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Nitrogen-doped Graphene-Supported Transition-metals Carbide Electrocatalysts for Oxygen Reduction Reaction.

Chen M, Liu J, Zhou W, Lin J, Shen Z - Sci Rep (2015)

Bottom Line: 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).

View Article: PubMed Central - PubMed

Affiliation: 1] School of Applied Science, Harbin University of Science and Technology, Harbin 150080, P.R. China [2] Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 637371, Singapore.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus

(a) RDE polarization curves for ORR performance of FeMo Carbide/G-800, FeMo Carbide/NG-800 and commercial 20% Pt/C in O2-saturated 0.1 M KOH with disk rotation rate of 800 rpm. (b) RDE curves of the FeMo Carbide/NG-800 at a scan rate of 2 mV s-1 with various rotation rates from 400 to 1600 rpm in O2-saturated 0.1 M KOH. The inset shows the Tafel plot of the FeMo Carbide/NG-800 derived by the mass-transport correction of the corresponding RDE data. (c) The current density Jk of 20% Pt/C, FeMo Carbide/G-800, and FeMo Carbide/NG catalysts with various annealing temperatures (700, 800 and 900 oC) at two different potentials, -0.8, -0.6 and -0.4 V respectively. (d) The dependence of electron transfer number (n) on the potential for FeMo Carbide/G-800 and FeMo Carbide/NG catalysts with different annealing temperatures (700, 800 and 900 oC) and corresponding electrochemical impedance spectroscopy measured at -0.30 V (e). The inset of (e) shows an equivalent electrical circuit consisting of the electrolyte resistance (Rs), interface charge transfer resistance (Rct) and constant phase element (CPE). (f) Current (i)–time (t) chronoamperometric responses obtained for both FeMo Carbide/NG-800 (black line) and 20% Pt/C catalysts (red line) at -0.55 V in O2-saturated 0.1 M KOH solution to methanol. The arrow indicates the addition of 2% (weight ratio) methanol into the O2-saturated electrochemical cell.
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f5: (a) RDE polarization curves for ORR performance of FeMo Carbide/G-800, FeMo Carbide/NG-800 and commercial 20% Pt/C in O2-saturated 0.1 M KOH with disk rotation rate of 800 rpm. (b) RDE curves of the FeMo Carbide/NG-800 at a scan rate of 2 mV s-1 with various rotation rates from 400 to 1600 rpm in O2-saturated 0.1 M KOH. The inset shows the Tafel plot of the FeMo Carbide/NG-800 derived by the mass-transport correction of the corresponding RDE data. (c) The current density Jk of 20% Pt/C, FeMo Carbide/G-800, and FeMo Carbide/NG catalysts with various annealing temperatures (700, 800 and 900 oC) at two different potentials, -0.8, -0.6 and -0.4 V respectively. (d) The dependence of electron transfer number (n) on the potential for FeMo Carbide/G-800 and FeMo Carbide/NG catalysts with different annealing temperatures (700, 800 and 900 oC) and corresponding electrochemical impedance spectroscopy measured at -0.30 V (e). The inset of (e) shows an equivalent electrical circuit consisting of the electrolyte resistance (Rs), interface charge transfer resistance (Rct) and constant phase element (CPE). (f) Current (i)–time (t) chronoamperometric responses obtained for both FeMo Carbide/NG-800 (black line) and 20% Pt/C catalysts (red line) at -0.55 V in O2-saturated 0.1 M KOH solution to methanol. The arrow indicates the addition of 2% (weight ratio) methanol into the O2-saturated electrochemical cell.

