The use of different types of reduced graphene oxide in the preparation of Fe-N-C electrocatalysts: capacitive behavior and oxygen reduction reaction activity in alkaline medium (original) (raw)
Related papers
2014
In this paper, the reduced graphene oxide (rGO) is synthesized from graphite oxide (GO) via microwave exfoliation method, and used to support non-noble metal Fe-N X based electrocatalysts (Fe-N X /rGO) for the oxygen reduction reaction (ORR). Tripyridyl triazine (TPTZ) is used as a ligand for Fe-N X catalyst preparation. The obtained catalyst presents a high content of pyridinic (N1) and pyrrolic (N2) nitrogen types on the catalyst surface (40.0% and 52.3% atomic concentrations, respectively) with Fe atomic content of 0.7%. A catalyst loading of 0.5 mg cm À2 with a ionomer-to-carbon (ITC) mass ratio of 0.2 deposited on the glassy carbon electrode allows the highest ORR activity with the specific current of À0.35 mA mg À1 at a cell voltage of 0.8 V (vs. RHE). The overall electron transfer number obtained is of 3.98. Stability tests in acidic solution for this catalyst are also performed.
IOP Conference Series: Earth and Environmental Science
Non-precious metals (NPM) such as iron and nitrogen-doped carbon (Fe-N-C) have been actively studied as alternative electrocatalysts to platinum for oxygen reduction reaction (ORR) in proton exchange membrane fuel cell (PEMFC). However, its low stability is associated to the structural morphology of the electrode made of Fe-N-C and its support that has restricted the mass transfer of fuel and product. In this work, it was attempted to assess the role of RGO derived from sengon wood as catalyst support to Fe-N-C catalyst, and study the effect of the Fe-N-C to RGO ratio, on the ORR activity and durability in acidic medium. This work revealed that Fe-N-C/RGO at the weight ratio of 2:0.2 demonstrated the highest onset potential of 0.91 V, with high limiting current density of 5.7 mA/cm2, owing to the uniform active site distribution on the Fe-N-C/RGO surface compared to other samples with different weight ratio. It was indicated in this work that an improve in the kinetic activity was o...
2019
Fuel cells are energy converters that use hydrogen-based fuels. They are noise-free and highly efficient. They have important advantages which include high tolerance to impurities in the fuel, using various fuel types directly or through additional fuel converting systems. Fuel cell components are interconnectors, gas diffusion layers, electrodes and membranes. “Membrane Electrode Assembly” (MEA) is the part that includes opposing electrodes (anode – cathode) and the membrane between them. Reaction kinetics are accelerated by catalyst materials embedded into the MEA, which are conventionally platinum and other noble metals. Production of noble metal is hard to conduct and their resources are constantly decreasing as their demand increases which results in rising prices. Furthermore, for the purpose of using less noble metal by increasing particles’ surface areas; they are produced in nanoscale but it is difficult to control the kinetic behavior of particles in nanoscale. Alternative...
International Journal of Hydrogen Energy, 2016
In this work the electrocatalytic performance of nitrogen-doped graphene (NG)-based nonprecious metal (NPM) catalysts for oxygen reduction reaction (ORR) have been compared with their counterparts while supported on multiwalled carbon nanotubes (MWCNTs). Fe and Co nanoparticles were precipitated on NG (M/NG, M ¼ Fe, Co) and for comparison on MWCNTs (M/MWCNT, M ¼ Fe, Co) using a modified polyol method. The electrocatalytic properties of all catalysts towards oxygen reduction reaction in 0.1 M KOH solution were investigated. In comparison with M/MWCNTs, M/NG catalysts exhibited higher ORR activity, which indicates a better electrocatalytic performance of nitrogen-doped graphene compared to those which were supported by MWCNTs. Chronoamperometric results also demonstrated that the Co/NG catalyst was more stable for ORR in alkaline solution rather than Co/MWCNT and commercial Pt/C.
Advanced Sustainable Systems
Polymer electrolyte fuel cells (PEFCs) based on hydrogen oxidation and oxygen reduction are considered a promising technology for emission-free energy conversion. [1] However, the sluggish kinetics of the oxygen reduction reaction (ORR) on the cathode side necessitates an effective electrocatalyst. In commercial applications, Pt or Pt-alloy nanoparticles immobilized on carbon supports (Pt/C) are employed as ORR catalysts. [2,3] However, Pt-based catalysts suffer from drawbacks such as low selectivity and hence high gas crossover sensitivity, [4] carbon monoxide (CO) poisoning, [5] and chemical and mechanical instability [6,7] in addition to the scarcity and high cost of Pt. [8] These problems impede the use of Pt in large-scale applications, making development of Pt-free catalysts a critical part of fuel cell research. In this context, metalfree heteroatom-doped carbon materials, such as doped graphene and carbon nanotubes (CNTs) or mesoporous carbons, have been discovered as promising alternative catalysts. [9-14] In the pioneering work of Gong et al., vertically aligned nitrogen-containing CNTs were demonstrated as metal-free ORR catalysts. [15] In that work, supplemented by quantum mechanical calculations, the ORR catalytic activity was explained on the basis of the electron-accepting nitrogen atoms inducing a relatively high positive charge density on the adjacent carbon atoms, hence activating them as active sites for the ORR. In this context, heteroatom-doped graphene-based materials, with a 2D structure, high electron mobility, and large specific surface area, are considered promising for ORR catalysis. [16,17] Qu et al. [18] first showed ORR catalysis for nitrogendoped graphene (N-G). N-G was demonstrated to exhibit ORR catalytic activity with long-term stability and tolerance to fuel crossover and poisoning effects in alkaline electrolyte. Analogous to N-doped CNTs, the mechanism of the catalytic activity was explained as an effect of the charge polarization induced by the difference in electronegativity between N (χ = 3.04) and C (χ = 2.55), which facilitates O 2 adsorption. In order to further enhance the catalytic activity of heteroatom-doped Recently, it has been demonstrated that doping of graphene by elements such as N, S, or F creates active sites for the oxygen reduction reaction (ORR). This results from bond polarization caused by the difference in electronegativity between heteroatom dopants and carbon, and/or the presence of defects within the graphene lattice. In this work, fluorine, nitrogen, and sulfur tridoped reduced graphene oxide (F,N,S-rGO) is designed to combine these catalytically active sites. F,N,S-rGO can be inexpensively synthesized by a facile and scalable route involving pyrolysis at 600 °C of sulfur-doped rGO in the presence of Nafion and dimethyl formamide (DMF). The pyrolysis of Nafion and DMF provides F • and N • radicals which serve as doping agents. Rotating disk electrode investigations reveal the ORR catalytic activities of F,N,S-rGO in both acidic and alkaline media, which are consistent with the real performances of the respective polymer electrolyte fuel cells (PEFCs). Maximum power densities of 14 and 46 mW cm −2 are obtained for the acidic and alkaline PEFCs, respectively, using F,N,S-rGO as ORR catalysts. To the best of knowledge, this is the first report on the synthesis of F,N,S tridoped rGO and on its ORR activity in both acidic and alkaline PEFCs.
