Generating energy from banana peel

Energy in hydrogen can be harnessed by generating electricity with it

In the 1985 science fiction film Back to the Future, a flamboyant inventor modifies his car into a plutonium-powered time machine and travels back and forth in time. During a visit to the year 2015, he updates his engine so that it will now take any form of matter for generating energy — even a carrot or two tossed into the “tank” will do.

Well, 2015 has gone past us. Fusion-powered vehicles are still beyond the horizon. And we keep hoping for new and better ways of extracting clean energy from renewable sources. Such as carrots, or maybe bananas — which is indeed what has been achieved by a research group working at the Swiss Federal Institute of Technology in Lausanne ( Chemical Science, 2022).

Their version of the banana split involved the splitting of biomass — banana peel, orange peel, coconut shells — by flashes of light emanating from a xenon lamp.

But before looking at this innovative approach, a few words about what makes hydrogen an attractive energy source. Storing large quantities of energy in a modest amount of space is a vital requirement, and hydrogen has an impressive energy storage capacity. While classifying fuels in terms of their energy value (also called heating value), the deciding elements are carbon, hydrogen and oxygen. Hydrogen has an energy value that is seven times that of carbon.

In the burning of wood, carbon and hydrogen are oxidised in a heat-generating reaction, the end products of which are carbon dioxide and water. The former is a greenhouse gas, contributing to global warming. Burning of hydrogen gives us only water and heat. A smarter way to harness the energy in hydrogen would be to generate electricity with it. This is achieved in a proton exchange membrane fuel cell where, in the presence of a metal catalyst, a hydrogen molecule is split into protons and electrons, with the electrons providing the current output.

Such fuel cells are now used to power a few light passenger transport vehicles in some parts of the world. Unlike electric cars, hydrogen-powered cars have a refuelling time of only about five minutes. Commercially available hydrogen-powered cars have fuel tanks that can carry 5-6 kg of compressed hydrogen, with each kilo providing a range of about 100 km (and emitting nine litres of water, mostly as steam).

The limited popularity of hydrogen as fuel is due to production and distribution restraints. It is safer to handle than domestic cooking gas.