Design of piezoelectric ZnO based catalysts for ammonia production from N₂ and H₂O under ultrasound sonication

Using mechanical waste energy to drive the ammonia production from N₂ and water under ambient conditions is of great significance yet still very challenging. In this work, we designed ZnO microrods and ZnO-Ag heterostructures that exhibited high activity, selectivity, and stability in the production of ammonia under ultrasound sonication. Combining the piezoelectric force microscopy (PFM), temperature programed desorption of N₂ (N₂-TPD), electron spin resonance (ESR), electrochemical analysis with finite element numerical simulation, we found that the size and morphology of ZnO greatly impacted the shape deformation as well as the piezoelectric potential across the material, while the oxygen vacancies were essential for the adsorption and activation of N₂. Loading Ag NPs onto ZnO could further enhance the N₂ fixation activity by generating local strain at the Ag-ZnO interface, enhancing the chemical adsorption of N₂, and facilitating the separation of piezo-generated electrons and holes. Our work demonstrates the design principles of highly active piezoelectric catalysts for N₂ fixation.