2D, 3D nanostructure materials for electrochemical energy storage and conversion

Bui Thi Hoa 한양대학교 대학원 2020 국내박사

Energy is an essential factor for sustainable development and poverty eradication. Due to the growing of global energy demand and increasing levels of greenhouse gases and pollutants, scientists nowadays are paying a huge attention to establish a new energy technology, which is clean, environmentally friendly, and cost effective. In my doctoral research, I have demonstrated on the development of 2D and 3D nano structure materials for energy storage and energy conversion technology in the lithium rechargeable batteries (Li-X batteries; X=S,Se) field, electrochemistry such as water splitting: oxygen evolution reaction, hydrogen evolution reaction (HER, OER) and oxygen reduction reaction (ORR). In chapter 1, we introduced about two-dimensional transition metal dichalcogenides. We discuss about the background, general information about synthesis methodology, physical/chemical properties, and potential applications of two-dimensional transition metal dichalcogenides. Similarly, we also introduced about three-dimensional nanostructure materials Prussian Blue and Metals-based Prussian Blue. It provided information about the current research state of Prussian Blue and Metals-based Prussian Blue as preparation methods and application fields. Moreover, we have discussed about the tendency of research about energy storage and energy conversion technology. In chapter 2, we introduced a new strategy to fabricate multi-layered graphene structure embedding in situ generated selenides active cathode materials for high-power Li-Se battery by exploiting the MoSe2- multilayered graphene (Gr- MoSe2) structure. The MoSe2 has been synthesized by applying a reflux system and selenoacetamide were used as Se precursor without using any reduced reagent. Moreover, this strategy also introduced the generation in situ a layer of graphene in the interlayer of MoSe2, which improves the Litium -Selenium battery’s performance. Moreover, the shuttle effects can be effectively controlled, and the multi-layered graphene structure becomes a promising cathode platform for Li-Se batteries. In chapter 3, we presented a strategy to successfully synthesize the hybrid MoS-Se-multilayered graphene (MoS-Se-Gr) composite by applying a closed reflux system with two different S and Se precursor ratios of 1:1 and 5:1, then multilayered graphene was formed by calcination processes in inert conditions. The multi-layered graphene structure generated an in situ SSe active cathode material for high performance and long cycling life Li/S-Se battery by electrochemically reduction (lithiation) of MoS-Se-multilayered graphene (MoS-Se-Gr) structure. The multilayered graphene became an ideal platform to reduce shuttling effects by providing the space for the formation of intermediate lithium S-Se during discharging/charging processes. In addition, with the existence of multilayer graphene and the hybrid structure of coupled S and Se in composite materials improves electrical properties and reduce the internal resistance of cathode for getting high capacities and long cycle lifetime of Lithium /Sulfur-Selenium battery. In chapter 4, we developed an aqueous-solution based chemical transformation approach for the formation of cobalt hexacyanoferrate (Co-HCF= Co3[Fe(CN)6]2). Cobalt hexacyanoferrate has been deposited as a Prussian blue analog metal–organic-framework on a substrate using an ion-exchange chemical transformation route. When the Co-HCF film was investigated as a catalyst for electrochemical oxygen evolution reaction (OER). The Co-HCF crystals has demonstrated the superior electrocatalytic performance on water-oxidation from alkaline and neutral electrolytes, which is competitive to the catalytic performance demonstrated by the many outstanding water-oxidation catalysts. In chapter 5, we designed the thin film of nickel based Prussian blue analog hexacyanoferrate (Ni-HCF: Ni3[Fe(CN)6]2), particularly via electrochemical anodization route. Hydrogen is one of the friendly fuels to the environment, and the most widely used in key industrial process. Consequently, hydrogen is going to play an important role in energy carrier economy in the future. The production of molecular hydrogen by electrochemical splitting of water is becoming very promising for the development of clean energy technology. Unfortunately, the cathodic process for hydrogen evolution reaction (HER) in electrochemical water splitting devices are traditionally facilitated by noble metals such as platinum. However, due to the rising cost of platinum, significant advances have been achieved to identify HER electrocatalysts in alternate to platinum. The obtained Ni-HCF film achieved high performance for electrochemical hydrogen evolution reaction, suggesting an interesting candidate and promising routes for identifying highly active HER electrotrocatalysts with high performance for electrochemical HER in 1 M KOH electrolyte with the long-term electrochemical durability. Furthermore, this work reports on designing the metal-HCF electrode based on full-water splitting device consisting of the binder-free Ni-HCF film on Ni-plate and Co-HCF film on carbon paper, as HER and OER electrodes, which is promising for overall water splitting.

