photoelectrode

A photoelectrode is an electrode that operates under illumination to convert light into electrical signals by photoelectric processes. In photoelectrochemistry, the photoelectrode is typically a semiconductor that absorbs photons to generate electron–hole pairs, which drive surface redox reactions and enable solar-to-chemical or solar-to-electrical energy conversion. Common materials include n-type and p-type semiconductors such as titanium dioxide, hematite, BiVO4, WO3, ZnO, and other light-absorbing materials like CdS, CdSe, or silicon in certain configurations. In photoelectrochemical cells, a photoelectrode can function as a photoanode (holes injected into electrolyte) or as a photocathode (electrons injected into electrolyte). Operation relies on favorable band alignment: the conduction band edge should be above the redox couple for electron extraction, and the valence band should be below the redox potential for hole extraction. Charge separation and transport to the surface, where electrochemical reactions occur, are governed by bulk transport and surface recombination dynamics, with surface states influencing efficiency.

Strategies to improve performance include surface modification, cocatalysts, nanostructuring to increase surface area, and protective layers to enhance stability. In water splitting, photoelectrodes form the working interface of photoelectrochemical cells that drive hydrogen and oxygen evolution, often in tandem to increase photovoltage. Key performance metrics include photocurrent density, open-circuit potential, incident photon-to-current efficiency, applied bias photon efficiency, and stability under illumination. Beyond energy conversion, photoelectrodes find use in sensors and photodetectors where light-induced current or potential changes enable detection. The field intersects materials science, electrochemistry, and renewable energy research.