Photoelectrochemical investigations of complex formation phenomena on oriented n‐pyrite (FeS2) crystal surfaces

Quantum yields of illuminated single crystalline n-pyrite (FeS2)/electrolyte junctions were measured at λ = 632.8 nm and found to be significantly higher in the presence of negatively charged redox species, such as I− and [Fe(CN)6]4− in contrast to species like Fe2+. Higher photocurrents and photovoltages at (100) n-pyrite rotating disc electrodes in comparison with (111) electrodes fabricated from the same single crystal are obtained. Further, (100) n-pyrite electrode surfaces were treated with pyrazine and 4,4'-bipyridine. A significant decrease of dark current and a shift of the equilibrium potential in 0.5 M FeSO4 is ascribed to chemical complex formation between the electron donating ligands and the Lewis acidic Fe(II) centres of the (100) n-pyrite surface. In the case of pyrazine treatment an enhancement of photocurrent and photovoltage could be observed. The observed phenomena are discussed in terms of coordinated chemical surface complex formation and charge transfer properties.