"Critical Materials Challenges in Photoelectrochemical Hydrogen Production"
A "Transforming Energy" Lecture
by Eric Miller
November 16, 2012
The US Department of Energy’s (DOE) Fuel Cell Technologies Program (FCT) has made significant progress in fuel cell technology advancement and cost reduction, highlighted by reducing the cost of automotive fuel cells by more than 80% since 2002. Research and development of enabling technologies for the widespread production of affordable renewable hydrogen, though, remains a daunting challenge. Near-term utilization of current reforming and electrolytic processes are viewed as necessary for early hydrogen markets, but there remains a critical need for transitioning to industrial-scale renewable hydrogen production for the longer term. Photoelectrochemical (PEC) hydrogen production, using sunlight to directly split water, is one of the key promising solar-to-hydrogen technologies for large-scale production of affordable renewable hydrogen. Although PEC water-splitting has been investigated for several decades, the research has focused mainly on titanium-dioxide or other metal-oxide based semiconductor systems which are stable in aqueous electrolytes, but which are generally limited in performance by their excessively wide bandgaps. It is well-understood today that new advanced semiconductor structures utilized in innovative reactor designs are needed for practical large-scale PEC hydrogen-production systems. Appropriately, the primary DOE R&D efforts in this area focus on the discovery, engineering and optimization of advanced PEC materials, and on the evaluation of promising PEC system designs. In terms of PEC materials, the challenging set of requirements includes adequate light absorption over the solar spectrum, development of photo-induced potentials thermodynamically adequate to split water, high charge separation and carrier collection efficiency, stability in suitable aqueous solutions, and favorable kinetics for the gas evolution reactions. In terms of PEC systems and reactor designs, high conversion efficiency to reduce the solar collection footprint is critical to minimize capital costs. Promising pathways under investigation in the DOE FCT R&D portfolio for achieving high PEC efficiencies and low hydrogen production costs are discussed in this talk. Exciting recent progress, including the achievement of new solar-to-hydrogen efficiency records, will be highlighted for specific PEC materials classes, including the III-V crystalline semiconductors, copper-chalcopyrite polycrystalline semiconductors as well as new mixed-metal oxides.
Dr. Eric L. Miller currently serves as the Hydrogen Production Technology Development Manager with the Hydrogen and Fuel Cell Technologies Program at the US DOE Office of Energy Efficiency and Renewable Energy. Dr. Miller received his Ph.D. and M.S degrees in Electrical Engineering from the University of Hawaii at Manoa, with a graduate-level research focus on developing materials for renewable energy conversion applications. He received dual undergraduate degrees from Cornell University in Applied and Engineering Physics and Computer Science. His professional career in alternative energy R&D, with emphasis on solar energy and on hydrogen and fuel cell development, has spanned more than twenty years; including work with the Oak Ridge National Laboratory, the NASA Lewis (aka Glenn) Research Center, Sunpower Inc., and the University of Hawaii at Manoa. Dr. Miller is generally recognized as a world leader in the field of Photoelectrochemical (PEC) hydrogen production, specializing in semiconductor-based materials, devices and systems for cost-effective PEC solar water-splitting; and currently serves as leader of the PEC task for the International Energy Agency’s Hydrogen Implementing Agreement.