The U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) last week said that its scientists have recaptured the record for highest efficiency in solar hydrogen production via a photoelectrochemical (PEC) water-splitting process.
The new solar-to-hydrogen efficiency record is 16.2 percent, topping a reported 14 percent efficiency in 2015 by a team made up of researchers from Helmholtz-Zentrum Berlin, TU Ilmenau, Fraunhofer ISE and the California Institute of Technology.
A paper in Nature Energy, titled “Direct Solar-to-hydrogen Conversion via Inverted Metamorphic Multijunction Semiconductor Architectures,” outlines how the new record was achieved.
NREL said that the PEC cell represents a significant change from the concept device the paper’s co-author, John Turner, developed at NREL in the 1990s.
According to NREL, both the old and new PEC processes employ stacks of light-absorbing tandem semiconductors that are immersed in an acid/water solution (electrolyte) where the water-splitting reaction occurs to form hydrogen and oxygen gases. But unlike the original device made of gallium indium phosphide grown on top of gallium arsenide, the new PEC cell is grown upside-down, from top to bottom, resulting in a so-called inverted metamorphic multijunction device.
Another key distinguishing feature of the new advancement was depositing a very thin aluminum indium phosphide “window layer” on top of the device, followed by a second thin layer of gallium indium phosphide, NREL said.
Turner’s initial breakthrough created a new way to efficiently split water using sunlight as the only energy input to make renewable hydrogen.
NREL researchers are looking for methods of increasing the lifespan of the PEC device in addition to further efficiency gains.
The authors of the paper in Nature Energy are Turner, James Young, Myles Steiner, Ryan France, and Todd Deutsch, all from NREL, along with Henning Döscher of Philipps-Universität Marburg in Germany.