Staircase cyclic voltammetry of electrocatalytic reaction inhibited by the product
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ORIGINAL PAPER
Staircase cyclic voltammetry of electrocatalytic reaction inhibited by the product Šebojka Komorsky-Lovrić 1 & Milivoj Lovrić 1 Received: 27 February 2020 / Revised: 12 March 2020 / Accepted: 13 March 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract A model of electrocatalytic reaction influenced by the potential dependent inhibition is developed. The response of investigated mechanism is anomalous voltammogram consisting of two anodic peaks. The relationship between two peak currents and the parameters of electrode reaction was analysed theoretically. Keywords Staircase voltammetry . Electrocatalytic reaction . Inhibition by product . Simulation
Introduction
product of catalytic reaction forms the adsorbed complex with the oxidized form of catalyst [26]:
A deactivation and subsequent reactivation of electrode surface occur during the oxidation of methanol [1–7], ethanol [8–12], glycerol [12, 13], and formic acid [14, 15]. They are caused by the formation and dissolution of surface oxide [16–18] or by the adsorption and desorption of intermediates [19–21]. In the cyclic voltammetry these mechanisms are manifested by anodic peaks in both anodic and cathodic branches. Similar phenomena are observed in the protein film voltammetry [22–24] and the reduction of chloroauric acid [25]. In the latter case a prominent maximum of cathodic current appears when potential scanning proceeds in the anodic direction. This current is explained by the evolution of hydrogen catalysed by short-lived adsorbed gold particles. In this paper it is demonstrated that anomalous voltammograms may appear in the electrocatalytic reactions under the influence of potential dependent inhibition by the product.
Ered;ads ↔Eox;ads þ e−
ð1Þ
Eox;ads þ S→Ered;ads þ P
ð2Þ
Eox;ads þ P↔ðEox PÞads
ð3Þ
The model A totally irreversible electrocatalytic oxidation of dissolved substrate that is coupled to the reversible electrode reaction of adsorbed catalyst is considered. It is assumed that the Dedicated to the best friend, Professor Fritz Scholz, on the occasion of his 65th birthday * Milivoj Lovrić
1
Zagreb, Croatia
During the experiment, the surface concentration of catalyst does not change. The substrate cannot be electro-oxidized on the bare electrode surface due to very slow electron transfer. The investigated mechanism can be represented by the following system of differential equations and the starting and boundary conditions: ∂cS =∂t ¼ D∂2 cS =∂x2
ð4Þ
∂cP =∂t ¼ D∂2 cP =∂x2 t ¼ 0;
x≥0 :
ð5Þ cS ¼
c*S ;
cP ¼ 0
cP →0 ¼ ΓEred exp F E−E 0 =RT
t > 0;
x→∞ :
x¼0:
ΓEox
cS →c*S ;
ΓEred þ ΓEox þ ΓEox P ¼ ΓE;tot
ð6Þ ð7Þ ð8Þ ð9Þ
−1 ΓEox P Γ−1 E ox cP;x¼0
ð10Þ
Dð∂cS =∂xÞx¼0 ¼ k cat ΓEox cS;x¼0
ð11Þ
Dð∂cP =∂xÞx¼0 ¼ −k cat ΓEox cS;x¼0
ð12Þ
I=FA ¼ k cat ΓEox cS;x¼0
ð13Þ
KEP ¼
In the staircase voltammetry the equation dΓEox =dt ¼ 0 is satisfied at the end of the potential step, when the current is
J Solid State Electrochem
measured [27]. Differential Eqs. (4) and (5) are transfor
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