## 3 Results and Discussion
Figure 1: Anodic and cathodic polarisation curves of copper in a borate buffer (pH 7.4) with 0.01 M NaCl and 3-sulphinypropyl-5-amino-1\(H\)-1,2,4-triazole (**a**), 3-sulphinyIlbutyl-5-amino-1\(H\)-1,2,4-triazole (**b**), 3-sulphinyIlpentyl-5-amino-1\(H\)-1,2,4-triazole (**c**) and 3-phenethylsulphiny-5-amino-1\(H\)-1,2,4-triazole (**d**) at the following concentrations: 1,1\({}^{\prime}\)-0; 2,2\({}^{\prime}\)-0.01 mM; 3,3\({}^{\prime}\)-0.10 mM; 4,4\({}^{\prime}\)-1.00 mM. When the organic additives are added to the neutral solution or when \(C_{\text{inh}}\) increases, the shape of the impedance diagram does not change but the radius of the semicircle increases significantly. The radius change is obtained for substances A and B with increasing additive concentration. For substances C and D, the radii of the semicircles are close for all the studied concentrations. In the region of low frequencies, the curvature of all the Nyquist plot increases and tends to be linear, which is accounted for by the transport problems of the electrochemical process. A regression analysis of the impedance spectroscopy data was used to determine the most probable equivalent circuit modeling the processes at the interface copper-solution (Figure 3). Figure 3: The equivalent circuit model used to fit the EIS response (\(R_{\Omega}\)—direct-current resistance, \(\mathit{CPE}\)—constant phase element, \(R_{\text{P}}\)—polarisation resistance of the electrochemical reaction, \(\mathit{BW}\)—Warburg impedance). Figure 2: The Nyquist diagrams of copper in borate buffer (pH 7.4) + 10 mM NaCl in the presence of 3-sulphvinylpropyl-5-amino-1\(H\)-1,2,4-triazole (**a**), 3-sulphvinylbutyl-5-amino-1\(H\)-1,2,4-triazoleole (**b**), 3-sulphvinylpentyl-5-amino-1\(H\)-1,2,4-triazoleole (**c**) and 3-phenethylsulphinyl-5-amino-1\(H\)-1,2,4-triazoleole (**d**) at concentrations of 0.01 (1), 0.10 (2), and 1.00 mM (3). Table 3 presents the values of the following circuit elements: \(R_{\Omega}\) (direct-current resistance of the solution), \(\mathit{CPE}\) (constant phase element), \(R_{\mathrm{P}}\) (polarisation resistance of the electrochemical reaction), and \(BW\) (Warburg impedance). Admittance for constant phase element is described as  
\[Y_{\mathrm{CPE}}=Y_{0}\left(\mathrm{j}\omega\right)^{n} \tag{9}\]  
where j is the imaginary root, \(\omega\) the angular frequency, \(Y_{0}\) the magnitude and \(n\) is the exponential term. \(R_{\mathrm{P}}\) is significantly higher in solutions with an organic additive and increases when \(C_{\mathrm{inh}}\). We can thus say that the changes in the Nyquist plot are most probably caused by the decrease in the double-layer capacitance resulting from the adsorption of the inhibitor molecules at the interface copper/solution on the one hand, and the increase in the polarisation resistance resulting from the formation of a protective film on the copper surface on the other. Additional evidence for the formation of the film is the rapid growth of Warburg impedance in the presence of the inhibitor (Table 3). This means either that the diffusion of the soluble corrosion product on the electrode's surface slows down, or that the barrier properties of the protective film blocking the aggressive elements of the solution increase. Linear segments were not obtained on the Nyquist plots (plot 4 in Figure 2c,d) at high frequencies. The observed non-linearity can be associated with the formation of a film of organic matter on the surface of copper. The inhibition efficiency (\(\eta_{\mathrm{inh}}\), %)  
\[\eta_{\mathrm{inh}}\ =\left(1-\frac{R_{\mathrm{P,0}}^{EIS}}{R_{\mathrm{P,inh}}^{EIS }}\right)\mathrm{100\%} \tag{10}\]  
was calculated using the values of charge transfer resistance without (\(R_{\mathrm{P,0}}^{EIS}\)) and with the inhibitor (\(R_{\mathrm{P,inh}}^{EIS}\)). Efficiency values for inhibitors A and B are below 70%, while for compounds C and D, they are up to 89% (Table 3).