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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

Title
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
Author
장진호
Keywords
all vanadium redox mechanism; hydrogen evolution reaction; vanadium(II) oxide; electrocatalyst; vanadium redox flow battery
Issue Date
2019-11
Publisher
AMER CHEMICAL SOC
Citation
ACS APPLIED MATERIALS & INTERFACES, v. 11, no. 45, Page. 42066-42077
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.
URI
https://pubs.acs.org/doi/10.1021/acsami.9b12676https://repository.hanyang.ac.kr/handle/20.500.11754/155249
ISSN
1944-8244; 1944-8252
DOI
10.1021/acsami.9b12676
Appears in Collections:
COLLEGE OF NATURAL SCIENCES[S](자연과학대학) > CHEMISTRY(화학과) > Articles
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