In a hydrogen-oxygen fuel cell, combustion of hydrogen occurs to
(a) generate heat
(b) create potent

Q: Why doesn't the combustion of hydrogen in a fuel cell just generate heat like a normal fire?

In a fuel cell, the oxidation of hydrogen and the reduction of oxygen are physically separated into two different compartments. Because the electrons must travel through an external wire to get from the fuel to the oxidant, the chemical energy is converted directly into electrical work (potential difference) rather than being dissipated as heat.

Q: Is producing high purity water the main goal of a fuel cell?

While high purity water is a fantastic and useful byproduct (especially in space missions), it is not the primary goal. The main objective of any cell, including a fuel cell, is to generate electricity by creating a potential difference.

Q: What is the role of the electrolyte like KOH in this cell?

The electrolyte provides the ions (like $OH^-$) necessary to complete the internal circuit. It allows ions to flow between the electrodes to maintain electrical neutrality while the electrons flow through the external wire.

Q: Why is it called 'combustion' if there is no actual fire?

In chemistry, combustion is fundamentally an exothermic redox reaction between a fuel and an oxidant (usually oxygen). Even though there is no visible flame in a fuel cell, the overall chemical reaction ($2H_2 + O_2 \rightarrow 2H_2O$) is identical to burning hydrogen, hence it is referred to as combustion.

Q: Are fuel cells 100% efficient?

No, they are not 100% efficient due to thermodynamic limitations and internal resistance, but they are significantly more efficient (often 60-70%) than traditional thermal power plants (which are limited by the Carnot cycle efficiency of around 30-40%).

Question

In a hydrogen-oxygen fuel cell, combustion of hydrogen occurs to

Options:

(A) generate heat

(B) create potential difference between the two electrodes

(C) produce high purity water

(D) remove adsorbed oxygen from electrode surfaces

Sigma Percentile · Accepted Answer

### The Magic of Fuel Cells

Imagine a device that takes fuel and, instead of burning it in a roaring fire, directly converts its chemical energy into electricity. That is the magic of a fuel cell. When we hear the word "combustion," we usually picture flames, heat, and smoke. But in the elegant world of electrochemistry, combustion can be tamed and harnessed to do electrical work.

### Analyzing the Setup

Let's look at the classic Hydrogen-Oxygen fuel cell. We have two porous carbon electrodes infused with a suitable catalyst like finely divided platinum or palladium. These electrodes are immersed in an aqueous electrolyte, typically concentrated Sodium Hydroxide ($NaOH$) or Potassium Hydroxide ($KOH$).

Hydrogen gas ($H_2$) is bubbled through the anode compartment, while Oxygen gas ($O_2$) is bubbled through the cathode compartment.

### The Master Equations

At the anode, hydrogen undergoes oxidation. It reacts with the hydroxide ions from the electrolyte to form water, releasing electrons in the process:

$$H_2(g) + 2OH^-(aq) \rightarrow 2H_2O(l) + 2e^-$$

These released electrons cannot swim through the electrolyte. They are forced to travel through an external wire to reach the cathode. This flow of electrons is exactly what we call an electric current!

At the cathode, oxygen gas eagerly waits for these electrons. It undergoes reduction, reacting with water to regenerate the hydroxide ions:

$$O_2(g) + 2H_2O(l) + 4e^- \rightarrow 4OH^-(aq)$$

### The Core Takeaway

The overall reaction is simply the formation of water: $2H_2(g) + O_2(g) \rightarrow 2H_2O(l)$. However, because we separated the oxidation and reduction half-reactions, the energy that would have been lost as heat is instead used to drive electrons through a circuit.

**This creates a potential difference between the two electrodes.** Therefore, the combustion of hydrogen in a fuel cell is specifically designed to generate this potential difference, making option (b) the correct answer. As a beautiful bonus, the only byproduct is high-purity water, which was famously used by astronauts for drinking during the Apollo space missions!

Animated Solution for Chemistry - Electrochemistry: In a hydrogen-oxygen fuel cell, combustion of hydrogen occurs to

Select Answer:

Visualized Solution

The Hydrogen-Oxygen Fuel Cell

Reaction at Anode

Reaction at Cathode

Generation of Electricity

Conclusion

The Way Forward

The Sigma Insight: Electrochemical Cells

The Magic of Fuel Cells

Analyzing the Setup

The Master Equations

The Core Takeaway

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