Role of surface states and adsorbates in time-resolved photocurrent measurements and photovoltage generation at phthalocyaninatozinc(II)-photocathodes

Influence of Electron-withdrawing Substituents on Photoelectrochemical Surface Phenomena at Phthalocyanine Thin Film Electrodes

The influence of electron-withdrawing substituents on the photoelectrochemical properties of phthalocyanines is shown in a comparison between hexadecafluorophthalocyaninatozinc(II) ( F 16 PcZn ) and the unsubstituted phthalocyaninatozinc(II) ( PcZn ). The role of surface states in the photoelectrochemistry of both materials has been investigated by time-resolved photocurrent measurements in the millisecond range. The charging and discharging of surface states could clearly be seen as spikes at the beginning and the end of illumination. Surface states were filled with photogenerated electrons at PcZn and with photogenerated holes at F 16 PcZn . In the steady state under illumination only cathodic photocurrents were detected at PcZn , while at F 16 PcZn both cathodic and anodic photocurrents were observed. An adsorption step of electroactive species prior to the charge transfer was derived from the dependence of the steady state photocurrents on the electrolyte concentration for both materials. The concentration dependence of the charging and discharging currents, however, showed that charge transfer from surface states to the electrolyte occurs at PcZn , while at F 16 PcZn the surface states only represent recombination centres.

The pH Response and Sensing Mechanism of n-Type ZnO/Electrolyte Interfaces

Ever since the discovery of the pH-sensing properties of ZnO crystals, researchers have been exploring their potential in electrochemical applications. The recent expansion and availability of chemical modification methods has made it possible to generate a new class of electrochemically active ZnO nanorods. This reduction in size of ZnO (to a nanocrystalline form) using new growth techniques is essentially an example of the nanotechnology fabrication principle. The availability of these ZnO nanorods opens up an entire new and exciting research direction in the field of electrochemical sensing. This review covers the latest advances and mechanism of pH-sensing using ZnO nanorods, with an emphasis on the nano-interface mechanism. We discuss methods for calculating the effect of surface states on pH-sensing at a ZnO/electrolyte interface. All of these current research topics aim to explain the mechanism of pH-sensing using a ZnO bulk- or nano-scale single crystal. An important goal of these investigations is the translation of these nanotechnology-modified nanorods into potential novel applications.