Relationships between structure and activity of carbon as a multifunctional support for electrocatalysts

Abstract

We report on new insights into the relationships between structure and activity of glassy carbon (GC), as a model material for electrocatalyst support, during its anodization in acid solution. Our investigation strongly confirms the role of CFGs in promotion of Pt activity by the "spill-over" effect related to CO(ads) for methanol electrooxidation (MEO) on a carbon-supported Pt catalyst. Combined analysis of voltammetric and impedance behaviour as well as changes in GC surface morphology induced by intensification of anodizing conditions reveal an intrinsic influence of the carbon functionalization and the structure of a graphene oxide (GO) layer on the electrical and electrocatalytic properties of activated GC. Although GO continuously grows during anodization, it structurally changes from being a graphite inter-layer within graphite ribbons toward a continuous GO surface layer that deteriorates the native structure of GC. As a consequence of the increased distance between GO-spaced graphite layers, the GC conductivity decreases until the case of profound GO exfoliation under drastic anodizing conditions. This exposes the native, yet abundantly functionalized, GC texture. While GC capacitance continuously increases with intensification of anodizing conditions, the surface nano-roughness and GO resistance reach the highest values at modest anodizing conditions, and then decrease upon drastic anodization due to the onset of GO exfoliation. We found for the first time that the activity of a GC-supported Pt catalyst in MEO, as one of the promising half-reactions in polymer electrolyte fuel cells, strictly follows the changes in GC nano-roughness and GO-induced GC resistance. The highest GC/Pt MEO activity is reached when optimal distance between graphite layers and optimal degree of GC functionalization bring the highest amount of CFGs into intimate contact with the Pt surface. This confirms the promoting role of CFGs in MEO catalysis.

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

“…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]. The PI and PII plateaus are correlated as previously evidenced to the oxygen reduction reactions of the inherent oxygen species trapped in the pores or linked to the easily oxidized function groups of graphite surface respectively [3,21e23].…”

Platinum electrocatalyst supported on glassy carbon: a dynamic response analysis of Pt activity promoted by substrate anodization

“…Further detailed analysis of electrochemical impedance measurements on GC, combined with cyclic voltammetry and morphological changes of GC surface, upon intensication of anodizing conditions, revealed an intrinsic inuence of the carbon functionalization and the structure of a graphene oxide (GO) layer on the electrical and electrocatalytic properties of activated GC. 17 While GC capacitance continuously increased with intensication of anodizing conditions, the surface nano-roughness and GO resistance reached the highest values at modest anodizing conditions, and then decreased upon drastic GC anodization due to the onset of GO exfoliation. The activity of the GC-supported Pt catalyst for MEO strictly followed the changes in GC nano-roughness and GO-induced GC resistance.…”

Tailoring the supercapacitive performances of noble metal oxides, porous carbons and their composites

“…Carbon blacks of high surface area are known as double-layer capacitors, although the pseudocapacitive contribution of carbon functional groups (CFGs), which can be created by chemical or electrochemical activation of carbonaceous materials, 13,43-45 can be significant. Electrochemical oxidation of even smooth glassy carbon surfaces (low surface area) 13,45 considerably increases the capacitance due to the formation of CFGs and surface roughening. Abundant creation of CFGs was achieved by modest oxidation, which caused the largest separation of capacitive loops in proton-rich solution, as shown in Fig.…”

“…The spectra were registered around the potential of the redox transitions of the CFGs in 0.50 mol dm -3 H 2 SO 4 . The lines present the response of a 2-branch RC ladder EEC in each case 13. …”

“…The main representatives of the first type of EC are different forms of powdered carbons 1 (carbon blacks, 2-6 their single-and multi-walled nanotube forms [7][8][9] and graphene sheets [10][11][12], although some contribution of carbon functional groups at the surface of activated carbons could cause the pseudocapacitive behavior. 13 The diverse group of pseudo-capacitors can be subdivided according to the processes from which the pseudo-capacitance originates. Three main processes are involved: redox transitions of the electrode material itself, electrosorption and intercalation.…”