ELECTROCHEMICAL INVESTIGATION OF THE ENERGETICS OF IRRADIATED FES2 (PYRITE) PARTICLES

The band energies of FeS2 particles (approximately 10-mu-m) were estimated by collection of electrons generated by irradiation of the particles in the presence of a hole acceptor (e.g., tartrate ion) at an inert collector electrode. Electrons were collected directly from the particles or by the mediator Ru(NH3)6(3+), where the resulting +2 state is oxidized at the electrode. The variation of the steady-state photocurrent in the presence of mediator as a function of pH allowed estimation of the quasi-Fermi level for electrons and located the conduction and valence band edges at -0.1 and +0.9 V vs SCE, respectively, at pH 0, and -0.9 and +0.1 V vs SCE, respectively, at pH 14. Modification of the FeS2 surface with Pt produced a small (ca. 0.1 V) negative shift in the potential for photocurrent onset.