Synergistic View of Magnetism, Chemical Activation, and Oxygen Reduction Reaction as Well as Oxygen Evolution Reaction Catalysis of Carbon-Doped Hexagonal Boron Nitride from First Principles

Although substitution of carbon (C) in hexagonal boron nitride (hBN) has been reported to form islands of graphene; C-doped hBN has also been experimentally reported in recent years to be a possible catalytic host to the oxygen reduction reaction (ORR), as well as a possible ferromagnet at room temperature. In this work, we explore from first principles the connection between these different aspects of C-doped hBN. We find the formation of graphene islands covering unequal number of B and N sites in hBN to be energetically plausible. They possess a net non-zero magnetic moment and are also found to be substantially more chemically active than their nonmagnetic counterparts covering equal number of B and N sites. On-site Coulomb repulsion between electrons, known to be responsible for magnetism in bipartite lattices such as graphene and hBN, is also found to play a central role in chemical activation of not only the C atoms at the zigzag interface of magnetic graphene islands and hBN but also boron (B) sites in the immediate hBN neighborhood. However, such activated B or C due to substitution at the B site, which is energetically more favorable than that at the N site, has been reported to be unfavorable for the ORR. Advantageously, we find that the activation of C at B sites moderates systematically with increasing size of graphene islands, paving the way for abundance of efficient catalytic sites at the edges of magnetic graphene islands covering more B sites than N sites. Accordingly, as an alternate to precious metals for electrodes, we propose a class of graphene-hBN hybrids with lattices of magnetic graphene islands embedded in hBN, which can be metallic.