A complete fuel cell system primarily consists of a fuel cell stack, a hydrogen supply system, an air supply system, and a water-thermal management system. The air supply system is responsible for delivering air at a certain pressure and flow rate to the cathode of the stack to participate in the reaction.

To ensure the cleanliness, pressure, humidity, and flow rate of the supplied air meet the stack entry requirements, the air supply system typically includes components such as an air filter, air flow meter, air compressor, intercooler, membrane humidifier, three-way valve, and backpressure valve.

This article focuses on the air filter.

As the primary channel for the air intake of a fuel cell, the air filter must not only remove particulate matter from the air but also effectively eliminate harmful chemical gas impurities such as sulfides, nitrogen oxides, and nitrogen hydrides. This prevents catalyst poisoning in the stack, enhances system stability, and extends system lifespan.

While ensuring filtration efficiency, the design of the air filter must also consider minimizing pressure loss during air supply. Excessive pressure loss can lead to increased system power consumption and reduced volumetric power density of the entire fuel cell system.

Fuel Cell Air Filter

Structurally, the air filter is divided into two main parts: the housing and the filter element.

Housing:

The housing of the air filter primarily serves a supportive and fixed function. Currently, there are two main types of housings: cylindrical and flat-panel. The two structures are similar, but the flat-panel design is more suitable for passenger vehicles where lower volume occupancy is required. Cylindrical air filters offer higher filtration efficiency and lower pressure resistance but are bulkier, making them more suitable for commercial vehicles.

The housing is equipped with air intake and outlet ports, as well as mounting holes. Some designs also include dedicated dust discharge ports to remove accumulated dust. The entire housing is connected via clamps for easy installation and replacement of the filter element.

Filter Element:

The filter element is the core component of the fuel cell air filter. It is formed by folding filter media into a specific structure to increase the adsorption area, dust-holding capacity, and service life.

The filter paper used in the filter media exhibits excellent air permeability and effectively adsorbs particulate matter in the air, serving as the physical filtration stage. Commonly used physical adsorption materials include glass fiber, polypropylene, or polypropylene-polyester composites. Glass fiber offers good cost-effectiveness and controllable fiber size and porosity but has a relatively low dust-holding capacity. Polypropylene-polyester composites are optimized versions of polypropylene materials with higher dust-holding capacity but poorer cost-effectiveness.

Additionally, activated carbon is incorporated to adsorb sulfides, nitrogen oxides, and other harmful gases. Activated carbon contains numerous micropores that trap free molecules, fixing them within the pores. Some modified activated carbon materials even feature chemical components that react with pollutants, converting them into fixed compounds or harmless gases, achieving a chemical adsorption effect.

Design Considerations

During the design process of a fuel cell air filter, the pressure drop, adsorption capacity, and filtration type are first determined based on the types of pollutants in the intake air and the air flow rate. Subsequently, appropriate filter media materials are selected, and the filtration area and filter thickness are designed.

A well-designed air filter directly impacts the service life and output efficiency of the fuel cell stack.

Influencing Factors:

Generally, the pressure drop of an air filter is proportional to the airflow velocity and the thickness of the filter media. At a given airflow rate, the airflow velocity is inversely proportional to the filtration area. Therefore, a pleated structure is often adopted to increase the filtration area while reducing filter thickness, thereby minimizing pressure drop.

The pleated structure is characterized by pleat height and pleat count, which influence the pleat spacing. When the pleat spacing is large (with low pleat height and fewer pleats), air flows smoothly, resulting in minimal pressure drop. However, as pleat spacing decreases, airflow becomes turbulent, increasing resistance and raising the pressure drop.

Reducing the thickness of the filter element linearly decreases the pressure drop but also reduces filtration efficiency and service life.

Furthermore, the stacking height of activated carbon also affects the pressure drop of the air filter. As shown in the figure below, the pressure drop increases with higher airflow velocity. At the same airflow velocity, the pressure drop also increases linearly with the stacking height of activated carbon. Therefore, to achieve optimal performance, the structural and material design of the filter element must be carefully balanced.

Future Trends

As fuel cell system power continues to rise, market demands for higher volumetric power density are also increasing. Air filter design is evolving toward integration, multifunctionality, and the development of new materials.

In the future, trends will include compact designs, shorter connecting pipelines, and the integration of sensors and other components. Additionally, due to the limited variety of chemical adsorption materials, new filter media alternatives must be developed to achieve higher adsorption capacity, lower pressure drop, and longer service life.