Ultrasound-Driven Defect Engineering in TiO2-x Nanotubes─Toward Highly Efficient Platinum Single Atom-Enhanced Photocatalytic Water Splitting

Single-atom catalysts(SACs) have demonstrated superior catalyticactivity and selectivity compared to nanoparticle catalysts due totheir high reactivity and atom efficiency. However, stabilizing SACswithin hosting substrates and their controllable loading preventingsingle atom clustering remain the key challenges in this field. Moreover,the direct comparison of (co-) catalytic effect of single atoms vsnanoparticles is still highly challenging. Here, we present a novelultrasound-driven strategy for stabilizing Pt single-atomic sitesover highly ordered TiO2 nanotubes. This controllable low-temperaturedefect engineering enables entrapment of platinum single atoms andcontrolling their content through the reaction time of consequentchemical impregnation. The novel methodology enables achieving nearly50 times higher normalized hydrogen evolution compared to pristinetitania nanotubes. Moreover, the developed procedure allows the decorationof titania also with ultrasmall nanoparticles through a longer impregnationtime of the substrate in a very dilute hexachloroplatinic acid solution.The comparison shows a 10 times higher normalized hydrogen productionof platinum single atoms compared to nanoparticles. The mechanisticstudy shows that the novel approach creates homogeneously distributeddefects, such as oxygen vacancies and Ti3+ species, whicheffectively trap and stabilize Pt2+ and Pt4+ single atoms. The optimized platinum single-atom photocatalyst showsexcellent performance of photocatalytic water splitting and hydrogenevolution under one sun solar-simulated light, with TOF values beingone order of magnitude higher compared to those of traditional thermalreduction-based methods. The single-atom engineering based on thecreation of ultrasound-triggered chemical traps provides a pathwayfor controllable assembling stable and highly active single-atomicsite catalysts on metal oxide support layers.