Introduction
Alkali fuel cells (AFCs) represent one of the earliest and most thoroughly developed fuel cell technologies. Their high electrical efficiency, low operating temperatures, and ability to produce potable water have made them particularly valuable in aerospace and specialized terrestrial applications.
This article presents a comprehensive overview of alkali fuel cell technology, tracing its historical development and examining its practical applications. Emphasis is placed on electrochemical operation, key engineering advancements, and the factors that have influenced both adoption and decline relative to competing fuel cell systems.
Alkali Fuel Cell Technology
Alkali fuel cells operate using compressed hydrogen and oxygen as reactants and typically employ an aqueous potassium hydroxide (KOH) solution as the electrolyte. Operating temperatures generally range between 150°C and 200°C (300°F to 400°F), enabling relatively fast reaction kinetics and high efficiency.
A simple, colorful 3D illustration of an Alkali Fuel Cell. It shows a box with ‘Hydrogen’ entering the left side and ‘Oxygen’ entering the right side. A lightbulb is connected to the top, glowing bright yellow. A drop of blue water is dripping out of the bottom pipe. The background is a starry space scene.
Electrochemical Operating Principle
In alkali fuel cells, electrical energy is generated through the controlled migration of ions and electrons:
• Hydroxide ions (OH⁻) migrate from the cathode to the anode through the alkaline electrolyte
• At the anode, hydrogen reacts with hydroxide ions to form water and release electrons
• The released electrons flow through an external circuit, supplying electrical power
• At the cathode, electrons react with oxygen and water to generate additional hydroxide ions
This closed-loop electrochemical process continues as long as hydrogen and oxygen are supplied.
A 2D cross-section diagram of an Alkali Fuel Cell. The left wall is labeled ‘Anode (-)’ and the right wall is labeled ‘Cathode (+)’. In the middle, a liquid labeled ‘Potassium Hydroxide (KOH)’ is shown. Arrows show ‘OH-‘ ions swimming from right to left. A wire connects the top of the two walls, with electrons ‘e-‘ flowing from left to right through a lightbulb.
Performance Characteristics
Alkali fuel cells are capable of achieving:
• Electrical efficiencies of up to 70 percent
• Low pollutant emissions
• High-quality water production
These characteristics made AFCs particularly suitable for environments requiring high reliability and minimal waste, such as crewed spacecraft.
Technical Limitations
Despite their advantages, alkali fuel cells face significant technical challenges:
• Carbon dioxide sensitivity, which leads to carbonate formation in the electrolyte
• Requirement for high-purity hydrogen and oxygen
• Historically high reliance on platinum catalysts
Carbonate formation interferes with ion transport and electrode reactions, significantly reducing cell performance and lifespan. Since many hydrogen production methods generate CO₂ as a byproduct, this sensitivity has limited broader deployment of AFCs.
A microscopic view comparison. Left side: ‘Clean Electrolyte’ showing clear liquid with moving particles. Right side: ‘Poisoned Electrolyte’ showing jagged white crystals (carbonate) blocking the path of the particles.
Alkali Fuel Cell History
The modern development of alkali fuel cells is largely attributed to Francis Thomas Bacon, whose work in the late 1930s marked a turning point in fuel cell engineering.
Early Innovations
Bacon’s contributions included:
• Replacing acidic electrolytes with potassium hydroxide, reducing corrosion
• Introducing porous gas-diffusion electrodes to increase reaction surface area
• Using pressurized gases to prevent electrolyte flooding
Over two decades of development culminated in large-scale demonstrations of alkali fuel cell system
Industrial and Military Demonstrations
One of the most notable demonstrations occurred in 1959, when Allis-Chalmers unveiled a farm tractor powered by a stack of 1,008 alkali fuel cells producing approximately 15 kW of power. This system demonstrated the feasibility of AFCs for heavy-duty applications.
Subsequent projects included:
• Fuel-cell-powered golf carts
• Submersibles
• Forklifts
These efforts were supported in part by the U.S. Air Force, highlighting military interest in silent, low-emission power sources.
A black and white historical-style sketch of the 1959 Allis-Chalmers fuel cell tractor. It looks like a normal vintage tractor but the engine area is filled with a large boxy stack of cells. A driver is sitting on top waving.
Contributions from Union Carbide and European Researchers
During the 1950s and 1960s, Union Carbide advanced AFC technology through the work of Karl Kordesch, who developed carbon-based gas-diffusion electrodes.
Notable demonstrations included:
• A fuel-cell-powered mobile radar unit
• A fuel-cell-powered motorcycle
• Conceptual designs for undersea fuel-cell-powered bases
Concurrently, Eduard Justi developed nickel-based gas-diffusion electrodes, further advancing electrode durability and performance.
Adoption by NASA
In the early 1960s, aircraft engine manufacturer Pratt & Whitney licensed Bacon’s patents and secured contracts with NASA.
Alkali fuel cells were selected to power:
• Apollo program
• Space Shuttle program
Their selection was driven by:
• High efficiency
• Exceptional reliability
• Onboard production of potable water
Alkali Fuel Cell Applications
Aerospace Applications
Alkali fuel cells remain most strongly associated with crewed spaceflight. In both the Apollo and Space Shuttle programs, AFCs provided:
• Primary electrical power
• Clean drinking water
• Quiet and vibration-free operation
These attributes outweighed cost concerns in mission-critical environments.
A realistic rendering of the Space Shuttle orbiter in orbit with its cargo bay doors open. Inside the cargo bay, highlight the location of the three fuel cell power plants with a glowing outline.
Terrestrial and Transport Applications
Although AFCs have proven expensive for widespread commercial use, several experimental and niche applications have been explored.
In 1998, the Zero Emission Vehicle Company introduced a prototype hydrogen-powered taxi in London. The vehicle used a 5 kW alkali fuel cell, producing:
• Zero tailpipe emissions
• Significantly reduced noise levels
The system reportedly utilized cobalt-based catalysts instead of platinum, addressing cost concerns. Related projects included delivery vehicles, airport tow-tugs, and fuel-cell-powered boats.
Underwater Power
Submarines and underwater bases need power without using air from the surface. Since AFCs use stored Oxygen and Hydrogen, they are perfect for deep-sea exploration.
A concept art drawing of a futuristic yellow submarine exploring the ocean floor. The back of the submarine shows a compartment labeled ‘Alkali Fuel Cell Power System’. No bubbles are coming out, indicating a closed system.
Conclusion
Alkali fuel cells occupy a foundational position in the history of electrochemical power generation. Their high efficiency, clean operation, and proven reliability in aerospace applications demonstrate the technical strengths of the technology.
However, sensitivity to carbon dioxide, fuel purity requirements, and cost challenges have limited widespread adoption in modern commercial markets. Despite increasing competition from alternative fuel cell technologies, alkali fuel cells continue to offer valuable insights and potential in controlled and specialized applications.
Ongoing research into electrolyte chemistry, catalyst optimization, and system integration may yet enable renewed relevance for alkali fuel cell technology in future energy systems.
Critical Reasoning:
If engineers can invent a filter that removes CO2 from the air cheaply, do you think Alkali Fuel Cells would become popular for cars again? Why?
