An Oxygen Reduction Study of Graphene-Based Nanomaterials of Different Origin (original) (raw)
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Reduced graphene oxide (RGO) was obtained by chemical synthesis from multi walled carbon nanotubes. Using a suitable oxidant, we longitudinally " unzipped " nanotubes to form graphene oxide nanoribbons and then obtained RGO with a proper reductant. Standard redox potentials of carboxy groups were used for choosing oxidant and reductant. It has been shown that the required oxidant potential in acid medium should be more + 0.528 V and reductant potential in alkaline medium-less – 1.148 V. Current-potential curves for oxygen electrodes based on RGO, obtained by using the oxidants K 2 Cr 2 O 7 , KMnO 4 and the reductants NaH 2 PO 2 , Na 2 SO 3 , were analyzed. The electrochemical characteristics of RGO in the oxygen reduction reaction were depended on the redox power of the reagents. We demonstrated that obtained RGO could be promising material for oxygen electrodes of fuel cells.
Nitrogen-Doped Graphene Oxide Electrocatalysts for the Oxygen Reduction Reaction
ACS Applied Nano Materials
Platinum group metal-free (PGM-free) electrocatalysts for the oxygen reduction reaction (ORR) often exhibit a complex functionalized graphitic structure. Because of this complex structure, limited understanding exists about the design factors for the synthesis of high-performing materials. Graphene, a two-dimensional hexagonal structure of carbon, is amenable to structural and functional group modifications, making it an ideal analogue to study crucial properties of more complex graphitic materials utilized as electrocatalysts. In this paper, we report the synthesis of active nitrogen-doped graphene oxide catalysts for the ORR in which their activity and four-electron selectivity are enhanced using simple solvent and electrochemical treatments. The solvents, chosen based on Hansen's solubility parameters, drive a substantial change in the morphology of the functionalized graphene materials by (i) forming microporous holes in the graphitic sheets that lead to edge defects and (ii) inducing 3D structure in the graphitic sheets that promotes ORR. Additionally, the cycling of these catalysts has highlighted the multiplicity of the active sites, with different durability, leading to a highly selective catalyst over time, with a minimal loss in performance. High ORR activity was demonstrated in an alkaline electrolyte with an onset potential of ∼1.1 V and half-wave potential of 0.84 V vs RHE. Furthermore, long-term stability potential cycling showed minimal loss in half-wave potential (<3%) in both N 2-and O 2-saturated solutions with improved selectivity toward the four-electron reduction after 10000 cycles. The results described in this work provide additional understanding about graphitic electrocatalysts in alkaline media that may be utilized to further enhance the performance of PGM-free ORR electrocatalysts.
Reduced graphene oxide: a promising electrode material for oxygen electrodes
Journal of Nanostructure in Chemistry, 2013
A method for the chemical synthesis of reduced graphene oxide has been developed. It is based on the chemical oxidation of multiwalled carbon nanotubes by means of heptavalent manganese with subsequent reduction. Sodium hypophosphite and sulfite were used as reductants. It has been confirmed by different methods that reduced graphene oxide is obtained. Current-potential curves for electrodes based on reduced graphene oxide in an oxygen fuel cell mock-up with alkaline electrolyte have been studied. It has been found that the characteristics of the electrode of graphene oxide reduced with sodium hypophosphite in oxygen reduction reaction are three to four times higher than those of the electrode of starting multiwalled carbon nanotubes. The electrodes based on reduced graphene oxide are superior to multiwalled carbon nanotube-MnO 2 composite in characteristics. The characteristics of oxygen electrodes based on reduced graphene oxide were stable during 6-month tests. The reduced graphene oxide obtained promises much as a material for the oxygen electrodes of electrochemical power sources.
ACS applied materials & interfaces, 2014
Currently, the fundamental factors that control the oxygen reduction reaction (ORR) activity of graphene itself, in particular, the dependence of the ORR activity on the number of exposed edge sites remain elusive, mainly due to limited synthesis routes of achieving small size graphene. In this work, the synthesis of low oxygen content (<2.5±0.2 at. %), few layer graphene nanosheets with lateral dimensions smaller than a few hundred nanometers were achieved using a combination of ionic liquid assisted grinding of high purity graphite coupled with sequential centrifugation. We show for the first time that the graphene nanosheets possessing a plethora of edges exhibited considerably higher electron transfer numbers compared to the thicker graphene nanoplatelets. This enhanced ORR activity was accomplished by successfully exploiting the plethora of edges of the nanosized graphene as well as the efficient electron communication between the active edge sites and the electrode substrat...
