Analyses of Electrochemically Generated Ionic Solids and Liquids by Bromine

Abstract

In this thesis, quaternary ammonium polybromide (QBr2n+1) droplets and heptyl viologen bromide dual redox ionic complexes were electrochemically studied through stochastic chronoamperometric analyses. The first part contains the comparison of ion partition coefficients at an interface between water and electrochemically generated quaternary ammonium polybromide (QBr2n+1) droplets (water│QBr2n+1) in QBr aqueous solutions containing different acids (HAs). The concentration of Br− in QBr2n+1, CBr-(QBr2n+1) is linearly proportional to CA-(aq) with the proportionality constant, which was estimated from the difference between the two partition coefficients of H+ and A− from water toward QBr2n+1, KH+-KA-, and the ratio of the mean activity coefficient of the aqueous over that of the QBr2n+1 phase, γ±,aq/γ±,QBr2n+1. CBr-(QBr2n+1) also shows the linear function of CQ+(aq) with (γ±,aq/γ±,QBr2n+1)KQ+ as its proportionality constant. The stochastic chronoamperometric analyses of QBr2n+1 droplets during their particle-impacts on Pt UME in acidic solutions containing either N-methyl-N-ethyl pyrrolidinium bromide (MEPBr) or ethylpyridinium bromide (EPyBr) as model QBrs can provide indirect information about CBr-(QBr2n+1). Based on the experimental data, the relative order to be KC+(Li+ or Na+), KH+, and KA-: KC+(Li+ or Na+)<KH+<KA-, where KHSO4-<KClO4-<KCl- in KA- and KNa+<KLi+ in KC+ was estimated. Also, it was found that Br−-IT at water|QBr2n+1 is effectively limited by A−-IT in the acidic solutions, and Cl− is most significantly transferred to QBr2n+1, leading to the complete inhibition of Br−-IT into QBr2n+1.

Next, mechanism of heptyl viologen dibromide (HVBr2) as a dual-redox species in redox-enhanced electrochemical capacitor (Redox-EC) was investigated. HV2+ is electrochemically reduced to HV+· and form a solid complex, [HV+··Br-] on an anode while Br- is electro-oxidized to Br3- and render [HV2+·2Br3-] on a cathode during the charging process of Redox-EC. Based on these reactions, it was presented that detailed electrochemical studies of formation of [HV2+·2Br3-] and [HV+··Br-], their redox features, and galvanic exchange reactions between the two types of dual-redox ionic solids on Pt ultramicroelectrode (UME) in neutral (0.33 M Na2SO4) and acidic (1 M H2SO4) solutions. Most importantly, through voltammetric and particle-impact electrochemical analyses, the redox and galvanic exchange reactions of the two dual-redox ionic solid complexes involve H+ transfer, which is the key process to limit the overall kinetics of the electrochemical reactions. The proton accompanied galvanic exchange reaction based on computational simulation was also rationalized.|본 학위 논문에서는, 확률적 시간대전류법 분석을 통한 4차 암모늄 폴리 브롬화물과 헵틸 비올로겐 브롬화물 이중 산화환원 이온성 복합체의 전기화학적인 연구를 다루고 있다. 제 1장에서는 산(HAs)의 농도를 다르게 한 QBr 수용액에서 전기화학적으로 형성된 4차 암모늄 폴리 브롬화물 (QBr2n+1) 방울과 물 사이의 계면에서 이온 분배계수를 비교하였다. QBr2n+1에서 브롬화물(Br-)의 농도는 CA-(aq)에 선형으로 비례하며, 이는 물에서 QBr2n+1 방향으로 H+와 A-의 분배 계수들 사이의 차이(KH+-KA-) 및 QBr2n+1 상과 수용액 상의 평균 활동도 계수의 비(γ±,aq/γ±,QBr2n+1)로부터 추정되었다. 또한 CBr-(QBr2n+1)은 (γ±,aq/γ±,QBr2n+1)KQ+를 비례 상수로 하여 에 일차 함수라는 것을 보여준다. N-메틸-N-에틸 피롤리디늄 브롬화물(MEPBr) 또는 에틸피롤리디늄 브롬화물(EPyBr)을 포함하는 산성 용액 조건으로 백금 초소형 전극(UME)에서 입자 충돌을 관측했을 때, QBr 모델로서 QBr2n+1 방울의 확률적 시간대전류법 분석은 CBr-(QBr2n+1)에 대한 간접적 정보를 제공할 수 있으며, 이를 통해 KNa+<KLi+<KH+<KHSO4-<KClO4-<KCl-로서, KC+(Li+or Na+)와 KH+, KA-의 상대적 크기를 추정하였다. 또한, 산성 용액에서의 물|QBr2n+1 브롬화물 이동이 음이온의 이동에 의해 효과적으로 제약을 받으며, QBr2n+1로의 브롬화물 이동이 완전히 막히면서 염화물이 QBr2n+1로 가장 잘 이동한다는 것을 확인하였다.

