NREL pioneers better way to make renewable hydrogen

Scientists at the US National Renewable Energy Laboratory (NREL) have developed a method of boosting the longevity of high-efficiency photocathodes in photoelectrcochemical water-splitting devices.
NREL pioneers better way to make renewable hydrogen

The use of a photoelectrochemical (PEC) device is a promising way to produce hydrogen. A PEC cell absorbs sunlight and converts that energy into hydrogen and oxygen by splitting water molecules. Unfortunately, high efficiency devices developed to date quickly degrade in the acidic solution to which the cell is exposed. The challenge of making a more durable cell must be overcome before renewable hydrogen from PEC devices can become commercially viable.

Research fellow John Turner developed the concept of using an integrated tandem cell, based on the NREL high-efficiency tandem solar cell, to split water and produce hydrogen, 18 years ago. He designed a tandem solar cell containing layers of gallium indium phosphide (GaInP2) and gallium arsenide (GaAs) semiconductors to absorb the sunlight and produce the power necessary for the photoelectrochemical water-splitting reaction. Turner's device held the record for the highest solar-to-hydrogen efficiency, until it was finally eclipsed in 2015.

The paper, A graded catalytic-protective layer for an efficient and stable water-splitting photocathode, published in the new issue of Nature Energy, describes how NREL researchers determined that greater photocathode stability and high catalytic activity can be achieved by depositing and annealing a bilayer of amorphous titanium dioxide (TiOx) and molybdenum sulfide (MoSx) onto GaInP2.

During a 20-hour durability test, the photocathode retained 80 percent of the initial electricity generated. The TiOx and MoSx produced a catalyst protection layer and served to protect the GaInP2 from the acidic solution.

Benefits from the NREL research come by producing hydrogen from renewable sources, instead of the steam reforming natural gas process now commonly in use. That process releases carbon dioxide into the atmosphere, thereby contributing to the greenhouse effect.

“This paper, along with our previous paper on surface protection published in Nature Materials, shows that considerable improvement in the stability and activity of these photoelectrochemical devices can be made” said Turner.

Jing Gu, a postdoc with Turner, lead the effort. She is now an assistant professor at San Diego State University. Along with Turner, the co-authors all were from NREL: Jing Gu, Jeffery A. Aguiar, Suzanne Ferrere, Xerxes Steirer, Yong Yan, Chuanxiao Xiao, James L. Young, Mowafak Al-Jassim, and Nathan R. Neale.

The research was funded by the Energy Department's Office of Science, Office of Basic Energy Sciences, Solar Photochemistry Programme. This effort benefits from work on photoelectrochemical water splitting being funded out of the department's Fuel Cell Technologies Office.

NREL is the U.S. Department of Energy's primary national laboratory for renewable energy and energy efficiency research and development. NREL is operated for the Energy Department by The Alliance for Sustainable Energy, LLC.

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National Renewable Energy Laboratory (NREL)

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Battery cars are relatively simple vehicles, which is why a century ago their development preceded gasoline cars. Though they came a long way since then, battery cars still need to be charged, and with raw power made elsewhere. Such is not the case with hydrogen cars -- or gasoline cars for that matter -- which make their power from the fuel they carry onboard. Automotive engineers took this nagging fact into account, and took into account also the finite capacity of our electric grid. They rightly concluded that there is an inherent limitation with battery cars -- one that does not go away with high capacity batteries or with fast chargers. This might explain why 62% of automotive executives believe battery-powered cars will fail and 78% believe hydrogen fuel cell cars are the future.