Investigation on the relation between molecular architecture and perturbed photophysical properties of self-assembled conjugated systems

Bui, Thi Hoa Chonnam National University 2019 국내박사

본 논문은 분자 구조와 일련의 자기 조립 컨쥬게이션 계의 교란된 광물리 특성 사이의 관계에 대해 조사한다. 처음에는 짧은 전체적인 소개가 제 1 장에서 주어졌다. 제 2 장에서는 자기 조립 구조와 구조적 이동성에 따라 비극성 및 극성 외부 사슬을 갖는 벌크 테트라페닐에틴 (tetraphenylethene; TPE) 유도체의 응집 유도 방출 특성을 연구했다. 비극성 도데실 및 극성 디에틸렌옥사이드 사슬을 갖는 벌크 TPE 유도체는 실온에서 각각 액정(liquid crystal; LC) 및 결정성 상으로 존재한다. 상이한 외부 도데실 사슬의 수는 LC 단계에서 방향족 패킹 기하 구조 및 전반적인 이동 특성에 영향을 미쳤다. 우리는 이동형 LC 특성이 응집체에서 바람직하지 않은 비방사 로컬 사이트의 수를 최소화하고, TPE 유도체의 J-형 커플링이 된 전이 쌍극자들의 지그재그 쌓임 기둥 구조를 유도하기 때문에 대량의 TPE 유도체의 모바일 LC 특성이 높은 AIE 효율성을 위해 매우 중요하다는 것을 입증했다. AIE 발광체의 모바일 LC 특성은 매우 효율적인 고체 상태 발광에 유리할 수 있다. 반면, 극성 외부 체인을 갖는 TPE는 표면 트랩 상태 및 다결정 도메인 구조 내의 다양한 결손 부위에 의해 발생된 많은 바람직하지 않은 전자 상태를 포함하는 다결정이며, 낮은 발광 효율을 초래한다. 제 3 장에서는 트리페닐아민(tetraphenylamine; TPA) 치환기를 갖는 붕소–디피 로메틴 (boron-dipyrromethene; BODIPY) 유도체의 생리학적 성질과 바이오 이미징에의 적용 가능성을 조사하였다. 치환 위치 (meso/β) 및 치환기의 수는 유도체의 분자 내 전하 이동(intramolecular charge transfer; ICT) 방출에 크게 영향을 미친다. 분광학 및 이론적 결과에 기초하여, BODIPY상의 TPA의 β- 치환은 BODIPY 잔기의 HOMO를 효과적으로 교란시키고, β-치환된 TPA를 갖는 BODIPY 유도체는 무극성 및 중간 극성 용매에서 약 640 nm의 강한 ICT 발광을 보인다. 프로펠러와 같은 비평면 형상을 갖는 TPA 치환체는 인접한 BODIPY 유도체 단위 사이의 H-형 응집을 방지할 수 있다. BODIPY 유도체의 β-치환 TPA에 의한 응집 유도 발광 증진 (aggregation-induced emission enhancement; AIEE) 거동을 확인했고, 하여 이는 고농도 및 응집 조건 하에서 높은 발광 효율을 유지하는데 유리하다. β- 치환된 TPA를 갖는 BODIPY 유도체의 붉은색 발광 및 AIEE 특성이 바이오 이미징에 유효한 특성들이기 때문에, 우리는 가장 간단한 BODIPY 유도체로 L-929 섬유아세포를 감염시키려 시도했다. 단일 β-치환 TPA (화합물 2)를 갖는 BODIPY 유도체는 다공성 실리카 나노 입자에 효과적으로 담았고, 화합물 2 - 실리카 나노 입자 (2-SNPs)는 높은 광 안정성을 나타내었다. 2-SNP로 감염한 후의 세포의 광학 이미지는 양호한 세포 흡수 및 붉은색 형광을 나타내며, 2-SNP가 바이오 이미징을 위한 유망한 후보임을 시사한다. 제4 장에서는 폴리(N-아이소프로필아크릴레이트) (poly (N-isopropylacrylate); NIPAM) 기반 나노 겔의 이중 광/열 응답 형 다색 형광의 변조가 보고되었다. 열 반응성 pNIPAM내의 가교 결합된 매트릭스는 FRET 수용체로서 Fröster 공명 에너지 전달 (Förster resonance energy transfer; FRET) 주개 및 광 변색 스파이로파이랜 (spiropyran; SP) 염료와 정전기적 인력으로 결합된 니트로벤조옥사다이아졸 (nitrobenzoxadiazole; NBD) 단위체와 공유 결합되었다. 이 나노 겔은 NBD 부분의 형광에 해당하는 녹색 형광을 발광한다. 그러나 자외선을 조사하면 SP 형태의 C-O 스파이로 결합이 깨지고 분자는 메로시아닌 (merocyanine; MC) 형태를 취하게되어 옅은 분홍색 색을 띄는 나노 겔을 생성하게 된다. 특히, NBD와 SP 염료 사이의 열 반응성 FRET 과정에 의해 물에서 나노 겔의 선택적 형광 강도가 조절되었다. 고온에서, 나노 겔의 형광은 보다 효율적으로 FRET 공정에 의해 적색 편이 및 증대되었다. 나노 젤은 세포질에서 잘 분포되어 있으며 광 전환이 가능한 바이오 이미징 약제 및 나노 열 계량기와 같은 응용을 위해 준세포 환경에서 뛰어난 광 변색 기능을 보였다. 마지막으로 다환 방향족 탄화수소 (polycyclic aromatic hydrocarbons; PAHs)에서 질소 -헤테로 원자의 기능과 융합된 질소-헤테로 고리 화합물의 구성 방향족 고리 (인돌, 페닐)에 대한 융합 효과가 제5 장에서 논의되었다. 우리는 질소 원자의 주요 역할 융합된 질소-헤테로 고리 화합물은 PAH에 열역학적으로 안정한 방향족 5 각형 고리를 도입하고 6각형 고리만 갖는 일반적인 PAH와 비교하여 분자 구조를 교란시켰다. 고립되고 거대 고리 전류는 융합된 부분의 다른 기능을 명확히 보여 주었다. 하나는 동일 평면상의 기하적 구조를 유도하지만, 다른 하나는 거대 고리 π 전자 비확산의 형성에 전적으로 관여한다. 