Fuel Cells
Hydrogen fuel cell stacks
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Fuel Cells
Fuel cells. No matter how familiar you are with them, reading their name always brings images from a distant future. They’ve been used in numerous sci-fi movies, books and video games to portray clean and limitless energy that powers up the cities of the future and our martian colonies. They’ve also been a highly controversial news topic since they have been the technology of the future for the last 30 years. As controversial as this sounds, it is absolutely true. They’ve been around since 1839 with various iterations coming in and out of fashion.
Fuel cells are being used in pilot projects and can power up high performance cars and applications. But why are they still “under development”? What keeps them from being the technology of the future and what can we do to bring the future closer to us? That’s what we are going to discuss in this quick ELI5 of fuel cells. What are they? How do they work? What kinds of products and technologies are coming into play to create energy out of thin air?
Like batteries, fuel cells are energy converters – they use an electrochemical reaction to take the chemical energy stored in a fuel source and convert it to electricity. Unlike batteries, which contain a fixed supply of energy, fuel cells do not require recharging. As long as fuel is continuously supplied to the fuel cell, electricity, water and heat will be produced
How does a fuel cell work?
So, how does a fuel cell work? In principle the concept of a fuel cell is pretty simple.
- Hydrogen gets in from anode side
- Oxygen comes in from the cathode side
- A couple of reduction and oxidation reactions happen within the system.
- Electricity and other byproducts such as heat and water come out.
To expand a little bit on #3, electrons are stripped off from the atoms at the anode side. In the case of PEM fuel cells, H+ ions are produced according to the reaction:
2 H₂(g) → 4 H⁺(aq) + 4 e⁻ (aq)
The electrons and H+ ions will travel according to their designated pathways and will be used in the cathode for the reduction reaction:
O₂(g) + 4 H⁺(aq) + 4 e⁻ (aq) → 2 H₂O (l)
Hydrogen and Oxygen get in. Electricity (and water) gets out.
A fuel cell is a clean energy source with the only byproducts being electricity (power), heat and water. A single fuel cell alone only produces a few watts of power; therefore, several fuel cells can be stacked together to create a fuel cell stack. When combined in stacks, the fuel cells’ output can vary greatly, from just a few kilowatts of power to multi-megawatt installations.
You can generalize and say that it is a kind of battery that makes electricity on the fly. This is an example for the sake of simplicity. You can replace Hydrogen with any other suitable fuel and Oxygen with any other suitable oxidizing agent and you’d get the same result. Also what comes in/out depends on the type of Ion exchange membrane and catalyst that we are going to use.
Five Major Types of Fuel Cells (PEMFCs, SOFCs, DMFCs, AFCs, and PAFCs) and Their Applications
Fuel cells are electrochemical devices that convert chemical energy into electrical energy. There are several different types of fuel cells, each with its own unique characteristics and applications. Here are a few things about some of the most common types of fuel cells:
Proton Exchange Membrane Fuel Cells (PEMFCs): These are the most common type of fuel cells and are widely used in automotive applications. They use a polymer electrolyte membrane and require hydrogen and oxygen as fuel and oxidant, respectively. PEMFCs are known for their high efficiency, low emissions, and fast start-up times.
Solid Oxide Fuel Cells (SOFCs): These fuel cells operate at high temperatures (typically above 800 °C) and use a solid oxide electrolyte. They can operate on a variety of fuels, including hydrogen, natural gas, and biogas, making them suitable for a wide range of applications, including power generation and cogeneration.
Direct Methanol Fuel Cells (DMFCs): DMFCs are similar to PEMFCs but use methanol as a fuel instead of hydrogen. They are typically smaller and more compact than PEMFCs and are used in portable applications such as mobile phones and laptops.
Alkaline Fuel Cells (AFCs): These fuel cells use an alkaline electrolyte (usually potassium hydroxide) and were among the first types of fuel cells to be developed. They are primarily used in niche applications such as spacecraft and submarines.
Phosphoric Acid Fuel Cells (PAFCs): These fuel cells use phosphoric acid as an electrolyte and operate at temperatures of around 150 °C. They are often used in stationary power generation applications, such as in hospitals and office buildings.
PAFCs share the same set of reactions with PEMFC. The only difference is the injection (and expulsion) of a phosphoric acid electrolyte in PAFCs
These are just a few examples of the many types of fuel cells that exist. Each type has its own unique characteristics and advantages, making them suitable for a range of different applications.
Frequently Asked Questions about Fuel Cells
Water electrolyzers and fuel cells are both electrochemical devices but serve opposite purposes. Electrolyzers use electrical energy to drive a non-spontaneous chemical reaction, splitting water (H2O) into hydrogen (H2) and oxygen (O2) gases. This process, known as water electrolysis, is essential for hydrogen production, supporting the hydrogen economy by enabling large-scale hydrogen generation for energy storage and transport.
In contrast, fuel cells convert chemical energy from fuels like hydrogen directly into electrical energy without combustion. They operate through redox reactions where hydrogen is oxidized at the anode, releasing electrons, and oxygen is reduced at the cathode, accepting electrons. The resulting electrical energy can power various applications, making fuel cells a key technology for clean energy production.
Is a fuel cell a battery?
As both are electrochemical devices in nature, the working principles of batteries and fuel cells are similar. The key difference is that fuel cells are open systems that convert chemically bound energy supplied from external fuels, such as hydrogen, methanol, and hydrazine, whereas batteries are closed systems that convert chemical energy integrated into their structure. Not considering material degradation, fuel cells will continue operating as long as fuels are being supplied. Batteries, on the other hand, must be recharged once the stored chemical energy within it has been converted, else, its useful life ends. This fundamental distinction in their energy sources influences their respective roles and applications in various energy and power generation systems.
Fuel cells offer flexibility in the fuel type that can be used:
Hydrogen: When produced using renewable electricity – like solar, wind and hydropower – hydrogen is completely decarbonized and produces zero emissions. Hydrogen fuel cells (i.e. fuel cells that are fueled by hydrogen) produce power, heat and water and release no carbon dioxide or other pollutants into the air.
Natural gas: As widespread production of green hydrogen is still in progress, natural gas is currently the most-used fuel to power fuel cells. In this case the fuel cells are not completely emission-free, but they do offer significantly lower emissions than other fuels, like oil and coal.
Methanol: Methanol is used as fuel in DMFCs due to its high energy density, ease of storage, and liquid state at room temperature, making it more convenient than hydrogen.
Can graphitized carbon fiber papers be used in fuel cells?
Graphitized carbon fiber papers can be used in fuel cells. They are commonly utilized as gas diffusion layers (GDLs) in proton exchange membrane (PEM) fuel cells. The graphitized carbon fiber paper serves as a crucial component that facilitates the distribution of reactant gases (like hydrogen and oxygen) across the catalyst layer, ensures efficient electron conduction, and provides structural support to the membrane electrode assembly (MEA). Its graphitized structure enhances electrical conductivity, while the porous nature allows for effective gas and water management, which is essential for maintaining optimal fuel cell performance.
Why do fuel cells use thin GDLs?
Carbon papers for Fuel Cells & Electrolyzers
How Will the Impending PFAS-ban Affect Fuel Cells?
