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Scientists at the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) have developed a “better way” to make hydrogen using renewable energy according to a paper published this month in Nature Energy.
Hydrogen has many potential applications and is already used to upgrade crude oil for fuel production and in the synthesis of ammonia (which is critical in food production). Today, this hydrogen is commonly produced using steam reformation processes that rely on natural gas. But, scientists have been working on ways to swap out this fossil fuel for renewable energy sources.
One such method includes the use of photoelectrochemical (PEC) devices that can absorb sunlight and use it directly to split water molecules. Broadly 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.
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These PEC devices have significant promise but scientists have struggled to produce a design that is durable enough to become commercially viable. However, according to the new paper, 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.
Reference: Gu, J., Aguiar, J. A., Ferrere, S., Steirer, K. X., Yan, Y., Xiao, C., Young, J. L., Al-Jassim, M., Neale, N. R. and Turner, J. A. (2017) ‘A graded catalytic–protective layer for an efficient and stable water-splitting photocathode’, Nature Energy. Nature Publishing Group, 2, p. 16192. Available at: http://dx.doi.org/10.1038/nenergy.2016.192.