Single-atom rhodium on BaTiO₃ for enhanced piezocatalytic H₂O₂ production via promotion of oxidative ability

Piezocatalysis is a promising method for generating green hydrogen peroxide (H₂O₂), however, improving the surface charge transfer kinetics remains challenging. In this study, we develop tetragonal barium titanate (BTO) nanoparticles modified with surface-anchored rhodium single-atom (RhSA) cocatalysts. Detailed structural characterization confirmed that the Rh species are atomically dispersed as Rh³⁺ coordinated with surface oxygen of BTO without forming clusters or being incorporated into the BTO lattice. Piezoresponse force microscopy revealed that RhSA does not affect the intrinsic piezoelectric polarization of the BTO. However, the BTO-RhSA catalyst produced 1.5 times more H₂O₂ than pristine BTO did under ultrasonic excitation. Mechanistic studies using (piezo)electrochemical measurements demonstrated that unlike conventional noble metal cocatalysts, which typically enhance the reduction kinetics, the RhSA sites on BTO do not promote the oxygen reduction reaction (ORR). Instead, they significantly accelerate the oxidation of isopropanol as a sacrificial reagent by efficiently utilizing the piezo-generated positive charges. This work establishes a surface-engineering strategy in which isolated atomic sites selectively boost positive charge-driven reactions, enabling the independent control of reduction and oxidation pathways and providing new design principles for high-performance piezocatalytic systems.