우리는 PAH의 5각형 고리의 도입과 융합 횟수가 PAH의 구조적 및 전자적 섭동을 유도하고 큰 PAH에서 컨쥬게이션 경로와 π-전자 비편재화를 제어하는 효과적인 방법이 될 수 있다고 제안했다. This dissertation investigates on the relation between molecular architecture and perturbed photophysical properties of several series of self-assembled conjugated/conjugated systems. At first, a short general introduction was given in chapter 1. In chapter 2, depending on the self-assembled structure and structural mobility, aggregation-induced emission characters of bulk tetraphenylethene (TPE) derivatives with nonpolar and polar exterior chains was studied. The bulk TPE derivatives with nonpolar dodecyl and polar di(ethylene oxide) chains are in liquid crystal (LC) and crystalline phase, respectively, at room temperature. The different number of exterior dodecyl chain affected the aromatic packing geometry and the overall mobile character in the LC phase. We demonstrated that the mobile LC character of the TPE derivatives in bulk is crucial for high AIE efficiency because the mobile LC character is effective in minimizing the number of undesirable nonemissive local sites in aggregates and inducing a homogeneous zigzag-stacked columnar structure with j-type coupled transition dipoles of the TPE derivatives. The mobile LC characteristics of AIE luminogens can be advantageous for highly efficient solid-state emission. On the other hand, TPE with polar exterior chains is polycrystalline which contains many undesirable electronic states caused by surface trap states and various defect sites inside the polycrystalline domain structure, resulted in low emission efficiency. In chapter 3, the photophysical properties of boron-dipyrromethene (BODIPY) derivatives with triphenylamine (TPA) substituents and their applicability to bio-imaging was investigated. The substituted position (meso/β) and the number of substituents strongly affected to intramolecular charge transfer (ICT) characteristic of the derivatives. Based on the spectroscopic and theoretical results, the β-substitution of TPA on BODIPY hybridizes locally-excited and intramolecular charge transfer characters in the S1 state because of strong coupling between the HOMOs of BODIPY and TPA moieties; consequently, the BODIPY derivatives with β-substituted TPAs exhibit strong red-color emission around 640 nm in non-polar and moderately polar solvents. Furthermore, the TPA substituent with propeller-like nonplanar geometry could prevent H-type aggregation between neighboring BODIPY derivative units and induce the aggregation-induced emission enhancement (AIEE) characteristic, which is helpful to maintain their emission efficiency under highly concentrated and condensed conditions. Since the red-color emission and AIEE property of