Continuous and Scalable Laser Synthesis of Atom Clusters with Tunable Surface Oxidation for Electrocatalytic Water Splitting

The laser-based synthesis of colloidal nanoparticles consists of several established methods to produce high-purity, active, and durable metal and oxide catalysts. Among them, only laser fragmentation in a liquid jet produces monodisperse, sub-5 nm nanoparticles in a fully continuous operation. However, the nanoparticle yield and laser power-specific productivity are still below the established gram-scale laser ablation method. In addition, little is known about how the initial particle size, oxidation, and the number of laser pulses affect the generated particle size and oxidation state, especially when using commercial microparticles. In this work, we address these shortcomings with the example of iridium as an important benchmark catalyst for the acidic oxygen evolution reaction. Starting from iridium microparticles, a significant improvement in the laser power-specific productivity of nanoparticles was observed when the initial particle concentrations were increased to several grams per liter. The number of applied laser pulses controls the degree of nanoparticles' surface oxidation, as shown by XPS measurements and DFT calculations, while the monodisperse ∼2 nm product particle diameter was unaffected by the initial particle size and concentration, highlighting the process robustness. Additionally, the particles exhibit a benchmark level of catalytic activity with the lowest overpotential of 0.33 V vs RHE @ 10 mA/cm 2 . To summarize, the continuous laser fragmentation of microparticles in water has great potential in the green synthesis of ultrasmall catalysts.