4-6 carbophene: A two-dimensional carbon material with Dirac cone and superior activity for electrochemical oxygen reduction reactions

The positive exploration of efficient and cost-effective electrocatalysts for the oxygen reduction reaction (ORR) is crucial for the sustainable development of energy conversion and storage technologies. Recently, a new type of two-dimensional (2D) carbon crystals, called 4-6 carbophene, has been successfully synthesized. It consists of a four-carbon ring and a six-carbon ring. In this work, we have discovered that 4-6 carbophene is a twodimensional Dirac cone material through density-functional theory (DFT) calculations. Therefore, we further investigated the oxygen reduction reaction on 4-6 carbophene to understand its catalytic properties. The results demonstrate that on 4-6 carbophene, the ORR prefers a direct four-electron pathway. Under acidic conditions, the ORR overpotential of 4-6 carbophene is as low as 0.59 V, which is comparable to some metal benchmark catalysts, demonstrating that 4-6 carbophene is a metal-free ORR candidate catalyst. In addition, the richly charged carbon atoms on 4-6 carbophene exhibit remarkable charge transfer when binding to the adsorbed intermediates. This results in a strong binding strength. Thus, 4-6 carbophene has favorable ORR catalytic activity. This work not only provides promising low-cost catalysts in pure carbon materials for ORR, promoting the development of metal-free ORR catalysts, but also enhances the understanding of Dirac cone two-dimensional materials for applications in catalysis.