Tuning Surface Chemistry in 2D Layered BiOI by Facile Liquid-Phase Exfoliation for Enhanced Photoelectrocatalytic Oxygen Evolution

BiOI is a promising photoelectrocatalyst for oxidation reactions. However, the limited photoelectrocatalytic (PEC) activity necessitates the development of new strategies to modify its surface chemistry and thus enhance functional properties. Herein, we present a simple method to increase photocurrent in a BiOI-based photoanode by exfoliating microspheres of the oxyhalide produced through hydrothermal synthesis. Following exfoliation in isopropanol, the resulting layered BiOI-based colloid contains a greater variety of species, including Bi₂O₂CO₃, I₃⁻, IO₃⁻, Bi⁵⁺, and hydroxides, compared to the original BiOI. These additional species do not directly enhance the PEC oxygen evolution reaction (OER) performance. Instead, they are consumed or converted during PEC OER, resulting in more active sites on the photoelectrode and reduced resistance, which ultimately improves the water oxidation performance of the exfoliated BiOI. Over long-term chronoamperometry, the exfoliated BiOI demonstrates a photocurrent twice as high as that of the BiOI microspheres. Analysis of the species after PEC OER reveals that the combination of IO₃⁻, Bi⁵⁺, and I₃⁻ species on the BiOI is beneficial for charge transfer, thus enhancing the intrinsic PEC properties of the BiOI. This study offers new insights into the role of surface chemistry in determining PEC performance, aiding the optimization of 2D materials-based photoelectrocatalysts.