## 1 Introduction  
Battery electric vehicles (BEV) require a battery thermal management system (BTMS) to control the operating temperature and ensure a uniform heat distribution among the battery cells/packs [1]. Among the various BTMS configurations, indirect liquid cooling--using plates, jackets, and tubes arranged according to pack geometry--is the predominant method in current BEV designs [2, 3]. Water-glycol coolants, initially developed for internal combustion engine (ICE) vehicles, have become the predominant thermal management fluids for BEVs due to their desirable heat transfer properties, simplicity, and straightforward integration into vehicle architectures. In indirect cooling systems, the coolant circulates within plates and chambers without directly contacting the cells [4]. However, under abnormal conditions--such as accidental leakage, inadequate electrical insulation, or mechanical damage--the fluid may come into contact with the battery tabs, as illustrated in Figure 1. Since water-glycol mixtures are electrically conductive, its interaction with the electrical environment of battery packs may introduce safety concerns that are still poorly understood. In a pivotal study, [PERSON] and [PERSON] argued that glycol- and water-based coolants can dissociate under electric fields found in battery systems, generating flammable gases--such as hydrogen--through electrolysis. This mechanism, often overlooked, may contribute to fire ignition prior to thermal runaway, especially when coolant leaks occur in confined spaces where local electrical breakdown or arcing is possible [5]. If the coolant contacts polarized surfaces, such as the battery tabs, two main reactions occur at the cathode. At lower overpotentials, the oxygen reduction reaction (ORR) takes place with the direct or indirect conversion of oxygen into water. At higher overpotentials, the hydrogen evolution reaction (HER) reduces H\({}^{+}\), resulting in water splitting and H\({}_{2}\) gas generation, as described in Equation (1) [6; 7]. \[2\mathrm{H}_{2}\mathrm{O}+2\mathrm{e}^{-}\rightarrow\mathrm{H}_{2}+2\mathrm{OH} ^{-} \tag{1}\]  
The amount of H\({}_{2}\) gas generated by HER depends on the material and surface finishing of the tab, as well as the nature of the aqueous solution [8; 9]. In alkaline solutions, such as water-glycol coolants, the HER activity of copper is relatively low compared to other systems, since copper weakly binds hydrogen anions, and alkaline solutions slow HER kinetics due to the absence of more suitable proton donors (such as hydronium ions in acid solutions) [7; 9]. Despite the slower HER kinetics, the continuous generation of hydrogen at copper tabs in contact with coolants presents a significant safety risk. Even at reduced reaction rates, the continuous gas formation can lead to substantial hydrogen accumula  
Figure 1: Schematic of a bottom plate indirect cooling system in a battery electric vehicle (BEV), where the coolant remains confined within the cooling plate. In the event of mechanical damage or leakage, the coolant may come into contact with the polarized battery tabs, potentially resulting in a short circuit and hydrogen gas generation. tion, elevating the internal pressure of the cooling system, increasing the likelihood of a significant leakage event [10]. Moreover, the accumulation of hydrogen within the battery pack could potentially create an explosive atmosphere, since the energy needed to ignite hydrogen is 10\(\times\) lower than that of other flammable gases, such as methane or propane, making it prone to ignition even from short-lived sparks [11; 12]. These abnormal situations compromise the cooling system's functionality, resulting in overheating and ultimately triggering an irreversible thermal runaway [13].