Design of liquid-solid contact electrification-based nanogenerators for energy harvesting and sensor applications

국문 초록 (Abstract)

이 논문은 환경친화적이고 재생가능한 에너지 수확 방법인 마찰전기 발전소자의 목적에 부합하기 위해 자연에서 얻을 수 있는 해양 파도, 빗방울을 활용할 수 있는 액체-고체 접촉 대전에 대해 초점을 맞추고 있다. 액체-고체 접촉 대전은 실시간으로 변화하는 접촉 면적을 비롯한 액체의 특성 (염 농도, pH, 온도 등)에 큰 영향을 받아 발전량을 예측하는데 한계가 있다. 이러한 한계를 극복하기 위해 다양한 제조 방법 및 재료적 특성을 기반으로 한 새로운 발전 방식들이 제안된다. 또한 유체역학적 분석을 통해 다양한 조건에서 발전량을 예측할 수 있도록 하였다.
2장에서는 태양 전지에 부착하기 위해 투명한 액체-고체 접촉 대전 기반 발전소자를 제안하였다. 투명한 나노발전기를 제조하기 위해 전극은 전기수력학적 젯 프린팅, 대전층은 폴리디메틸실록산(PDMS)이 사용되었다. 인쇄된 전극은 인듐 주석 산화물(ITO) 유리에 비해 더 높은 투과율을 보였고 특정 범위 내에서 투과율 저하 문제를 해결하였다. 에너지 수확 성능은 무차원수인 Weber 수를 사용하여 분석되었다.
3장에서는 바람과 물방울을 활용하는 하이브리드 에너지 수확 시스템을 제안하였다. 변형률에 따라 일 함수가 변하는 금을 사용하여 새로운 발전 방식의 마찰전기 발전소자를 제안하였으며, 질량비, 굽힘 강성, Weber 수와 같은 변수를 통해 유체 역학적 분석을 수행하였다. 유체역학적 분석을 통해 발전이 가능한 범위와 발전량을 예측할 수 있다.
마지막으로, 반도체 분야의 오믹/쇼트키 접촉에서 관찰되는 정류 현상을 액체-고체 접촉 대전에 적용하여 액체-고체 계면에서 발생하는 현상을 분석하였다. 전기화 층의 일 함수를 조정하고, 액체의 특성을 기반으로 정류 동작을 분석하였다. 이 현상을 설명하기 위해 모트-쇼트키 분석을 사용하여 플랫 밴드 전위를 계산하였다. 결과는 센서 응용 분야에 정류 현상을 활용할 수 있는 잠재력을 보여주었다.

다국어 초록 (Multilingual Abstract)

This dissertation focuses on triboelectric nanogenerators (TENGs), which are eco-friendly and renewable energy harvesting methods, particularly utilizing liquids like ocean waves, raindrops, and sweat. It highlights the challenges of liquid-solid contact electrification posed by changes in contact areas and liquid properties (e.g., salt concentration, pH, temperature) in predicting energy output. To overcome these limitations, the study utilizes various fabrication methods and materials, leveraging fluid mechanical analysis to optimize energy harvesting.
Chapter 2 proposes a transparent liquid-solid contact electrification-based nanogenerator for integration with solar cells. The electrode was fabricated using electrohydrodynamic jet printing to create the transparent nanogenerator, and the electrification layer was composed of polydimethylsiloxane (PDMS). The printed electrode demonstrated higher transmittance compared to indium tin oxide (ITO) glass and resolved the issue of transmittance degradation within a specific range. Energy harvesting performance was analyzed using the dimensionless number, Weber number.
Chapter 3 introduces a hybrid energy harvesting system that leverages wind and water droplets. Gold, whose work function changes according to the strain, was used to optimize performance, and fluid mechanical analysis was conducted using parameters like mass ratio, bending stiffness, and Weber number.
Finally, the rectification phenomenon, commonly observed in Ohmic/Schottky contacts in the semiconductor field, was applied to liquid-solid contact electrification. The work function of the electrification layer was adjusted, and the rectification behavior was analyzed based on the properties of the liquid. To explain this phenomenon, the flat band potential was calculated using Mott-Schottky analysis. The results demonstrated the potential of utilizing the rectification phenomenon for sensor applications. Also, the charging time decreased when the rectification occurred, due to the direct current (DC) energy harvesting.

목차 (Table of Contents)

• Chapter 1. Introduction 1
• 1. Background and Motivation 1
• 1) Triboelectric nanogenerator 1
• 2) Structural design of triboelectric nanogenerator 8
• 3) Liquid-solid contact electrification in triboelectric nanogenerator 13
• 2. Dissertation scope 18
• Chapter 2. Structural Design of Liquid-Solid Contact Electrification-based Transparent nanogenerator 20
• 1. Fabrication of transparent electrode by electrohydrodynamic jet printing 20
• 1) Transparent electrode for hybrid energy harvesting 20
• 2) Electrohydrodynamic printing for transparent electrode 21
• 3) Optical and electrical performance of transparent electrode 27
• 2. Performance of transparent triboelectric nanogenerator 32
• 1) Fabrication of transparent triboelectric nanogenerator 32
• 2) Optical Performance of triboelectric nanogenerator 34
• 3. Hydrodynamics of liquid-solid contact electrification-based triboelectric nanogenerator 36
• 1) Experimental setup of the liquid-solid contact electrification-based triboelectric nanogenerator 36
• 2) Electric output sequence of liquid-solid contact electrification-based triboelectric nanogenerator 37
• 3) Energy harvesting according to the Weber number 40
• 4. Performance of liquid-solid contact electrification-based triboelectric nanogenerator 45
• 1) Comparison the performance of the printed electrode based-TENG and ITO glass based-TENG 45
• 2) Energy band diagram of the liquid-solid contact electrification-based triboelectric nanogenerator 47
• 3) Hybrid energy harvesting with solar cell 49
• 5. Conclusion 52
• Chapter 3. Structural Design of liquid-solid contact electrification-based flexible triboelectric nanogenerator 53
• 1. Structural design of flexible triboelectric nanogenerator 53
• 1) Flexible electrode for hybrid energy harvesting 53
• 2) Working mechanism of strain-induced electrification-based nanogenerator 55
• 3) Fabrication of strain-induced electrification based nanogenerator 57
• 2. Hydrodynamics of wind and liquid-solid contact electrification-based hybrid triboelectric nanogenerator 59
• 1) Experimental setup for strain-induced electrification-based nanogenerator by wind 59
• 2) Hydrodynamics in nanogenerator by wind 61
• 3) Hydrodynamics of nanogenerator by liquid 65
• 4) Hybrid energy harvesting with wind and liquid drop 69
• 3. Conclusion 70
• Chapter 4. Structural Design of pH Sensor based on the Liquid-solid Contact Electrification 71
• 1. Structural design of pH sensor 71
• 1) Liquid-solid contact electrification in sensor applications 71
• 2) Rectification phenomenon on liquid-solid contact electrification 72
• 3) 2D material doping in the electrification layer 75
• 4) Fabrication of pH sensors 76
• 2. Electrochemical analysis of pH sensor 83
• 1) Experimental setup of electrochemical analysis 83
• 2) Flat band potential of pH sensor with various pH solutions 91
• 3. Rectifying phenomena in electrical performance 92
• 1) Electrical performance of samples with different work functions and pH 92
• 2) Working mechanism of the pH sensor 96
• 3) Electrical output varies the droplet volume 97
• 4) Electrical output by the artificial sweat 98
• 5) Comparison of capacitor charging times 99
• 4. Conclusion 101
• Chapter 5. Conclusion 102
• References 105
• 논문요약 118