• Defect engineering creates asymmetric active sites in carbon materials, significantly enhancing electrocatalytic activity for CO2 reduction.
• The review systematically categorizes defect types, formation methods, and characterization techniques, offering a comprehensive framework for material design.
• Defective carbon-based catalysts offer a low-cost, stable alternative to metal-based catalysts, with potential for scalable industrial application.
• Key challenges include precise control of defect density and type, and the need for advanced in-situ characterization to correlate defects with performance.