Defining the origins of electron transfer at screen-printed graphene-like and graphite electrodes: MoO2 nanowire fabrication on edge plane sites reveals electrochemical insights.

Craig E Banks,Samuel J Rowley-Neale,Dale A C Brownson

doi:10.1039/c6nr04220a

Craig E Banks, Samuel J Rowley-Neale + Show 1 more

Open Access

https://doi.org/10.1039/c6nr04220a

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Journal: Nanoscale	Publication Date: Jan 1, 2016
Citations: 27	License type: cc-by

Affiliation: Manchester Metropolitan University

Abstract

Molybdenum (di)oxide (MoO2) nanowires are fabricated onto graphene-like and graphite screen-printed electrodes (SPEs) for the first time, revealing crucial insights into the electrochemical properties of carbon/graphitic based materials. Distinctive patterns observed in the electrochemical process of nanowire decoration show that electron transfer occurs predominantly on edge plane sites when utilising SPEs fabricated/comprised of graphitic materials. Nanowire fabrication along the edge plane sites (and on edge plane like-sites/defects) of graphene/graphite is confirmed with Cyclic Voltammetry, Scanning Electron Microscopy (SEM) and Raman Spectroscopy. Comparison of the heterogeneous electron transfer (HET) rate constants (k°) at unmodified and nanowire coated SPEs show a reduction in the electrochemical reactivity of SPEs when the edge plane sites are effectively blocked/coated with MoO2. Throughout the process, the basal plane sites of the graphene/graphite electrodes remain relatively uncovered; except when the available edge plane sites have been utilised, in which case MoO2 deposition grows from the edge sites covering the entire surface of the electrode. This work clearly illustrates the distinct electron transfer properties of edge and basal plane sites on graphitic materials, indicating favourable electrochemical reactivity at the edge planes in contrast to limited reactivity at the basal plane sites. In addition to providing fundamental insights into the electron transfer properties of graphite and graphene-like SPEs, the reported simple, scalable, and cost effective formation of unique and intriguing MoO2 nanowires realised herein is of significant interest for use in both academic and commercial applications.

Highlights

Optimising the coating process The method utilised for ‘decorating’ screen-printed electrodes (SPEs) with MoO2 was adapted from Zach et al.[32] and Walter et al.[30] whom recently reported the electrodeposition of molybdenum oxides onto BPPG electrodes to produce nanowire structures, which formed exclusively along edge plane steps and at edge plane like-sites/defects
We have shown that the electrochemical process of nanowire decoration occurs selectively onto the edge plane like-sites/defects of these graphitic materials
Comparison of the heterogeneous electron transfer (HET) rate constants, k°, at unmodified and nanowire coated SPEs shows a reduction in the electrochemical reactivity of SPEs when the edge plane sites are effectively blocked/coated with MoO2

Summary

Introduction

Carbon based electrode materials have long been utilised in a plethora of analytical and industrial electrochemical applications.[1,2,3,4,5,6,7,8] Their popularity has arisen due to their distinct advantages when compared to traditional noble metal based electrodes, such as being comparatively cheap and obtainable, whilst out-performing traditional metals with their structural polymorphism, chemical stability, wide operable potential windows and relatively inert electrochemistry.[1,2] despite the vast number of studies and applications for carbon-based electrodes, researchers disagree over which structural characteristic is the predominate origin of heterogeneous electron transfer (HET) kinetics at graphitic surfaces;[9,10,11,12,13] in contention as to whether it is the edge plane or (under certain limited conditions) measurable electrochemical activity is observed at the basal plane,[10,13,17,18,19] most notably when using scanning electrochemical cell microscopy.[10].

Results

Conclusion