Non-precious metal nanoparticles supported on nitrogen-doped graphene as a promising catalyst for oxygen reduction reaction: Synthesis, characterization and electrocatalytic performance (original) (raw)
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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.
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.
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.
Computational and Theoretical Chemistry, 2020
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Nitrogen-Doped Carbon Nanotube and Graphene Materials for Oxygen Reduction Reactions
Catalysts, 2015
Nitrogen-doped carbon materials, including nitrogen-doped carbon nanotubes (NCNTs) and nitrogen-doped graphene (NG), have attracted increasing attention for oxygen reduction reaction (ORR) in metal-air batteries and fuel cell applications, due to their optimal properties including excellent electronic conductivity, 4e − transfer and superb mechanical properties. Here, the recent progress of NCNTs-and NG-based catalysts for ORR is reviewed. Firstly, the general preparation routes of these two N-doped carbon-allotropes are introduced briefly, and then a special emphasis is placed on the developments of both NCNTs and NG as promising metal-free catalysts and/or catalyst support materials for ORR. All these efficient ORR electrocatalysts feature a low cost, high durability and excellent performance, and are thus the key factors in accelerating the widespread commercialization of metal-air battery and fuel cell technologies.
npj 2D Materials and Applications, 2021
Nitrogen-doped reduced graphene oxide is successfully synthesized and functionalized with hydroxylated copper ions via one-pot microwave-assisted route. The presence of cationic Cu coordinated to the graphene layer is fully elucidated through a set of experimental characterizations and theoretical calculations. Thanks to the presence of these hydroxyl-coordinated Cu2+ active sites, the proposed material shows good electrocatalytic performance for the oxygen reduction reaction, as evidenced by an electron transfer number of almost 4 and by high onset and half-wave potentials of 0.91 V and 0.78 V vs. the reversible hydrogen electrode, respectively. In addition, the N-doped Cu-functionalized graphene displays a superior current retention with respect to a commercial Pt/C catalyst during the stability test, implying its potential implementation in high-performance fuel cells and metal-air batteries.
Journal of Catalysis, 2014
Electrocatalysts are essential to two key electrochemical reactions, oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in renewable energy conversion and storage technologies such as regenerative fuel cells and rechargeable metal-air batteries. Here, we explored N-doped graphene as costeffective electrocatalysts for these key reactions by employing density functional theory (DFT). The results show that the substitution of carbon at graphene edge by nitrogen results in the best performance in terms of overpotentials. For armchair nanoribbons, the lowest OER and ORR overpotentials were estimated to be 0.405 V and 0.445 V, respectively, which are comparable to those for Pt-containing catalysts. OER and ORR with the minimum overpotentials can occur near the edge on the same structure but different sites. These calculations suggest that engineering the edge structures of the graphene can increase the efficiency of the N-doped graphene as efficient OER/ORR electrocatalysts for metal-air batteries, water splitting, and regenerative fuel cells.
Scientific reports, 2015
A novel and facile two-step strategy has been designed to prepare high performance bi-transition-metals (Fe- and Mo-) carbide supported on nitrogen-doped graphene (FeMo-NG) as electrocatalysts for oxygen reduction reactions (ORR). The as-synthesized FeMo carbide -NG catalysts exhibit excellent electrocatalytic activities for ORR in alkaline solution, with high onset potential (-0.09 V vs. saturated KCl Ag/AgCl), nearly four electron transfer number (nearly 4) and high kinetic-limiting current density (up to 3.5 mA cm(-2) at -0.8 V vs. Ag/AgCl). Furthermore, FeMo carbide -NG composites show good cycle stability and much better toxicity tolerance durability than the commercial Pt/C catalyst, paving their application in high-performance fuel cell and lithium-air batteries.
Bulletin of Materials Science, 2015
Here we report a remarkable transformation of nitrogen-doped multiwalled carbon nanotubes (MWCNTs) to size selective nitrogen-doped graphene quantum dots (N-GQDs) by a two-step electrochemical method. The sizes of the N-GQDs strongly depend on the applied anodic potential, moreover increasing potential resulted in a smaller size of N-GQDs. These N-GQDs display many unusual size-dependant optoelectronic (blue emission) and electrocatalytic (oxygen reduction) properties. The presence of N dopants in the carbon framework not only causes faster unzipping of MWCNTs but also provides more low activation energy site for enhancing the electrocatalytic activity for technologically daunting reactions like oxygen reduction. The smaller size of N-GQDs has shown better performance as compared to the large N-GQDs. Interestingly, N-GQDs-3 (size = 2.5 ± 0.3 nm, onset potential = 0.75 V) show a 30-mV higher positive onset potential shift compared to that of N-GQDs-2 (size = 4.7 ± 0.3 nm, onset potential = 0.72 V) and 70 mV than that of N-GQDs-1 (size = 7.2 ± 0.3, onset potential = 0.68 V) for oxygen reduction reaction (ORR) in a liquid phase. These result in the size-dependent electrocatalytic activity of N-GQDs for ORR as illustrated by the smaller sized N-GQDs (2.5 ± 0.3 nm) undoubtedly promising metal-free electrocatalysts for fuel cell applications.