## 2 Materials and Methods
### Potentiodynamic Polarisation Measurements  
Electrochemical measurements were performed at room temperature (\(\sim\)25 \({}^{\circ}\)C) on M1 electrodes in an unstirred borate buffer water solution (pH 7.4) with natural aeration in the presence of the inhibitor and 10 mM NaCl. A classical electrolytic three-electrode cell was used in order to accelerate tie-dependent measurements. Derivatives of 3-sulphvinyl-5-amino-1\(H\)-1,2,4-triazole synthesised at Voronezh State University were used. The technique was described in [27]. According to LCMS, the purity was at least 98%. Their solubility in water is \(>\)10 mM. Their names and structures are given in Table 1.  
A saturated silver chloride reference electrode was placed in a separate container linked to the electrolytic cell by an agar-agar-based salt bridge filled with a potassium nitrate saturated solution. The auxiliary electrode was a platinum grid. The working copper electrode was polished by K3000 solid surface (grit of 5.2-6.2 \(\upmu\)m), degreased in 96% ethanol, and washed with distilled water. The potentials of the working electrode (\(E\)) are given according to the standard hydrogen electrode (SHE) scale. The current density \(i\) was calculated by dividing the actual current \(I\) by the geometric area of the working electrode (0.75 cm\({}^{2}\)). Electrochemical measurements were performed using an IPC-PRO potentiostat (Frumkin Institute of Physical Chemistry and Electrochemistry Russian Academy of Sciences). In order to remove the oxide film appearing due to the air, the working Cu-electrode was polarised at \(E=-0.60\) V for 15 min prior to the experiment. The electrode was then held in the solution for about 3 to 5 min until the stable free corrosion potential (\(E_{\text{corr}}\)) was established. The working solution was then mixed with a NaCl solution while stirring so that the concentration of chloride ions would be \(C_{\text{Cl}}\)\({}^{-}=10\) mM. The studied inhibitors were also added to the solution in a concentration of \(C_{\text{inh}}=0.01\), 0.10, and 1.00 mM. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Symbol** & **Name** & **Formula** \\ \hline A & 3-sulphvinylpropyl-5-amino-1\(H\)-1,2,4-triazole & \\ B & 3-sulphvinylbutyl-5-amino-1\(H\)-1,2,4-triazole & \\ C & 3-sulphvinylpentyl-5-amino-1\(H\)-1,2,4-triazole & \\ D & 3-phenethylsulphvinyl-5-amino-1\(H\)-1,2,4-triazole & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Inhibitor names and structures. After the new \(E_{\text{corr}}\) value was established, the \(I\),\(E\) polarisation curve was registered by scanning the potential towards either the anode or the cathode direction at 0.2 mV/sec. The activation potential (\(E_{\text{act}}\)) was identified by a rapid increase in the current on the anode polarisation curve. Pits were then visually identified on the surface of the electrode. The measurement error for \(E_{\text{act}}\) was below 0.03 V.  
The rate of corrosion in the current units (\(i_{\text{corr}}\)) was determined by the polarisation resistance technique as summarized by [PERSON] [28; 29]. The polarisation curve was previously registered by scanning the potential from \(E=E_{\text{corr}}-0.03\) V to \(E=E_{\text{corr}}+0.03\) V at 0.2 mV/sec. The polarisation resistance \(R_{p}\) was then calculated as the slope of the polarisation curve, replotted with \(\Delta E\),\(j\)-coordinates (\(\Delta E=E-E_{\text{corr}}\)), at \(E_{\text{corr}}\). The polarisation curve was then plotted with coordinates 2.3-\(R_{p}\),\(i-\Delta E\), and the Tafel slopes of the half-reaction on the anode \(b_{a}\) and the cathode \(b_{c}\) was determined by means of the TableCurve program as the approximation parameter of the equation 2.3-\(R_{p}\),\(i=\frac{b_{a}\cdot b_{c}}{b_{a}+b_{c}}\)[\(\exp\left(\frac{\Delta E}{b_{a}}\right)-\exp\left(\frac{\Delta E}{b_{c}} \right)\)], which at \(\Delta E=0\) gives \(i_{\text{corr}}\). The measurements were performed at least 5 times for each of the studied concentrations of the inhibitor until reproducible data were obtained.