Understanding the Fundamentals of Fuel Cell Technology

What is a Fuel Cell?

Fuel cells generate electricity through an electrochemical reaction, without combustion. They convert chemical energy stored in hydrogen fuel into electricity via an electrochemical process. Different types of fuel cells are being developed for various applications including transportation, stationary, and portable power.

Proton Exchange Membrane Fuel Cells

Proton exchange membrane fuel cells, also known as polymer electrolyte membrane (PEM) fuel cells, are highly efficient and mainly used for transportation and stationary power applications. In a PEM fuel cell, hydrogen gas is supplied to the anode and oxygen or air is supplied to the cathode. Hydrogen molecules enter the anode where they are split into positive hydrogen ions (protons) and negatively charged electrons by a catalyst, typically platinum. The protons travel through the proton exchange membrane to the cathode, while the electrons are forced to travel an external circuit and generate direct current electricity. At the cathode, oxygen reacts with the protons and electrons to form water. The PEM fuel cell's polymer membrane electrolyte allows only the passage of positively charged hydrogen ions, blocking electrons. PEM fuel cells operate at relatively low temperatures, around 80°C.

Direct Methanol Fuel Cells

Direct methanol fuel cells (DMFCs) are similar to PEM fuel cells except that methanol is used as the fuel instead of hydrogen. Methanol is easier to store and transport than hydrogen. DMFCs have a polymer electrolyte membrane and produce electricity, water, and carbon dioxide from an electrochemical reaction of methanol and oxygen. Fuel cells a catalyst such as platinum-ruthenium to oxidize the methanol and bond to the protons. The electrolyte membrane allows hydrogen ions (protons) to pass through to the cathode while blocking the electrons, which must flow through the external circuit. At the cathode, oxygen reacts with the protons and electrons to form water. DMFCs are commonly used in portable power applications due to their ability to directly convert chemical energy to electricity without separate fuel processing. However, low efficiency and high costs compared to hydrogen PEM fuel cells limit wider use of DMFCs.

Phosphoric Acid Fuel Cells

Phosphoric acid fuel cells (PAFCs) were one of the earliest types of fuel cells developed with a liquid phosphoric acid electrolyte. They operate at high temperatures around 200°C. In a PAFC, hydrogen fuel is delivered to the anode and oxygen from air enters the porous cathode. Catalysts such as platinum dispersed on carbon paper electrodes induce the separation of hydrogen into protons and electrons. Protons migrate through the electrolyte to the cathode while the electrons flow through an external circuit, generating electricity. At the cathode, oxygen reacts with the protons and electrons to form water. PAFCs produce relatively high quality heat that can be used for cogeneration applications. However, phosphoric acid is corrosive and also causes platinum sintering which reduces catalyst performance over time, limiting the commercial use of PAFC technology.

Molten Carbonate Fuel Cells

Molten carbonate fuel cells (MCFCs) operate at high temperatures around 650°C. The electrolyte used is a molten carbonate salt mixture suspended in a porous, chemically inert ceramic lithium aluminum oxide matrix. This high temperature allows non-precious metals, such as nickel, to be used as catalysts. In the MCFC, hydrogen or hydrocarbon fuels supplied to the anode undergo oxidation, liberating electrons. The hydroxide ions produced diffuse through the electrolyte to the cathode. There, oxygen reacts with CO32- ions and electrons to form carbon dioxide and water. The high-temperature MCFC can use carbon monoxide or hydrocarbons as the fuel without the need for a fuel processor and also produces high-quality heat for cogeneration. MCFC plants are suitable for large stationary power generation. However, challenges include the electrolyte's crystallization at low carbon dioxide levels and corrosion due to carbonate melt.

Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) have a solid oxide electrolyte and operate at the highest temperatures of around 1000°C compared to other fuel cell types. The high temperature enables internal reforming of hydrocarbon fuels to hydrogen, removing the need for an external fuel processor. In an SOFC, oxygen ions are transported from the cathode to the anode through a solid ion conducting ceramic electrolyte. At the anode, oxidation of the fuel produces electrons that are drawn to the cathode through an external circuit, generating electricity. At the cathode, oxygen ions combine with the electrons to form water or carbon dioxide. SOFCs allow the use of non-precious metal catalysts and can be directly fueled by hydrogen, natural gas, or other carbon-containing fuels. Due to the high operating temperatures, SOFC systems start up quickly and also provide useful heat for cogeneration. However, challenges include material compatibility issues, electrolyte conductivity, and system durability over long-term operation.



fuel cells offer highly efficient power generation with potentially zero emissions. Various types are under development targeting transportation, stationary, and portable power applications. Advancements in catalysts, electrode structures, and electrolyte materials continue enabling higher performance, lower costs and wider commercialization of fuel cell technology. The clean energy produced by fuel cells can help reduce both oil consumption and air pollutant emissions worldwide. With further research and innovation, fuel cells are well positioned to play an important role in building a sustainable future energy system.

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