Visualization of bubble dynamic behaviors during photoelectrochemical water splitting with TiO2 photoelectrode

Unveiling micro- and nanoscale bubble dynamics for enhanced electrochemical water splitting

Bubbles generated during electrochemical and photoelectrochemical water splitting critically influence efficiency through complex factors, including chemical reactions, species transport, mass transfer at the three-phase interface, and bubble coverage. A detailed understanding of the nucleation, growth, coalescence, and detachment of micro- and nanoscale bubbles is vital for advancing water splitting technologies. Surface-attached bubbles significantly reduce the electrocatalytically active area of electrodes, leading to increased surface overpotential at a given current density. Consequently, their effective removal is pivotal for optimizing the electrolysis process. However, the intricate interplay among single bubble evolution, mass transport, bubble coverage, and overpotential remain inadequately understood. This review explores the fundamental mechanisms underpinning bubble evolution, with an emphasis on the Marangoni effect and its influence on bubble dynamics. Furthermore, recent advancements in understanding individual bubbles on micro and nano-electrodes are highlighted, offering valuable insights into scale-dependent bubble behavior. These findings enrich our knowledge of gas-liquid interfacial phenomena and underscore their industrial significance, presenting opportunities to enhance water splitting performance through optimized bubble dynamics.

Assessing elevated pressure impact on photoelectrochemical water splitting via multiphysics modeling

Photoelectrochemical (PEC) water splitting is a promising approach for sustainable hydrogen production. Previous studies have focused on devices operated at atmospheric pressure, although most applications require hydrogen delivered at elevated pressure. Here, we address this critical gap by investigating the implications of operating PEC water splitting directly at elevated pressure. We evaluate the benefits and penalties associated with elevated pressure operation by developing a multiphysics model that incorporates empirical data and direct experimental observations. Our analysis reveals that the operating pressure influences bubble characteristics, product gas crossover, bubble-induced optical losses, and concentration overpotential, which are crucial for the overall device performance. We identify an optimum pressure range of 6-8 bar for minimizing losses and achieving efficient PEC water splitting. This finding provides valuable insights for the design and practical implementation of PEC water splitting devices, and the approach can be extended to other gas-producing (photo)electrochemical systems. Overall, our study demonstrates the importance of elevated pressure in PEC water splitting, enhancing the efficiency and applicability of green hydrogen generation.

Tandem cells for unbiased photoelectrochemical water splitting

Hydrogen is an essential energy carrier which will address the challenges posed by the energy crisis and climate change. Photoelectrochemical water splitting (PEC) is an important method for producing solar-powered hydrogen. The PEC tandem configuration harnesses sunlight as the exclusive energy source to drive both the hydrogen (HER) and oxygen evolution reactions (OER), simultaneously. Therefore, PEC tandem cells have been developed and gained tremendous interest in recent decades. This review describes the current status of the development of tandem cells for unbiased photoelectrochemical water splitting. The basic principles and prerequisites for constructing PEC tandem cells are introduced first. We then review various single photoelectrodes for use in water reduction or oxidation, and highlight the current state-of-the-art discoveries. Second, a close look into recent developments of PEC tandem cells in water splitting is provided. Finally, a perspective on the key challenges and prospects for the development of tandem cells for unbiased PEC water splitting are given.