Single Photogenerated Bubble at Gas-Evolving TiO2 Nanorod-Array Electrode

This paper presents a study on single bubble photogenerated by 376 nm laser light at TiO2 nanorod-array electrode during photoelectrochemical (PEC) conversion. The surface properties of TiO2 nanorod-array electrode were investigated at first for a better understanding of the three-phase contact line behavior. The results indicate the light-induced hydrophilic effect of TiO2 nanorod-array electrode under illumination, which makes bubble tend to be pseudo-sphere shape during attaching on electrode. The experimental investigation on photogenerated bubble at TiO2 nanorod-array electrode shows that there is a linear relationship between cubic root of time and bubble radius, demonstrating the gas products from the surface reaction transferring into bubble through bubble bottom according to the analysis of the relative size between bubble and effective solid surface. Furthermore, the coupling effects between bubble and irradiance were discussed. The bubble scatter effect on light causes a local light intensity increase at electrode surface area on both sides of bubble, and leads to photocurrent increase especially at small bubble size. While the increase of irradiance causes the parameters of bubble evolution period, dissolved gas concentration for nucleation and departure diameter increase, but leads to bubble evolution rate and incident photon conversion efficiency (IPCE) decrease. These results suggest a lower irradiance is preferred for a higher PEC conversion efficiency from the aspects of IPCE and bubble evolution rate.