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

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.

High performance nano-Ni/Graphite electrode for electro-oxidation in direct alkaline ethanol fuel cells

“…In the reverse span, in addition to the two sloped regions, a cathodic peak C1 at 0.35 V and a double step plateau assigned as PI and PII are observed. C1 was attributed to the reduction of the difficult oxidized graphite surface functional groups [3]. A similar peak was observed during the anodization of glassy carbon GC in acidic solution and was correlated to the charge transfer of carbon surface functional groups [20].…”

“…However, just after this potential the current increases as the potential increases with a two different slopes successive regions which is recently attributed to the oxidation of the graphite surface functional groups and to the oxygen evolution reaction OER [3]. In the reverse span, in addition to the two sloped regions, a cathodic peak C1 at 0.35 V and a double step plateau assigned as PI and PII are observed.…”

“…7. These results reflect the strong relation between the cathodic peak C Ni/G and the oxidation currents beyond A3 as it can be correlated to reduction of the formed surface graphitic oxygen functional groups [3].…”

“…Our recent work dealt with detailed discussion of the different processes occurred through cyclic voltammetric curves of Fig. 3a [3]. In the forward span of the bare graphite (BG), the early observed cathodic current is usually attributed to the reduction of H 2 O and/or dissolved O 2 .…”

“…The most recent researches concerning the fine-tuning of the main parameters such as size, shape, and composition of Pt-based/carbon electrocatalysts in order to improve their performance towards the oxygen reduction reaction (ORR) has been assessed [2]. Our recent work concerned with monitoring the changes occurred on the graphite surface functional groups during the oxidation and reduction potential windows normally used for anodic and cathodic fuel cells studies [3]. Ni & Nibased Materials are known to have attractive activity toward the electro-oxidation of some organic and inorganic molecules like ethanol, methanol, ammonia, hydrazine hydrate and urea.…”