Hydrogen bubbles being generated in water from the illumination of a high-efficiency semiconductor-based PEC cell at room temperature. Image source: NREL.
Photoelectrochemical (PEC) hydrogen production offers a promising route to affordable hydrogen fuel by harvesting light from the sun and using water as feedstock. Researchers use a metric called solar-to-hydrogen (STH) efficiency as a standard way to evaluate PEC systems based on how effectively they convert energy from the sun into hydrogen. In 2016, the National Renewable Energy Laboratory broke a standing 18-year world record, demonstrating 16.2% STH efficiency over the previous 12% STH, well on its way to meeting the U.S. Department of Energy (DOE) target of 25%. Since then research efforts have continued to improve efficiency and durability of this technology through advanced and innovative materials. DOE's Fuel Cell Technologies Office within the Office of Energy Efficiency and Renewable Energy funded this work.
Sources:
Young et al., "Direct Solar-to-Hydrogen Conversion via Inverted Metamorphic Multi-Junction Semiconductor Architectures," Nature Energy 2 (2017): 17028.
Khaselev and Turner, "A Monolithic Photovoltaic-Photoelectrochemical Device for Hydrogen Production via Water Splitting," Science 280, no. 5362 (1998): 425.