Green hydrogen and fuel cells

The first principle

Hydrogen is not a source of energy but a carrier of it: there is almost no free hydrogen on earth, so it has to be split out of water or a fossil fuel, and that splitting always takes more energy than the hydrogen gives back. It is worth making only where electricity cannot do the job directly, as in fertiliser, refining, steel and long distance shipping, which need a molecule and not just a current. Whether hydrogen is clean depends entirely on how it was made, and that is why the colour, or better the measured emissions, matters more than the hydrogen itself.

The core

How hydrogen is made

• Steam methane reforming makes grey hydrogen. Natural gas reacts with steam at high temperature over a catalyst (CH₄ + H₂O → CO + 3H₂), and a second step turns the carbon monoxide into more hydrogen and carbon dioxide (CO + H₂O → CO₂ + H₂). The chemistry alone releases 5.5 kilograms of carbon dioxide for every kilogram of hydrogen, and the gas burnt to heat the process takes the total to about 9 to 12 kilograms, which is why nearly all of today's hydrogen is a large source of emissions.
• Electrolysis makes green hydrogen. A direct current passed through water splits it (2H₂O → 2H₂ + O₂), with hydrogen collecting at the negative electrode, the cathode, and oxygen at the positive anode. The minimum voltage is about 1.23 volts, real cells run near 1.8 to 2 volts, and a plant uses about 50 to 55 kilowatt hours of electricity per kilogram of hydrogen, so cheap renewable power is the main cost.
• Electrolysers come in types. Alkaline electrolysers, with a potassium hydroxide electrolyte, are mature and cheap; proton exchange membrane (PEM) electrolysers use a solid polymer and platinum group catalysts, are compact and follow the rise and fall of solar and wind well; and solid oxide electrolysers work at high temperature and can use waste heat.
• The colours are a shorthand. Grey is from gas, blue is grey with the carbon dioxide captured and stored, green is electrolysis on renewable power, brown or black is from coal, pink is electrolysis on nuclear power, turquoise splits methane into hydrogen and solid carbon, and white is natural hydrogen found in rocks.
• India defines green by emissions, not colour. The Green Hydrogen Standard notified by the Ministry of New and Renewable Energy (MNRE) on 18 August 2023 counts hydrogen as green if it is made from renewable energy and emits no more than 2 kilograms of carbon dioxide equivalent per kilogram of hydrogen, measured from well to gate and averaged over 12 months.

How a fuel cell works

• A fuel cell is electrolysis run backwards. Hydrogen enters at the anode, where a catalyst splits each molecule into two protons and two electrons (H₂ → 2H⁺ + 2e⁻); the membrane lets only the protons through, so the electrons travel round an outside circuit as current, and at the cathode they meet the protons and oxygen from the air to form water (O₂ + 4H⁺ + 4e⁻ → 2H₂O).
• It is not a heat engine. Because it converts chemical energy directly into electricity rather than burning fuel to drive a piston, a fuel cell is not bound by the Carnot limit, and it reaches about 40 to 60 per cent efficiency with water as its only exhaust.
• A fuel cell is not a battery. A battery stores its chemicals inside and runs down, while a fuel cell keeps working as long as hydrogen is supplied, so a fuel cell vehicle refuels in minutes but needs a hydrogen station.

Dimensions

• Physical. Hydrogen carries about 120 megajoules per kilogram, nearly three times petrol, but it is the lightest gas, so a litre of it holds very little energy; it has to be compressed to 350 to 700 times atmospheric pressure, cooled to minus 253 degrees Celsius, or carried as ammonia or methanol.
• Environmental. Green hydrogen can cut emissions in the hard to abate sectors, those where heat or a chemical molecule is needed and electrification alone does not work, but leaks matter because hydrogen in the air lengthens the life of methane, an indirect warming effect.
• Economic. Green hydrogen still costs several times as much as grey, so early demand needs public procurement, auctions or obligations; India's own grey hydrogen use in refineries and fertiliser, about 5 to 6 million tonnes a year, is the first market to replace.
• Safety. Hydrogen ignites over a wide range of mixtures in air and makes steel brittle over time, so pipelines, tanks and codes have to be built for it.
• Strategic. India imports most of its natural gas, much of its fertiliser and most of its oil, so domestic hydrogen and green ammonia made from Indian sunlight reduce exposure to fuel imports; energy security as economics is in the Economy note on the energy sector.

