Direct water splitting under visible light with nanostructured hematite and WO3 photoanodes and a GaInP2 photocathode

A p-GaInP2 photocathode was paired with nanostructured hematite and tungsten trioxide photoanodes to investigate the utility of these systems for direct water splitting under visible light illumination. For the hematite system, under illumination at open-circuit conditions, the potential of hematite shifts cathodically and that of the GaInP2 shifts anodically. Under short-circuit condition and visible light illumination, the combination of the two photoelectrodes can split water, though with a very low rate of a few mu A/cm(2) even at an intensity of 1 W/cm(2). It was determined that the very low photocurrent from the hematite nanorod photoelectrode limits the short-circuit current of the two-photoelectrode combination. Similar potential shifts were observed with the nanostructured WO3/GaInP2 combination. However, at light intensities below 0.2 W/cm(2), the short-circuited combination would not split water due to an insufficient potential difference. Above 0.2 W/cm(2), the combination can split water under visible light, with similar to 20 mu A/cm(2) obtained at 1 W/cm(2). A linear photocurrent-light intensity relationship was observed and was attributed to efficient charge transfer and a low recombination of the charge carriers. The bandgap and the associated absorption limit of WO3 remain a challenge for a higher efficiency system. (C) 2008 The Electrochemical Society.