A new study at the University of Bath’s Centre for Sustainable Chemical Technologies has enabled researchers to move a step closer to a cleaner, cheaper, and more sustainable method of producing hydrogen fuel from water using sunlight.
The pressure on global leaders to bring down carbon emissions considerably to solve a climate change emergency has created an urgent demand to create cleaner energy alternatives to burning fossil fuels. Hydrogen, a zero carbon emission fuel alternative, can be used to power cars and it generates only water as a by-product.
It can be produced by separating water into hydrogen and oxygen; however, the process needs significant amounts of electricity. The major part of electricity is produced by burning methane, hence scientists at the University of Bath are creating new solar cells that directly use light energy to break down water.
A majority of the solar cells available now on the market are composed of silicon; however, they are expensive and require a large quantity of extremely pure silicon to manufacture. Furthermore, they are relatively thick and heavy, which restricts their applications.
Perovskite solar cells that use materials with the 3D structure as in calcium titanium oxide are cheaper to produce, thinner, and can be easily printed onto surfaces. Furthermore, they can be operated in low-light conditions and can generate a higher voltage when compared to silicon cells, which means they could be employed indoors to power devices without the need to plug into the mains.
The drawback is that they are unstable in water, which poses a great hindrance in their development and also restricts their use for the direct production of clean hydrogen fuels.
The group of researchers and chemical engineers, from the University of Bath’s Centre for Sustainable Chemical Technologies, has found a solution to this issue by using a waterproof coating from graphite, the element used in pencil leads.
They tested the waterproofing by immersing the coated perovskite cells in water and using the collected solar energy to separate water into oxygen and hydrogen. The coated cells functioned underwater for 30 hours, which is 10 hours more than the last record.
After this time, the glue sandwiching the coat to the cells did not work; the researchers predict that the cells could be stabilized for a longer time by using more powerful glue.
Earlier, alloys consisting of indium were employed to guard the solar cells for water splitting but indium is a rare metal and is thus expensive. The mining process to extract indium is not sustainable.
The research group at Bath instead used commercially available graphite, which is very economical and much more sustainable when compared to indium.
Perovskite solar cell technology could make solar energy much more affordable for people and allow solar cells to be printed onto roof tiles. However at the moment, they are really unstable in water—solar cells are not much use if they dissolve in the rain! We’ve developed a coating that could effectively waterproof the cells for a range of applications. The most exciting thing about this is that we used commercially available graphite, which is much cheaper and more sustainable than the materials previously tried.
Dr Petra Cameron, Senior Lecturer in Chemistry, University of Bath
Although perovskite solar cells generate a higher voltage than silicon-based cells, it is still not sufficient to split water by using solar cells alone. To overcome this issue, the research group added catalysts to decrease the energy demand required to promote the reaction.
Currently hydrogen fuel is made by burning methane, which is neither clean nor sustainable. But we hope that in the future we can create clean hydrogen and oxygen fuels from solar energy using perovskite cells.
Isabella Poli, Marie Curie FIRE Fellow and PhD Student, Centre for Sustainable Chemical Technologies, University of Bath
The study was conducted in alliance with the SPECIFIC team at Swansea University.