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Q95 (IAS/2015) Science & Technology › New Materials, Energy & Environment-linked Tech › Hydrogen energy technologies Official Key

With reference to 'fuel cells' in which hydrogen-rich fuel and oxygen are used to generate electricity, consider the following statements : 1. If pure hydrogen is used as a fuel, the fuel cell emits heat and water as by-products. 2. Fuel cells can be used for powering buildings and not for small devices like laptop computers. 3. Fuel cells produce electricity in the form of Alternating Current (AC). Which of the statements given above is/are correct?

Result
Your answer: —  ·  Correct: A
Explanation

Fuel cells are electrochemical devices that convert chemical energy directly into electricity (DC) and heat, with oxygen passing over one electrode and hydrogen over the other, [1]reacting electrochemically to generate electricity, water, and heat.[1] Therefore, **Statement 1 is correct** - when pure hydrogen is used, the by-products are indeed heat and water.

**Statement 2 is incorrect** because fuel cell systems are excellent candidates for small-scale decentralized power generation and can supply combined heat and power to commercial buildings, hospitals, airports and military installations[2], but they are not limited to large applications. Fuel cell systems are modular and can be set up wherever power is needed[2], meaning they can potentially power small devices as well.

**Statement 3 is incorrect** because fuel cells convert chemical energy directly into electricity (DC)[1], not alternating current (AC). They produce direct current, which would need to be converted if AC power is required for specific equipment.

Therefore, only Statement 1 is correct, making option A the right answer.

Sources
  1. [1] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 22: Renewable Energy > 22.10 FUEL CELLS > p. 296
  2. [2] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 22: Renewable Energy > Fuel cells for power generation > p. 296
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Don’t just practise – reverse-engineer the question. This panel shows where this PYQ came from (books / web), how the examiner broke it into hidden statements, and which nearby micro-concepts you were supposed to learn from it. Treat it like an autopsy of the question: what might have triggered it, which exact lines in the book matter, and what linked ideas you should carry forward to future questions.
Q. With reference to 'fuel cells' in which hydrogen-rich fuel and oxygen are used to generate electricity, consider the following statements…
At a glance
Origin: Books + Current Affairs Fairness: Moderate fairness Books / CA: 7.5/10 · 2.5/10

This is a 'First Principles' Science question disguised as Current Affairs. While Fuel Cells were in the news, the answer relied entirely on 7th-grade physics (Cells = DC) and basic chemistry (H2 + O2 = H2O). Don't ignore NCERT basics while chasing high-tech magazines.

How this question is built

This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.

