Exploring the reactivity of distinct electron transfer sites at CVD grown monolayer graphene through the selective electrodeposition of MoO2 nanowires

• Published in: Scientific reports 2019-09, Vol.9 (1), p.1-9, Article 12814
• Main Authors: García-Miranda Ferrari, Alejandro, Foster, Christopher W., Brownson, Dale A. C., Whitehead, Kathryn A., Banks, Craig E.
• Format: Article
• Language: English
• Subjects: 639/638/161; 639/638/440; Ammonia; Atomic force microscopy; Defects; Electrochemistry; Electron transfer; Fabrication; Graphene; Humanities and Social Sciences; Kinetics; Microscopy; Molybdenum; multidisciplinary; Nanotechnology; Nanowires; Nucleation; Polymers; Raman spectroscopy; Scanning electron microscopy; Science; Science (multidisciplinary); Silver chloride
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-019-48022-6

The origin of electron transfer at Chemical Vapour Deposition (CVD) grown monolayer graphene using a polymer-free transfer methodology is explored through the selective electrodeposition of Molybdenum (di)oxide (MoO 2 ). The electrochemical decoration of CVD monolayer graphene with MoO 2 is shown to originate from the edge plane like- sites/defects. Edge plane decoration of MoO 2 nanowires upon monolayer graphene is observed via electrochemical deposition over short time periods only ( ca . −0.6 V for 1 second ( vs . Ag/AgCl)). At more electrochemically negative potentials ( ca . −1.0 V) or longer deposition times, a large MoO 2 film is created/deposited on the graphene sheet, originating and expanding from the original nucleation points at edge plane like- sites/defects/wrinkles. Nanowire fabrication along the edge plane like- sites/defects of graphene is confirmed with Cyclic Voltammetry, Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and Raman Spectroscopy. Monitoring the electrochemical response towards [Ru(NH 3 ) 6 ] 3+/2+ and comparing the heterogeneous electron transfer (HET) kinetics at CVD grown monolayer graphene prior and post nanowire fabrication reveals key understandings into the fundamental electrochemical properties of carbon materials. The HET kinetics ( k obs 0 ) at MoO 2 nanowire decorated monolayer graphene sheets, when edge plane like- sites/defects have been coated/blocked with MoO 2 , are significantly reduced in comparison to the unmodified graphene alternative. Interestingly, MoO 2 nucleation originates on the edge plane like- sites/defects of the graphene sheets, where the basal plane sites remain unaltered until the available edge plane like- sites/defects have been fully utilised; after which MoO 2 deposition propagates towards and onto the basal planes, eventually covering the entire surface of the monolayer graphene surface. In such instances, there is no longer an observable electrochemical response. This work demonstrates the distinct electron transfer properties of edge and basal plane sites on CVD grown monolayer graphene, inferring favourable electrochemical reactivity at edge plane like- sites/defects and clarifying the origin of graphene electro-activity.