## 3 Results and Discussion
### Effect of Different Copper Corrosion Inhibitors on HER Suppression  
In this study, BEV coolants were prepared with TTZ, BTZ, or MBT-Na, since those compounds are widely used in coolant formulations to prevent Cu corrosion, and their protection mechanism is well stablished [25]. The corrosion inhibition mechanism of the azoles is based on forming a strong adsorbed-chemisorbed protective film that forms complexes with Cu\({}^{+}\) ions, preventing the metal from reacting with the environment and forming species that lead to copper dissolution (mainly CuCl\({}^{2-}\)) [26]. TTZ is a derivative from BTZ, having a methyl group attached to one of the nitrogen atoms, while MBT-Na has a thiazole ring and a mercapto group.  
Table 3 summarizes the coolants used in this study along with their final pH and electrical conductivity.  
In order to obtain coolants with different corrosion inhibitors, but in the same electrical conductivity range, the total amount of corrosion inhibitors was kept constant at 100% relative to the TTZ amount present in the commercial BEV coolant. The synergistic effect of TTZ with BTZ or MBT-Na was also investigated.  
The LSV curves of coolants with different copper organic corrosion inhibitors are presented in Figure 4. The current evolution of coolants containing TTZ, BTZ and TTZ + BTZ are similar, indicating comparable suppression of cathodic processes. In coolants containing MBT-Na, a slight decrease in the absolute current associated with limiting oxygen diffusion is noticeable (around \(-1.5\) V). This difference is offset at higher potentials, and in the HER region, coolants containing MBT-Na present the higher absolute current density values among all tested coolants. Additionally, no synergy is observed from the combination of TTZ with BTZ or MBT-Na.  
In conclusion, none of the mixed-types copper corrosion inhibitors used in this study--TTZ, BTZ, and MBT-Na--effectively suppressed hydrogen formation, in contrast to what is described in the literature. Previous studies have reported differences in the adsorption ability of TTZ, BTZ and MBT-Na with synergistic effects when combined [27; 28; 29]. [PERSON] et al. showed that in aqueous solution, TTZ is more strongly absorbed on Cu surfaces than BTZ, possibly due to differences in solubility that regulates the adsorption [27]. Altaf  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Coolant** & **Cu Inhibitors** & \
\begin{tabular}{c} **Inhibitor Content** \\ **(Relative \%)** \\ \end{tabular} & **pH** &
\begin{tabular}{c} **eConductivity at 25 \({}^{\circ}\)C** \\ **(\#S/cm)** \\ \end{tabular} \\ \hline \multirow{5}{*}{BEV} & TTZ & 100 & 8.11 & 86.43 \\ \cline{2-4}  & MBT-Na & 100 & 8.26 & 108.13 \\ \cline{2-4}  & TTZ & 50 & 8.25 & 101.98 \\ \cline{2-4}  & BTZ & 100 & 8.14 & 97.60 \\ \cline{2-4}  & TTZ & 50 & 8.10 & 95.31 \\ \cline{2-4}  & & & & \\ \hline \hline \end{tabular} Note: TTZ: Tolytriazole; BTZ: Benzotriazole; MBT-Na: Sodium Mercaptobenzodiarole.  
\end{table}
Table 3: Summary of BEV coolants with different copper inhibitors and their corresponding pH and electrical conductivity at 25 \({}^{\circ}\)C.  
et al. reported a higher corrosion inhibition efficiency of MBT in respect to BTZ due to the structural difference between them, since copper has a higher affinity with towards the sulfur present on the MBT structure [30]. Nonetheless, as our study involves a complex glycol-based medium instead of an aqueous solution, the unique properties of the coolant may alter the adsorption behavior of the inhibitors, necessitating further investigation to understand their performance in this specific environment. Additionally, corrosion inhibitors studies that observe the decrease in cathodic reactions, such as HER, are often conducted at low overpotentials, whereas at high overpotentials, corrosion inhibitors are likely desorbed or corrosion-inhibiting layers are broken, compromising the protective ability of the azide/copper layer, and failing to prevent the hydrogen evolution reaction [31; 32].