Statement 1
Do fuel cells using pure hydrogen and oxygen to generate electricity emit water and heat as by-products?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 22: Renewable Energy > 22.10 FUEL CELLS > p. 296
Presence: 5/5
“Fuel cells are electrochemical devices that convert the chemical energy of a fuel directly and very efficiently into electricity (DC) and heat, thus doing away with combustion. The most suitable fuel for such cells is hydrogen or a mixture of compounds containing hydrogen. A fuel cell consists of an electrolyte sandwiched between two electrodes. Oxygen passes over one electrode and hydrogen over the other, and they react electrochemically to generate electricity, water, and heat.”
Why this source?
  • Directly describes fuel cells as electrochemical devices that convert fuel into electricity and heat.
  • Specifies that oxygen and hydrogen react electrochemically over electrodes to generate electricity, water, and heat.
Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 22: Renewable Energy > Types Of Hydrogen Based On Extraction Methods > p. 298
Presence: 2/5
“zz,to,z, Types Of Hydrogen Based On Extraction Methods Depending on the nature of its extraction, hydrogen is categorized into three categories, namely, grey, blue and green. • Grey Hydrogen: it is produced via coal or lignite gasification {black orbrown}, or via a process called steam methane reformation (SMR) of natural gas or methane (grey). These tend to be mostly carbon-intensive processes. • Blue Hydrogen: It is produced via natural gas or coal gasification combined with carbon capture. storage (CCS) or carbon capture use (CCU) technologies to reduce carbon emissions. . Green Hydrogen: It is produced using electrolysis of water with electricity generated by renewable energy.”
Why this source?
  • Confirms hydrogen is identified as the most suitable fuel for such cells.
  • Provides context on hydrogen as a fuel source, supporting the premise that hydrogen is used in fuel-cell systems.
Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 22: Renewable Energy > 2Z:7 COGENERATION > p. 293
Presence: 2/5
“Co-generation is producing two forms of energy from one fuel. One of the forms of energy must always be heat and the other may be electricity or mechanical. energy. In a conventional power plant, fuel is burnt in a boiler to generate high-pressure steam. This steam is used to drive a lurbine, which in turn drives an alternator through a steam turbine to produce electric power. The exhaust steam is generally condensed to water which goes back to the boiler. As the low-pressure steam has a large quantum of heat which is lost in the process of condensing, the efficiency of conventional power plants is only around 35%.”
Why this source?
  • Explains the general concept of producing electricity and heat from a single fuel (co-generation), supporting the plausibility of simultaneous electricity and heat output.
  • Reinforces that energy-conversion systems can yield both electricity and heat as useful outputs.
Statement 2
Can fuel cells using hydrogen-rich fuel and oxygen be used to provide power for buildings?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 22: Renewable Energy > Fuel cells for power generation > p. 296
Presence: 5/5
“Conventional large-scale power plants use nonrenewable fuels with significant adverse ecological and environmental impacts. Fuel cell systems are excellent candidates for small-scale decentralized power generation. Fuel cells can supply combined heat and power to commercial buildings, hospitals, airports and military installations at remote locations. Fuel cells have efficiency levels up to 55% as compared to 35-40% of conventional power plants. The emissions are significantly lower (CO₂ and water vapor being the only emissions). Fuel cell systems are modular (i.e., additional capacity can be added whenever required with relative ease) and can be set up wherever power is needed.”
Why this source?
  • Explicitly states fuel cell systems are excellent for small-scale decentralized power generation.
  • Specifically notes fuel cells can supply combined heat and power to commercial buildings, hospitals, airports and remote installations.
  • Mentions modularity and lower emissions, making them suitable where building power is needed.
Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 22: Renewable Energy > Renewabte energy comprises of > p. 287
Presence: 3/5
“• Solar energy – generated from the sun • Hydroelectric (hydel) energy – derived from water • Biomass energy – from firewood, animal dung, biodegradable waste and crop residues, when it is burnt. • Geothermal energy – energy from hot dry rocks, magma, hot water springs, natural geysers, etc. • Ocean thermal energy – from waves and also from tidal waves. • Co-generation – producing two forms of energy from one fuel. • Fuel cells are also being used as a cleaner energy source. Secondary source - non-renewable energy generated through the conversion of coal, oil, natural gas etc. The Government has up-scaled the target of renewable energy capacity to 75 GW by the year 2022, which includes 100 GW from solar, 60 GW from wind, 10 GW from bio-power and 5 GW from small hydro-power.”
Why this source?
  • Identifies fuel cells as a cleaner energy source within the renewable/non-conventional energy list.
  • Supports the general suitability of fuel-cell technology for distributed/clean power applications.
Indian Economy, Nitin Singhania .(ed 2nd 2021-22) > Chapter 21: Sustainable Development and Climate Change > National Hydrogen Energy Mission (NHM) - announced in Union Budget 2021-22 > p. 605
Presence: 3/5
“This mission will draw a roadmap for using Green Hydrogen as an energy source. It will focus on generation of hydrogen from green power resources. This Green Hydrogen Mission is crucial to decarbonise heavy industries and clean electric mobility. Hydrogen from renewable power is technically viable and it is vital for regional and national energy security. Green hydrogen energy is essential for India to meet its Nationally Determined Contributions.”
Why this source?
  • Describes national focus on Green Hydrogen as an energy source, indicating hydrogen’s viability for energy uses.
  • Links hydrogen production from renewable power to decarbonising energy — relevant to hydrogen-fuelled fuel cells for buildings.
Statement 3
Can fuel cells using hydrogen-rich fuel and oxygen be used to power small devices such as laptop computers?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 22: Renewable Energy > 22.10 FUEL CELLS > p. 296
Presence: 5/5
“Fuel cells are electrochemical devices that convert the chemical energy of a fuel directly and very efficiently into electricity (DC) and heat, thus doing away with combustion. The most suitable fuel for such cells is hydrogen or a mixture of compounds containing hydrogen. A fuel cell consists of an electrolyte sandwiched between two electrodes. Oxygen passes over one electrode and hydrogen over the other, and they react electrochemically to generate electricity, water, and heat.”
Why this source?
  • Explicitly defines fuel cells as electrochemical devices that convert chemical energy of a fuel directly into electricity (DC) and heat.
  • Identifies hydrogen (or hydrogen-containing mixtures) as the most suitable fuel and oxygen as the oxidant; they react electrochemically to generate electricity and water.
  • Directly supports the technical feasibility that hydrogen+oxygen fuel cells produce DC electricity usable by electronic devices.
Science-Class VII . NCERT(Revised ed 2025) > Chapter 3: Electricity: Circuits and their Components > SCIENCE AND SOCIETY > p. 40
Presence: 3/5
“Electric cells or batteries are compact portable sources of electrical energy that make the use of some electrical devices more convenient. These cells and batteries come in various shapes and sizes for diff erent purposes, such as cylindrical batteries for torchlights, clocks, remotes, toys; button cells for watches, hearing aids; rechargeable batteries for mobile phones, laptops, and electric vehicles.”
Why this source?
  • States that laptops are powered by rechargeable batteries — i.e., they require compact, portable DC power sources.
  • When combined with [1], supports the inference that an alternative portable DC source (fuel cell) could serve similar device-powering roles.
Statement 4
Do fuel cells using hydrogen-rich fuel and oxygen produce electrical power in the form of alternating current (AC)?
Origin: Web / Current Affairs Fairness: CA heavy Web-answerable

