Vibration Promotes Mass Transfer of Products in Photoelectrochemical Water Splitting by Enhancing Forced Convection

Abstract

Improving the productivity of photoelectrochemical water splitting hinges on discovering a viable method to facilitate bubble release from the surface of the photoelectrode, which, in turn, enhances the mass transfer of the resulting products. In this study, an experimental platform for photoelectrochemical water splitting to produce hydrogen by a coupled vibration system was built to realize the visualization of bubble behavior. By applying vibration to the electrode through a vibration exciter, this work explored how amplitude and frequency affect the photocurrent and geometric parameters during the bubble evolution process on the photoelectrode surface. Based on the expression of bubble coverage and gas evolution efficiency, mass transfer coefficients of gas products were deduced and calculated. The results showed that the increase in amplitude will increase the onset potential of nucleation, reducing the possibility of nucleation. Increasing the amplitude and frequency helps to release the bubbles from the electrode surface. For stationary electrodes, the mass transfer of gas products mainly depends on single-phase natural microconvection. For the vibrating electrode, macroscopic forced convection plays a dominant role. In this experiment, the average total mass transfer coefficient after applying vibration to the electrode can reach 11.16 × 10^–5 m/s, which is about 7.6 times the mass transfer coefficient under static conditions. Therefore, vibration can significantly improve the reaction efficiency and mass transfer during the water splitting process for hydrogen generation.