This paint converts humidity to hydrogen fuel

A new ink absorbs sunlight and moisture from air and produces hydrogen fuel. The ink, described in the journal ACS Nano, uses energy from sunlight to split water molecules into hydrogen and oxygen.

The ink can “be coated on any substrate, leading to efficient and low-cost hydrogen production from humid environments,” say researchers at the Royal Melbourne Institute of Technology in Australia who developed the formulation. That means houses painted with it could harvest solar energy and produce hydrogen fuel to power electric cars.

Hydrogen is a zero-emission fuel that, when burned, combines with oxygen to produce water. It holds promise for use in fuel cells, battery-like devices that generate electricity. Hydrogen fuel cell vehicles would only produce water as a waste product. But hydrogen is produced today from fossil fuels via processes that require a lot of energy.

Scientists have been attempting to produce hydrogen more sustainably by splitting water. This can be done using solar power and artificial photosynthesis techniques instead of fossil fuel electricity.

The Australian researchers made their solar paint with a material called amorphous molybdenum sulfide. The material is good at absorbing moisture and is an excellent catalyst that enables water molecules to split. It’s not the best at absorbing sunlight, however.

So the researchers mixed it with titanium oxide, a material used as white pigment in wall paints. They made a water-based suspension of a mixture containing 90 percent molybdenum sulfide and 10 percent titanium oxide. Then they coated this ink on a substrate that they exposed to moisture and sunlight.

The titanium oxide absorbs sunlight and produces charge-carrying electrons. The molybdenum sulfide catalysts use the electrons’ energy to split water molecules they have absorbed from the surrounding air. The hydrogen would have to be captured for use.

Ink-coated substrates are less efficient at producing hydrogen than catalyst particles suspended in an electrolyte. But the efficiency could be increased by using a more effective sunlight-absorbing material and by optimizing the device, the researchers say. In an interview, lead researcher Torben Daeneke says that they now plan to integrate the material with a gas separation membrane that would help to collect the hydrogen for storage and use.

Source: Daeneke T et al. Surface Water Dependent Properties of Sulfur-Rich Molybdenum Sulfides: Electrolyteless Gas Phase Water Splitting. ACS Nano. 2017.
Photo: Aditi Rao, Flickr Creative Commons
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