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One-dimensional (1D) nanostructures have wide applications in photocatalysts for water splitting. Their surfaces may impact the gas bubble nucleation rate, thus influencing the efficiency of gas evolution. However, the effects of the 1D nanostructured surfaces on the bubble nucleation have not been studied to date. Herein, these effects are theoretically analyzed, based on the changes of free energy for a bubble nucleus forming inside/outside a nanotube. The results show that compared to flat surfaces, the inner tube wall favors the bubble nucleation, while the outer wall has an opposite effect. These differences become increasingly significant with tube radius Rt reducing when Rt < 10r* (r*-bubble equilibrium radius). The size effect is further verified experimentally for bubble nucleation on TiO2 nanotube arrays. The sensitivity of bubble nucleation to nanostructure dimensions should be considered in designing high-efficient photocatalysts. [ABSTRACT FROM AUTHOR]

One-dimensional (1D) arrayed photoelectrodes usually present superior performance in photoelectrochemical (PEC) water splitting. This superiority is known to be attributed to directional transport of photogenerated charge carriers. Herein, we show that in addition to this intrinsic charge transport property, a 1D arrayed structure introduces nanoscale capillary wetting, which is also believed to contribute to the improved PEC performance. Our theoretical model predicts that this morphology-dependent capillarity leads to the formation of a liquid film between the photoelectrode surface and the adhered bubble (the generated H2/O2 bubble), thus largely reducing the blockage of active sites at the bubble base. This prediction has been experimentally demonstrated by taking arrayed TiO2 nanorods as a model photoelectrode, with the observation of the PEC activity within the bubble base. This work extends our knowledge toward hydrodynamic functionality involved in morphology-controlled photoelectrodes for enhanced PEC performance. [ABSTRACT FROM AUTHOR]