Recent progress in bubble dynamics and detachment mechanisms of photocatalytic water splitting microreactors for H₂ production: a review

Research on bubble dynamics is essential for enhancing the efficiency of photocatalytic water splitting for hydrogen production. This review systematically summarizes recent progress in this field from three complementary perspectives: bubble nucleation and growth, experimental and numerical research methodologies, and strategies for promoting bubble detachment. This work reconstructs bubble detachment strategies within a unified mechanical framework and offers a focused synthesis of bubble characteristics in confined microreactor environments. Bubble nucleation is predominantly concentration-driven and strongly coupled with catalyst surface structures; it can be effectively promoted through rational surface engineering or the introduction of surfactants. Bubble growth is governed by three distinct control regimes: inertial control, diffusion control, and chemical-reaction control. Experimentally, researches largely relies on combined electrochemical and optical diagnostics, yet high spatiotemporal resolution remains restricted by existing technical limitations. From a numerical perspective, molecular dynamics simulations are effective for probing nucleation mechanisms, while phase-field, level-set, and volume-of-fluid methods excel in simulating bubble growth and detachment. Based on a comprehensive multi-force equilibrium model, bubble detachment strategies are classified into three categories: surface-tension reduction, buoyancy enhancement, and force-balance disruption induced by external fields, with the underlying mechanisms systematically elucidated. Owing to pronounced microscale effects, bubble removal in microreactors is considerably more challenging than in conventional reactors, for which ultrasonic and gravitational fields have been demonstrated to be particularly effective regulation strategies. Overall, this review provides critical theoretical insights and technical guidance for optimizing bubble management and alleviating mass-transfer limitations in photocatalytic microreactor systems.