Role of catalysis in photoelectrochemistry

Illumination of a semiconductor electrode in an electrochemical cell can result in the flow of current and the generation of electrolysis products. The photoelectrolysis of H₂O to H₂ and 1/2 O₂ represents a potentially important solar energy conversion/storage system. The cathode half-reaction (H₂ evolution) and the anode half-reaction (O₂ evolution) are both processes that are well-known to be kinetically sluggish at the thermodynamic potential in conventional cells. Data will be presented showing that the kinetics for these processes need to be improved for semiconductor photoelectrodes. Improvement in the H₂ and O₂ evolution kinetics requires the use of electron transfer catalysts. An approach to improved H₂ evolution kinetics for illuminated p-type semiconductors employing redox active polymers (based on N,N′-dialkyl-4,4′-bipyridinium monomers) and catalysts dispersed in the polymer will be outlined.