A recent study published in Advanced Science introduces a novel catalytic approach known as flexocatalysis, which uses mechanical strain to induce electric polarization and drive chemical reactions.
The research focuses on nanoscale strontium titanate (SrTiO₃, or STO), a centrosymmetric perovskite oxide, and demonstrates its dual ability to catalyze hydrogen production and degrade organic pollutants under ultrasonic vibration. The findings point toward new, greener strategies for both clean energy generation and environmental cleanup.
Image Credit: Borri_Studio/Shutterstock.com
Background
This work centers on the flexoelectric effect—the generation of electric polarization in dielectric materials when subjected to a strain gradient. While typically weak in bulk materials, this effect becomes much more pronounced at the nanoscale due to the high strain gradients achievable in tiny structures.
Previous studies in piezocatalysis, which rely on the piezoelectric properties of non-centrosymmetric materials like BaTiO₃ or ZnO, have shown that mechanical energy can be converted into catalytic activity. However, piezocatalysis requires inherent piezoelectricity, limiting usable materials to those with specific symmetry properties.
Flexocatalysis, by contrast, operates through the flexoelectric effect, which is not bound by symmetry constraints. This expands the range of viable catalysts to include centrosymmetric materials like SrTiO₃. At the nanoscale, STO can generate internal electric fields strong enough to drive reactions like water splitting or organic degradation, despite lacking intrinsic piezoelectricity.
The Current Study
Researchers took a comprehensive experimental approach to assess the flexocatalytic potential of nano SrTiO₃. High-purity STO powder (99.5 %) underwent heat treatments at 1000 °C for 3 and 24 hours to modify particle sizes.
Structural integrity and phase composition were confirmed via X-ray diffraction (XRD) and Rietveld refinement, while transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) provided detailed images of particle morphology and size.
Surface characteristics were evaluated through Brunauer–Emmett–Teller (BET) surface area measurements, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Ultraviolet photoelectron spectroscopy (UPS) and UV-Vis spectroscopy were used to determine the materials’ electronic properties and band gaps.
Catalytic performance was tested by applying ultrasonic vibration, which induces strain gradients in the nanoparticles. For hydrogen production, STO was dispersed in water, and hydrogen evolution was measured in real time using standard gas quantification techniques. For organic degradation, Rhodamine B (RhB) was a model pollutant to monitor dye breakdown under the same ultrasonic conditions.
To better understand the underlying mechanisms, COMSOL Multiphysics simulations modeled how applied forces generate flexoelectric polarization within the nanoparticles.
Results and Discussion
In hydrogen evolution experiments, the smallest STO particles (untreated STO) produced hydrogen at an impressive rate of 1289.53 μmol/g/h after 4 hours under ultrasonic vibration.
This strong output, combined with the catalyst’s recyclability and structural stability, highlights the practical potential of the flexocatalytic approach. Reducing the particle size from 117 nm to 35 nm led to a 3.32-fold increase in hydrogen production, directly aligning with theoretical predictions that flexoelectric effects intensify as particle size decreases.
For organic degradation, nano STO degraded approximately 94 % of RhB within 3 hours, outperforming larger or heat-treated samples. This efficiency is linked to the formation of reactive oxygen species (ROS), such as hydroxyl radicals (∙OH) and superoxide ions (∙O₂⁻), which are generated through charge separation triggered by flexoelectric polarization.
The chemical pathways involved were detailed through reaction equations provided in the study, clarifying how this process breaks down pollutants.
Post-reaction analyses using XRD showed minimal structural changes in the STO, suggesting excellent durability and resistance to degradation. Slight shifts in diffraction peaks were noted, likely due to lattice relaxation from surface interactions during the reaction, but these did not compromise the catalyst’s overall stability.
Download your PDF copy now!
Conclusion
This study demonstrates that flexocatalysis can be a practical and environmentally conscious method for hydrogen production and organic pollutant degradation, offering an alternative to conventional piezocatalytic systems that rely on non-centrosymmetric materials.
The consistent performance and structural stability of nano SrTiO₃, even after repeated cycles, highlight its suitability for potential use in catalytic applications related to energy and environmental management.
By utilizing the flexoelectric effect in centrosymmetric materials, the work broadens the scope of materials that can be considered for mechanically driven catalysis. It also contributes to a deeper understanding of electromechanical behavior at the nanoscale, supporting further research into adaptable and efficient catalytic systems.
Journal Reference
Mondal, S., Das, R. C., Du, Y., Hou, Z., Konstantinov, K., Cheng, Z. (2025). Flexocatalytic Hydrogen Generation and Organics Degradation by Nano SrTiO₃. Advanced Science, 2025, DOI: 10.1002/advs.202500034, https://advanced.onlinelibrary.wiley.com/doi/10.1002/advs.202500034