In practice

• National Green Hydrogen Mission. Approved on 4 January 2023 with Rs 19,744 crore, of which Rs 17,490 crore is for the Strategic Interventions for Green Hydrogen Transition (SIGHT) programme, Rs 1,466 crore for pilots and Rs 400 crore for research. It aims at a production capacity of at least 5 million tonnes a year by 2030, with about 125 gigawatts (GW) of renewable capacity added for it, and MNRE is the nodal ministry.
• SIGHT has two parts. One pays incentives for making electrolysers in India and the other for producing green hydrogen; by March 2026 about 3,000 megawatts (MW) a year of electrolyser manufacturing had been awarded with Rs 4,440 crore of incentives, and about 8.62 lakh tonnes a year of green hydrogen production with Rs 5,294 crore.
• Green ammonia auctions. The Solar Energy Corporation of India (SECI) ran auctions in 2025 for green ammonia supplied to fertiliser plants, and winning bids fell to about Rs 55.75 and then Rs 51.8 per kilogram in mid 2025.
• Pilots. The mission funds pilots in steel, in shipping and ports, and in transport, and NTPC has run hydrogen fuel cell buses in Leh.

Issues and way forward

• Cost. Electrolysers and renewable power are the two largest costs, so cheaper round the clock renewable supply, waived transmission charges and Indian made electrolysers at scale are the levers.
• Demand. Producers will not build without buyers, so until a consumption obligation on industry is in force, demand rests mainly on auctions and public sector buyers.
• Water and land. Electrolysis needs about 9 litres of pure water per kilogram of hydrogen in theory and more in practice, so plants in dry coastal regions will rely on desalination.
• Storage and transport. Moving hydrogen is costly, so plants should sit near users or near ports, in clusters often called hubs, and export it as ammonia.
• Order of use. The cheapest gains come from replacing grey hydrogen already used in refineries and fertiliser, then steel made by direct reduction, then shipping fuels; cars, where batteries are more efficient, come last.
• Certification. Exports to the European Union and Japan need trusted measurement of emissions, so India's standard has to be backed by an accredited certification system.

Common confusions

• Fuel cell and electrolyser. An electrolyser uses electricity to split water into hydrogen and oxygen, while a fuel cell joins hydrogen and oxygen to make electricity and water; one stores energy as fuel, the other releases it.
• Fuel cell and battery. A battery stores its own chemicals and must be recharged, while a fuel cell runs as long as hydrogen is fed to it.
• Green and blue hydrogen. Both aim at low emissions, but green avoids carbon dioxide by using renewable power, while blue makes it from gas and then captures most of it.
• Hydrogen as a source and as a carrier. Hydrogen on earth is almost all bound in water and hydrocarbons, so it carries energy from where it was made, like electricity, rather than being a primary source like coal or sunlight.
• Colour and standard. A colour describes a route, while India's standard sets a measured ceiling of 2 kilograms of carbon dioxide equivalent per kilogram of hydrogen.

For the exam

• Keyword bank: energy carrier, electrolysis, alkaline and PEM electrolysers, steam methane reforming, colours of hydrogen, Green Hydrogen Standard, well to gate emissions, fuel cell, proton exchange membrane, green ammonia, hard to abate sectors, SIGHT programme, consumption obligation.
• Previous year questions: Practise the previous year questions on this topic →
• Use in an answer:
  • Introduction with data: The National Green Hydrogen Mission of January 2023, with Rs 19,744 crore, aims to build at least 5 million tonnes a year of green hydrogen production capacity in India by 2030.
  • Introduction with a source: India's Green Hydrogen Standard of August 2023 defines green hydrogen by a measured limit of 2 kilograms of carbon dioxide equivalent per kilogram, not by colour.
  • Conclusion: Green hydrogen is a way of turning cheap Indian sunlight into a molecule, and it pays first where a molecule is already needed, in fertiliser, refining and steel.
  • Conclusion: Falling green ammonia prices show the cost gap can close, but lasting demand, certification and Indian made electrolysers will decide whether India becomes a producer or only a buyer.