Defect chemistry in electrocatalysis: mechanistic insights and design principles for sustainable energy conversion and environmental remediation

The dual imperatives of carbon-neutral chemical manufacturing and advanced wastewater remediation require high-performance electrocatalysts capable of orchestrating complex, multi-electron reactions. However, pristine catalyst lattices are fundamentally bottlenecked by linear scaling relations. This critical review establishes defect engineering as the definitive strategy for bypassing these thermodynamic limitations, offering a unified mechanistic framework that bridges sustainable energy conversion and environmental remediation. Moving beyond empirical material catalogues, this work systematically interrogates how localized structural imperfections—vacancies, dopants, and synergistic interfaces—act as precision atomic-scale electronic regulators. By modulating the transition-metal d-band center and triggering spatial charge redistribution, defects successfully decouple intermediate binding energies to steer reaction pathways thermodynamically. A comprehensive analysis elucidates the electronic origins of defect-mediated performance across green ammonia synthesis (nitrogen and nitrate reduction) and advanced wastewater treatment (electro-Fenton, targeted non-radical persulfate activation, and priority pollutant electroreduction). Furthermore, this review challenges the pervasive assumption of static active sites, emphasizing how operando interrogation reveals the highly dynamic, transient nature of defect architectures under applied electrochemical bias. Finally, the frontier of artificial intelligence-guided discovery and multi-defect synergy is highlighted, charting a translational roadmap from atomic-level precision to robust industrial reactor integration. Ultimately, this review elevates defect electrocatalysis from a purely descriptive phenomenon into a predictive, quantitatively guided design discipline essential for achieving closed-loop global sustainability.