Numerical simulation

The numerical simulation was performed using the transport of diluted species module of the COMSOL Multiphysics software. For the simulation, the cross-section of the MXene-derived Pt/TiO₂ microrobots was considered. To emulate the MXene structure, the TiO₂ microparticles were designed as 10 rectangles with a size of 100 nm × 2 μm and inter-distance of 100 nm, placed inside an 8 × 4 μm² rectangle. Pt deposition can occur on the multi-layered side or the flat side of the TiO₂ microparticles. Pt deposition on the multi-layered side was designed using 100 × 50 nm² rectangles attached to the TiO₂ rectangles on their left side. Pt deposition on the flat side was designed using a 50 nm × 2 μm rectangle attached to the last TiO₂ rectangle on the right. The H₂ generation at the interface between Pt and water due to the photogenerated electron-hole pairs in TiO₂ was simulated by choosing water/Pt boundaries as the generation ones. To calculate H₂ diffusion for 0.1 s light irradiation, an H₂ diffusion coefficient in water at 25 °C of 5.11 × 10⁻⁹ m² s⁻¹ was used, while the photogeneration rate was set to 1 mmol m⁻² s⁻¹.