Graphitic Carbon Nitride Sheet Supported Single-Atom Metal-Free Photocatalyst for Oxygen Reduction Reaction: A First-Principles Analysis.

Designing metal-free photocatalysts for oxygen reduction reaction (ORR) is an important step toward the development of sustainable and alternative energy resources because ORR plays a key role in fuel cell reactions. An efficient photocatalyst for ORR must possess suitable band positions with respect to electrochemical potentials of ORR, minimize energy losses due to charge transport and electron-hole recombination, and have kinetically suitable electron transfer properties. Using first-principles theoretical studies, we herein demonstrate that a single Si atom doped on the alternative pores of the porous graphitic carbon nitride (g-C6N6) surface has satisfied the above criteria and has the potential to be an efficient photocatalyst for ORR. Our study reveals that molecular oxygen, chemisorbed on the dopant atom of the doped surface via an end-on fashion, is activated and readily reduced with a very low onset potential (-0.07 V) via a four-electron transfer pathway. Thus, the doped system can act as an efficient metal-free photocathode in fuel cells.