Superclean: Light and quantum dots turn plants into hydrogen
Hydrogen is often touted as a clean fuel source, as its use in cars only produces water vapor as a byproduct. The truth is though, that producing hydrogen in the first place can often be a process that relies on natural gas or other polluting chemicals that can damage the environment. Finding a way to produce hydrogen simply and cleanly would go a long way toward eventual use of the gas as a fuel source. And that's exactly what researchers at the University of Cambridge (UC) have done, adding to a host of other green possibilities that have been proposed for creating the gas.
In the new Cambridge method, as with several other methods, the researchers used biomass as a starting point. In particular, they focused on lignocellulose, the support structure found in plants.
"Lignocellulose is nature's equivalent to armoured concrete," said Moritz Kuehnel, from UC's department of chemistry and joint lead author on a new paper about the study. "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."
While lignocellulose can be converted into hydrogen, the researchers say that up to this point, the processes that do so rely on high heat, which means a good deal of energy needs to go into the task. Their new method relies simply on light along with a collection of nanoparticles.
The particles are actually very small semiconductors called cadmium sulfide quantum dots. First, they are suspended in alkaline water. Then, the biomass is added, the solution is beamed with light that mimics sunlight, and the dots go to work using the light to fuel a process in which they convert the biomass into hydrogen. The gas then rises out of the solution where it can be collected.
In the study, a variety of unprocessed biomass was successfully used including paper, leaves and pieces of wood.
"Our sunlight-powered technology is exciting as it enables the production of clean hydrogen from unprocessed biomass under ambient conditions," said Erwin Reisner, the head of UC's Christian Doppler Laboratory for Sustainable SynGas Chemistry where the research was carried out. "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."
The work of the researchers, which has been published in the journal Nature Energy, can now be added to other less energy intensive ways of producing hydrogen including another sunlight-based process that uses grass to produce the gas; an enzyme-based process that breaks down parts of the corn plant to release hydrogen; and a solar-powered way to split the water molecule into its constituent parts thanks to the use of hematite.
Source: University of Cambridge