Web source
Presence: 5/5
"Statement 3 is incorrect. Fuel cells produce electricity in the form of direct current (DC), not alternating current (AC)."
Why this source?
  • Directly states that the claim (that fuel cells produce AC) is incorrect.
  • Explicitly identifies the actual electrical output form as DC, not AC.
Web source
Presence: 5/5
"Fuel cells produce electricity in the form of direct current (DC)."
Why this source?
  • States plainly that fuel cells produce electricity as direct current (DC).
  • Explains DC behavior (electrons flow in only one direction), reinforcing the distinction from AC.
Web source
Presence: 4/5
"If the fuel cell is used to power equipment that uses AC, the direct current will have to be converted to alternating current."
Why this source?
  • Explains that when AC-powered equipment is used, the fuel cell's direct current must be converted to AC.
  • Implying fuel cells output DC rather than AC by describing the need for inversion.

Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 22: Renewable Energy > 22.10 FUEL CELLS > p. 296
Strength: 5/5
“Fuel cells are electrochemical devices that convert the chemical energy of a fuel directly and very efficiently into electricity (DC) and heat, thus doing away with combustion. The most suitable fuel for such cells is hydrogen or a mixture of compounds containing hydrogen. A fuel cell consists of an electrolyte sandwiched between two electrodes. Oxygen passes over one electrode and hydrogen over the other, and they react electrochemically to generate electricity, water, and heat.”
Why relevant

Explicitly states fuel cells convert chemical energy of a fuel directly into electricity (DC) and heat.

How to extend

A student can combine this with the fact that DC is not AC to infer fuel cells natively produce DC, not AC.

Science-Class VII . NCERT(Revised ed 2025) > Chapter 3: Electricity: Circuits and their Components > 3.2 A Simple Electrical Circuit > p. 36
Strength: 4/5
“Caution — Our body is a conductor of electricity. Electric current passing through our body may cause severe injury or even death. Always handle electrical appliances with care. Never touch switches or plugs with wet hands, or use electrical devices in wet areas, or handle equipment with damaged insulation or broken plugs. Have you ever wondered how the electricity from a cell or battery is diff erent from the electricity coming from a wall socket? Electricity from batteries usually powers small devices and is of a type called Direct Current (DC). In contrast, the electricity from power plants that come to the wall socket is known as Alternating Current (AC) and can run larger appliances.”
Why relevant

Explains that electricity from cells/batteries is of the type called Direct Current (DC), contrasting with wall-socket Alternating Current (AC).

How to extend

Use this general rule for electrochemical cells to treat fuel cells similarly and question whether fuel-cell output is AC.

Science , class X (NCERT 2025 ed.) > Chapter 11: Electricity > 11.2 ELECTRIC POTENTIAL AND POTENTIAL DIFFERENCE > p. 173
Strength: 4/5
“This difference of potential may be produced by a battery, consisting of one or more electric cells. The chemical action within a cell generates the potential difference across the terminals of the cell, even when no current is drawn from it. When the cell is connected to a conducting circuit element, the potential difference sets the charges in motion in the conductor and produces an electric current. In order to maintain the current in a given electric circuit, the cell has to expend its chemical energy stored in it.”
Why relevant

Describes that a cell/battery generates a potential difference by chemical action and drives current — reinforcing cells as DC sources.

How to extend

Extend the pattern that chemical-electrochemical sources produce DC to hypothesize fuel cells also produce DC.

Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 22: Renewable Energy > az.r.z. Concentrated Solar Power (CSP) or solar thermal technology. > p. 288
Strength: 5/5
“Commonly used fluids are synthetic oil, molten salt and pressurized steam. The power generated - Direct Current (DC) is converted to Alternating Current (AC) with the use of inverters.”
Why relevant

Says power generated as Direct Current (DC) is converted to Alternating Current (AC) with the use of inverters.

