Carbon-based materials for electrocatalytic energy conversion: from understanding to designing

Renewable energy technologies are crucial for alleviating the energy crisis and pollution, electrocatalytic reactions such as ORR, HER and OER are prospective energy conversion pathways. Although metal-based electrocatalysts are currently employed in electrochemical reactions, they encounter a series of issues of supply and price. Therefore, the development of new environmentally friendly, efficient, and low-cost electrochemical catalysts is imminent. Carbon-based materials such as amorphous carbons and nanostructured carbons have drawn extensive attention in electrocatalysis research due to their cost-effectiveness, environmental friendliness, and stability in acid and alkali media. In the initial stage, the heteroatoms embedded in the carbon skeleton (such as N, P, S, and B) were identified as active sites of carbon-based electrocatalysts. Subsequently, further investigations revealed that structural defects in carbon rings can disrupt the electronic conjugation system, which in turn affects the charge distribution and thereby enhance catalytic activity. Recently, our group has proposed a novel mechanism of defective carbon-based materials for electrochemical reactions, suggesting that the introduction of topological defects can boost electrocatalytic activity. Subsequently, extensive research has been carried out with direct evidence to prove different defects as active sites. Herein, we will emphasize the advancement of carbon-based electrocatalysts by a comprehensive understanding of catalyzing mechanisms. Then, the methodologies for controllably synthesizing doped carbons and carbons with defective structures will be summarized. Ultimately, we will outline the key challenges in designing intricate carbon active sites, particularly defect structures, provide insights into characterization techniques for investigating mechanisms, and importantly, look forward to future developments and opportunities.