Proton Exchange Membrane Fuel Cells (PEMFC) boast advantages such as high efficiency, cleanliness, and zero emissions, making them promising for widespread application. In practical applications, 40% to 60% of the chemical energy from the fuel is converted into electrical energy, while the remaining energy is mostly converted into thermal energy. If heat cannot be promptly dissipated from the cell, the system temperature will continue to rise, leading to localized overheating of individual cells or specific areas within the cell, severely impacting the normal operation of the fuel cell.

I. Importance of thermal management

The main heat sources in the process of fuel cell operation are ohmic resistance heating, reaction entropy heat, irreversible electrochemical reaction heat, water vapor condensation heat release, compressed air heat and environmental radiation heat, the latter two can be ignored.

  II. Cooling scheme for fuel cells

The main heat dissipation pathways for fuel cells are threefold: water vaporization from within the cell, radiative cooling of the stack, and heat removal by circulating cooling media. The latter is the primary method of heat dissipation for fuel cells. For PEMFCs, cooling methods can be broadly categorized into two types: single-phase cooling and phase change cooling.

1. Single-phase cooling

Single-phase cooling method is to use the sensible heat of cooling medium to take away the heat generated in the working process of fuel cell. There are two types: air cooling and liquid cooling, which are the most widely used cooling technology at present.

(1) Air cooling

Air cooling is the simplest method of cooling, where air passes through cooling plates or cathodes to carry away waste heat generated by fuel cells. The structure of the cooling system is also relatively simple. This type of heat dissipation is commonly used in low-power (≤5kW) PEMFC systems that have fewer components, lower costs, and higher system efficiency, such as in drone power systems and portable power sources.

Fuel cell system with air cooling

(2) Liquid cooling

Liquid cooling is designed to separate the coolant flow path between the cathode and anode plates of the fuel cell, and relies on forced convection heat transfer of the coolant to remove the heat generated during the operation of the fuel cell.

The coolant can be deionized water or a mixture of water and ethylene glycol. The specific heat capacity of liquids is greater than that of air, making liquid cooling more efficient in terms of heat transfer and lower flow rates compared to air cooling. Using liquid cooling, the temperature distribution in fuel cells becomes more uniform; however, it involves many components and complex structures, with significant power consumption for accessories used in heat dissipation, typically around 10% of the effective output power. For high-power (over 5 kW) fuel cells, such as those used in vehicles, liquid cooling is the most commonly employed method.

Take the vehicle fuel cell as an example, its thermal management system mainly includes coolant pump, heat exchanger, water tank, fan, pressure sensor and other components.

  III. Phase change cooling

Phase change cooling is to cool the heat source by using the characteristic of absorbing a large amount of heat when the object changes phase. The commonly used phase change cooling methods in fuel cells are evaporation cooling and heat pipe heat dissipation.

(1) Evaporative cooling

The evaporative cooling of fuel cells involves the coolant and air entering the system from the cathode side together. The coolant typically used is deionized water. The coolant can humidify the air, increasing the moisture content in the proton exchange membrane, thereby enhancing the performance of the fuel cell. At the same time, most of the coolant is carried into the core area of the reaction heat source by the air and evaporates, carrying away the heat generated during the reaction. An evaporative cooling fuel cell system does not require a humidifier, as evaporation and condensation heat exchange are more efficient than single-phase convection heat exchange, significantly reducing the load on the cooling water pump and radiator.

(2) Heat pipe heat dissipation

Heat pipe cooling involves embedding the heat pipe into a bipolar plate. In the absence of external power, the heat pipe transfers a large amount of heat over long distances through its cross-sectional area for cooling. The material of the heat pipe is typically copper or aluminum alloy, ensuring that the temperature at the heat source remains well-distributed. Research on the application of heat pipe cooling technology in fuel cell applications is still in its early stages and requires further development.

Thermal management is crucial for the performance of fuel cells, affecting their efficiency, lifespan, and safety. Currently, the most widely used technology in the fuel cell field is single-phase cooling. Phase change cooling technology, with its uniformity and high efficiency, is a highly promising research direction. At the same time, effective thermal management control strategies are key to ensuring the proper operation of fuel cells. For instance, when the temperature of the fuel cell rises and the thermal management system cannot provide sufficient heat dissipation, control strategies on the power system platform should consider measures such as limiting the output power of the fuel cell to enhance its lifespan, safety, and durability. To improve the heat dissipation capability of the fuel cell thermal management system, efforts must also be made to increase the operating temperature of the fuel cell and improve the temperature characteristics of the fuel cell materials. For example, if the operating temperature of the fuel cell is increased to 95℃, the heat dissipation capacity of the thermal management system can be improved by more than 50%.