How to extend

A student can infer that if a device produces DC but AC is needed, an inverter is used — so fuel-cell DC could be converted to AC when required.

Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 22: Renewable Energy > 2Z:7 COGENERATION > p. 293
Strength: 3/5
“Co-generation is producing two forms of energy from one fuel. One of the forms of energy must always be heat and the other may be electricity or mechanical. energy. In a conventional power plant, fuel is burnt in a boiler to generate high-pressure steam. This steam is used to drive a lurbine, which in turn drives an alternator through a steam turbine to produce electric power. The exhaust steam is generally condensed to water which goes back to the boiler. As the low-pressure steam has a large quantum of heat which is lost in the process of condensing, the efficiency of conventional power plants is only around 35%.”
Why relevant

Describes conventional power plants driving alternators via turbines to produce electric power (implying generation of AC by mechanical alternators).

How to extend

Contrast electrochemical DC sources (fuel cells) with mechanical alternators that produce AC, to distinguish native AC generation from conversion.

Pattern takeaway: UPSC Science & Tech questions often use 'Arbitrary Negation' (e.g., 'cannot be used for small devices') to trap you. In technology, unless there is a critical mass constraint (like Nuclear), scaling down is usually possible. Always trust fundamental definitions (Cell = DC) over vague application claims.
How you should have studied
  1. [THE VERDICT]: Sitter. Solvable purely by eliminating Statement 3 using Class VII Science (Cells produce DC). Source: Shankar IAS (Environment) + NCERT Science.
  2. [THE CONCEPTUAL TRIGGER]: Energy Conversion Devices. Moving beyond 'Renewable Energy' lists to understanding 'How it works' (Input -> Process -> Output).
  3. [THE HORIZONTAL EXPANSION]: Memorize the 'Cell Profile': 1) Input: Hydrogen/Methanol. 2) Output: DC Electricity + Water + Heat. 3) Efficiency: ~60% (vs 35% for thermal). 4) Types: PEMFC (Laptops/Cars), SOFC (Buildings). 5) Comparison: Batteries store energy; Fuel Cells convert fuel continuously.
  4. [THE STRATEGIC METACOGNITION]: Adopt the 'Engineer's Mindset' for Tech questions. Always ask: Is the output AC or DC? What are the waste products? Can it scale up (Grid) or down (Mobile)? UPSC tests these physical constraints, not just the benefits.
Concept hooks from this question
📌 Adjacent topic to master
S1
👉 Fuel cells as electrochemical converters (electricity, water, heat)
💡 The insight

Reference [1] explicitly states fuel cells electrochemically convert hydrogen and oxygen to electricity, water and heat—this is the core fact behind the statement.

High-yield for environment/energy questions: explains why fuel cells are considered low-emission power sources and connects to topics like clean energy technologies and emission footprints. Master by linking fuel-cell chemistry to policy debates on hydrogen economy and transport electrification.

📚 Reading List :
  • Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 22: Renewable Energy > 22.10 FUEL CELLS > p. 296
🔗 Anchor: "Do fuel cells using pure hydrogen and oxygen to generate electricity emit water ..."
📌 Adjacent topic to master
S1
👉 Hydrogen as a fuel: production categories
💡 The insight

Reference [4] identifies hydrogen as the primary fuel and classifies its production (grey/blue/green), which matters when assessing environmental impact of hydrogen-based systems.

Important for UPSC essays/GS on energy transition and climate policy: distinguishes fuel availability and lifecycle emissions (green vs grey hydrogen). Prepare by studying production methods, emissions implications, and policy measures like electrolysis and CCS.

📚 Reading List :
  • Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 22: Renewable Energy > Types Of Hydrogen Based On Extraction Methods > p. 298
🔗 Anchor: "Do fuel cells using pure hydrogen and oxygen to generate electricity emit water ..."
📌 Adjacent topic to master
S1
👉 Co-generation (combined heat and power) principle
💡 The insight

Reference [3] highlights the concept of producing heat and electricity from one fuel source, reinforcing that energy systems can produce both simultaneously.

Useful for questions on energy efficiency and power-sector design: shows how systems recover waste heat to raise overall efficiency. Learn through examples (thermal plants, CHP) and compare with fuel-cell efficiency advantages.

📚 Reading List :
  • Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 22: Renewable Energy > 2Z:7 COGENERATION > p. 293
🔗 Anchor: "Do fuel cells using pure hydrogen and oxygen to generate electricity emit water ..."
📌 Adjacent topic to master
S2
👉 Fuel cells for decentralized power & combined heat-and-power (CHP)
💡 The insight

Reference [1] directly states fuel cells can supply CHP to buildings and remote installations; [3] classifies fuel cells as cleaner energy.

