The development of a photoelectrochemical cell involves the creation of photoanodes (which oxidize water to generate electrons) and photocathodes (which recover electrons to convert water into hydrogen). These electrodes need to combine light collection, charge separation and catalysis, and represent highly complex technological objectives. For the anode, the energy of photons from the sun is required, as the water oxidation reaction is thermodynamically unfavorable. For the cathode, photons are also needed because the electrons do not have a sufficiently reducing potential to reduce the protons. This double input of photons is found in the natural process of photosynthesis, where water oxidation involves the collection of photons from the sun at photosystem II, and the electrons produced at the end of the chain are re-energized by photons at photosystem I to make them reactive for the reduction of NAD and thenCO2 or water.
This lecture discusses the latest bioinspired molecular systems for proton-to-hydrogen photoreduction (potential active materials for photocathodes), most often assemblies of a photosensitizer molecule and a metal complex (non-noble metals) for water reduction catalysis. The following examples are described in greater detail: (i) cobaloximes or dinuclear iron complexes (models of the active site of iron hydrogenases) associated with photosensitizers such as Ru(diimine)3, Ir(diimine), Re(phen) (CO)3, organic dyes (eosin, rose of Bengal), Zn porphyrin ; (ii) purified enzymatic systems combining a hydrogenase for catalysis and photosystem I; (iii) the first solid photocathodes based on photosensitizing nanoparticles(quantum dots) functionalized with synthetic catalysts and fixed on gold electrodes.
