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U.S. Department of Energy Energy Efficiency and Renewable Energy

Photoelectrochemical Water Splitting

Photo of hydrogen beam generated from PV cell

Another promising option for the long term is photoelectrolysis. Here, light shining on a photoelectrochemical cell immersed in water produces bubbles of hydrogen and oxygen.

In this process, hydrogen is produced from water using sunlight and specialized semiconductors called photoelectrochemical materials. In the photoelectrochemical (PEC) system, the semiconductor uses light energy to directly dissociate water molecules into hydrogen and oxygen. Different semiconductor materials work at particular wavelengths of light and energies.

Research focuses on finding semiconductors with the correct energies to split water that are also stable when in contact with water. Photoelectrochemical water splitting is in the very early stages of research but offers long-term potential for sustainable hydrogen production with low environmental impact.

Learn more about photoelectrochemical hydrogen production in Technoeconomic Analysis of Photoelectrochemical (PEC) Hydrogen Production.

Potential Designs for Photoelectrochemical Water-Splitting Systems

Single PEC Slurry-Phase Reactor System for Water Splitting


Graphic of a single PEC slurry-phase reactor system for water splitting: Sunlight shines on a photo reactor (low cost, shallow, stirred tub; transparent cover) with outgoing oxidation product and hydrogen. The outgoing hydrogen leads to a condenser/dryer that leads to Br2(1)/H2O leading back to the photo reactor. The condenser/dryer also leads to hydrogen going to a hydrogen compressor and hydrogen storage. Additionally, an electrolyte recirculation tank leads to the photo reactor. An electrolyte adjustor and cleanup/purification process (both with sensors) lead to the electrolyte recirculation tank. Feedstock (e.g. H2O, HCL, HBr, and biomass) leads to the cleanup/purification box.


Dual Photosystem Slurry-Phase Reactor System for Overall Water Splitting (Br3- Transfer Ion Example)

Graphic of dual photosystem slurry-phase reactor system for overall water splitting example (Br3- transfer ion): Sunlight is at the center of this image with two photo reactors to the left and right of the sun. Photo reactor A – H2 generated (e.g. 6HBr arrow 3H2 + 2Br3-; low cost, shallow, stirred tub; transparent cover with outgoing hydrogen and ions. Outgoing hydrogen leads to a condenser/dryer, which leads to Br2(1)/H2O with leads to outgoing ions from photo reactor A to photo reactor B. The condenser/dryer also leads to outgoing H2, which leads to a hydrogen compressor and hydrogen storage. Photo reactor B – O2 generated (e.g. 4Br3- + 6H2O arrow 12 HBr + 3O2; low cost, shallow, stirred tub; transparent cover) with outgoing oxygen and HBr. The HBr arrow leads to an electrolyte recirculation tank, which leads back to photo reactor A. Feedstock (e.g. H2O, HCL, HBr, biomass) leads to cleanup/purification, which leads to water and then to photo reactor B. The cleanup/purification, along with an electrolyte adjustor (both with sensors), lead to the electrolyte recirculation tank.


Photoelectrode System Block Diagram

Graphic of photoelectrode system block diagram: Sunlight leads to a photoelectrode reactor (transparent tube or flat plate cover; active photoelectrode sheets; electrolyte flow channels; membrane gas separators, as needed) with an optional tracking system. Arrows from the photoelectrode reactor lead to an oxygen bubbler (with oxygenated electrolyte) with oxygen output and to a hydrogen bubbler (with hydrogenated electrolyte) with hydrogen output leading to a hydrogen compressor and hydrogen storage. The oxygen bubbler and hydrogen bubbler lead to a re-circulated electrolyte and then to an electrolyte recirculation tank with an emergency drain. This tank leads to a pump that leads back to the photoelectrode reactor. An electrolyte adjustor with a sensor leads to the electrolyte recirculation tank. A water inlet leads to a water purifier with a sensor, which also leads to the recirculation tank.


Photoelectrode Reactor Schemes

Graphic of two photoelectrode reactor schemes: The tubular reactor image consists of a series of tubes with green and red circles at the end. Red (O2) and green (H2) arrows point up from the base and into the tubes. The flat plate reactor image consists of a photoelectrode sheet with ion-exchange paths between an O2 (H2) channel with red circles above an H2 (O2) channel with green circles. Above this area, a triangular shaped transparent cover plate contains more red circles.