High-yield for UPSC questions on energy options and decentralized infrastructure: explains alternatives to centralised thermal power, links to urban energy planning and disaster-resilient power supply. Master by comparing use-cases (commercial buildings, hospitals, airports) and policy implications.

📚 Reading List :
  • Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 22: Renewable Energy > Fuel cells for power generation > p. 296
  • Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 22: Renewable Energy > Renewabte energy comprises of > p. 287
🔗 Anchor: "Can fuel cells using hydrogen-rich fuel and oxygen be used to provide power for ..."
📌 Adjacent topic to master
S2
👉 Hydrogen as an energy carrier (Green Hydrogen)
💡 The insight

References [5] and [7] discuss green hydrogen production and carbon intensity, underpinning hydrogen’s role as fuel for fuel cells.

Important for questions on energy transition and national missions (e.g., NHM): connects renewable electricity, hydrogen production, and decarbonisation strategies. Study policy documents, production methods (green/blue/grey), and implications for industry and buildings.

📚 Reading List :
  • Indian Economy, Nitin Singhania .(ed 2nd 2021-22) > Chapter 21: Sustainable Development and Climate Change > National Hydrogen Energy Mission (NHM) - announced in Union Budget 2021-22 > p. 605
  • Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 22: Renewable Energy > Types Of Hydrogen Based On Extraction Methods > p. 298
🔗 Anchor: "Can fuel cells using hydrogen-rich fuel and oxygen be used to provide power for ..."
📌 Adjacent topic to master
S2
👉 Efficiency, emissions and modularity vs conventional power plants
💡 The insight

Reference [1] gives fuel cell efficiency (~55%) and lower emissions; [6] gives conventional plant efficiency (~35%) for contrast.

Useful for comparative questions on energy technologies and environmental impact: explains why fuel cells may be chosen for buildings and decentralised systems. Prepare by memorising typical efficiency ranges, emission characteristics, and modular deployment advantages.

📚 Reading List :
  • Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 22: Renewable Energy > Fuel cells for power generation > p. 296
  • Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 22: Renewable Energy > 2Z:7 COGENERATION > p. 293
🔗 Anchor: "Can fuel cells using hydrogen-rich fuel and oxygen be used to provide power for ..."
📌 Adjacent topic to master
S3
👉 Fuel cell working principle & electrical output
💡 The insight

Reference [1] describes fuel cells as electrochemical devices producing DC electricity from hydrogen and oxygen, which is the core technical basis for powering devices.

High-yield for UPSC: understanding energy-conversion devices is often tested in both GS (environment/technology) and essay/current-affairs contexts. It connects to chemistry (redox reactions), engineering (power generation), and environmental impact (emissions). Prepare by mastering basic working principles, inputs/outputs, and typical applications.

📚 Reading List :
  • Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 22: Renewable Energy > 22.10 FUEL CELLS > p. 296
🔗 Anchor: "Can fuel cells using hydrogen-rich fuel and oxygen be used to power small device..."
🌑 The Hidden Trap

Microbial Fuel Cells (MFCs). Since standard Fuel Cells are asked, the next logical step is biological variants. MFCs use bacteria to oxidize organic matter (wastewater) to generate electricity. Key constraint: Low power output, suitable for sensors but not heavy grid use.

⚡ Elimination Cheat Code

The 'Universal Cell Rule': In Physics, any device named 'Cell' (Solar Cell, Electrochemical Cell, Fuel Cell, Battery) generates Direct Current (DC) because it relies on chemical/potential gradients moving electrons in one direction. Alternating Current (AC) requires mechanical rotation (Turbines) or digital inversion. Statement 3 claims AC -> Eliminate B, C, and D instantly. Answer is A.

🔗 Mains Connection

Connect to Economy (Energy Security): Fuel Cells are the demand-side tech for the 'National Green Hydrogen Mission'. The goal isn't just clean air; it's reducing the Current Account Deficit by replacing imported coking coal in steel plants and diesel in heavy trucking with domestic Green Hydrogen.

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In the context of proposals to the use of hydrogen-enriched CNG (H-CNG) as fuel for buses in public transport, consider the following statements : 1. The main advantage of the use of H-CNG is the elimination of carbon monoxide emissions. 2. H-CNG as fuel reduces carbon dioxide 'and hydrocarbon emissions. 3. Hydrogen up to one-fifth by volume can be blended with CNG as fuel for buses. 4. H-CNG makes the fuel less expensive than CNG. Which of the statements given above is/are correct?