Coalescence and detachment of double bubbles on electrode surface in photoelectrochemical water splitting

Abstract

Bubble evolution plays a vital role in the photoelectrochemical (PEC) water-splitting process. However, quantitatively relating nucleation site distribution to bubble dynamics and reaction current remains elusive. Here, we investigate the coalescence and detachment processes of double bubbles with different nucleation site spacing (S) using electrochemical measurements and high-speed microscopic imaging. The study reveals three types of detachment mode: the periodic buoyancy-driven detachment mode, the transition mode, and the periodic coalescence-driven detachment mode. These modes are influenced by the coalescence process, which alters the S and results in changes to the bubble detachment radius and detachment frequency. Meanwhile, significant differences in the average reaction current can be obtained by changing S at the same potential. This study elucidates the fundamental relationship between bubble coalescence and detachment characteristics, which provides guidance for optimal design of the electrode morphology in a PEC water-splitting system.