Effects of Surface Pretreatment of Glassy Carbon on the Electrochemical Behavior of V(IV)/V(V) Redox Reaction

Abstract

This paper provides a systematic approach to investigate the reaction of V(IV)/V(V) redox couple and mainly focuses on the effect of surface roughness and functional groups derived from the pre-treatment on the electrochemical behavior of glassy carbon in V(IV)/V(V) solutions. 600-grit, 1200-grit and 4000-grit SiC sandpapers were utilized to change the roughness of the electrode surfaces. Cyclic voltammetry (CV) within different potential ranges were applied in advance to alter oxygen functional groups on the electrode surface as well as surface roughness. CV and electrochemical impedance spectroscopy (EIS) were then used to investigate the electrode behavior in 1 M V(IV)/V(V) (1:1) solution on glassy carbon electrodes. Scanning electron microscopy (SEM) was employed to characterize the surface roughness. X-ray photoelectron spectroscopy (XPS) was adopted to analyze the surface oxygen functional groups. It is shown that polishing and CV scans within different potential ranges can vary the electrochemical response of glassy carbon to V(IV)/V(V) couples significantly. Increased surface roughness is seen to be beneficial for the redox reaction while oxygen functional groups such as C=O and C-O-C tends to reduce the activity of glassy carbon.

Mass Transfer and Reaction Kinetic Enhanced Electrode for High‐Performance Aqueous Flow Batteries

“…We believe that the 1 min E‐GF electrode preserves an optimum balance between the conductivity, surface area, and wettability since the conductivity decreases with an increase in exfoliation time (Table S2, Supporting Information) that negatively influences the performance of the electrode. This behavior is also consistent with the study reported on the electrochemical oxidation of graphite felt electrode by Cao et al, where they concluded that the kinetics of the vanadium redox reactions are always dependent on two competing factors, the amount of incorporated oxygen groups and surface area of the electrode. Simultaneously, the E‐GF electrode becomes more hydrophilic as the exfoliation time increases, facilitating better electrolyte accessibility.…”

“…The peak at 284.6 eV is associated with the core level carbon atoms (CC/CC) in the graphitic carbon, whereas, the peaks at 285.8, 286.9, and 288.8 eV were assigned to the hydroxyl (CO), ester (COO)/carbonyl (CO), and carboxyl (OCO) functional groups, respectively. Another peak at 290.5 eV was also present in both of the electrodes attributable to the π to π* shake up satellite contributions . The intensities of all peaks related to the oxygen functional groups were increased in the E‐GF electrode compared to the pristine GF electrode, implying the incorporation of oxygen groups in the E‐GF electrode.…”

Vanadium (V) reduction reaction on modified glassy carbon electrodes – Role of oxygen functionalities and microstructure

“…However, more recent studies have refuted the role of oxygen functionalities as electro-active sites. These studies suggest that there may be other factors affecting activity including surface wettability, carbon microstructure, roughness and surface area effects [10][11][12][13]. Correlations between carbon structure and sp 2 carbon content have been related to improvements in activity [11].…”

“…It has been proposed by several authors that oxygen functional groups play a key role in facilitating the electron transfer process for V(V) reduction at carbon electrode surfaces [8,18,35]. More recent studies have negated the catalytic role of oxygen groups towards V(V) reduction, and have suggested that other properties such as surface roughness and carbon microstructure play a role in improving electrode kinetics [11,13,36]. In order to gain further insight into the properties affecting activity from this study, activity trends with O/C ratio and carbon structure were investigated.…”

“…It has been shown by several authors that edge-sites are more active than basal sites for both V(II) oxidation and V(V) reduction [10,14,15]. These studies on different carbon surfaces have indicated that the kinetics of the vanadium redox reactions depend strongly on the type of carbon used and on the preparation of the electrode surface itself [13,16]. While oxygen functionalities could play a role in improving wetting properties of the electrode surface, their role as electroactive sites remains unclear.…”