Solar-powered process draws hydrogen from biomass

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Using solar power, a team of scientists at the University of Cambridge has sequestered hydrogen from biomass in a cheap, sustainable process.

Lignocellulose is the main component of plant biomass, but up to now its conversion into hydrogen has only been achieved through a gasification process which uses high temperatures to decompose it fully.

“Lignocellulose is nature’s equivalent to armoured concrete,” said Dr Moritz Kuehnel at the University of Cambridge. “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 utilisation 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. 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.

Joint lead author of the study, Dr David Wakerley said: “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.

“Our system is able to convert the long, messy structures that make up biomass into hydrogen gas, which is much more useful. We have specifically designed a combination of catalyst and solution that allows this transformation to occur using sunlight as a source of energy.

“With this in place we can simply add organic matter to the system and then, provided it’s a sunny day, produce hydrogen fuel.”

The team used different types of biomass in their experiments. Pieces of wood, paper and leaves were placed in test tubes and exposed to solar light. The biomass didn’t require any processing beforehand.

“Our sunlight-powered technology is exciting as it enables the production of clean hydrogen from unprocessed biomass under ambient conditions,” said Dr. Erwin Reisner, who also worked on the project. “We see it as a new and viable alternative to high-temperature gasification and other renewable means of hydrogen production.

“Future development can be envisioned at any scale, from small-scale devices for off-grid applications to industrial-scale plants and we are currently exploring a range of potential commercial options.”

It is hoped that hydrogen could eventually form part of a green, carbon-free energy network that could replace fossil fuels in some use cases. In September, the world’s first four-seater passenger plane powered solely by hydrogen took to the skies in Germany.

Saudi Arabian researchers have also demonstrated a material mesh, created using a mix of metal and polymer, that is capable of generating hydrogen and fresh water from wastewater. 

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