Lattice distortion and morphology modulation enhanced piezocatalytic activity of Ca-doped Sr2Nb2O7 towards H2O2 production and piezo-self-Fenton degradation

Piezocatalysis is emerging as a powerful mechanochemical approach in environmental and sustainable chemical processes. However, the efficiency of a piezocatalyst remains low and there is an opportunity to design and produce high performance catalysts systems. Here we show that Ca²⁺ doped Sr₂Nb₂O₇ performs over 4-fold better than pure Sr₂Nb₂O₇ in producing H₂O₂ (168 μmol·g⁻¹·h⁻¹) from water through the indirect oxygen reduction reaction (ORR) pathway. This improvement is attributed to enhanced piezoelectric response and optimized charge carrier dynamics in the doped system as verified by the PFM results, finite element simulation and electrochemical characterizations. Combining XRD refinement, Raman spectral analysis and DFT calculations, the enhanced piezoelectric response was mainly attributed to the lattice rotational distortions within Nb-O octahedron arising from Ca²⁺ substitution at the A-site of the perovskite structure. In addition, a morphological transition from three-dimensional nanocubes to two-dimensional nanosheets was also induced by the doping. This morphology evolution not only endowed Ca_0.8Sr_1.2Nb₂O₇ with large surface area and abundant reactive sites, but also enhanced its strain-responsive behavior under applied stress and facilitated charge transport. Furthermore, a H₂O₂ self-supplied piezo- Fenton system was successfully established to degrade organic dye pollution RhB through the introduction of trace Fe²⁺, and it showed over 100 % increase in the degradation rate compared to that without Fe²⁺. It was believed the introduced Fe²⁺ effectively activate the in-situ generated H₂O₂, giving rising to the mass generation of highly oxidative ·OH which prompted degradation. We anticipate that this study will pave the way for further investigation of controlled lattice distortion and morphology engineering leading to high performance piezocatalysts.