Maarg Manthan · Topic 12.3

Fuel Cells and Microbial Fuel Cells

Environment & Ecology › Energy Resources · Topic 12.3

A fuel cell is an electrochemical device that converts the chemical energy of a fuel, usually hydrogen, and an oxidant, usually oxygen from air, directly into electricity, with water and heat as the main by-products. It has an anode where fuel is oxidised, a cathode where oxygen is reduced and an electrolyte between them that lets ions pass; because it does not burn the fuel, it is quiet, efficient and low in pollutants, and works as long as fuel is supplied. William Grove demonstrated the principle in 1839. Main types are the polymer electrolyte membrane (PEM) fuel cell, the alkaline fuel cell used in the Apollo spacecraft, the phosphoric acid, molten carbonate and solid oxide fuel cells. A microbial fuel cell (MFC) uses bacteria that oxidise organic matter in waste water at the anode, releasing electrons that flow through an external circuit to the cathode, so that it can treat waste water and generate electricity together. India's National Green Hydrogen Mission, approved in January 2023, supports hydrogen and fuel cell use.

5 min read · UPSC Prelims · Environment & Ecology · Energy Resources

At a Glance

Input Hydrogen and oxygen
Output Electricity, water, heat
First shown William Grove, 1839
Space use Alkaline cells in Apollo
MFC Bacteria and waste water
Exam link UPSC Prelims, Environment & Ecology: Energy Resources

Where Does It Fit?

This topic follows the ocean energy topics and covers a different clean technology. It leads to biofuels and biogas, which are fuels from biomass. Previous topic: Tidal Energy and Wave Energy. Next topic: Biofuels and Biogas.

How Does a Fuel Cell Work and What Are Its Types?

Type	Features and uses
Polymer electrolyte membrane (PEMFC)	Low temperature of about 80 C; quick start; used in cars and buses
Alkaline fuel cell (AFC)	Potassium hydroxide electrolyte; high efficiency; used on Apollo and Space Shuttle missions
Phosphoric acid fuel cell (PAFC)	About 200 C; used in stationary power plants
Molten carbonate fuel cell (MCFC)	About 650 C; large stationary power
Solid oxide fuel cell (SOFC)	800 to 1,000 C; high efficiency; stationary power and combined heat and power
Direct methanol fuel cell	Uses methanol as fuel; for small portable devices
Reaction	At the anode 2H2 gives 4H+ and 4 electrons; at the cathode O2 with the electrons and H+ gives water

What Are Microbial Fuel Cells and Where Are Fuel Cells Used?

Microbial fuel cell: bacteria oxidise organic matter in waste water in an oxygen-free anode chamber
Electron flow: electrons travel through an external circuit to the cathode and combine with oxygen and protons to form water
Membrane: a proton exchange membrane separates the two chambers
MFC benefits: waste water treatment together with electricity and low sludge
MFC limits: low power, high cost of electrodes, and not yet commercial at large scale
Transport: fuel cell buses and cars with hydrogen
Stationary: backup power for telecom towers and hospitals
National Green Hydrogen Mission: launched in 2023 to build green hydrogen production and use, with a target of 5 million tonnes by 2030

What Else Should You Remember?

Electrochemical conversion: chemical energy is converted straight to electricity without combustion
Efficiency: often 40 to 60 percent electrical, and higher if heat is also used
Hydrogen sources: grey from natural gas, blue with carbon capture, green from electrolysis using renewable power
Green hydrogen: hydrogen made by splitting water with renewable electricity
Electrolyser: device that splits water into hydrogen and oxygen using electricity
Storage challenge: hydrogen is light and hard to store and transport
Safety: hydrogen is flammable and needs careful handling
Catalyst: platinum is widely used in PEM cells and adds to cost
Apollo missions: fuel cells gave electricity and drinking water to astronauts
Hydrogen buses in India: pilot hydrogen fuel cell buses have been run in Delhi, Leh and other places
Hydrogen Valleys: proposed clusters for hydrogen production and use
MFC wastewater: works well with sewage, food and distillery waste
Exoelectrogens: bacteria that can transfer electrons to an electrode, such as Geobacter and Shewanella
Anode chamber: oxygen-free so that bacteria use the electrode as electron acceptor
MFC power: usually milliwatts to a few watts per cubic metre, enough for sensors and small devices
Biosensors: MFCs can be used to sense pollution in water
Biohydrogen: microbial electrolysis cells can make hydrogen from waste
Redox reaction: oxidation at the anode and reduction at the cathode
Waste heat: fuel cell heat can be used in combined heat and power
Emissions: hydrogen fuel cells emit only water at the point of use
Costs: fuel cells are costly, but costs are falling with scale
Link to previous: see Tidal Energy and Wave Energy
Link to next: see Biofuels and Biogas
Link to renewables: see Renewable Energy and Sustainable Development
Caution: hydrogen is clean only when produced from low-carbon sources, so ask how it is made
Exam hint: remember anode, cathode, electrolyte and the by-product water
Fuel cell vehicles: hydrogen cars and buses refuel in minutes and have longer range than most battery vehicles, but need hydrogen stations
Hydrogen in industry: green hydrogen could replace fossil hydrogen in fertiliser and refining and clean up steel making
Fuel cell stack: many cells are joined in series to give enough voltage for vehicles and plants
Mission targets: the Mission targets large electrolyser capacity and a pool of green hydrogen hubs

