Science and Technology › Energy technology

Hydrogen and bioenergy

Hydrogen and fuels made from biology: green hydrogen and how it is made, stored and used, fuel cells, ethanol blending and its feedstock, biogas, and aviation fuel from biomass. Prelims has asked about the raw materials allowed under the National Policy on Biofuels and how green hydrogen is produced.

UPSC has asked

Prelims 2025: battery electric and fuel cell vehicles as alternative powertrains
Prelims 2023: uses of green hydrogen as fuel and in fuel cells
Prelims 2020: raw materials allowed under the National Policy on Biofuels

Showing 1 of 6 subjects, those that changed from 1 to 15 September 2026.Show all

Green hydrogen

Photocatalytic water splitting

Prelims and Mains

Electrolysis has to be given electricity before it can split anything, and that electricity is most of the cost. Photocatalysis skips the step: a photocatalyst absorbs sunlight and uses that energy directly to pull the water molecule apart.

The catalyst has to separate the charges that light creates before they recombine, which is what limits the yield.
Most photocatalysts that work are built on costly inorganic semiconductors or on precious metals, so the cost sits in the catalyst.
The Centre for Nano and Soft Matter Sciences (CeNS), Bengaluru, has made a metal-free organic photocatalyst for splitting water with sunlight.
It pairs aspartic acid, an amino acid, with perylene diimide, a light absorbing organic molecule, in place of a precious metal.
In water the pair self-assembles into two dimensional nanosheets, which give nearly 18 per cent more photocurrent than the bulk form.

What changed

9 Sep 2026
PIB, 9 Sep 2026: Self-assembly of organic molecules opens a new path to green hydrogen production (opens in a new tab)

E20: Petrol blended with 20 per cent anhydrous ethanol by volume. The number is the ethanol share, so E20 (20 per cent) is a stronger blend than E10 (10 per cent).

Anaerobic digestion: The breakdown of organic matter by bacteria in the absence of oxygen, which gives off biogas.

Press mud: The solid residue left behind when sugarcane juice is filtered in a sugar mill.

second-generation ethanol: Ethanol made from non-food biomass such as crop stubble or bagasse, by breaking down cellulose, so it does not compete with the food plate.

blue water: Water drawn from rivers, canals and groundwater, as against green water, which is rainfall held in the soil. Blue water is the scarce one, so it is the honest measure of a crop's water cost.

carburettor: An older fuel mixing device that cannot sense the extra oxygen ethanol brings and adjust for it, so the engine runs lean, with too little fuel for the air it draws in.

Green hydrogen: Hydrogen made by splitting water with electricity from renewable sources, so the making of it releases no carbon dioxide, unlike hydrogen reformed from natural gas.