Hexagonal Boron Nitride/Reduced Graphene Oxide Heterostructures as Promising Metal-Free Electrocatalysts for Oxygen Evolution Reaction Driven by Boron Radicals

Abstract

Developing highly efficient earth-abundant alternatives to traditional noble metal catalysts is essential for clean and sustainable energy-conversion and energy-storage technologies, yet still challenging in limited active sites and weak resistance to electrochemical corrosion. Herein, density-functional theory calculations demonstrate that hexagonal boron nitride (h-BN), albeit often being considered inert, can generate boron-active radicals at defective sites by forming heterogeneous structures with graphene-containing point vacancies, leading to a substantial electron delocalization and charge transfer, indicating a superior catalytic activity. Experimentally, the van der Waals heterostructure is rationally designed with h-BN nanosheets (BNNs) anchored on reduced graphene oxide (rGO) as strongly coupled composite catalysts. Despite the poor conductivity in BN and lower catalytic activity in rGO, the created heterostructures demonstrate unexpected, improved oxygen evolution reaction (OER) activity with excellent stability in alkaline electrolyte. Qualitative analysis of the valence band offset and theoretical calculation reveal that the formation of heterostructures can significantly drive the electron transfer between C and B atoms near the vacancies across the interface and cause a half-metallic property of BN, decreasing the free energy barrier of four-electron OER kinetics. Herein, the synthetic schemes of h-BNNs are guided as highly active metal-free OER electrocatalysts.