Defect engineering on electrocatalysts for sustainable nitrate reduction to ammonia: Fundamentals and regulations

Electrocatalytic nitrate (NO₃ ^-) reduction to ammonia (NH₃) is a "two birds-one stone" method that targets remediation of NO₃ ^--containing sewage and production of valuable NH₃. The exploitation of advanced catalysts with high activity, selectivity, and durability is a key issue for the efficient catalytic performance. Among various strategies for catalyst design, defect engineering has gained increasing attention due to its ability to modulate the electronic properties of electrocatalysts and optimize the adsorption energy of reactive species, thereby enhancing the catalytic performance. Despite previous progress, there remains a lack of mechanistic insights into the regulation of catalyst defects for NO₃ ^- reduction. Herein, this review presents insightful understanding of defect engineering for NO₃ ^- reduction, covering its background, definition, classification, construction, and underlying mechanisms. Moreover, the relationships between regulation of catalyst defects and their catalytic activities are illustrated by investigating the properties of electrocatalysts through the analysis of electronic band structure, charge density distribution, and controllable adsorption energy. Furthermore, challenges and perspectives for future development of defects in NO₃RR are also discussed, which can help researchers to better understand the defect engineering in catalysts, and also inspire scientists entering into this promising field.