An-Najah Staff

Narrow band semiconductors are suitable catalysts for visible light-to-electricity conversions under photo-electrochemical (PEC) conditions, but are unstable to such conditions. Simple techniques have been developed to stabilize n-GaAS electrodes in PEC experiments. Porphyirinatomanganese (MnP, as mixture of two different oxidation numbers MnII and MnIII) complexes were chemically anchored to the electrode surface via anchoring ligands. The modified n-GaAs electrodes showed enhanced conversion efficiencies. Moreover, the band edge positions were shifted toward more positive potentials. This was manifested in photo current vs. potential curves and in Mott-Schottky plots. However, the anchoring ligands and the attached ions peeled away from the electrode surface and the electrode stability could not be permanently retained by this technique. A better technique was then developed. Metalloporphyrine complexes, embedded inside polysiloxane matrices, were attached to n-GaAs electrodes. The resulting n-GaAs/Polysiloxane/MnP electrode systems showed enhanced conversion efficiency and stability at the same time. The results are rationalized based on ability of the MnP system to behave as redox couple that catalyzes charge transfer at the electrode/liquid interface.  The technique is useful for other mono-lithic narrow band gap semiconductor electrodes, such as n-GaInP2. Results on using this technique other types of semiconductor electrodes will also be presented.