Hybrid organic/inorganic band-edge modulation of p-Si(111) photoelectrodes: effects of R, metal oxide, and Pt on H2 generation.

Abstract

The efficient generation of dihydrogen on molecularly modified p-Si(111) has remained a challenge due to the low barrier heights observed on such surfaces. The band-edge and barrier height challenge is a primary obstruction to progress in the area of integration of molecular H2 electrocatalysts with silicon photoelectrodes. In this work, we demonstrate that an optimal combination of organic passivating agent and inorganic metal oxide leads to H2 evolution at photovoltages positive of RHE. Modulation of the passivating R group [CH3 → Ph → Naph → Anth → Ph(OMe)2] improves both the band-edge position and ΔV (Vonset - VJmax). Subsequent atomic layer deposition (ALD) of Al2O3 or TiO2 along with ALD-Pt deposition results in to our knowledge the first example of a positive H2 operating potential on molecularly modified Si(111). Mott-Schottky analyses reveal that the flat-band potential of the stable Ph(OMe)2 surface approaches that of the native (but unstable) hydride-terminated surface. The series resistance is diminished by the methoxy functional groups on the phenyl unit, due to its chemical and electronic connectivity with the TiO2 layer. Overall, judicious choice of the R group in conjunction with TiO2|Pt effects H2 generation on p-Si(111) photoelectrodes (Voc = 207 ± 5.2 mV; Jsc = -21.7 mA/cm(2); ff = 0.22; ηH2 = 0.99%). These results provide a viable hybrid strategy toward the operation of catalysts on molecularly modified p-Si(111).