Chemically derivatized n-type silicon photoelectrodes. Stabilization to surface corrosion in aqueous electrolyte solutions and mediation of oxidation reactions by surface-attached electroactive ferrocene reagents

Abstract

Derivatization of n-type Si photoelectrode surfaces with (1,1'-ferrocenediyljdichlorosilane results in the persistent attachment of photoelectroactive ferrocene species. Derivatized surfaces have been characterized by cyclic voltammetry in EtOH or H₂O electrolyte solutions. Such surfaces exhibit persistent oxidation and reduction waves, but the oxidation requires illumination as expected for an n-type semiconductor. The oxidation wave is observed at potentials ~300 mV more negative than at Pt, reflecting the ability to oxidize ferrocene contrathermodynamically by irradiation. Derivatized n-type Si can be used to sustain the oxidation of solution-dissolved ferrocene under conditions where "naked" Si is incapable of doing so. Further, derivatized n-type Si has been used in an aqueous electrolyte to oxidize Fe(CN)₆⁴⁻. Finally, the photooxidation of solution species has been demonstrated to occur via photogeneration of holes in the Si, oxidation of the surface-attached species, and then oxidation of the solution species by the surface-attached oxidant, providing the first direct proof of mediated electron transfer for any derivatized electrode. Derivatized electrodes can be used to sustain the conversion of light to electricity but the efficiencies are low. Based on results for 632.8-nm irradiation, solar energy conversion efficiencies of ~1% can be obtained.

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