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Reaction Mechanisms at the n ‐ FeS2 / I Interface: An Electrolyte Electroreflectance Study

1991; Institute of Physics; Volume: 138; Issue: 11 Linguagem: Inglês

10.1149/1.2085415

1945-7111

Pedro Salvador, D. Tafalla, H. Tributsch, H. Wetzel,

Minerals Flotation and Separation Techniques

Monocrystalline (pyrite) in contact with the redox couple was studied by electrolyte electroreflectance (EER) and conventional electro‐ and photoelectrochemical techniques. The EER signal originating from the , direct transition in pyrite can be used to determine precisely its flatband potential , even in the presence of a high concentration of bandgap surface states, which is typical for this semiconducting transition metal sulfide. We have also been able to show that dynamic measurements are possible under situations where capacitance studies are extremely complicated. Experimental evidence is given on strong interaction of I− and with the surface, via complex formation with Fe3+ lattice ions generated by hole capture during anodic polarization or illumination. Small shifts of about 50 mV toward negative potentials indicate that specific adsorption is stronger for than for I− species. Moreover, shifts of more than 1 V towards negative values can also be observed under cathodic polarization. This behavior is correlated to surface accumulation of electrons which accompanies electroreduction. A comprehensive model for surface photoreactions is proposed. This takes into account the catalytic role of the semiconductor surface in kinetics of charge transfer to the electrolyte. Both the very positive (high electronic affinity) and the high density of bandgap states, probably associated with lattice impurities, seem to determine the photovoltage limitations which are inherent to the system.