Active sites and mass/charge transport engineering in carbon-based catalysts for electrochemical CO₂ reduction reaction

The electrochemical CO₂ reduction reaction (CO₂RR) offers a dual benefit: closing the carbon cycle, while simultaneously storing renewable energy in chemical bonds. Carbon-based catalytic materials, as exceptional electrocatalysts, exhibit excellent conductivity, robust stability, tunable surface functionality, and unique capability to construct metal–carbon synergistic interfaces. In CO₂RR, carbon-based catalytic materials stand out duple critical functions among series roles: (i) active site engineering governing intrinsic activity, and (ii) mass/charge transport dictating effective active sites utilization. Synergistic optimization of these elements constitutes the “catalytic activity-transport kinetics” binary model for performance enhancement. This review dissects active sites design via defect engineering, heteroatom doping, and metal-carbon composites, coupled with mass/charge transport engineering through electronic conductivity modulation, surface hydrophobicity control, and hierarchical porosity optimization. We further critically examined the challenges and opportunities in CO₂RR, with a focus on the integrated design bottlenecks constraining high-performance catalyst development. By integrating these dual engineering paradigms, structure–performance correlations were established to guide the rational design of carbon-based CO₂RR catalysts.