## 1 Introduction
By raising the concentration of O2 at the cathode, the O2 reduction reaction rate is accelerated, resulting in reduced activation overpotential. [PERSON] [21] found that reducing activation losses due to O2 enrichment improves overall cell efficiency across a wide range of current densities, leading to higher cell voltage and ultimately enabling enhanced power delivery at an equivalent current density. [PERSON] [26] demonstrated that increasing the O2 concentration in the feed streams of a PEMFC stack not only enhances power output but also reduces the overall intake air flow rate to the cathode by a greater percentage than the level of enrichment. According to [PERSON] [27], there was a significant increase in air usage. Additionally, they determined that the optimal enrichment percentage for the stack is around 45% in mass fraction. It was observed that beyond this range, specifically between the natural concentration of O2 and this value, an increase in cell temperature occurs due to a higher number of O2 molecule collisions, leading to potential losses. In addition to its direct impact on O2 voltage and power output, increasing the concentration of O2 offers further advantages. O2 enrichment effectively mitigates local O2 depletion conditions that can arise when the cathode's O2 supply falls short of the electrochemical reaction's demands [28]. Enriching the cathode feed stream with O2 boosts the available O2 concentration, ensuring a balanced supply of reactants and enhancing power delivery, particularly during periods of high demand [29]. Moreover, elevated O2 concentrations prevent the build-up of high-energy reaction intermediates, such as oxygen adsorbed on the cathode, which can otherwise react with other cell constituents. Averting such reactions and the resultant production of highly reactive oxygen species leads to the reduced degradation of the catalysts and the membrane [30]. However, it also presents challenges and potential drawbacks, including oxidative stress and elevated thermal control requirements and oxidative stress [31]. Elevated O2 levels can induce oxidative stress in high-temperature conditions [31] and promote the formation of high-energy species, leading to degradation, particularly if O2 permeates the anode [30]. Nevertheless, these drawbacks can be effectively mitigated through meticulous cell design and appropriate thermal management [31]. [PERSON] [12] also found that the corrosion effects on metallic bipolar plates materials can be significantly stronger on the cathode side, so increased levels of O2 may limit the implementation of such materials. In addition, introducing supplementary equipment and control mechanisms adds complexity and increases energy costs. Therefore, exploring alternatives that minimize energy consumption while optimizing the O\({}_{2}\) enrichment is crucial in addressing these concerns [32]. From these findings, it can be concluded that a higher O\({}_{2}\) concentration in the cathode stream increases the electrical power produced (at equal H\({}_{2}\) consumption), improving the fuel cell stack performance as an individual element. To achieve a certain level of enrichment, O\({}_{2}\) can be supplied from a pure O\({}_{2}\) source or directly obtained from the atmosphere using N\({}_{2}\)/O\({}_{2}\) separation techniques. For on-board generation, the most typically used techniques encompass chemical separation methods, such as absorption on molten salts or the utilization of mixed ionic-electronic conductors, which operate at extremely high temperatures or cryogenic distillation techniques necessitating temperatures below \(-150\)\({}^{\circ}\)C [33]. It should be noted, however, that the extreme temperatures associated with these air enrichment techniques are outside the working range of a typical PEMFC and can induce damage during its operation [34]. An alternative separation technique, which would not require altering the air temperature but rather its pressure, involves the utilization of polymeric membranes for N\({}_{2}\)-O\({}_{2}\) separation [35].