Oxygen reduction reaction on spontaneously and potentiodynamically formed Au/TiO2 composite surfaces

Oxygen reduction catalyzed by Au-TiO2 nanocomposites in alkaline media

Au-TiO2 nanocomposites were prepared by chemical deposition of gold nanoparticles onto TiO2 nanocolloids that were synthesized by a hydrothermal method. Transmission electron microscopic measurements showed that the TiO2 colloids exhibited an average diameter of about 5 nm and clearly defined lattice fringes that were consistent with those of anatase TiO2 and formed rather large agglomerates that spanned a few hundred nanometers in length. Additionally, gold nanoparticles were found to be embedded within the TiO2 matrices, and the size increased with increasing gold loading but all ranged from 10 to 50 nm in diameter. Consistent results were obtained in X-ray diffraction measurements. Electrochemical studies demonstrated that the resulting Au-TiO2 nanocomposites exhibited apparent electrocatalytic activity in oxygen reduction that was markedly improved as compared to that of TiO2 particles alone, as reflected in the onset potential, number of electron transfers involved, and kinetic current density. Among the series, the best catalyst for oxygen reduction was identified with the Au/Ti atomic ratio of 5.2%. The enhanced oxygen reduction kinetics was ascribed to the dissociation of water and formation of surface-adsorbed hydroxyl moieties that was facilitated by the loading of gold nanoparticles onto the TiO2 colloids.

Got TiO2 nanotubes? Lithium ion intercalation can boost their photoelectrochemical performance

Cations such as H(+) and Li(+) are intercalated into TiO(2) nanotube arrays by subjecting them to short-term electrochemical pulses at controlled potentials (<-1.0 V vs Ag/AgCl). The intercalation of these small cations has a profound effect toward enhancing photocurrent generation under UV light irradiation. A nearly three-fold increase in the photoconversion efficiency (IPCE) was observed upon intercalation of Li(+) ions into TiO(2) nanotube arrays. The intercalation process is visualized by the color change from gray to blue. Spectroelectrochemical measurements were carried out to monitor the absorption changes at different applied potentials. The analysis of the V(oc) decay following termination of UV light shows a significant decrease in the rate of recombination of accumulated electrons upon Li(+) ion intercalation.