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In the present study we describe a novel three-dimensional spectral boundary element algorithm for interfacial dynamics in Stokes flow and/or gravity. The main attraction of this approach is that it exploits all the benefits of the spectral methods (i.e., exponential convergence and numerical stability) with the versatility of the finite element method. In addition, it is not affected by the disadvantage of the spectral methods used in volume discretization to create denser systems. Our algorithm also exploits all the benefits of the boundary element techniques, i.e., a reduction of the problem dimensionality and great parallel scalability. To achieve continuity of the interfacial geometry and its derivatives at the edges of the spectral elements during the droplet deformation, a suitable interfacial smoothing is developed based on a Hermitian-like interpolation. An adaptive mesh reconstructing procedure based on the relevant lengths of the spectral elements is also described. In addition, we consider the inertialess motion of a buoyant droplet left to rise (or sediment) near a vertical solid wall and compare our numerical results with analytical predictions. In our study we emphasize the need for computational studies for the accurate determination of droplet migration near solid walls. [ABSTRACT FROM AUTHOR]

Bubble evolution from photo(electro)catalytic water splitting plays a vital role in the interfacial mass transport on photocatalyst surface. However, little success has been achieved to optimize this process, restricted by the poor understanding. Herein, taking photoelectrochemical (PEC) water splitting over a titanium dioxide (TiO 2 ) nanorod-array electrode as a model system, experiments were performed to study single oxygen bubble dynamics by combining electrochemical measurement and high-speed microscopic imaging. The experimental results indicate that the departure of bubble from photoelectrode is retarded by light irradiation, but the traditional bubble departure criterions fail to predict the bubble departure diameters especially in high light intensity. Additional analysis reveals that the light irradiation causes the Marangoni force acting on the evolving bubble, because it induces temperature rise and generates dissolved gas. A modified force balance model for bubble departure from photoelectrode was developed by adding Marangoni force. This modified model that takes account of the light-induced temperature rise and the dissolved gas, agrees well with the experimental data and can be extended to other photo(electro)catalytic reactions. [ABSTRACT FROM AUTHOR]

• An expression for single bubble coverage on the photoelectrode surface is proposed. • The mass transfer is dominated by single-phase free convection in low current density. • The mass transfer coefficient peaks in the inertia-controlled bubble growth phase. • Periodic illumination accelerates bubble detachment and enhances mass transfer. The limitation of the transfer of gas products within the photocatalytic system is the key to the efficiency of the water splitting, which is directly influenced by the bubble evolution process on the catalyst surface. In this study, the entire process of bubble evolution on the surface of a superhydrophilic TiO 2 photoelectrode was simultaneously measured visually and electrochemically. The bubble growth and detachment characteristics were investigated under different laser powers and constant bias voltages. An expression for the bubble coverage characterized by the bubble radius and photocurrent, which is applicable to the photoelectrocatalytic water splitting, was proposed to accurately obtain the mass transfer coefficient during bubble evolution. The mass transfer mechanism of gas product transfer in the low current density range dominated by single-phase free convection was revealed. The mass transfer coefficient was found to increase in the inertia-controlled phase and decrease in the chemical reaction-controlled phase of bubble growth. Furthermore, a method to accelerate bubble detachment from the photoelectrode surface by periodic illumination was proposed, which could significantly enhance the gas product transfer process. [Display omitted] [ABSTRACT FROM AUTHOR]