A synergistic view of magnetism, chemical activation, and ORR as well as OER catalysis of carbon doped hexagonal boron nitride from first-principles

TL;DR

This study uses first-principles calculations to explore how carbon doping in hexagonal boron nitride creates magnetic, chemically active graphene islands that could serve as efficient, metal-free catalysts for oxygen reduction and oxygen evolution reactions.

Contribution

It reveals the connection between magnetism, chemical activation, and catalytic activity in C-doped hBN, proposing graphene-hBN hybrids as potential metal-free catalysts.

Findings

Graphene islands with magnetic moments form on C-doped hBN.

Activated B and C sites enhance chemical activity at edges.

Larger graphene islands increase catalytic site abundance.

Abstract

Carbon(C) doped hexagonal boron nitride(hBN) has been experimentally reported in recent years to be a possible catalytic host to oxygen reduction reaction(ORR), as well as a possible ferromagnet at room temperature. Substitution by C in hBN has been also reported to form islands of graphene. In this work, we explore from first principles, the connection between these different aspects of C doped hBN. We find 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 non-magnetic counterparts covering equal number of B and N sites. On-site Coulomb repulsion between electrons, known to be responsible for magnetism in bipartite lattices like 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 of boron(B) sites in the immediate hBN neighborhood. However, such activated B or C due to substitution at B site, which is energetically more favorable than at N site, has been reported to be unfavorable for 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.