## 3 Results and Discussion  
### Effect of Copper Corrosion Inhibitor Concentration on HER Suppression  
In this study, coolants standard BEV and ICE coolants were manufactured with different amounts of Cu corrosion inhibitor (TTZ), to evaluate the influence of the inhibitor concentration on the suppression of hydrogen evolution. A series of solutions were prepared with TTZ concentrations at 20%, 50%, 100%, 200%, and 430% relative to a standard reference concentration (a baseline against which all relative percentages are compared). The final pH and electrical conductivity of each solution are presented in Table 2. Minimal variations in pH and electrical conductivity are a consequence of TTZ addition. TTZ is a well-described copper corrosion inhibitor. It forms a chemisorbed protective film on the copper surface, reducing both copper oxidation and the cathodic reactions [22; 23]. Thus, different cathodic current evolution in coolants with different TTZ concentrations could be expected. LSV curves of BEV and ICE coolants with different TTZ concentrations are presented in Figure 3a,b, respectively. The current evolution of all tested solutions follows the same pattern: at lower overpotentials, up to--2 V vs. Ag/AgCl, the absolute value of current initially increase due to the oxygen reduction reaction (arrow 1) reaching a plateau due to its limiting diffusion in the electrolyte (arrow 2) [24]. With an increase in overpotential, the absolute value of current increases linearly due to the hydrogen evolution reaction (arrow 3). In BEV solutions, the variation in TTZ concentration suppressed the oxygen evolution reaction at lower overpotentials. However, at high overpotentials, it was not effective in suppressing or decreasing the hydrogen evolution reaction. In ICE coolants, the solutionwithout TTZ presented a lower onset overpotential for the hydrogen evolution, as shown in the inset of Figure 3b (yellow curve). Solutions containing TTZ present lower current values at \(-1.4\) V (vs. Ag/AgCl), suggesting some cathodic inhibition at lower overpotentials. These results indicate that TTZ contributes to some cathodic inhibition of HER, although only at lower overpotentials. At higher overpotentials, this difference is offset, and the final current value at \(-5\) V is comparable. All the curves presented fluctuations in the current evolution at higher overpotentials due to intense hydrogen evolution on the electrode surface. When comparing the current density values of the coolants with 100% TTZ, the standard BEV coolant exhibited a current 96% lower than that of the standard ICE coolant. This difference can be attributed to the different coolants' formulation and electrical conductivity, as discussed further in the Section 3.3. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Coolant**} & \multicolumn{2}{c}{**Tolyttriazole**} & \multirow{2}{*}{**pH**} & \multirow{2}{*}{**eConductivity at 25 \({}^{\circ}\)C (\(\mu\)S/cm)**} \\  & **(Relative \%)** & & & \\ \hline \multirow{6}{*}{BEV} & 20 & 8.16 & 89.63 \\  & 50 & 8.12 & 90.82 \\  & 100 & 8.11 & 86.43 \\  & 200 & 8.00 & 92.57 \\  & 430 & 8.01 & 109.14 \\ \hline \multirow{6}{*}{ICE} & 0 & 7.54 & 2520.0 \\  & 50 & 7.62 & 2476.8 \\  & 100 & 7.54 & 2576.8 \\  & 200 & 7.50 & 2654.0 \\  & 430 & 8.40 & 2623.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summary of BEV and ICE coolants solutions with different TTZ concentrations and their corresponding pH and electrical conductivity at 25 \({}^{\circ}\)C.  
Figure 3: Linear sweep voltammetry curves of (**a**) BEV and (**b**) ICE coolants with different TTZ concentrations. In conclusion, all coolants tested show similar or higher absolute current densities at \(-5\) V (vs. Ag/AgCl) compared to the 100% TTZ solution. If TTZ concentration were effective in suppressing HER at high overpotentials, we would expect a decrease in the absolute current density values, which was not observed.