (FTO) and annealed at 500℃ yielded an optimal photocurrent density of ~988 μA cm^-2 at 0.1 V vs. Ag/AgCl under simulated illumination conditions. The annealing process minimized the defects in TiO₂ and assisted in the formation of close contacts between the FTO and TiO₂ nanorods, which allowed for efficient electron transport. The stepwise introduction of ZnIn₂S₄ and CdS on annealed TiO₂ enhanced absorption in the visible range and electron/hole separation in CdS/ZnIn2S4/TiO₂. Additionally, the Ni(OH)₂ cocatalyst functioned in hole trapping and improved the stability of the photoelectrode through timely consumption of the photogenerated charges, particularly the holes.

4. Synthesis of Gradient Core/Shell Quantum Dot Photocatalyst
1) CdZnS/ZnS Core/Shell Quantum Dot
Among the studied CdS based samples, the CdS/ ZnS 4times demonstrates remarkably enhanced photocurrent compared to the CdS and CdS/CdS/ZnS 3times over the entire potential window. Each J-V graph shows four light curves under light condition taken at four separate scan. It was ssen that after first scan measurement photocurrent decrses and then for the next three cycles it is nearly same. The presence of ZnS leads to the enhancement of transient photocurrent response of CdS from 384 μA cm^-2 to 698 μAcm^-2 for CdS/ZnS 4 times), almost 2 times higher than that of the pure CdS. Moreover, the transient photocurrents were rapid, steady and reproducible during three switched on–off cycles. When the light is interrupted during chopping condition, the accumulated holes in the surface state gradually vanish, and a spike is observed. The initial decay of the photocurrent indicates that a fraction of h+ which reaches the semiconductor surface, instead of capturing e−from the electrolyte, either accumulates at the surface or recombines with electrons from the conduction band. After recombination of the excessive h+, the generation and transfer of electron−hole pairs reach equilibration ,and a constant current is formed. Upon light illumination, the photocurrent increases sharply and the current intensity returns quickly to the dark current state when the light is turned off. With the addition of ZnS on CdS, the heterostructure photocatalysts have lower recombination of electron–hole pairs than pure CdS, which promotes the more effective migration of charge-carriers and the photocatalytic activity.

5. System Construction consisting of Large Sized Heterojunction Photoanode
(1) Fabrcation of Large Sized Photoanode (10x10cm²):
(a) CdS Nanoflower/TiO₂ Nanorod
(b) Al₂O₃/CdS/Zr:Fe₂O₃ Nanorod

(2) System construction consisting of large sized photoanode for inoor and outdoor test

(출처 : Summary 18p)

목차 Contents

• 표지 ... 1
• 제출문 ... 2
• 요 약 서 ... 3
• 요 약 문 ... 6
• SUMMARY ... 16
• 목차 ... 23
• 그림목차 ... 24
• 1. 연구개발과제의 개요 ... 33
• 1-1. 연구개발 목적 ... 33
• 1-2. 연구개발의 필요성 ... 36
• 1-3. 연구개발 범위 ... 40
• 2. 국내외 기술개발 현황 ... 41
• 3. 연구수행 내용 및 결과 ... 43
• 3-1. 연구개발의 내용(범위) 및 최종목표 ... 43
• 3-2. 연구개발 결과 및 토의 ... 43
• 3-3. 연구개발 결과 요약 ... 111
• 4. 목표달성도 및 관련분야 기여도 ... 113
• 4-1. 목표달성도 ... 113
• 4-2. 관련분야 기여도 ... 113
• 5. 연구결과의 활용계획 ... 116
• 6. 연구과정에서 수집한 해외과학기술정보 ... 118
• 7. 연구개발결과의 보안등급 ... 119
• 8. 국가과학기술종합정보시스템(NTIS)에 등록한 연구시설·장비 현황 ... 119
• 9. 연구개발과제 수행에 따른 연구실 등의 안전조치 이행실적 ... 119
• 10. 연구개발과제의 대표적 연구실적 ... 120
• 11. 기타사항 ... 121
• 12. 참고문헌 ... 121
• 끝페이지 ... 122