다음으로, 산화환원 증진 전기화학적 커패시터 (Redox-EC)에서의 헵틸 비올로겐 이브롬화물 (HVBr2) 이중 산화환원 종의 반응 기작이 연구되었다. Redox-EC의 충전과정 동안, 양극에서 HV2+는 HV+·로 전기화학적으로 환원되어 고체 복합체인 [HV+··Br-]를 형성하며, 음극에서는 Br-가 Br3-로 전기화학적으로 산화되어 고체 복합체인 [HV2+·2Br3-]를 형성한다. 이러한 반응들을 기반으로 하여, 중성(0.33 M Na2SO4)과 산성(1 M H2SO4) 용액에서 두 가지 종류의 이중 산화환원 이온성 고체 간의 갈바니 교환 반응 및 이들의 산화환원 양상, [HV2+·2Br3-]과 [HV+··Br-] 형성의 전기화학적 연구를 기술하였다. 전압전류적과 입자 충돌 전기화학적 분석을 통해, 이중 산화환원 이온성 고체 복합체의 산화환원과 갈바니 교환 반응은 수소 이동을 포함하며, 전기화학적 반응의 전체 속도를 제한하는 중요 과정임을 밝혀내었다. 계산화학 시뮬레이션에 기반 하여 수소가 동반된 갈바니 교환 반응 역시 증명되었다.; In this thesis, quaternary ammonium polybromide (QBr2n+1) droplets and heptyl viologen bromide dual redox ionic complexes were electrochemically studied through stochastic chronoamperometric analyses. The first part contains the comparison of ion partition coefficients at an interface between water and electrochemically generated quaternary ammonium polybromide (QBr2n+1) droplets (water│QBr2n+1) in QBr aqueous solutions containing different acids (HAs). The concentration of Br− in QBr2n+1, CBr-(QBr2n+1) is linearly proportional to CA-(aq) with the proportionality constant, which was estimated from the difference between the two partition coefficients of H+ and A− from water toward QBr2n+1, KH+-KA-, and the ratio of the mean activity coefficient of the aqueous over that of the QBr2n+1 phase, γ±,aq/γ±,QBr2n+1. CBr-(QBr2n+1) also shows the linear function of CQ+(aq) with (γ±,aq/γ±,QBr2n+1)KQ+ as its proportionality constant. The stochastic chronoamperometric analyses of QBr2n+1 droplets during their particle-impacts on Pt UME in acidic solutions containing either N-methyl-N-ethyl pyrrolidinium bromide (MEPBr) or ethylpyridinium bromide (EPyBr) as model QBrs can provide indirect information about CBr-(QBr2n+1). Based on the experimental data, the relative order to be KC+(Li+ or Na+), KH+, and KA-: KC+(Li+ or Na+)<KH+<KA-, where KHSO4-<KClO4-<KCl- in KA- and KNa+<KLi+ in KC+ was estimated. Also, it was found that Br−-IT at water|QBr2n+1 is effectively limited by A−-IT in the acidic solutions, and Cl− is most significantly transferred to QBr2n+1, leading to the complete inhibition of Br−-IT into QBr2n+1.

Next, mechanism of heptyl viologen dibromide (HVBr2) as a dual-redox species in redox-enhanced electrochemical capacitor (Redox-EC) was investigated. HV2+ is electrochemically reduced to HV+· and form a solid complex, [HV+··Br-] on an anode while Br- is electro-oxidized to Br3- and render [HV2+·2Br3-] on a cathode during the charging process of Redox-EC. Based on these reactions, it was presented that detailed electrochemical studies of formation of [HV2+·2Br3-] and [HV+··Br-], their redox features, and galvanic exchange reactions between the two types of dual-redox ionic solids on Pt ultramicroelectrode (UME) in neutral (0.33 M Na2SO4) and acidic (1 M H2SO4) solutions. Most importantly, through voltammetric and particle-impact electrochemical analyses, the redox and galvanic exchange reactions of the two dual-redox ionic solid complexes involve H+ transfer, which is the key process to limit the overall kinetics of the electrochemical reactions. The proton accompanied galvanic exchange reaction based on computational simulation was also rationalized.