Boosting Piezoelectric Catalytic Ammonia Synthesis: A Synergistic Approach with Sulfur Vacancy Engineered CdS Pyramid-Surface Nanospheres

The nitrogen reduction reaction (NRR) is essential for sustainable ammonia synthesis but suffers from low selectivity and sluggish kinetics due to hydrogen evolution. Piezocatalysis offers a promising alternative by leveraging strain-induced polarization to enhance reaction specificity and efficiency. We develop a sulfur vacancy-engineered cadmium sulfide (CdS) piezoelectric catalytic system to optimize nitrogen activation. Sulfur vacancies improve nitrogen adsorption, enhance charge separation, and lower the hydrogenation energy barrier, overcoming limitations of traditional electrocatalysts. Through a systematic investigation of charge separation mechanisms, combining theoretical calculations and experimental validation, we demonstrate the crucial role of sulfur vacancies and surface morphology in optimizing catalytic performance. Finite element method (FEM) simulations reveal that the pyramid-like CdS surface generates a strong piezopotential under mechanical stress, enhancing charge transfer and redox reactions. Density functional theory (DFT) calculations show sulfur vacancies increase electron availability near the Fermi level, facilitating dinitrogen activation and stabilizing intermediates. Therefore, the optimized CdS catalyst achieves an ammonia production rate of 1702 µg g^-1 h^-1—four times higher than pristine CdS—demonstrating the effectiveness of defect engineering in piezoelectric catalysis. This study highlights the synergy between piezoelectric activation and defect engineering, offering insights into charge separation and advancing piezoelectric catalysis for sustainable ammonia synthesis.