US researchers develop green method for renewable hydrogen production

The method uses a photoelectrochemical device and does not release carbon dioxide.

Researchers at the US Department of Energy's National Renewable Energy Laboratory (NREL) have used a photoelectrochemical (PEC) device to develop a carbon-efficient method for hydrogen production.

The method can boost the longevity of high-efficiency photocathodes in PEC water-splitting devices. A PEC cell absorbs sunlight and converts that energy into hydrogen and oxygen by splitting water molecules.

The researchers determined that better photocathode stability and high catalytic activity can be achieved by depositing and annealing a bilayer of amorphous titanium dioxide (TiOx) and molybdenum sulphide (MoSx) onto a solar cell made up of layers of gallium indium phosphide (GaInP2). During a 20-hour durability test, the photocathode retained 80% of the initial electricity generated. The TiOx and MoSx produced a catalyst protection layer and served to protect the GaInP2 from the acidic solution that the cell is exposed to.

Current high efficiency devices degrade quickly in the acidic solution. The challenge of making a more durable cell must be overcome before renewable hydrogen from PEC devices can become commercially viable.

John Turner, a research fellow at NREL, said: "This shows that considerable improvement in the stability and activity of these PEC devices can be made.”

The production method developed by NREL produces hydrogen from renewable sources, instead of the steam reforming natural gas process that is commonly in use at the moment. The latter process releases carbon dioxide into the atmosphere, contributing to the greenhouse effect.

Hydrogen is currently used to upgrade crude oil for fuel production and in the synthesis of ammonia, which is important for food production.

The findings are described in a paper titled A graded catalytic-protective layer for an efficient and stable water-splitting photocathode, and was published in the journal Nature Energy.