Mentions: The oxygen reduction reaction (ORR) activity of various graphene-supported FeMo carbide materials was evaluated by cyclic voltammetry (CV) (Fig. S6) and rotating disk electrode (RDE) measurements (Fig. 5)41, respectively. Compared with featureless CV curves in N2-saturated 0.1 M KOH solution (black line), well-defined oxygen reduction peaks were observed for all electrodes in the O2-saturated KOH solution (red line), revealing the ORR catalytic activity of the graphene-supported FeMo carbide materials. It was noted that the cathodic current of CV curves for all graphene-supported FeMo carbide electrodes display similar reduction peak between −0.5 and −0.3 V (vs. Ag/AgCl), which is attributed to the electrocatalytic oxygen reduction on the electrode23283042. However, the corresponding onset potential, half-wave potential and diffusion-limited currents are different for various electrodes, depending on the catalyst materials. As seen from the results in Fig. S6 and Table S4†, the onset (E1) and half-wave potentials (E2) are the E1 = −0.20 V and E2 = −0.51 V for N-free FeMo Carbide/G-800 (Fig. S6a &Table S4), respectively, lower than those of N-doped graphene supported FeMo carbides, i.e. E1 = −0.14 to −0.09 V and E2 = −0.37 to −0.33 V for FeMo Carbides/NG (Figs. S6 b-f &Table S4). The up-shift of on-set and half-wave potentials clearly indicates that N-doping can enhance catalyst performance for ORR. Moreover, the reduction peaks between −0.5 and −0.3 V become more clear and well-defined with the increasing annealing temperature from 700 to 900 degree, which is attributed to the increased N-doping level (4.2, 4.7 and 4.9% respectively in Table S2†) and thus the enhanced electric conductivity of the catalysts (see impedance data in Fig. 5e). The abovementioned results were further verified via linear sweep voltammery (LSV) measurements on a rotating disk electrode (RDE) for deferent graphene-supported FeMo carbide materials, along with the commercial Pt/C electrode, at a scan rate of 2 mV/s in O2-saturated 0.1 M KOH solution. The polarization curves of graphene-supported FeMo carbide electrodes in Fig. 5a exhibits two-step process, indicating a mixture of two-electron and four-electron reduction processes. The onset potential and half-wave potential for FeMo Carbide/G-800 are E1 = −0.20 V and E2 = −0.51 V, remarkably lower than those of FeMo Carbide/NG-800 in Fig. 5a (i.e. E1 = −0.09 V and E2 = −0.33 V). The current density for FeMo Carbide/G-800 is 1.3 mA/cm2 at −0.40 V, 2.3 mA/cm2 at −0.6 V, and 3.0 mA/cm2 at −0.8 V, respectively, much lower than 2.3 mA/cm2 (at −0.40 V), 3.0 mA/cm2 (at −0.60 V) and 3.5 mA/cm2 (at −0.80 V) for FeMo Carbide/NG-800 (see Fig. 5c & Table S4†). The enhanced ORR current density on FeMo Carbide/NG-800 appears to be attributed to the better dispersion of metal carbides and hence more active sites on NG-800 (vs. G-800). Nevertheless both FeMo Carbides on G-800 and NG-800 catalysts in Fig. 5a are still not comparable to commercial Pt/C catalysts. The polarization profile of Pt/C in Fig. 5a shows much better ORR performance with high onset potential (E1 = 0.06 V), high half-wave potential (E2 = −0.08 V) and high diffusion-limited current (4.0 mA/cm2 at −0.8 V).


Nitrogen-doped Graphene-Supported Transition-metals Carbide Electrocatalysts for Oxygen Reduction Reaction.

