Sunlight and Quantum Dots Help Scientists Make Fuel of the Future

0
1949
Paper releasing gaseous hydrogen under solar light Credit: Dept of Chemistry
Paper releasing gaseous hydrogen under solar light
Credit: Dept of Chemistry

Tiny semiconductor nanocrystals, more commonly known as quantum dots are one of those few gifts of nanotechnology that seem to be good at everything they do.

Recently, scientists have found yet another use for these tiny crystals opening yet another door for their already-growing list of applications. The application here being the sustainable production of fuel from biomass.

The research team from the University of Cambridge has come up with a clean and efficient technique to produce hydrogen from biomass using sunlight and quantum dots as catalysts thereby eliminating the use of heat and energy that are usually used to obtain fuel from biomass.

“Our sunlight-powered technology is exciting as it enables the production of clean hydrogen from unprocessed biomass under ambient conditions,” says one of the researchers, Erwin Reisner.

“We see it as a new and viable alternative to high-temperature gasification and other renewable means of hydrogen production.”

Hydrogen is being considered as the fuel of the future. It is a clean source with only water as the by-product when used in cars. Biomass, especially lignocellulose has been identified as a good biofuel source but its conversion to hydrogen has only been achieved through a gasification process which uses high temperatures to decompose it fully.

A piece of paper placed in front of a solar light source
A piece of paper placed in front of a solar light source

However, with their technique, the researchers have used a photocatalytic process to convert this biomass into hydrogen and other important organic chemicals in the presence of sunlight and cadmium sulfide quantum dots suspended in alkaline water.

What’s more, this technique can even be adapted to use different types of biomass like wood, paper, leaves etc and can also be scaled up easily. Also, the biomass doesn’t require any processing beforehand.

“There’s a lot of chemical energy stored in raw biomass, but it’s unrefined, so you can’t expect it to work in complicated machinery, such as a car engine,” explains, David Wakerley, one of the lead authors of the study.

“Our system is able to convert the long, messy structures that make up biomass into hydrogen gas, which is much more useful. … With this in place, we can simply add organic matter to the system and then, provided it’s a sunny day, produce hydrogen fuel.”

 How does it work?

Biomass has been a source of heat and energy since the beginning of recorded history.  The planet’s oil reserves are derived from ancient biomass which has been subjected to high pressures and temperatures over millions of years. Lignocellulose is the main component of plant biomass and up to now its conversion into hydrogen has only been achieved through a gasification process which uses high temperatures to decompose it fully.

Dr Moritz Kuehnel, from the Department of Chemistry at the University of Cambridge, joint lead author on a new research paper published in Nature Energy, says 

“Lignocellulose is nature’s equivalent to armoured concrete. It consists of strong, highly crystalline cellulose fibres, that are interwoven with lignin and hemicellulose which act as a glue. This rigid structure has evolved to give plants and trees mechanical stability and protect them from degradation, and makes chemical utilization of lignocellulose so challenging.”

The new technology relies on a simple photocatalytic conversion process. Catalytic nanoparticles are added to alkaline water in which the biomass is suspended. This is then placed in front of a light in the lab which mimics solar light. The solution is ideal for absorbing this light and converting the biomass into gaseous hydrogen which can then be collected from the headspace. The hydrogen is free of fuel-cell inhibitors, such as carbon monoxide, which allows it to be used for power.

The nanoparticle is able to absorb energy from solar light and use it to undertake complex chemical reactions. In this case, it rearranges the atoms in the water and biomass to form hydrogen fuel and other organic chemicals, such as formic acid and carbonate.

With this research, the team has tackled one of the major challenges facing modern society- What to do with the waste it generates? As natural resources decline in abundance, using waste for energy is becoming more pressing for both governments and business.

Original paper: Nature Energy