Engineering strategies to minimize bubble-induced optical losses in photoelectrochemical water splitting

• Bubble formation in PEC water splitting and the associated loss are investigated. • Quantitative correlation with key bubble characteristics is provided. • Operation at elevated pressure suppresses the bubble-induced optical loss. • Lower buffer concentration reduces bubble number, increases size, and reduce loss. Gas bubble evolution presents a significant challenge to achieving efficient solar water splitting by blocking catalytic active sites, increasing electrolyte ohmic resistance, and scattering incident solar photons. The bubble-induced optical loss is especially important in photoelectrochemical (PEC) cells, as specific cell configurations require light to travel through the electrolyte before reaching the photoelectrodes. Understanding bubble characteristics under various operating conditions and the associated bubble-induced optical losses is essential to optimize the PEC water splitting efficiency. In this study, we use optical measurements and bubble shadowgraphy to demonstrate that operating PEC water splitting systems at elevated pressure (up to 4 bar) reduces bubble-induced optical losses by a factor of four, with only a minimal (∼1%) increase in thermodynamic cell voltage. In addition, lowering the electrolyte buffer concentration further mitigates the bubble-induced optical losses, albeit at the cost of increased overpotential due to higher ohmic resistance and increased adhesion of the larger bubbles. These quantitative results provide valuable insights into the design and practical implementation of PEC water splitting cells, and the approach can be extended to other gas-evolving photoelectrochemical conversion systems.