Effects of Supporting Electrolyte and pH on Charge Transport within Electropolymerized Poly(o-phenylenediamine) Films Deposited on Graphite Electrodes

Abstract

The homogeneous charge-transport process within electropolymerized electroactive poly(o-phenylenediamine) (PPD) films on graphite electrodes in various supporting electrolytic solutions (i.e., NaCl, NaClO4, Na2SO4, LiCl, CF3COONa, tetraethylammonium chloride (TEACl) and sodium p-toluenesulfonate (NaPTS)) at various pH’s was examined by potential-step chronoamperometry and chronocoulometry. The overall charge-transport process was found to obey Fick’s diffusion laws and thus the apparent diffusion coefficients (Dapp) for the diffusion-like charge-transport process were estimated. The Dapp values for the oxidation and reduction processes (i.e., Dappa and Dappc) were almost the same at pH 1.0 irrespective of the thickness of PPD films and were actually independent of the supporting electrolytes except for NaPTS. As pH was increased from 1 to 7, the Dappa values decreased slightly from ca. 5.6×10−8 to 1.6×10−8 cm2 s−1 and the Dappc values did more largely from ca. 5.6×10−8 to 2.2×10−9 cm2 s−1. This behavior was essentially common to all the supporting electrolytes examined. Such pH dependences of Dappa and Dappc are discussed on the basis of the fact that the charge-transport process within PPD films involves the intrinsic electron-transfer process between adjacent electroactive sites as well as the proton addition–elimination process, the charge-compensating counterion motion, the motion of solvent and the segmental motion of the polymeric chain. Especially, it is demonstrated that in this system the proton addition–elimination process must necessarily occur in order for the charge-transport process to proceed.

Application of poly(o-phenylenediamine) in rechargeable cells

“…The insignificant participation of the dopant anion during oxidation [24] is responsible for the poor conductivity of the polymer. The redox peak currents decreased with increase in pH which was attributed to the decrease in the apparent rate of charge transport in the film [22]. In the present work, the cyclic voltammograms of the PoPD film deposited on both Pt and carbon substrates showed good redox characteristics up to pH 4 ( Figure 2).…”

“…In a similar way, the use of a galvanostatic method also resulted in a rapid increase in the potential with no effective film deposition. Cyclic voltammetry technique was invariably used for the electrodeposition of PoPD [12,13,22,23]. Therefore, in the present study, the growth of PoPD at Pt was followed by cycling between )0.3 and 1.2 V vs SCE at 50 mV s )1 (Figure 1).…”

Electropolymerization of o‐phenylenediamine on Pt‐electrode from aqueous acidic solution: Kinetic, mechanism, electrochemical studies and characterization of the polymer obtained

“…Poly( ortho ‐phenylenediamine) P( o‐ PD) has many attractive properties. P( o‐ PD) can be prepared electrochemically in acid, neutral, and alkaline solutions and is very stable in both aqueous solutions and air 29–38. The ease of dissolution of P( o‐ PD) in organic solvents, such as dimethylsulfoxide (DMSO), dimethylformamide (DMF), and etc., makes it one of the so‐called soluble electroactive polymers and thus provides more flexibility in the studies of its structures 36, 37.…”

“…To the best of the our knowledge, the kinetic studies of electrochemical preparation of P( o‐ PD) are not investigated in the literature but, in case of the structure of P( o‐ PD), there are many trails in the literature 34–38…”

Electrosynthesis of poly(o-phenylenediamine) in ionic liquid and its properties

“…Then the peak currents decreased slightly with an increase in pH, and we suggest that the overall redox reaction of the polymer comprises a two-electron and two-proton process. The possible scheme for the redox reaction is shown in Figure 6 [17] . Figure 7 shows UV-vis spectra of PPD polymer in dimethyl sulfoxide, prepared in different constant potentials, 0.35, 0.4, 0.5 V, respectively.…”