A team of scientists at the University of Cambridge has developed a way of using CdS nanoparticles and solar power to generate hydrogen from biomass in a way that is sustainable and relatively cheap to produce.
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.
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 utilisation of lignocellulose so challenging."
Solar-driven photocatalytic reforming of lignocellulose to H2 at ambient temperature offers a sustainable route towards this goal, but this reaction is currently limited to noble-metal-containing systems that operate with low activity under ultraviolet light.
The new technology relies on a simple photocatalytic conversion process. CdS nanoparticles are added to alkaline water in which the biomass is suspended. These conditions cause the dots to become coated with oxide/hydroxide in situ, presenting a strategy to improve their photocatalytic performance. The system operates under visible light, is stable beyond six days and is even able to reform unprocessed lignocellulose, such as wood and paper, under solar irradiation at room temperature.
The hydrogen is free of fuel-cell inhibitors, such as carbon monoxide, which allows it to be used for power.
Joint lead author, David Wakerley, also of the Department of Chemistry, says: "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 technology was developed in the Christian Doppler Laboratory for Sustainable SynGas Chemistry at the University of Cambridge. The head of the laboratory, Erwin Reisner, adds: "Our sunlight-powered technology is exciting as it enables the production of clean hydrogen from unprocessed biomass under ambient conditions. 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."
With the help of Cambridge Enterprise, the commercialisation arm of the University, a UK patent application has been filed and talks are under way with a potential commercial partner.
'Solar-driven reforming of lignocellulose to H2 with a CdS/CdOx photocatalyst' by David Wakerley et al: Nature Energy 2, Article number: 17021 (2017)