IB Chemistry Topic R1.3.5 Fuel Cells Revision Notes (SL/HL)

IB Chemistry Topic R1.3.5 Fuel Cells Revision Notes (SL/HL) | RevisionDojo

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Hydrogen Fuel Cells: Converting Chemical Energy into Clean Electricity

Definition

Fuel cell

A fuel cell is a device that converts chemical energy directly into electrical energy through a redox reaction.

Unlike traditional combustion engines, which rely on burning fuels to generate heat, fuel cells produce electricity without combustion.
This makes them highly efficient and environmentally friendly.
The key difference between a fuel cell and a traditional battery lies in how they operate.
While batteries store a finite amount of chemical energy internally, fuel cells are continuously supplied with fuel from an external source, allowing them to generate electricity indefinitely, as long as fuel is available.

Analogy

Think of a fuel cell as a power plant rather than a storage tank.
A battery is like a tank that runs out once its stored energy is used, while a fuel cell keeps generating power as long as you keep supplying it with fuel.

The Hydrogen Fuel Cell: A Clean Energy Solution

Definition

Hydrogen fuel cell

The hydrogen fuel cell is one of the most commonly discussed types of fuel cells. It uses hydrogen gas ($H_2$) as a fuel and oxygen gas ($O_2$) from the air to produce water ($H_2O$), electricity, and heat.

The process is clean, efficient, and produces no harmful emissions.

Note

The following process is explained using knowledge from Reactivity 3.2.

Reactions in a Hydrogen Fuel Cell

Let’s explore what happens inside a hydrogen fuel cell step by step:

At the Anode (Oxidation):
1. Hydrogen gas ($H_2$) is fed into the anode, where it encounters a platinum-based catalyst.
2. The catalyst splits the hydrogen molecules into protons ($H^+$) and electrons ($e^-$).
3. The half-equation for the oxidation reaction is: $$2H_2 \rightarrow 4H^+ + 4e^-$$
Electron Flow:
1. The electrons cannot pass through the proton exchange membrane (PEM), so they are forced to travel through an external circuit, creating an electric current that can power devices.
Proton Movement:
1. The protons ($H^+$) pass through the PEM to the cathode.
At the Cathode (Reduction):
1. Oxygen gas ($O_2$) is fed into the cathode, where it reacts with the incoming protons and electrons to form water.
2. The half-equation for the reduction reaction is:
  $$
  O_2 + 4H^+ + 4e^- \rightarrow 2H_2O
  $$
Overall Reaction:
1. The overall redox reaction in the hydrogen fuel cell is:
  $$
  2H_2 + O_2 \rightarrow 2H_2O
  $$

The Same Cell in an Alkaline Electrolyte

A hydrogen fuel cell can also run with an alkaline electrolyte. The overall reaction is the same, but the half-equations are written using hydroxide ions (OH⁻).

At the anode (oxidation): $$2H_2 + 4OH^- \rightarrow 4H_2O + 4e^-$$
At the cathode (reduction): $$O_2 + 2H_2O + 4e^- \rightarrow 4OH^-$$

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Note

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Tip

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Hydrogen Fuel Cells: Converting Chemical Energy into Clean Electricity

Definition

Fuel cell

A fuel cell is a device that converts chemical energy directly into electrical energy through a redox reaction.

Unlike traditional combustion engines, which rely on burning fuels to generate heat, fuel cells produce electricity without combustion.
This makes them highly efficient and environmentally friendly.
The key difference between a fuel cell and a traditional battery lies in how they operate.
While batteries store a finite amount of chemical energy internally, fuel cells are continuously supplied with fuel from an external source, allowing them to generate electricity indefinitely, as long as fuel is available.

Analogy

Think of a fuel cell as a power plant rather than a storage tank.
A battery is like a tank that runs out once its stored energy is used, while a fuel cell keeps generating power as long as you keep supplying it with fuel.

The Hydrogen Fuel Cell: A Clean Energy Solution

Definition

Hydrogen fuel cell

The process is clean, efficient, and produces no harmful emissions.

Note

The following process is explained using knowledge from Reactivity 3.2.

Reactions in a Hydrogen Fuel Cell

Let’s explore what happens inside a hydrogen fuel cell step by step:

At the Anode (Oxidation):
1. Hydrogen gas ($H_2$) is fed into the anode, where it encounters a platinum-based catalyst.
2. The catalyst splits the hydrogen molecules into protons ($H^+$) and electrons ($e^-$).
3. The half-equation for the oxidation reaction is: $$2H_2 \rightarrow 4H^+ + 4e^-$$
Electron Flow:
1. The electrons cannot pass through the proton exchange membrane (PEM), so they are forced to travel through an external circuit, creating an electric current that can power devices.
Proton Movement:
1. The protons ($H^+$) pass through the PEM to the cathode.
At the Cathode (Reduction):
1. Oxygen gas ($O_2$) is fed into the cathode, where it reacts with the incoming protons and electrons to form water.
2. The half-equation for the reduction reaction is:
  $$
  O_2 + 4H^+ + 4e^- \rightarrow 2H_2O
  $$
Overall Reaction:
1. The overall redox reaction in the hydrogen fuel cell is:
  $$
  2H_2 + O_2 \rightarrow 2H_2O
  $$

The Same Cell in an Alkaline Electrolyte

A hydrogen fuel cell can also run with an alkaline electrolyte. The overall reaction is the same, but the half-equations are written using hydroxide ions (OH⁻).

At the anode (oxidation): $$2H_2 + 4OH^- \rightarrow 4H_2O + 4e^-$$
At the cathode (reduction): $$O_2 + 2H_2O + 4e^- \rightarrow 4OH^-$$

Definition

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Note

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Tip

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Structure 1. Models of the particulate nature of matter5 subtopics

Structure 2. Models of bonding and structure4 subtopics

Structure 3. Classification of matter2 subtopics

Reactivity 1. What drives chemical reactions?4 subtopics

Reactivity 2. How much, how fast and how far?3 subtopics

Reactivity 3. What are the mechanisms of chemical change?4 subtopics

IB Chemistry R1.3.5 Fuel Cells Notes

Structure 1. Models of the particulate nature of matter5 subtopics

Structure 2. Models of bonding and structure4 subtopics

Structure 3. Classification of matter2 subtopics

Reactivity 1. What drives chemical reactions?4 subtopics

Reactivity 2. How much, how fast and how far?3 subtopics

Reactivity 3. What are the mechanisms of chemical change?4 subtopics

Hydrogen Fuel Cells: Converting Chemical Energy into Clean Electricity

The Hydrogen Fuel Cell: A Clean Energy Solution

Reactions in a Hydrogen Fuel Cell

The Same Cell in an Alkaline Electrolyte

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

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Hydrogen Fuel Cells: Converting Chemical Energy into Clean Electricity

The Hydrogen Fuel Cell: A Clean Energy Solution

Reactions in a Hydrogen Fuel Cell

The Same Cell in an Alkaline Electrolyte

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

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