Cyclic Voltammetry Coupled with Faradic Adsorption/Desorption Processes: A Finite Element Simulation

doi:10.13208/j.electrochem.190411

Abstract

Abstract:

Heterogeneous electron transfer (HET) coupled with Faradic adsorption/desorption is the fundamental processes involved in hydrogen evolution reaction, oxygen reduction reaction, carbon dioxide reduction reaction, and methanol oxidation reaction. However, the electrochemical behaviors of HET coupled with Faradic adsorption/desorption are complicated, and difficult to get the interface reaction kinetics quantitatively. In this paper, finite element method was adopted to simulate the cyclic voltammetric behaviors of HET coupled with Faradic adsorption/desorption processes by using the Fick’s second law and Langmuir isotherm. The cyclic voltammograms when reactant or product adsorbed weakly or strongly were simulated, and they agreed well with the classical results. In addition, taking the reactant adsorption for example, the effects of scanning rate, saturated adsorption and adsorption equilibrium constant on cyclic voltammograms were investigated. The simulation demonstrates that weak adsorption can be magnified with the increasing scanning rate, and the peak current changes gradually from being proportional to the square root of scanning rate to being proportional to the scanning rate. The difference between anodic and cathodic peak currents is linearly related to saturated adsorption. Therefore, the quantitative characterization of saturated adsorption is realized by correlating the difference between anodic and cathodic peak currents to the saturated adsorption. With the increasing adsorption equilibrium constant, the weak adsorption transfers to strong adsorption, and the adsorption/desorption peaks separate from diffusion peaks to form prepeaks or postpeaks. The potential-dependent adsorption equilibrium constant was also simulated, which demonstrates that it can further change the shape and position of adsorption/desorption peaks. The quantitative method based on this model can help researchers to obtain saturated adsorption and adsorption equilibrium constant quantitatively from the cyclic voltammograms coupled with Faradic adsorption/desorption processes. The simulation can also help researchers to understand the different cyclic voltammetric behaviors between surface processes and diffusion processes, and would be constructive for the study of electrocatalysis involving adsorption/desorption processes.

Key words: adsorption/desorption, heterogeneous electron transfer, electrode process, cyclic voltammetry, finite element simulation

CLC Number:

O646.54

GUO Jia-yao, CHEN Duan, ZHANG Jie, ZHAN Dong-ping. Cyclic Voltammetry Coupled with Faradic Adsorption/Desorption Processes: A Finite Element Simulation[J]. Journal of Electrochemistry, 2020, 26(2): 281-288.

Figures/Tables 6

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Tab. 1

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Parameter	Value
D_i	7.4 × 10^-6 cm²·s^-1
E⁰	0.19 V vs. SCE
r_e	1 mm
n	1
α	0.5
C_Ox^*	0 mmol·L^-1
C_Re^*	0.5 mmol·L^-1
k⁰	5 cm·s^-1