**3.1.2 Kinetic studies**

The electropolymerization kinetics was investigated by using aqueous solution containing (different monomer concentrations in the range between 0.01 and 0.04M in case of OCP and in the range between 0.3 and 0.6M in case of OHP where H2SO4 concentration in the range between 0.3 and 0.6M at 303 K in both case. The cyclic voltammogram for each monomeric systems and the relation between the log i pII vs log [monomer] or log i p11 vs log [H2SO4] are plotted from which linear relations were obtained.

### **3.1.2.1 Effect of monomer concentration on the electropolymerization processes**

The influence of OCP and OHP concentrations on the CV behavior was studied using scan rate of 25 mVs-1 is shown in Figure7 (a and b). The voltammograms show that, the anodic peak current densities (i*pI1*) increase with the increasing of the monomer concentration. This is obvious due to the increased availability of the electroactive species, OCP and OHP in solution, which is again in accordance with Eq.(4).

At higher monomer concentrations (i.e. concentration > 0.04 M for OCP and concentration > 0.08 M for OHP), no noticeable increase in peak currents was observed. This suggests that, at higher concentration, the oxidation reaction is not limited by diffusion alone

A double logarithmic plot of the current density related to oxidation peaks (II) against monomers concentrations are graphically represented in Figure 7 (c and d). Straight lines with slope of 1.1 for OCP and 0.96in case of OHP were obtained. Therefore, the reactions order with respect to both monomers concentration is a first-order reaction.

#### **3.1.2.2 Effect of H2SO4 concentration on the polymerization process**

The influence of acid concentration in the range between (0.3 and 0.6M) on the CV using of OCP or OHP using scan rate of 25 mVs-1 is represents in Figure 8 (a and b). Voltammograms show that, the anodic peak current densities (i*pI1*) increase with the increasing of the acid concentration in both cases. At higher acid concentrations for both cases (i.e. concentration > 0.6 M), no noticeable increase in peak currents were observed but, it began to decrease as a result of degradation and the solubility of the polymer film from the platinum surface. A double logarithmic plot of the current density related to oxidation peaks (II) against acid concentrations in the range between 0.3 and 0.6M is graphically represented in Figure8 (c and d). Straight lines with slope of 0.98 in case of OHP and of 0.74in case of OHP were obtained. Therefore, the reactions may be considered as first-order with respect to H2SO4 concentration in both cases. Depending upon the above results, the kinetic rate laws obtained from this method can be written as:

*For OCP; RP,E = kE [monomer]1.1 [acid]0.98 and* 

*For OHP; RP,E = kE [monomer]0.96 [acid]0.74* 

Where, RP,E is the electropolymerization rate and kE is the kinetic rate constant.

is controlled by charge transfer process. When the polymers become thick, the diffusion of reactant inside the film becomes the slowest step, the process changed to diffusion transfer,

The intercepts in Figure 6 are small and negative, -0.60 and -0.53 for OCP and OHP respectively, which could be attributed to a decrease of the active area of the working electrode during the positive scan [Zanartu et al , 2002] or the increase of the covered area of working electrode by the adhered polymer sample, which confirm the data of Figure 4 .

The electropolymerization kinetics was investigated by using aqueous solution containing (different monomer concentrations in the range between 0.01 and 0.04M in case of OCP and in the range between 0.3 and 0.6M in case of OHP where H2SO4 concentration in the range between 0.3 and 0.6M at 303 K in both case. The cyclic voltammogram for each monomeric systems and the relation between the log i pII vs log [monomer] or log i p11 vs log [H2SO4] are

The influence of OCP and OHP concentrations on the CV behavior was studied using scan rate of 25 mVs-1 is shown in Figure7 (a and b). The voltammograms show that, the anodic peak current densities (i*pI1*) increase with the increasing of the monomer concentration. This is obvious due to the increased availability of the electroactive species, OCP and OHP in

At higher monomer concentrations (i.e. concentration > 0.04 M for OCP and concentration > 0.08 M for OHP), no noticeable increase in peak currents was observed. This suggests that,

A double logarithmic plot of the current density related to oxidation peaks (II) against monomers concentrations are graphically represented in Figure 7 (c and d). Straight lines with slope of 1.1 for OCP and 0.96in case of OHP were obtained. Therefore, the reactions

The influence of acid concentration in the range between (0.3 and 0.6M) on the CV using of OCP or OHP using scan rate of 25 mVs-1 is represents in Figure 8 (a and b). Voltammograms show that, the anodic peak current densities (i*pI1*) increase with the increasing of the acid concentration in both cases. At higher acid concentrations for both cases (i.e. concentration > 0.6 M), no noticeable increase in peak currents were observed but, it began to decrease as a result of degradation and the solubility of the polymer film from the platinum surface. A double logarithmic plot of the current density related to oxidation peaks (II) against acid concentrations in the range between 0.3 and 0.6M is graphically represented in Figure8 (c and d). Straight lines with slope of 0.98 in case of OHP and of 0.74in case of OHP were obtained. Therefore, the reactions may be considered as first-order with respect to H2SO4 concentration in both cases. Depending upon the above results, the

**3.1.2.1 Effect of monomer concentration on the electropolymerization processes** 

at higher concentration, the oxidation reaction is not limited by diffusion alone

order with respect to both monomers concentration is a first-order reaction.

**3.1.2.2 Effect of H2SO4 concentration on the polymerization process** 

kinetic rate laws obtained from this method can be written as:

Where, RP,E is the electropolymerization rate and kE is the kinetic rate constant.

*For OCP; RP,E = kE [monomer]1.1 [acid]0.98 and For OHP; RP,E = kE [monomer]0.96 [acid]0.74* 

which confirms the data in Figure 4.

plotted from which linear relations were obtained.

solution, which is again in accordance with Eq.(4).

**3.1.2 Kinetic studies** 

Fig. 7. Cyclic voltammetry curves showing the effect of monomers concentration on electropolymerization and its related double logarithmic plot.

Electropolymerization of Some Ortho-Substituted Phenol Derivatives on Pt-Electrode from

respectively for OHP.

Aqueous Acidic Solution; Kinetics, Mechanism, Electrochemical Studies and Characterization of… 33

ΔS\*/2.303R}. From slopes and intercepts the values of ΔH\* and ΔS\* were found to be 31.54 k J mol-1 and -99.68 JK-1 mol -1, respectively for OCP and 19.87k J mol-1 and –286.69 JK-1 mol -1,

Fig. 9. Cyclic voltammetry curves for the effect of temperature on the electropolymerization,

The obtained polymer films adhere Pt-electrode -after preparation at the optimum conditions of preparation (0.04M monomer and 0.6M Acid for OCP and 0.08M monomer

Arrhenius plot and Eyring equation plot

**3.2 Electroactivity of the Pt-polymer film** 

Fig. 8. Cyclic voltammetry curves showing the effect of acid concentration on electropolymerization and its related double logarithmic plot.
