Revealing the intrinsic relation between heteroatom dopants and graphene quantum dots as a bi-functional ORR/OER catalyst

Abstract

The dopants such as boron, nitrogen, phosphorous, and sulfur are essential for graphene quantum dots (GQDs) performance in ORR/OER process. Nevertheless, the accurate descriptions of dopant effects are still largely missing for GQDs catalyst. In this work, a relation is established between the intrinsic properties of dopants and the performance of GQDs as bi-functional catalyst in ORR/OER. The dopants break down the pi-electron network and induce spin fluctuation. It is found that the adsorption strength of key oxygen intermediates (O*, OH*, and OOH*) is well correlated with intrinsic bond strength index (IBSI). The detailed free energy pathways for both ORR and OER are presented for various doped GQDs which is used to identify the rate-limiting step and overpotential. It was proposed that pyridine nitrogen is the best dopant which yields lowest overpotential. In the end, a reactivity map is provided which enables a rational design of GQDs catalyst.