A cheaper, cleaner and more sustainable way of making hydrogen fuel from water using sunlight is closer with new research from the University of Bath’s Centre for Sustainable Chemical Technologies. The team used a commercial thermal graphite sheet and a mesoporous carbon scaffold to encapsulate metal-halide perovskites (CsPbBr3) as an inexpensive and efficient waterproofing strategy. The study is published in the open access journal Nature Communications.
Most solar cells currently on the market are made of silicon; these are expensive to make and require a lot of very pure silicon to manufacture. They are also quite thick and heavy, which limits their applications.
Perovskite solar cells, using materials with the same 3D structure as calcium titanium oxide, are cheaper to make, thinner and can be easily printed onto surfaces. They also work in low light conditions and can produce a higher voltage than silicon cells.
The downside is they are unstable in water—a huge obstacle in their development and also limiting their use for the direct generation of clean hydrogen fuels.
The team of scientists and chemical engineers, from the University of Bath’s Centre for Sustainable Chemical Technologies, solved this problem by using a waterproof coating from graphite.
Metal-halide perovskites have been widely investigated in the photovoltaic sector due to their promising optoelectronic properties and inexpensive fabrication techniques based on solution processing. Here we report the development of inorganic CsPbBr3-based photoanodes for direct photoelectrochemical oxygen evolution from aqueous electrolytes. We use a commercial thermal graphite sheet and a mesoporous carbon scaffold to encapsulate CsPbBr3 as an inexpensive and efficient protection strategy.
We achieve a record stability of 30 h in aqueous electrolyte under constant simulated solar illumination, with currents above 2 mA cm−2 at 1.23 VRHE. We further demonstrate the versatility of our approach by grafting a molecular Ir-based water oxidation catalyst on the electrolyte-facing surface of the sealing graphite sheet, which cathodically shifts the onset potential of the composite photoanode due to accelerated charge transfer. These results suggest an efficient route to develop stable halide perovskite based electrodes for photoelectrochemical solar fuel generation.—Poli et al.
They tested the waterproofing by submerging the coated perovskite cells in water and using the harvested solar energy to split water into hydrogen and oxygen. The coated cells worked underwater for 30 hours—ten hours longer than the previous record.
After this period, the glue sandwiching the coat to the cells failed; the scientists anticipate that using a stronger glue could stabilize the cells for even longer.
Previously, alloys containing indium were used to protect the solar cells for water splitting, however indium is a rare metal and is therefore expensive and the mining process to obtain it is not sustainable.
The Bath team instead used commercially available graphite, which is very cheap and much more sustainable than 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
Perovskite solar cells produce a higher voltage than silicon-based cells, but still not enough needed to split water using solar cells alone. To solve this challenge, the team is adding catalysts to reduce the energy requirement needed to drive the reaction.
The research was done in collaboration with the SPECIFIC team at Swansea University.
Poli, Hintermair, Regue, Kumar, Sackville, Baker, Watson, Eslava & Cameron (2019) “Graphite-protected CsPbBr3 perovskite photoanodes functionalised with water oxidation catalyst for oxygen evolution in water” Nature Communications doi: 10.1038/s41467-019-10124-0