fotoanodo

A photoanode, or fotoanodo, is a semiconductor electrode that serves as the anode in a photoelectrochemical cell when it is illuminated. It absorbs light to generate electron–hole pairs; the photogenerated holes migrate to the surface to oxidize chemical species in contact with the electrolyte, while the electrons are conducted through the external circuit to the counter electrode.

In operation, a photoanode relies on light-induced charge separation. The holes drive oxidation reactions at the semiconductor–electrolyte interface, such as water oxidation in solar fuel applications, and the electrons flow through an external circuit to reduce species at the opposite electrode. Effective charge separation, surface catalysis, and chemical stability are critical for performance.

Materials commonly used for photoanodes are n-type metal oxides, including TiO2, hematite (Fe2O3), WO3, BiVO4, and SrTiO3. These materials often have wide band gaps that limit visible-light absorption, so strategies such as dye sensitization, surface catalysts (cocatalysts), and nanostructuring are employed to improve light harvesting and charge transfer. Band alignment is essential: the valence-band edge must be sufficiently positive to oxidize substrates (e.g., water), and the conduction-band edge must provide electrons to the external circuit. Stability in aqueous environments is a major challenge, with many materials prone to photocorrosion without protective coatings or robust cocatalysts.

Applications include photoelectrochemical water splitting for hydrogen production, solar fuel generation, and roles within dye-sensitized solar cells where a photoanode (often dye-sensitized TiO2) injects electrons into the semiconductor. Ongoing research aims to enhance efficiency, stability, and cost through new materials, doping, and architectural innovations.