Photoelectrochemical cells based on bis-aniline-crosslinked CdS nanoparticle-carbon nanotube matrices associated with electrodes

The electrochemical preparation of a bis-aniline-crosslinked CdS nanoparticle-carbon nanotube matrix on electrode surfaces is described. The optimal electrode was prepared by the electropolymerization of thioaniline-functionalized CdS nanoparticles (NPs) and aniline-tethered carbon nanotubes (CNTs), using 80 electropolymerization cycles at a CdS NPs: CNTs (w/w) ratio of 5.5. The photocurrent generated by the electrode, in the presence of triethanolamine as electron-donor, reveals a quantum yield of Phi = 2.4%, ca. seven-fold higher than for a monolayer of CdS NPs crosslinked to the electrode by bis-aniline bridges. The enhanced photocurrents in the CdS NP-CNT composite were attributed to the trapping of the photogenerated conduction-band electrons in the semiconductor NPs by the CNTs, and their effective transport to the electrode, a process that facilitated charge separation. The bias potential applied to the electrodes affected the resulting photocurrents, and enhanced photocurrents were observed when the bis-aniline bridges existed in their oxidized quinoid state. This was attributed to the improved trapping of the conduction-band electrons by the electron-acceptor (relay) bridging units. The supramolecular association of N, N'-dimethyl-4,4'-bipyridinium, MV2+, to the pi-donor bis-aniline bridging units resulted in a photocurrent quantum yield of phi = 6.1%. The enhanced quantum yield was attributed to the effective trapping of the conduction-band electrons by the pi-acceptor MV2+ relay units associated with the pi-donor bridging elements, and the efficient transport of the electrons to the electrode by the conductive CNT matrix. These processes facilitated and improved charge separation and provided a competitive path to degradative electron-hole recombination in the semiconductor particles.