PEM Fuel Cells Explained — and How SOFCs Enable Reliable, Always-On Power

A proton exchange membrane (PEM) fuel cell is a type of electrochemical energy system that generates electricity by combining hydrogen and oxygen. Instead of combustion, though, a PEM fuel cell (PEMFC) uses a chemical reaction to convert the energy stored in hydrogen directly into electrical power. This process only produces water and heat as byproducts. As you can imagine, that makes it a very attractive option for low-emission power generation.

PEM fuel cells have relatively low operating temperatures and can respond quickly to changing power demands — you can see why they’re suited for applications like transportation and portable power.

To understand why PEM fuel cells are so versatile and useful, it may help to look inside the cell itself. Below, we’ll address how hydrogen is split, how protons move through the membrane, and how the whole process produces electricity.

How Do PEM Fuel Cells Work?

A PEM fuel cell has two electrodes: an anode and a cathode. They are separated by a thin polymer membrane that acts as the proton exchange membrane. When hydrogen fuel reaches the anode side of the cell, a catalyst breaks the hydrogen molecules into protons and electrons.

The membrane allows the protons, and only the protons, to pass through to the cathode. The electrons have to travel through an external circuit. These electrons moving through the circuit are what generate usable electrical power.

What are the protons doing while this is going on? When they reach the cathode, they combine with oxygen and return electrons. This reaction forms water, which then exits the system along with the heat generated during operation.

Now, let’s take a look at the actual components that make this system work.

Components of a PEM Fuel Cell

The following parts make up a PEM fuel cell:

Membrane Electrode Assembly: Consists of the PEM, catalyst layers, gas diffusion layers, and gaskets.
Proton Exchange Membrane (PEM): This thin membrane allows the positively charged protons to pass through while blocking the electrons.
Catalyst layers: Layers of catalyst sit on the anode and cathode sides of the membrane. They encourage hydrogen molecules to split at the anode and promote oxygen reduction at the cathode, producing water.
Bipolar plates: These stacked conductive plates manage the flow of electricity and gases between cells, sending hydrogen to the anode and oxygen to the cathode.
Gas diffusion layers: Situated between the catalyst and bipolar layers, gas diffusion layers are porous carbon paper that ensure proper gas distribution.
Gaskets: These gas-tight seals help prevent leakage of gases and coolant.

Now that we’ve discussed the hardware, it’s time to see where PEM fuel cells are used in the real world.

Applications of PEM Fuel Cells

Low operating temperatures, quick startup, and a compact system design make PEM fuel cells particularly suitable for applications that require responsive, efficient power. Some PEMFC applications include:

Transportation: PEM fuel cells can be found in hydrogen fuel cell electric vehicles, or FCEVs. Because they can quickly respond to changing loads and handle varying power demands, they’re particularly suited for passenger cars, buses, ferries, and industrial equipment.
Backup and emergency power systems: PEM fuel cells have also been used in the backup systems for telecommunications networks, data centers, and more.
Portable and mobile devices: Their lightweight design makes PEM fuel cells an interesting option for powering small, portable devices like laptops, mobile phones, and battery chargers, though exploration of this area is just getting started.

Advantages and Limitations

PEM cells offer several advantages that make them a viable alternative to other energy solutions.

For one, these cells produce energy through a clean chemical reaction that emits only water and heat as a by-product. The reaction does not combust fuel, so there are no greenhouse gas emissions. Because these fuel cells do not generate any harmful pollutants, they offer a clean, sustainable solution that supports decarbonization and net-zero emission goals.

PEM fuel cells are also highly efficient. When producing energy, these fuel cells can achieve efficiencies of 40 to 60%. In contrast, combustion engines can only achieve 20 to 35% efficiency. This is important because higher efficiency translates to lower costs and better productivity.

Scalability is another benefit of PEM fuel cells. There are many applications for these cells, from small portable devices to large industrial operations, because they use a stack-based design. This means you can easily scale your operations up or down.

With that said, PEM fuel cells bring with them some glaring limitations:

Hydrogen requirements: To function properly, PEM fuel cells require high-purity hydrogen, which comes with an exceptionally high price point.
Expensive catalysts: Catalysts are often made of platinum (or other precious metals), which also come with high price points.
Infrastructure limitations: Hydrogen infrastructure is expanding, but it is still largely in its infancy compared to more traditional fossil fuels. Those who wish to use hydrogen fuel must work around the challenges of shipping and storing it.
Water management difficulty: The membrane must maintain a certain level of moisture to conduct protons, but the required levels depend on the operating temperature of the fuel cell. If too much or too little water reaches the cell, performance drops significantly.
Possibility of degradation: Internal components, like the membrane and catalyst, can age and corrode, reducing efficiency and the overall performance of PEM fuel cells — and even impacting their lifespan.

The trajectory of PEM fuel cells is tied to broader developments in the hydrogen economy. PEM fuel cells are promising, but hydrogen itself must become more accessible and cost-effective for them to become more practical across industries.

Alternatives to PEM Fuel Cells

Now, PEM fuel cells aren’t the only available fuel cells. For instance, solid oxide fuel cells (SOFC) are another sustainable energy solution.

Just like PEM fuel cells, solid oxide fuel cells use a chemical reaction to convert fuel into energy, without emitting greenhouse gases. However, when comparing PEMFC vs. SOFC, we find some key differences.

For starters, the electrolyte in solid oxide fuel cells is a simple ceramic material, so this technology does not require the expensive, precious metals associated with PEM fuel cells. Solid oxide fuel cells are also considered more durable, with longer lifespans than their PEM counterparts.

Compared to PEM fuel cells, solid oxide fuel cells are also more flexible in the types of fuel they can use. While PEM fuel cells use only hydrogen, solid oxide fuel cells can generate electricity from various fuel sources, including hydrogen, natural gas, and biogas. This provides versatility and helps reduce some of the high costs associated with acquiring pure hydrogen.

Solid oxide fuel cells are among the most efficient fuel cell technologies. Because these fuel cells deliver uninterrupted, always-on power, they’re well-suited for operations that require continuous electricity, such as data centers, microgrids, hospitals, universities, and Combined Heat and Power (CHP) systems.

Learn More About PEM Alternatives

Fuel cells hold significant promise for the future energy landscape, and PEM fuel cells are one part of that growing ecosystem. They have potential, but more research and infrastructure are needed to make them effective across multiple industries.

Those who need large-scale, continuous power can turn to Bloom Energy, a leader in the SOFC industry. Bloom uses solid oxide fuel cells to generate reliable, clean, always-on power. Contact us today to learn more about Bloom’s energy initiatives.

RESOURCES

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