A breakthrough “solar paint” could see buildings transformed into hydrogen-producing powerhouses.
The system, developed by RMIT researchers, could provide a carbon and water neutral source of hydrogen for use in fuel cells, as well as feedstock for the production of fertilisers and pharmaceuticals.
Lead researcher Dr Torben Daeneke told The Fifth Estate the team had created a new way of producing hydrogen.
“Nobody has done this before.”
It’s a two-component system, the main part of which is a catalyst developed by the RMIT team – a synthetic molybdenum-sulphide that has two benefits. One, it can absorb moisture from humid air, much like the silica gel used to keep food and medicines dry, and two, it can convert that moisture into hydrogen and oxygen.
The second part of the system is titanium dioxide, a white pigment already used in normal wall paints, and products like toothpaste.
“It’s well-known and cheap. It’s already in everything,” Daeneke says.
The titanium dioxide absorbs high energy radiation from the sun, UV light, and uses it to drive the reaction.
“It’s a system where we can basically grab moisture from the air and use catalytic properties to turn it into hydrogen.”
Daeneke says the system has been formatted as an ink or paint “that can literally be painted on any surface”.
“You can imagine a brick wall that is transformed into hydrogen-producing real estate.”
What is yet to happen is the development of a method of capturing the hydrogen.
One idea is to use a hydrogen-permeable silicon rubber membrane.
“We’re already making them in our lab for other purposes.”
The system has only been tested in a lab environment, so final figures could be far off what would be produced in a final system, but so far about 5-10 litres of hydrogen gas can be produced per day over an average day, which Daeneke says is not insignificant.
The best areas for production are those that aren’t hit by direct sunlight, which Daeneke says makes it perfect to use “where it is not economical to use solar PV”.
“They work together. It’s an additional ingredient to what is already out there.”
Carbon and water neutral
A key benefit of the technology is that it is both carbon and water neutral.
Unlike other methods of producing hydrogen, which depend on purified water, the system does not require liquid water.
“We’re just working with humidity,” Daeneke says.
“If you have poor quality water or wastewater, you can utilise the vapour that comes off that.”
Other methods of producing hydrogen have been problematic. Electrolysis, for example, usually uses platinum as an electrode, making it expensive. Daeneke says another issue is that it needs purified water, as contaminants can ruin the electrode.
Both electrolysis and “steam reforming”, another method of producing hydrogen, are very energy and carbon intensive.
“At the moment it is a real issue; 95 per cent of hydrogen uses fossil fuels.”
Daeneke says the researchers are just at the beginning of the breakthrough, but he is very excited about where this will lead in the future.
“I could see this is probably useful for urban areas in places not quite suitable for photovoltaics. Alternatively it could be used where it is really remote and where it’s not easy to generate hydrogen with other means.”
Daeneke’s colleague, Professor Kourosh Kalantar-zadeh, said the technology would be particularly useful in hot, dry areas near the sea.
“The sea water is evaporated by the hot sunlight and the vapour can then be absorbed to produce fuel,” he said.
“This is an extraordinary concept – making fuel from the sun and water vapour in the air.”
The research, Surface Water Dependent Properties of Sulfur Rich Molybdenum Sulphides – Electrolyteless Gas Phase Water Splitting, has been published in ACS Nano.