Scientists improve device that produces renewable hydrogen from sunlight

Scientists at the US Department of Energy’s National Renewable Energy Laboratory (NREL) have improved a device that is used to make hydrogen from solar energy.

Hydrogen is a promising source of clean fuel. Today, it is already used to upgrade crude oil for fuel production and in the synthesis of ammonia (which is critical in food production). But it is commonly produced using steam reformation processes that rely on natural gas, and scientists have been working on ways to produce hydrogen from renewable energy sources instead of fossil fuel.

One method that has been developed is the use of photoelectrochemical (PEC) devices that can absorb sunlight and use it directly to split water molecules. Generally speaking, these devices can convert the energy in sunlight into hydrogen and oxygen without the need for natural gas and at potentially higher efficiencies than electrolysis.

Though very promising, PEC devices are not durable enough to be commercialized. However, researchers have made a significant stride in improving the durability of PEC devices, bringing them one step closer to commercialization.

Their new method is based on research produced 18 years ago by John Turner, a research fellow at NREL who has been with the labs since 1979. In his earlier work, Turner designed a tandem solar cell comprised of several layers of gallium indium phosphide (GaInP2) and gallium arsenide (GaAs) semiconductors. These layers absorb sunlight and produce enough power to split water molecules into hydrogen and oxygen.

Turner’s device held the record for the highest solar-to-hydrogen conversion efficiency until 2015. But, despite this high efficiency the device struggled to make sense commercially as it degraded quickly.

In their new design, researchers have improved on Turner’s design by inserting a protective layer – comprised of titanium dioxide (TiO2) and molybdenum sulfide (MoSx) – to defend the GaInP2 layers from the negative effects of the acidic solution to which they are exposed. In turn, they have been able to increase the longevity of this PEC device.

This research effort was led by Jing Gu, a postdoc researcher who worked with John Turner before becoming an assistant professor at San Diego State University. The other co-authors are all based at NREL and include (in addition to Turner) Jing Gu, Jeffery A. Aguiar, Suzanne Ferrere, Xerxes Steirer, Yong Yan, Chuanxiao Xiao, James L. Young, Mowafak Al-Jassim, and Nathan R. Neale.