Unraveling V(V)-V(IV)-V(III)-V(II) Redox Electrochemistry in Highly Concentrated Mixed Acidic Media for a Vanadium Redox Flow Battery: Origin of the Parasitic Hydrogen Evolution Reaction
- Authors
- Lee, Jihye; Muya, Jules Tshishimbi; Chung, Hoeil; Chang, Jinho
- Issue Date
- Nov-2019
- Publisher
- AMER CHEMICAL SOC
- Keywords
- all vanadium redox mechanism; hydrogen evolution reaction; vanadium(II) oxide; electrocatalyst; vanadium redox flow battery
- Citation
- ACS APPLIED MATERIALS & INTERFACES, v.11, no.45, pp.42066 - 42077
- Indexed
- SCIE
SCOPUS
- Journal Title
- ACS APPLIED MATERIALS & INTERFACES
- Volume
- 11
- Number
- 45
- Start Page
- 42066
- End Page
- 42077
- URI
- https://scholarworks.bwise.kr/hanyang/handle/2021.sw.hanyang/146909
- DOI
- 10.1021/acsami.9b12676
- ISSN
- 1944-8244
- Abstract
- We present a mechanistic understanding of the full redox electrochemistry of V(V)-V(IV)-V(III)-V(II) and the origin of the parasitic hydrogen evolution reaction (HER) during electroreduction of either V3+ or VO2+ in a highly concentrated mixed acidic solution based on both electroanalytical and computational approaches. First, we found that the VO2+/VO2+ redox reaction is well explained by the EC/EC square scheme. We also found that V3+ is electrochemically oxidized to V4+ and subsequently undergoes a transition to stable VO2+ via hydrolysis. In the V3+/V2+ redox reaction via voltammetric analysis at scan rates greater than 0.05 V/s, the voltammograms are well explained based on a simple 1e(-) transfer reaction scheme. However, at the longer time scale observed in the chronoamperograms with constantly applied potentials where V3+ is electrochemically reduced to V2+, we found that a significant HER occurs because of possible formation of an electrocatalyst related to the V(II)O species, V(II)(catalyst). We suggest that V(II)O is kinetically formed from V2+ via hydrolysis only when a local concentration of V2+ is high in the vicinity of a GC electrode surface, and V(II)O is adsorbed on a GC surface to form V(II)(catalyst). To extend our mechanistic pathway, electroreduction of VO2+ to V(II) was also analyzed, revealing that VO2+ is electroreduced to VO+ and further reduced to VO in addition to disproportionation of VO+. Eventually, V(II)(catalyst) forms on a GC electrode, resulting in a significant HER. The computational calculation strongly supports the possible formation of V(II)(catalyst). The calculation shows that neither V3+ nor V2+ can form stable intermediates during the HER, while V(II)O has the highest proton affinity compared with V(III)(O+) and V(IV)O2+, indicating a plausible electrocatalytic property of V(II)O for the HER.
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