Molecules, 2018
Electrocatalysts for the oxygen reduction (ORR) reaction play an important role in renewable energy technologies, including fuel cells and metal-air batteries. However, development of cost effective catalyst with high activity remains a great challenge. In this feature article, a hybrid material combining ZnO nanoparticles (NPs) with reduced graphene oxide (rGO) is applied as an efficient oxygen reduction electrocatalyst. It is fabricated through a facile one-step hydrothermal method, in which the formation of ZnO NPs and the reduction of graphene oxide are accomplished simultaneously. Transmission electron microscopy and scanning electron microscopy profiles reveal the uniform distribution of ZnO NPs on rGO sheets. Cyclic voltammograms, rotating disk electrode and rotating ring disk electrode measurements demonstrate that the hierarchical ZnO/rGO hybrid nanomaterial exhibits excellent electrocatalytic activity for ORR in alkaline medium, due to the high cathodic current density (9....
Applied Nano
Multiple heteroatom-doped graphene is of great interest for developing an efficient electrocatalyst for oxygen reduction reaction (ORR). To maximize the electrocatalytic performance of doped graphene, the competitive doping mechanism caused by the different atomic sizes of dopants should be developed. Herein, three different heteroatoms (e.g., N, P and B) are competitively introduced into reduced graphene oxide (RGO) using both single- and two-step processes. The total quantity of heteroatoms for ternary RGO synthesized using the two-step process is lower than that when using the single-step process. Higher ORR electrocatalytic activity for the two-step-synthesized RGO compared to the single-step-synthesized RGO can be explained by: (a) a high amount of P atoms; (b) the fact that B doping itself decreases the less electrocatalytic N moieties such as pyrrole and pyridine and increases the high electrocatalytic moieties such as quaternary N; (c) a high amount of B atoms itself within ...
Towards efficient oxygen reduction reaction electrocatalysts through graphene doping
Electrochimica Acta, 2019
The incessant and drastic growth of global energy demand make it imperative to develop new affordable high-quality materials at a large scale to act as powerful electrocatalysts (ECs) on the relevant energy reactions. Here, we report the synthesis and characterization (FTIR, Raman, XPS, XRD, TEM and SEM) of new engineered electrocatalysts based on situ co-precipitation of Co 3 O 4 or Mn 3 O 4 nanoparticles in the presence of N, S-doped graphene (Co/N 3 S 3-GF and Mn/N 3 S 3-GF). The nitrogen, sulphur dual-doped graphene was achieved by a scalable dry ball-milling procedure followed by thermal treatment using graphene flakes as carbon source and trithiocyanuric acid as the precursor. The three materials prepared were applied as electrocatalysts for the oxygen reduction reaction (ORR) and demonstrated excellent electrocatalytic performance in alkaline medium with Co/N 3 S 3-GF and Mn/N 3 S 3-GF presenting onset potentials of 0.87 V vs. RHE. These were comparable to Pt/C onset potential (0.91 V). All materials showed good diffusionlimiting current densities (-3.49-4.17 mA cm-2) and selectivity for the 4-electron O 2 reduction to H 2 O. Furthermore, the Co/N 3 S 3-GF and Mn/N 3 S 3-GF electrocatalysts presented good tolerance to methanol poisoning and good stability with current retentions (76-81%). The approach followed in this work showed that affordable, simple and scalable procedures can be applied to develop ORR electrocatalysts with enhanced performances.
The New Graphene Family Materials: Synthesis and Applications in Oxygen Reduction Reaction
Catalysts, 2016
Graphene family materials, including graphene quantum dots (GQDs), graphene nanoribbons (GNRs) and 3D graphene (3D-G), have attracted much research interest for the oxygen reduction reaction (ORR) in fuel cells and metal-air batteries, due to their unique structural characteristics, such as abundant activate sites, edge effects and the interconnected network. In this review, we summarize recent developments in fabricating various new graphene family materials and their applications for use as ORR electrocatalysts. These new graphene family materials play an important role in improving the ORR performance, thus promoting the practical use in metal-air batteries and fuel cells.
ACS Applied Energy Materials, 2021
Carbon-based nanomaterials (fullerenes, carbon nanotubes, graphene derivatives, etc.) are promising cost-effective catalyst alternatives to noble metal catalysts for the oxygen reduction reaction (ORR). Herein, we report on the synthesis and characterization of graphene-based derivatives with various aspect ratios. All the synthesized materials were critically probed for activity and stability for ORR in acidic and alkaline electrolytes. Namely, a comparison study on the influence of aspect ratio and N-doping on ORR electroactivity in acidic and alkaline electrolytes of quasi-1D N-doped heat-treated graphene oxide nanoribbons (N-htGONr) with 2D N-doped heat-treated graphene oxides (N-htGO) was done. Moreover, we also investigated the influence of metallic impurities on the ORR activity in acidic and alkaline media. We have shown that a higher aspect ratio plays an important role in improving ORR activity. Furthermore, when comparing N-doped derivatives with non-doped derivatives, the ORR activity in 0.1 M HClO 4 is increased by N-doping; however, in 0.1 M KOH, the N-doping effect is overshadowed by inherent transition metal impurities, i.e., iron. In this respect, we have established a linear correlation between onset potential for ORR, iron concentration, and BET specific surface area of graphene-based derivatives. The present study will aid in the critical assessment and development of non-metallic catalysts for the electrochemical energy conversion devices.