Electricity Production and Efficiency of PEM Fuel Cells

Proton Exchange Membrane (PEM) fuel cells are renowned for their high efficiency and ability to generate electricity from hydrogen and oxygen. This article provides a comprehensive overview of how PEM fuel cells produce electricity and their overall efficiency, including factors that can influence their performance.

Electricity Production

Power Output: PEM fuel cells can produce a wide range of power outputs, typically varying from a few watts to several megawatts, depending on the size and application. Small fuel cells used in portable devices can generate around 1-100 watts, while larger systems utilized in vehicles or stationary applications can produce several kilowatts to megawatts.

Efficiency

Electrical Efficiency: Under optimal conditions, the electrical efficiency of PEM fuel cells ranges from 40 to 60 percent. This means that 40 to 60 percent of the energy in the hydrogen fuel is converted into electrical energy. When considering the total system efficiency, including heat recovery in combined heat and power (CHP) systems, the overall efficiency can exceed 80 percent.

Factors Influencing Efficiency

Operating Conditions: Temperature, pressure, and humidity can significantly affect the performance of PEM fuel cells. Optimal operating conditions are essential for maintaining high efficiency.

Fuel Quality: The purity of hydrogen and the presence of contaminants can impact the efficiency and longevity of the fuel cell. High-quality, contaminant-free hydrogen is crucial for optimal performance.

System Design: The design of the fuel cell stack and balance of plant components also plays a significant role in the overall efficiency. Efficient design can enhance the performance and durability of the fuel cell.

Practical Examples

The efficiency of PEM fuel cells is influenced by several factors, including the air pump, the active catalytic matrix, and the heater. For instance, the air pump used in large-scale applications, such as the Bosch fuel cell air pump for a 150 kW fuel cell, requires an input of 400V at 20 kW. This means that it consumes 13 percent of the fuel cell's output at full power, considering some overhead margin. Alternatively, variable flow efficiency could lead to higher consumption. The heater is primarily used during warm-up periods; however, it may be required to compensate for the hydrogen decompression if the PEM inefficiency heat is not sufficient.

In general, the overall efficiency of a PEM fuel cell system typically ranges from 60 to 65 percent, considering all the aforementioned factors. A well-designed fuel cell with optimal operating conditions and high-quality hydrogen can achieve even higher efficiencies.