A critical review on the role of structural defects in electrochemical nitrate reduction catalysts: From mechanisms to formation strategies

The electrochemical nitrate reduction reaction (e-NO 3 RR) offers a sustainable pathway for simultaneously mitigating nitrate pollution and valorizing nitrate into high-value nitrogen-based compounds. However, the reaction involves sluggish multistep proton–electron transfer processes and suffers from competing pathways that yield undesired byproducts. Engineering structural defects has emerged as a powerful and versatile strategy to enhance the catalytic performance of e-NO 3 RR. Despite significant progress, a comprehensive mechanistic understanding of defect formation, evolution, and their influence on catalytic behavior remains incomplete. This review provides an integrative and critical overview of recent advances in defect engineering for e-NO 3 RR electrocatalysts, highlighting how diverse defect classes reconfigure the electronic structure, modulate surface chemistry, and steer reaction pathways toward improved activity and selectivity. Furthermore, strategies for defect creation and regulation, along with state-of-the-art characterization techniques that afford real-time mechanistic insights, are systematically examined. Finally, key challenges, including precise defect control, stability under operating conditions, and scalability, are discussed, and future research directions are proposed to guide the rational design of defect-derived materials for efficient and sustainable nitrate electroreduction.