Defect-engineered Ru-decorated Al-doped ZnO nanorod arrays for enhanced interfacial charge transfer

High-performance nanostructured electrodes requiring large surface areas and low resistance are vital for advanced optoelectronic and electrochemical applications. Here, we report the synthesis of vertically aligned Al-doped ZnO (AZO) nanorod arrays as a versatile conductive scaffold. By modulating the zinc-amine complex equilibrium and Al precursor concentration during hydrothermal growth, we precisely controlled the nanorods’ aspect ratio and packing density. Structural and chemical analyses revealed that ∼1 at% Al substitutes Zn²⁺ sites in the wurtzite lattice and generates oxygen vacancies (Vo), confirmed by O 1s XPS. This synergistic dual-donor mechanism drastically reduces sheet resistance to ∼10² Ω/sq without structural collapse. Importantly, we identified a critical trade-off between this bulk conductivity and the necessary porosity for electrolyte mass transport. To evaluate interfacial charge transport, the AZO arrays were surface-functionalized with Ruthenium (Ru), forming a 3D Ru-decorated nanorod architecture. In a liquid-redox model system (dye-sensitized solar cells), electrochemical impedance analysis confirmed that the highly conductive AZO core and catalytic Ru shell synergistically minimized interfacial charge transfer resistance, achieving highly competitive performance compared to standard platinum electrodes. This work establishes the AZO nanorod array as a versatile and highly tailorable electrode platform demonstrating superior interfacial kinetics for diverse applications ranging from sensors to electrocatalysis.