Surface functionality and electrochemical investigations of a graphitic electrode as a candidate for alkaline energy conversion and storage devices.

Ahmed B Soliman,Hamdy H Hassan,Hesham S Abdel-Samad,Sayed S Abdel Rehim

doi:10.1038/srep22056

Abstract

Graphite is a typical electrocatalyst support in alkaline energy conversion and storage devices such as fuel cells, supercapacitores and lithium ion batteries. The electrochemical behaviour of a graphite electrode in 0.5 M NaOH was studied to elucidate its surface structure/electrochemical activity relationship. Graphite voltammograms are characterized by an anodic shoulder AI and a cathodic peak CI in addition to the oxygen reduction reaction plateaus, PI and PII. AI and CI were attributed to oxidation and reduction of some graphite surface function groups, respectively. Rotating ring disk electrode (RRDE) study revealed two different oxygen types assigned as inner and outer oxygen. The inner oxygen was reduced via the more efficient 4-electron pathway. The outer oxygen reduction proceeded with a lower efficient 2-electron pathway. The calculated percentages of the 4-electron pathway were ranged from 70% to 90%. A full mechanism for the graphite surface function groups changes over the studied potential window was suggested through the combination between the voltammetric, FT-IR and Raman results.

Highlights

Non-interacting support and tackled it from surface area point of view[4]
We report a novel insight on the structure/activity relationship of graphite electrode (GE) in alkaline medium and a special concern was subjected towards the oxygen reduction reaction (ORR) on its surface
Our findings strongly confirm that the surface function groups (SFG) of the graphite could be divided into and more difficult oxidized groups, E-OxSFGs and D-OxSFGs, respectively

Summary

Introduction

It has proved that the SFG’s undergo critical changes within the medium and the potential window in which the graphite electrode play a vital indirect role in both electrochemically obtained behaviour and response. The origin of the SFG’s in the graphite is attributed mainly to the chemisorbed oxygen[15]. They are composed of alcoholic, phenolic, carboxylic, lactonic, oxygen containing alicyclic compounds, ... Few studies correlated the overlapped peaks of the G-band for nano diamond (ND) to the C= C, G-band, OH and C= O surface functional groups[24,28]. The aim of this work is to investigate the major significant role of the graphite SFG’s and their effects on using the graphite as a support for the electrocatalytic active phase in direct alkaline fuel cell

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