Direct Light-Driven Water Oxidation by a Ladder-Type Conjugated Polymer Photoanode

A conjugated polymer known for high stability (poly[benzimidazobenzophenanthroline], coded as BBL) is examined as a photoanode for direct solar water oxidation. In aqueous electrolyte with a sacrificial hole acceptor (SO32-), photoelectrodes show a morphology-dependent performance. Films prepared by a dispersion-spray method with a nanostructured surface (feature size of similar to 20 nm) gave photocurrents up to 0.23 +/- 0.02 mA cm(-2) at 1.23 V-RHE under standard simulated solar illumination. Electrochemical impedance spectroscopy reveals a constant flat-band potential over a wide pH range at +0.31 V-NHE. The solar water oxidation photocurrent with bare BBL electrodes is found to increase with increasing pH, and no evidence of semiconductor oxidation was observed over a 30 min testing time. Characterization of the photo-oxidation reaction suggests H2O2 or center dot OH production with the bare film, while functionalization of the interface with 1 nm of TiO2 followed by a nickel-cobalt catalyst gave solar photocurrents of 20-30 mu A cm(-2), corresponding with 02 evolution. Limitations to photocurrent production are discussed.