Garden grass can unlock "green" energy

RESEARCHERS have discovered a hydrogen extraction method from grass that could become a source of cheap and clean renewable energy.

A team from Cardiff University and Queens University Belfast, UK has shown that significant amounts of hydrogen can be unlocked from fescue grass using sunlight and a cheap catalyst.

The team investigated the process of photocatalysis to convert water and cellulose – a key component of plants and the most abundant biopolymer on Earth – into hydrogen using sunlight and three metal catalysts based on palladium, gold, and nickel combined with titanium dioxide. Particular interest was given to the nickel catalyst as it is the most abundant and economical catalyst tested.

In the first experiments, the researchers combined the catalysts with cellulose and subjected the mixture to light from a desk lamp. At 30 minute intervals the researchers collected gas samples from the mixture and measured the volume of hydrogen that was produced.

Cellulose is used as a sacrificial agent to consume the oxygen-derived species produced and prevent the recombination with hydrogen during the water-splitting process.

To test the practical applications of this reaction, the researchers repeated the experiment with fescue grass, obtained from a domestic garden.

The results at laboratory scale found around 0.6 cm³ of hydrogen was produced from 200 ml of water using grass, whereas experiments conducted with purified samples of cellulose can produce around 1.4 cm³ of hydrogen. The team also found the three different metal nanoparticles did not affect the properties of the titanium dioxide.

Michael Bowker, professor of Surface Science at Cardiff University, said: “To the best of our knowledge, this is the first time that this kind of raw biomass has been used to produce hydrogen in this way. This is significant as it avoids the need to separate and purify cellulose from a sample, which can be both arduous and costly.”

Bowker told The Chemical Engineer that the next step for the team will be to find new materials for the catalyst that absorb light over the full spectrum, as TiO₂ is limited to absorbing certain frequencies of UV and visible light in the spectrum. He also said the team will investigate the use of sawdust as an alternative to garden grass.

Proceedings A, DOI: 10.1098/rspa.2016.0054