ELECTROCHEMICAL FEATURES OF ELECTRODES MODIFIED WITH MULTIPLE NANO CONTACTS (MNCS) FROM COLLOIDAL NOBLE-METAL PARTICLES

The key problem for the direct conversion of solar energy in photoelec trochemical cells is catalysis. The deposition of electrocatalytic met als onto the surface of the semiconductor electrode dan provide the ne cessary catalysis for chemical reactions. In photoelectrochemical devi ces these reactions are driven by the minority charge carriers produce d upon illumination. To avoid a simultaneous increase of the majority carrier transfer-the loss current which decreases the efficiency of th e photon energy conversion device-a new way of metallizing semiconduct or surfaces has been developed. By depositing colloidal metal particle s onto semiconductor surfaces, well defined Multiple Nano Contacts (MN Cs) are prepared. The surface modification by MNCs changes the catalyt ic properties of the semiconductor surface dramatically with negligibl e disturbance of the semiconductor surface energetics. This has been v erified here by performing electrochemical experiments with gold MNCs of different sizes (6-100 nm) deposited on p-GaAs electrodes. Calculat ions and experiments using bulk gold electrodes prove that a very smal l surface coverage of metal particles is sufficient to prevent charge carrier diffusion problems in the electrolyte. Investigations performe d with platinized gold particles elucidate the great influence of the spherical diffusion for the transfer of ions across the diffusion laye r, The different electrochemical properties of semiconductor electrode s modified with deposits from metal ion solutions compared to MNC modi fied electrodes are verified with time resolved potentiostatic measure ments. These current/time measurements reveal that a gold coverage of less than half a monolayer deteriorates the advantageous properties of the semiconductor/electrolyte interface for energy conversion.