Global NEST International Conference on Environmental Science & Technology
Nitrogen co-doped with fluorine on reduced graphene oxide (rGO) was prepared by one-pot hydrothermal treatment method. The scanning electron microscopy (SEM) images and X-ray photoelectron microscopy (XPS) spectra revealed the successful doping of nitrogen and fluorine into the rGO. The Brunauer-Emmett-Teller (BET) results demonstrated high surface area of N-F-rGO that are favorable for oxygen adsorption. The results show that N-F-rGO catalyst has improved the catalytic performance electrode for the ORR in alkaline environment than the fluorine undoped N-rGO. The Koutechy-Levich (KL) analysis and rotating ring disk electrode (RRDE) measurements suggest that N-F-rGO dominantly favors a 4e- reduction process. The nitrogen co-doped with fluorine on rGO exhibited remarkable long-term stability towards the ORR than Pt/C. These improved electrochemical properties indicate that N-F-rGO will be a promising candidate for cost-effective electrode material for application of non-polluting alte...
Noble-Metal-Free Iron Nitride/Nitrogen-Doped Graphene Composite for the Oxygen Reduction Reaction
ACS Omega, 2019
Considerable effort has been devoted recently to replace platinum-based catalysts with their non-noble-metal counterparts in the oxygen reduction reaction (ORR) in fuel cells. Nitrogen-doped carbon structures emerged as possible candidates for this role, and their earth-abundant metaldecorated composites showed great promise. Here, we report on the simultaneous formation of nitrogen-doped graphene and iron nitride from the lyophilized mixture of graphene oxide and iron salt by high-temperature annealing in ammonia atmosphere. A mixture of FeN and Fe 2 N particles was formed with average particle size increasing from 23.4 to 127.0 nm and iron content ranging from 5 to 50 wt %. The electrocatalytic oxygen reduction activity was investigated via the rotating disk electrode method in alkaline media. The highest current density of 3.65 mA cm −2 at 1500 rpm rotation rate was achieved in the 20 wt % catalyst via the four-electrode reduction pathway, exceeding the activity of both the pristine iron nitride and the undecorated nitrogen-doped graphene. Since our catalysts showed improved methanol tolerance compared to the platinumbased ones, the formed non-noble-metal system offers a viable alternative to the platinum-decorated carbon black (Pt/CB) ORR catalysts in direct methanol fuel cells.
Nitrogen-Doped Graphene Oxide as Efficient Metal-Free Electrocatalyst in PEM Fuel Cells
Nanomaterials
Nitrogen-doped graphene is currently recognized as one of the most promising catalysts for the oxygen reduction reaction (ORR). It has been demonstrated to act as a metal-free electrode with good electrocatalytic activity and long-term operation stability, excellent for the ORR in proton exchange membrane fuel cells (PEMFCs). As a consequence, intensive research has been dedicated to the investigation of this catalyst through varying the methodologies for the synthesis, characterization, and technologies improvement. A simple, scalable, single-step synthesis method for nitrogen-doped graphene oxide preparation was adopted in this paper. The physical and chemical properties of various materials obtained from different precursors have been evaluated and compared, leading to the conclusion that ammonia allows for a higher resulting nitrogen concentration, due to its high vapor pressure, which facilitates the functionalization reaction of graphene oxide. Electrochemical measurements ind...
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.
Journal of The Electrochemical Society, 2012
A novel NPMC using pyrimidine-2,4,5,6-tetramine sulfuric acid hydrate (PTAm) as a nitrogen precursor and graphene nanosheets as catalyst supports was prepared and characterized. We investigate the effect of different pyrolysis temperatures on the catalysts' ORR activity along with detailed surface analysis to provide insight regarding the nature of the ORR active surface moieties. The NPMC sample heat treated at 800 • C was found to display optimal ORR activity and H 2 O selectivity, specifically, an onset potential of 0.853 V vs RHE, a half-wave potential of 0.682 V vs RHE, and a H 2 O selectivity of ca. 99.9%. High stability through an accelerated durability testing (ADT) protocol was demonstrated and attributed to the high graphitic content of the catalyst support material. This novel NPMC demonstrates promising electrocatalyst activity and superior durability over commercial Pt/C catalyst for ORR under the studied conditions, rendering graphene nanosheets as an ideal replacement to traditional nanostructured carbon support materials.