Tailoring the electrochemical properties of 2D-hBN via physical linear defects: physicochemical, computational and electrochemical characterisation.

Alejandro García-Miranda Ferrari,Dale A C Brownson,Ahmed S Abo Dena,Christopher W Foster,Samuel J Rowley-Neale,Craig E Banks

doi:10.1039/c9na00530g

Abstract

Monolayer hexagonal-boron nitride films (2D-hBN) are typically reported within the literature to be electrochemically inactive due to their considerable band gap (ca. 5.2–5.8 eV). It is demonstrated herein that introducing physical linear defects (PLDs) upon the basal plane surface of 2D-hBN gives rise to electrochemically useful signatures. The reason for this transformation from insulator to semiconductor (inferred from physicochemical and computational characterisation) is likely due to full hydrogenation and oxygen passivation of the boron and/or nitrogen at edge sites. This results in a decrease in the band gap (from ca. 6.11 to 2.36/2.84 eV; theoretical calculated values, for the fully hydrogenated oxygen passivation at the N or B respectively). The 2D-hBN films are shown to be tailored through the introduction of PLDs, with the electrochemical behaviour dependent upon the surface coverage of edge plane-sites/defects, which is correlated with electrochemical performance towards redox probes (hexaammineruthenium(iii) chloride and Fe2+/3+) and the hydrogen evolution reaction. This manuscript de-convolutes, for the first time, the fundamental electron transfer properties of 2D-hBN, demonstrating that through implementation of PLDs, one can beneficially tailor the electrochemical properties of this nanomaterial.

Highlights

A family of 2D materials such as 2D-hBN, MoSe2, MoS2, WSe2, antimonene and phosphorene[1,2] have recently been isolated and utilised within an array of electrochemical applications, ranging from sensing to energy storage and generation.[1,3] Boron nitride (BN) is a structural analogue of graphite, in which an equal number of boron and nitrogen atoms form a honeycomb lattice structure[4] of sp[2] bonded layers.[5]
The electrochemical properties of Chemical Vapour Deposition (CVD) grown 2D-hBN are rst characterised with cyclic voltammetry (CV) using Ru(NH3)6Cl33+/2+ (RuHex), which is a near ideal[25] outer-sphere probe, and (NH4)2Fe(SO4)[2], (Fe2+/3+), which is selected as an inner-sphere redox probe due to its sensitivity to oxide groups on the electrode's surface.[25]
Our previous work on 2D materials has asserted that active edge plane-sites/defects are the origin of electron transfer,[26] attention was turned to attempting to introduce such sites, through investigating the creation of physical linear defects (PLDs) upon the surface of the 2D-hBN

Summary

Introduction

2D-hBN has a wide band gap (ca. 5.2–5.8 eV),[11,12] which means it is classi ed as an electrical insulator,[12] it is widely applied as a charge leakage barrier-layer in electronic equipment.[5,13] Interestingly, 2D-hBN has been used to tailor the band gap of graphene (creating graphene-hBN interfaces).[13,14] It has been demonstrated that 2D-hBN's band gap can be decreased/modi ed by creating thin strips of single layered 2D-hBN nanosheets; producing nanoribbons (NRs), which contain a honeycomb lattice with either armchair or zig-zag edges that possess active dangling bonds.[15]. By controlling the hydrogenation ratio, the electronic and magnetic properties of zig-zag-terminated 2D-hBN-NRs can be precisely tailored, modulating their band gap.[18] most recently in electrochemistry, 2D-hBN has been computationally explored as 264 | Nanoscale Adv., 2020, 2, 264–273. We demonstrate that the electrochemical response of 2D-hBN can be tailored through the introduction of physical linear defects (PLDs) upon the surface of the 2D-hBN. This transforms 2D-hBN from a previously reported electrochemically inert material into one that gives rise to electrochemically useful signatures/activity. Given that the current accepted model of 2D-hBN is that of it being an insulator/inert material within electrochemical applications, this work shows that its behaviour is more complex than initially reported

Electrochemical and physicochemical characterisation

Electrochemical application

Conclusions