Effect of Surfactant Concentration on the Behavior of Single Oxygen Bubble in Photoelectrochemical Water Splitting

The control of bubble growth and departure during the process of photoelectrochemical water splitting is crucial for enhancing gas production efficiency. By introducing varying concentrations of surfactants into the electrolyte and using a synchronous measurement system, we examined how the change in surfactant concentration affects bubble nucleation and growth characteristics. The results indicate that bubbles’ critical nucleation potentials initially decrease and subsequently increase with increasing surfactant concentration, reaching a minimum value when the concentration is 1 × 10^-7 M. In contrast, bubble growth periods and departure diameters reach their maximum values. Further analysis shows that the gas production rate and the average gas evolution efficiency reach their maximum when the surfactant concentration is 1 × 10^-7 M, indicating that adding an appropriate amount of surfactant is advantageous for gas production. In addition, a force equilibrium model incorporating the Marangoni force at various surfactant concentrations was developed to predict oxygen bubbles’ departure diameter. The predicted values exhibit excellent concurrence with the experimental data. The solutal Marangoni force is the primary determinant that affects bubble departure diameter when the surfactant concentrations are below approximately 4 × 10^-6 M, while the thermal Marangoni force assumes precedence when concentrations exceed about 4 × 10^-6 M.