Why Does It Matter for the Exam?

Fuel: Hydrogen
Byproduct: Water
Space use: Alkaline cell
Current affairs link: Green Hydrogen Mission
Common errors: treating all hydrogen as clean

As an analytical point, a fuel cell is only as clean as its fuel. Hydrogen from renewables makes it a strong clean option for heavy transport and industry, while grey hydrogen only moves emissions elsewhere.

Why Is This Topic Important?

Input H2, O2
Output Power, water
Check Source of H2

What Came Next?

The next topic covers biofuels and biogas. Next topic: Biofuels and Biogas.

Key People and Terms

Fuel cell Direct power cell
Anode Fuel electrode
Cathode Oxygen electrode
Electrolyte Ion path
MFC Microbial fuel cell
Green hydrogen Hydrogen from renewable power

Exam Corner

Points to Remember

Output: power, water, heat.
Discovered 1839.
Space: alkaline cell.
MFC uses bacteria.
Mission approved 2023.

Do Not Confuse With

Fuel cell and battery Fuel supplied outside versus stored inside
Green and grey hydrogen Renewable versus fossil source
MFC and fuel cell Bacteria-driven versus hydrogen-driven

Memory Hook

Hydrogen in, oxygen in, power and water out, bacteria do it in waste.

Mains Angle

Questions ask for working and types. These points help.

Working Anode, cathode
Use Transport
Limit H2 source

A Question You May Face

An original practice question, not a past paper question.

“Explain the working of a fuel cell and microbial fuel cell and their significance for clean energy.”

How to Answer

Working Electrodes.
Types PEM, SOFC.
MFC Waste water.
Limit Source of H2.

GS Relevance

Prelims: working, types, uses, MFC. GS Paper 3: clean energy technologies.

Frequently Asked Questions

What is a fuel cell?

A fuel cell is a device that converts the chemical energy of a fuel, usually hydrogen, and oxygen directly into electricity through an electrochemical reaction, producing only water and heat. It has an anode, a cathode and an electrolyte, and it keeps generating power as long as fuel and oxygen are supplied, unlike a battery that stores its energy.

What are the types of fuel cells?

The main types are the polymer electrolyte membrane fuel cell used in vehicles, the alkaline fuel cell used in spacecraft, the phosphoric acid fuel cell, the molten carbonate fuel cell and the solid oxide fuel cell used in stationary power, and direct methanol fuel cells for small devices. They differ in electrolyte, temperature and use.

What is a microbial fuel cell?

A microbial fuel cell uses bacteria to break down organic matter in waste water in an oxygen-free anode chamber, releasing electrons that flow through an external circuit to the cathode to produce electricity. It can treat waste water and make power together, but the power output is still low and costs are high.

What is green hydrogen and why does it matter for fuel cells?

Green hydrogen is made by splitting water into hydrogen and oxygen using renewable electricity in an electrolyser. When used in a fuel cell it gives power with only water as the by-product, so the whole chain is low-carbon. Hydrogen made from natural gas or coal is not green because it causes emissions.

What is the National Green Hydrogen Mission?

The National Green Hydrogen Mission, approved by the Union Cabinet in January 2023, aims to make India a global hub for production, use and export of green hydrogen and its derivatives, with a target of about 5 million tonnes of annual green hydrogen production capacity by 2030. It supports electrolysers, pilot projects and hydrogen use in industry and transport.

PYQ Practice — Statement Analysis

1 A fuel cell produces electricity without combustion.

True

By an electrochemical reaction.

2 Alkaline fuel cells were used in the Apollo missions.

True

They gave power and water.

3 A microbial fuel cell uses sunlight.

False

It uses bacteria and organic matter.

4 All hydrogen is green hydrogen.