Alkaline Fuel Cells

Alkaline Fuel Cells (AFCs) are among the oldest types of fuel cells—and still one of the most efficient for converting hydrogen and oxygen into electricity. They’re compact, lightweight, and ideal for situations where space and energy efficiency matter most.

Used by NASA during the Apollo space missions, AFCs are trusted technology for high-performance environments. But they also come with limitations that affect their use in everyday settings.

Let’s break down how AFCs work, their pros and cons, and where they’re most useful.

What Is an Alkaline Fuel Cell?

An Alkaline Fuel Cell uses a special liquid (usually potassium hydroxide, or KOH) as the electrolyte. This liquid moves hydroxyl ions (OH⁻) from the air side (cathode) to the fuel side (anode)—where electricity is produced.

Two Types of AFC Designs

1. Mobile Electrolyte AFCs
   1. Liquid KOH circulates between the electrodes.
   1. Water and heat are removed as the fluid flows.
2. Immobile Electrolyte AFCs
   1. A thick KOH paste is held in a solid matrix.
   1. Water evaporates into the hydrogen stream and is later condensed.

Operating Characteristics

Parameter	Value
Operating Temp	65–220°C (150–430°F)
Operating Pressure	~15 psig (1 barg)
Voltage per Cell	~1.1 to 1.2 VDC
Electrolyte	Potassium Hydroxide (KOH)

Electrochemical Reactions in AFCs

Anode Reactions:

1. H₂ + 2K⁺ + 2OH⁻ → 2K + 2H₂O
2. 2K → 2K⁺ + 2e⁻

These reactions release electrons and form water at the anode side.

Cathode Reactions:

1. ½O₂ + H₂O → 2OH
2. 2OH + 2e⁻ → 2OH⁻

Oxygen reacts with water to form hydroxyl ions, which migrate to the anode.

Overall Cell Reaction:

• H₂ + ½O₂ → H₂O

In both mobile and immobile systems, water is the by-product, but its removal method varies based on the electrolyte type.

Advantages of Alkaline Fuel Cells

Despite being an older technology, AFCs offer several compelling advantages in the right environment:

Benefit	Description
Low Operating Temperature	Ideal for portable and space-based systems
High Electrical Efficiency	Converts more fuel into electricity (up to 60%)
Fast Startup	Can reach 50% power at ambient temperature—great for quick deployment
Minimal Platinum Requirement	Reduces cost vs. PEM fuel cells
Low Corrosion Risk	Chemically stable under operating conditions
Compact & Lightweight	Ideal for aerospace and low-weight applications
Simple System Design	Easier to integrate and operate

Key Features at a Glance

Feature	Detail
Temperature	150–430°F (65–220°C)
Pressure	~15 psi
Voltage per Cell	1.1–1.2 VDC
Fuel Type	Pure Hydrogen
Oxidant	Pure Oxygen or CO₂-free air

Why Choose Alkaline Fuel Cells?

Top Advantages:

• Fast startup – reaches 50% power at room temp
• High efficiency – more energy from less fuel
• No expensive platinum needed
• Low temperature operation
• Simple and lightweight system
• Low corrosion risk – longer component life

Summary Table: Alkaline Fuel Cells (AFCs)

Feature	Alkaline Fuel Cells (AFCs)
Electrolyte	Potassium Hydroxide (KOH) – mobile or paste-based
Ion Conducted	Hydroxyl Ion (OH⁻)
Operating Temp	65–220°C (150–430°F)
Fuel Type	Pure Hydrogen
Oxidant Requirement	Pure Oxygen or CO₂-free Air
Startup Time	Fast – 50% power at ambient temp
Efficiency	High (up to 60%)
CO₂ Tolerance	Very Low (max ~350 ppm)
Best Use Cases	Space missions, portable systems, lab-scale research