 

 

1、Understanding ion exchange membrane An ion exchange membrane (IEM) is a thin barrier that allows ions to be selectively passed from one electrode of an electrochemical device to another, including but not limited to water electrolysis cells and fuel cells. The ion-exchange membrane consists of a three-dimensional polymer matrix functionalized with charged (or ion-exchange) groups. These fixed charge groups completely or partially repel similarly charged ions (isoions) out of the membrane and allow ions with different charges (counterions) to pass through the membrane. In hydroelectrolytic cells and fuel cells, efficient ion transport is important for achieving high performance, reducing overpotential, and ensuring the overall effectiveness of relevant electrochemical processes.

2、Key considerations when choosing a appropriate IEM

According to the type of fixed charge group in the polymer backbone, IEM can be divided into two types: cationic (CEM) and anion (AEM) exchange membrane. The cation exchange membranes contain fixed negatively charged ions that allow the cations to move on the membrane. Conversely, AEM carries positively charged groups that selectively allow the transport of anions. In addition to these two basic classifications, the IEM can also be a proton exchange membrane (PEM), a bipolar membrane, an amphotropic membrane, and a mixed matrix membrane. In water electrolytic cells and fuel cells, PEM and AEM are the most useful. PEM is a special CEM that can transport protons (H + ions).

1. When choosing an ion exchange membrane, the first consideration is the type of fuel cell and water electrolytic tank. The operation of fuel cells and water electrolytic cells involves the transport of ions; the type of ion to be transmitted determines the appropriate type of ion exchange membrane to be used. Polymer electrolyte membrane water electrolytic cell (PEMWE) and fuel cell (PEMFC) operating under acidic conditions are required to transport H + ions. Thus, both PEMFC and PEMWE use the PEM. In contrast, anion exchange membrane fuel cells (AEMFC) and anion exchange membrane water electrolytic cell (AEMWE) operate in alkaline environments. Both AEMFC and AEMWE used the AEM.

Once the type of IEM suitable for the fuel cell and water electrolytic cell has is identified, it is time to go deeper into the specific characteristics that produce target efficiency and performance.

2、The IEM performance and the balance between them

In general, the properties of the IEM are determined by the characteristics of the polymer backbone and the fixed charge that constitutes its structure. In particular, the density, wettability (hydrophobic or hydrophilic) and morphology of the polymer matrix, as well as the type and concentration of charged functional groups, can affect the performance of IEM. The mechanical, chemical and thermal properties of IEM are mainly influenced by the polymer backbone, while the electrochemical properties, conductivity and overselectivity are determined by the concentration of the fixed charge. Click here to learn more about the key IEM features.

High-performance IEM shall have high ionic conductivity, high ion exchange capacity, near-uniform overselectivity, and excellent dimensional, chemical, mechanical, and thermal stability. However, it is not easy to meet all of these requirements. We can't do everything, and in most cases, we have to find the perfect balance between these features.

3. Working conditions

When finding a suitable IEM for your application, you should also consider working conditions, including temperature, pressure, and humidity levels. Working conditions can affect not only IEM performance, but also its stability. Some IEM have the best performance at high temperatures, while others are designed for low temperature applications. Ensure that the selected IEM supports the device usage environment.

4, the cost of membrane materials

Suppose that we have found a perfectly optimized membrane with both good performance and stability. Another factor to be considered is the cost. Usually, high requirements for performance and stability require high material costs. Therefore, balancing performance requirements and budget constraints is critical because the cost of IEM affects the overall cost of fuel cells and water systems.

Choosing the right ion exchange membrane is the key point in the design of efficient and durable hydrolysis cells and fuel cell systems. By carefully considering the above factors and conducting appropriate tests, you can make informed decisions based on the specific application requirements. Please contact us, our application engineers and in-house hydrolysis cell and fuel cell experts will help you select the best product for your application. Let's work together to pave the way for the development of clean and sustainable energy solutions.