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Nitrogen-doped carbon produced by chlorination process of Ti(C,N) and its electrochemical properties

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Authors
이문균
Advisor
정인호
Major
공과대학 재료공학부
Issue Date
2019-02
Publisher
서울대학교 대학원
Description
학위논문 (박사)-- 서울대학교 대학원 : 공과대학 재료공학부, 2019. 2. 정인호.
Abstract
Ti(C,N) solid solution과 염소간의 반응을 통한 N-doped carbon (CN) 의 합성, 그리고 붕소 추가를 통해 hollow structured B,N co-doped carbon (CNB) 을 얻는 결과는 기존 실험에서 보고가 되었습니다. 허나, 이들 선행연구에서는 질소 치환이 가능 할 수 있었던 이유와, Ti(C,N) 의 질소의 양에 따른 구조적 변화 및 중공구조(hollow structure)를 얻는 메커니즘의 관한 이해는 다소 불충분 하였습니다.



불충분 했던 형성 메커니즘을 더 명확히 규명하고자, 본 졸업논문에서는 제 1부는 메커니즘에 대해 재론하고자 합니다.



제 1부에서 얻어진 이해를 통해 제 2부에서는 기존의 N-doped carbon을 에너지 소재의 특성 측면에서 어떻게 향상시킬 수 있는가?를 재료의 열역학적 결정학적 측면에서 살펴보고 이를 바탕으로 새로운 공정을 제시하였습니다. 본 공정을 통하여 capacitance가 크게 향상된 N-doped carbon (CN) 을 합성할 수 있으며, 본 소재가 에너지 저장 소재(슈퍼-커패시터)로서 높은 응용 가능성을 가짐을 보였습니다.



마지막으로 제 3부에서는 새로운 합성법을 통해 얻어진 Fe-CNB합성 메커니즘 및 전기화학 촉매(ORR)로의 응용을 논하고자 합니다. 앞에서 얻어진 결과 및 이해를 바탕으로, 탄소체(carbon) 표면에 전이금속 원자들을 효과적으로 치환할 수 있는 방법을 제시하였으며, 이 과정에서 붕소의 도입이 Fe 원자가 N-doped carbon (CN) 에 원자단위로 효과적으로 치환되는데 중요한 역할을 함을 제시하였습니다. 원자단위로 분포된 Fe-Nx 의 경우 Pyridinic-N 주변의 Fe, 즉 Fe-N4 로 형성된 구조로 존재할 때 열역학적으로 가장 안정합니다. 붕소의 도입은 Fe-CN에서 pyridinic-N의 안정성을 높여, Fe-N4 형성을 극대화 시키며, 합성된 Fe-CNB가 높은 촉매 특성(ORR)을 보이는 주요인자로 작용함을 증명하였습니다.
Since the first demonstration of carbide-derived carbon (CDC), extensive research over varieties of metal carbides has been conducted and examined for use in numerous applications including supercapacitor, catalysis/catalyst support, gas storage/separation etc. Despite outstanding performances from CDC, due to limited variable compositions in metal carbide have drawn back its further uses as advanced material.

Previously, we have demonstrated one-step chlorination process to functionalize CDC materials by heteroatoms-doping (nitrogen and boron) having microporous to hollow structured carbon materials. The functionalized CDC material exhibited an enhancement in several applications, including CO2 storage and oxygen reduction reaction (ORR). However, the mechanism involving nitrogen doping and the formation of hollow carbon still remained unclear at the time.

In this thesis in part 1, we have revisited the nitrogen-doped carbon (CN) materials produced from the chlorination process using titanium carbonitride to explore and propose a possible mechanism involving nitrogen doping and the formation of hollow carbon material in terms of experimental and theoretical.

In part 2, we explore how to improve the existing N-doped carbon for energy storage material. Based on thermodynamic and crystallographic aspect, we propose a novel process to synthesize N-doped carbon. The process involves vacuum-annealing of starting material (titanium carbonitride) prior to chlorination reaction and this has confirmed a noticeable improvement in volumetric capacitance that is comparable to graphene materials.

Lastly, part 3 discusses how to prepare atomically dispersed Fe-CNB material and its electrocatalysts applications such as the oxygen reduction reaction. Based on the previous results and understandings, a novel in-situ method for effective doping of transitional metal atoms on the surface of nitrogen-doped carbon materials is proposed. In this work, the introduction of boron significantly increased the availability of pyridinic-N functional groups in CN materials, which allows Fe atoms to effectively bond to the surrounding four nitrogen atoms by forming Fe-N4 structure. The introduction of boron increases the stability of pyridinic-N in Fe-CN, and maximizes Fe-N4 formation, which is thermodynamically the most stable coordinated structured form. Consequently, atomically dispersed Fe-CNB demonstrated high electrochemical ORR catalytic properties. Moreover, the large-scale fabrication is also possible by this in-situ route, without any toxic acid leaching or post-treatment process involved.
Language
eng
URI
https://hdl.handle.net/10371/151819
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College of Engineering/Engineering Practice School (공과대학/대학원)Dept. of Material Science and Engineering (재료공학부) Theses (Ph.D. / Sc.D._재료공학부)
  • mendeley

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