Fuel Cells: Why They Aren’t Quite Like Batteries

A fuel cell makes electricity from a fuel and oxygen. It does not burn the fuel. It does not run down like a battery, as long as fuel keeps arriving. In the UPSC question, this difference decides three statements.

1.1 How does a hydrogen fuel cell work?

A fuel cell has two electrodes with an electrolyte between them. The electrodes are the negative anode and the positive cathode. Here is the path, step by step.

• Hydrogen is fed to the anode. Air is fed to the cathode.
• A catalyst at the anode splits hydrogen molecules into protons and electrons.
• The electrons cannot cross the electrolyte. They flow through an outside circuit. That flow is the electricity.
• The protons move through the electrolyte to the cathode.
• At the cathode, protons, electrons and oxygen join to make water and heat.

1.2 Why is a fuel cell not quite like a battery?

A fuel cell works like a battery in one way. Both turn chemical energy into electricity through two electrodes.

The difference lies in the supply. A battery holds its chemicals inside and runs down. A fuel cell is fed fuel from outside and keeps going.

The Class 12 book says the same. In a fuel cell, the reactants are fed continuously to the electrodes. The products are removed continuously. So the cell runs as long as the reactants are supplied.

With pure hydrogen, only water and heat come out, besides the electricity. This is statement 1 of the exam question, and it is correct. With other fuels, the answer changes.

2.1 Why does pure hydrogen give only water and heat?

Hydrogen has no carbon. At the cathode, hydrogen and oxygen combine to form water. That is the whole reaction.

DOE says that if hydrogen is the fuel, the only products are electricity, water and heat. It also says hydrogen fuel cells emit no air pollutants that cause smog at the point of operation.

2.2 What if the fuel is not pure hydrogen?

Some systems run on hydrogen-rich fuels such as methanol, gasoline, diesel or gasified coal. A device called a reformer first turns the fuel into a gas mixture that contains hydrogen.

DOE says both internal and external reforming release carbon dioxide. But fuel cells are so efficient that they give out less carbon dioxide than petrol engines.

So the “heat and water only” claim holds for pure hydrogen. It does not hold for every fuel.

2.3 Where does the hydrogen come from?

The fuel cell is clean at the point of use. How clean the whole chain is depends on how the hydrogen was made. DOE lists several ways.

• Natural gas reforming, also called steam methane reforming.
• Biomass gasification and other heat-driven processes.
• Electrolysis, which uses electricity to split water into hydrogen and oxygen.
• Biological processes, which use bacteria or algae. These are still at the research stage.

A fuel cell gives direct current (DC). Statement 3 of the exam question says alternating current (AC). That statement is wrong.

3.1 What is the difference between DC and AC?

In a DC circuit, electrons flow in one direction only. In an AC circuit, the flow reverses in regular cycles. Homes and workplaces use AC.

DOE says fuel cells produce electricity in the form of DC. If the equipment needs AC, the DC must be converted.

3.2 What are a stack and a power conditioner?

One cell makes less than 1 volt. That is too little for most uses. So many cells are joined in series into a fuel cell stack. A typical stack may hold hundreds of cells.

A power conditioner then adjusts the current, voltage and frequency for the job. An inverter turns DC into AC. This conversion costs only about 2 to 6 percent of the system’s efficiency.

Fuel cells come in many sizes. Statement 2 of the exam question says they suit buildings but not small devices like laptop computers. That statement is wrong.

4.1 Can a fuel cell power a laptop?

Yes. DOE says fuel cells can power systems as large as a utility power station and as small as a laptop computer.

Direct methanol fuel cells are often used for portable uses such as cell phones and laptop computers. They run on liquid methanol mixed with water.

4.2 Can a fuel cell run a vehicle?

Yes. A fuel cell electric vehicle carries hydrogen in a tank. Its fuel cell makes electricity for an electric motor.

• It emits only water vapour and warm air.
• It can refuel in about 5 minutes.
• It has a range of more than 300 miles, according to DOE.

PEM fuel cells suit cars, buses and heavy-duty trucks.

4.3 Can a fuel cell power a building or a power station?

Yes. This is the case statement 2 gets right. DOE lists buildings, transport and grid energy storage among the uses.

The exam trap is the word “not”. Fuel cells suit buildings and small devices too.

Fuel cells are named by the electrolyte they use. The electrolyte decides the temperature, the catalyst and the best use.

5.1 What are the main types?

• PEM (polymer electrolyte membrane): works at about 80°C. It starts fast and suits vehicles.
• Alkaline: one of the first types developed. It was the first type widely used in the US space programme.
• Phosphoric acid: the first type used commercially. It is mostly used for fixed power plants.
• Molten carbonate: works at about 650°C. It is built for utility and industrial power.
• Solid oxide: works at up to 1,000°C. It uses a ceramic electrolyte.
• Direct methanol: runs on methanol. It is used for portable power.

5.2 What did the Apollo fuel cell do?

The hydrogen-oxygen cell supplied electrical power in the Apollo space programme. The water it made was condensed and added to the astronauts’ drinking water.

The same book describes this cell. Hydrogen and oxygen are bubbled through porous carbon electrodes into a concentrated alkaline solution. Platinum or palladium catalysts speed up the electrode reactions.

• Cathode: O2 + 2H2O + 4e- gives 4OH-.
• Anode: 2H2 + 4OH- gives 4H2O + 4e-.
• Overall: 2H2 + O2 gives 2H2O.

Fuel cells skip the burning step, so they waste less energy. India wants hydrogen to grow, which could widen their use.

6.1 Why are fuel cells efficient?

A thermal power plant burns fuel to make steam. The steam turns a turbine. Energy is lost at each step.

A fuel cell converts the chemical energy straight into electricity. The Class 12 book puts the efficiency of the hydrogen-oxygen cell at about 70 percent. Thermal plants manage about 40 percent.

DOE says fuel cells are capable of exceeding 60 percent. NCERT says about 70 percent. For exams, remember the NCERT figure.

6.2 What is India’s National Green Hydrogen Mission?

The Union Cabinet approved the mission in January 2023. PIB posted the approval on 4 January 2023. Its initial outlay is Rs 19,744 crore. The Ministry of New and Renewable Energy coordinates it.

• The target is green hydrogen production of at least 5 million metric tonnes a year by 2030.
• That needs about 125 GW of new renewable energy capacity.
• The mission aims to cut fossil fuel imports and about 50 million tonnes of yearly emissions.

More green hydrogen supply could widen the use of fuel cells in India.

The question mixes one true statement with two false ones. Each false one has a clear fix.

7.1 What are the common traps?

• Pure hydrogen gives heat and water only. This is true.
• Fuel cells are not limited to buildings. They also power laptops and vehicles.
• Fuel cells give DC, not AC. An inverter converts it when needed.
• A fuel cell is not a battery. It keeps working as long as fuel is supplied.
• Other fuels give carbon dioxide. Only pure hydrogen is free of it at the cell.

7.2 Which exam asked this question?

UPSC CSP 2015, Q95 gave three statements about fuel cells. Only statement 1 is correct. So the answer is “1 only”.

View this question.