IR Spectroelectrochemical Cyclic Voltabsorptometry and Derivative Cyclic Voltabsorptometry

Abstract

In this paper, we report the IR (infrared) CVA (cyclic voltabsorptometry) and DCVA (derivative cyclic voltabsorptometry) spectroelectrochemical techniques to elucidate an electrochemical mechanism. First we set potassium ferrocyanide as an example to explain the validity of this method. Then the electrochemical redox of two compounds, 1,4-benzoquinone and 1,4-bis(2-ferrocenylvinyl)benzene, was selected to be examined with this method. 1,4-Benzoquinone exhibits two single-electron waves in the cyclic voltammetric (CV) experiment, whereas two electroactive groups (Fc) are contained in p-(Fc-CH=CH)(2)BZ, but only one redox wave is observed. IR CVA results show that three IR absorption peaks in 1,4-benzoquinone, 1232 cm(-1) (the absorption of final production), 1656 cm(-1) (the absorption of original reactant), and 1510 cm(-1) (the absorption of intermediate), and two IR absorption peaks in 1,4-bis(2-ferrocenylvinyl)benzene, 1620 cm(-1) (the absorption of final oxide production) and 1589 cm(-1) (the absorption of intermediate), can be used to track the electron transfer. On the basis of the IR absorbance at the appropriate monitored wavelength (mentioned above), we can analyze simultaneously the concentration change of the corresponding redox transition during CV scans. Also the combination of the DCVA spectroelectrochemical technique with theory analysis allows reconstructing the current-potential (i-E) curve for each step of electron transfer. The reconstructed i-E curve can help us to understand the electron-transfer process. We believe IR CVA and DCVA spectroelectrochemical techniques can be applicable to the study of a wide range of complex electrochemistry processes.

Direct evidence of hydrogen-bonding and/or protonation effect on p-benzoquinone electrochemical reduction by in situ IR spectroelectrochemical study

“…As is well-known, the two CV waves correspond to BQ ÅÀ /BQ and BQ 2À /BQ ÅÀ . The CV result obtained here is in agreement with those reported in the literature [15][16][17][18]. The rapid-scan IR spectra recorded in situ during the CV scan between 0 and À1.2 V, in the wavenumber range of 1150-1800 cm À1 are shown in Fig.…”

“…The redox mechanism has been shown to change as a function of solvent, pH and the buffer capacity. At present, an observation common to all the studies is that two consecutive electron transfers occur in aprotic media [13][14][15][16][17][18]. Two well-separated voltammetric waves are observed in CV experiment.…”

“…p-benzoquinone is the simplest quinone and has been studied extensively. Indeed the electron transfer of benzoquinone in aprotic media [13][14][15][16][17][18], organic-water mixed media [19,20], wellbuffered aqueous solution [1,[21][22][23][24][25][26][27], and unbuffered aqueous [23][24][25][26][27][28][29][30][31][32][33][34] solution has been studied through modern electroanalytical techniques from polarography, rapid-scan voltammetry, to spectroelectrochemistry [15][16][17][18]23,26,27].…”

“…For example, p-benzoquinone anion radical formed in the process of BQ electroreduction is observed by in situ ESR and UVvisible spectroelectrochemistry [23,26,27]. What is more, cyclic voltabsorptometry (CVA) developed by Bancroft et al provides information of how the species and concentration change during electrochemical process and derivative cyclic voltabsorptometry (DCVA) can help us understand the electron transfer mechanism of complex electrochemistry process [15,18,41].…”

“…We have introduced IR CVA and DCVA to explore the electrochemical mechanism [18]. It has been proved that the technique is applicable to the study of a wide range of complex electrochemistry processes.…”