Irreversible electrocatalyic reduction of V(V) to V(IV) using phosphomolybdic acid

Michael S. Freund, Nathan S Lewis

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Abstract

Although VO2 +(aq) reduction is kinetically slow at glassy carbon and Pt electrodes, phosphomolybdic acid is shown to catalyze the electrochemical reduction of VO2 +(aq) to VO2+(aq) in 1.0 M H2SO4(aq). A second-order rate constant of 33 M-1 s-1 was observed for this process. 31P NMR spectra demonstrated that PMo11VO40 4- and PMo10V2O40 5- were the dominant P-containing species under electrocatalytic conditions. The incorporation of V into the polyoxoanion led to a shift in potential from E°(VO2 +(aq)/VO2+(aq)) = +0.80 V vs Ag/AgCl for free VV/VIV to E°′ = +055 V vs Ag/AgCl for VV/VIV bound in the heteropolyoxometalate (PMo11VO40 4-). This shift in formal potential corresponded to an equilibrium constant of 1.7 × 104 M-1 for preferential binding of VV over VIV by the heteropolyoxoanion. This negative shift in redox potential, combined with the slow electrochemical kinetics of free VO2 +(aq) reduction and with the facile reaction of bound VIV with free VV in 1.0 M H2SO4(aq), resulted in the irreversible electrocatalytic reduction of VO2 +(aq) to VO2+(aq).

Original languageEnglish
Pages (from-to)1638-1643
Number of pages6
JournalInorganic Chemistry
Volume33
Issue number8
Publication statusPublished - 1994

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ASJC Scopus subject areas

  • Inorganic Chemistry

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