Sculpting with Light: Precise Nanoscale Positioning of Rh ₂ O ₃ Co-Catalyst for Solar-To-Fuel Photocatalysis

Precise placement of robust oxide cocatalysts on semiconductor nanostructures remains a bottleneck in designing durable photocatalysts. Here, we unveil a purely photochemical route that directs the nucleation of orthorhombic-phase Rh2O3 to a single domain on CdSe@CdS photocatalytic nanorods with over 85% fidelity. Three easily tuned levers govern the outcome–alkaline pH, excitation wavelength and the presence or absence of sodium persulfate (Na2S2O8) as a sacrificial electron acceptor/oxidant. Together they concentrate photogenerated holes at the CdSe seed, suppress rod-wide •OH chemistry and yield deterministic single-domain growth; flipping any one parameter reopens undesired multidomain nucleation. Time-resolved photoluminescence and XPS confirm that hole localization, rather than precursor type or concentration, triggers the switch. Beyond furnishing a synthetically simple “dial-in” recipe, this work maps the mechanistic landscape for coupling stable oxidation sites to photoactive semiconductors, charting a path toward efficient water-splitting architectures and other nanoscale redox systems.