the BODIPY derivatives with β-substituted TPAs are useful characteristics for bio-imaging application, we tried to apply the simplest BODIPY derivative to L-929 fibroblast cells. The BODIPY derivative with a single β-substituted TPA (compound 2) was effectively loaded into porous silica nanoparticles, and compound 2-loaded silica nanoparticles (2-SNPs) exhibited high photostability. The optical images of the cells after transfecting with 2-SNPs demonstrated a good cellular uptake, and red-color fluorescence, suggesting that 2-SNPs is a promising candidate for bio-imaging. In chapter 4, the modulation of the dual photo/thermo-responsive multicolor fluorescence of poly(N-isopropylacrylate) pNIPAM-based nanogels was reported. The thermo-responsive pNIPAM-crosslinked matrix was covalently copolymerized with nitrobenzoxadiazole (NBD) monomers as a Förster resonance energy transfer (FRET) donor and electrostatically conjugated with photochromic spiropyran (SP) dyes as a FRET acceptor. This nanogel emits green fluorescence corresponding to the fluorescence of the NBD moieties; however, when irradiated with UV light, the C-O spiro bond in the SP form is broken and the molecule adopts the merocyanine (MC) form, resulting in a light-pink color emitting nanogel. Notably, the selective fluorescence intensity of the nanogels in water was modulated by thermo-responsive FRET processes between the NBD and SP dyes. At higher temperatures, the fluorescence of the nanogels was red-shifted and enhanced by the more efficient FRET process. The nanogels were well-distributed in the cellular cytoplasm and showed excellent photochromic function in the subcellular environment for applications as photo-switchable bio-imaging agents and nanothermometers. Finally, the function of nitrogen-heteroatom in polycyclic aromatic hydrocarbons (PAHs) and fusion effect on constituent aromatic rings (indole, phenyl) of the fused N-heterocyclic compounds were discussed in chapter 5. We found that the major role of a nitrogen atom in the fused N-heterocyclic compounds is the introduction of thermodynamically-stable and aromatic five-membered ring in PAHs, and perturb the molecular structure compared to general PAHs with six-membered rings only. The localized and macrocyclic diatropic ring currents clearly demonstrated the different function of fused parts, one just induces coplanar geometry but the other is fully involved in the formation of macrocyclic π-electron delocalization. We proposed that the introduction of the five-membered ring in PAHs and the number of fusion times can be effective methods to induce structural and electronic perturbation of PAH as well as to control conjugation pathway and π-electron delocalization on large PAHs.