123rd General Meeting of the KCS

Type Poster Presentation
Area Electrochemistry
Room No. Exhibition Hall 2
Time 4월 18일 (목요일) 11:00~12:30
Code ELEC.P-445
Subject Revisit V(V)-V(IV)-V(III)-V(II) electrochemistry in highly concentrated acidic medium: origin of parasitic hydrogen evolution reaction (HER)
Authors Jihye Lee, Jinho Chang*
Department of Chemistry, Hanyang University, Korea
Abstract We present the through voltammetric analyses associated with V(V)-V(IV)-V(III)-V(II) redox chemistry occurring in highly concentrated mixed acidic medium based on digital voltammetric simulation for understanding electrochemistry in high energy density VRFB. Virtually, the proposed mechanism of VO2+/VO2+ and V3+/V2+ redox reactions on a carbon electrode are well described in each elementary steps. However, the proposed mechanistic pathway was remained questionable because, as the authors’ best knowledge, we could not find the reports to prove or identify the proposed reaction pathway through voltammetric analyses based on the thorough investigation from the digital voltammetric simulation. In addition, it has been known that hydrogen evolution reaction (HER) occurs as the side reaction during electro-reduction of V3+ in VRFB, which decline the coulombic efficiency of VRFB due to the partial consumption of charge during the charge process. In spite of the importance of understanding the origin of the parasitic HER occurring in VRFB, only a few articles have been reported, and therefore, main reason for this critical side reaction is still unrevealed. we found the generation of V(II) species as the side reaction, which could act as an electrocatalyst for HER, and this V(II) species could only exist when V3+ is electrochemically reduced on a glassy carbon electrode resulting in high local concentration of V2+ in the vicinity of the electrode surface. This vanadium catalyst disappears when the local high concentration of V2 + disappears and the catlyst effect disappears. This reaction is called the ‘phantom effect’. This ‘phantom’ effect of V(II) species could be also well explained based on the suggested mechanism. This effect occurs when the starting material of the reaction is V(Ⅳ)O2+ or V3+(Ⅲ). These starting materials can be reduced by electrochemical methods such as chronoamperometry or cyclic voltammetry to confirm the HER catalyst effect and phantom effect.
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