Chen M, Liu J, Zhou W, Lin J, Shen Z - Sci Rep (2015)

(a) RDE polarization curves for ORR performance of FeMo Carbide/G-800, FeMo Carbide/NG-800 and commercial 20% Pt/C in O2-saturated 0.1 M KOH with disk rotation rate of 800 rpm. (b) RDE curves of the FeMo Carbide/NG-800 at a scan rate of 2 mV s-1 with various rotation rates from 400 to 1600 rpm in O2-saturated 0.1 M KOH. The inset shows the Tafel plot of the FeMo Carbide/NG-800 derived by the mass-transport correction of the corresponding RDE data. (c) The current density Jk of 20% Pt/C, FeMo Carbide/G-800, and FeMo Carbide/NG catalysts with various annealing temperatures (700, 800 and 900 oC) at two different potentials, -0.8, -0.6 and -0.4 V respectively. (d) The dependence of electron transfer number (n) on the potential for FeMo Carbide/G-800 and FeMo Carbide/NG catalysts with different annealing temperatures (700, 800 and 900 oC) and corresponding electrochemical impedance spectroscopy measured at -0.30 V (e). The inset of (e) shows an equivalent electrical circuit consisting of the electrolyte resistance (Rs), interface charge transfer resistance (Rct) and constant phase element (CPE). (f) Current (i)–time (t) chronoamperometric responses obtained for both FeMo Carbide/NG-800 (black line) and 20% Pt/C catalysts (red line) at -0.55 V in O2-saturated 0.1 M KOH solution to methanol. The arrow indicates the addition of 2% (weight ratio) methanol into the O2-saturated electrochemical cell.
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f5: (a) RDE polarization curves for ORR performance of FeMo Carbide/G-800, FeMo Carbide/NG-800 and commercial 20% Pt/C in O2-saturated 0.1 M KOH with disk rotation rate of 800 rpm. (b) RDE curves of the FeMo Carbide/NG-800 at a scan rate of 2 mV s-1 with various rotation rates from 400 to 1600 rpm in O2-saturated 0.1 M KOH. The inset shows the Tafel plot of the FeMo Carbide/NG-800 derived by the mass-transport correction of the corresponding RDE data. (c) The current density Jk of 20% Pt/C, FeMo Carbide/G-800, and FeMo Carbide/NG catalysts with various annealing temperatures (700, 800 and 900 oC) at two different potentials, -0.8, -0.6 and -0.4 V respectively. (d) The dependence of electron transfer number (n) on the potential for FeMo Carbide/G-800 and FeMo Carbide/NG catalysts with different annealing temperatures (700, 800 and 900 oC) and corresponding electrochemical impedance spectroscopy measured at -0.30 V (e). The inset of (e) shows an equivalent electrical circuit consisting of the electrolyte resistance (Rs), interface charge transfer resistance (Rct) and constant phase element (CPE). (f) Current (i)–time (t) chronoamperometric responses obtained for both FeMo Carbide/NG-800 (black line) and 20% Pt/C catalysts (red line) at -0.55 V in O2-saturated 0.1 M KOH solution to methanol. The arrow indicates the addition of 2% (weight ratio) methanol into the O2-saturated electrochemical cell.
Mentions: The oxygen reduction reaction (ORR) activity of various graphene-supported FeMo carbide materials was evaluated by cyclic voltammetry (CV) (Fig. S6) and rotating disk electrode (RDE) measurements (Fig. 5)41, respectively. Compared with featureless CV curves in N2-saturated 0.1 M KOH solution (black line), well-defined oxygen reduction peaks were observed for all electrodes in the O2-saturated KOH solution (red line), revealing the ORR catalytic activity of the graphene-supported FeMo carbide materials. It was noted that the cathodic current of CV curves for all graphene-supported FeMo carbide electrodes display similar reduction peak between −0.5 and −0.3 V (vs. Ag/AgCl), which is attributed to the electrocatalytic oxygen reduction on the electrode23283042. However, the corresponding onset potential, half-wave potential and diffusion-limited currents are different for various electrodes, depending on the catalyst materials. As seen from the results in Fig. S6 and Table S4†, the onset (E1) and half-wave potentials (E2) are the E1 = −0.20 V and E2 = −0.51 V for N-free FeMo Carbide/G-800 (Fig. S6a &Table S4), respectively, lower than those of N-doped graphene supported FeMo carbides, i.e. E1 = −0.14 to −0.09 V and E2 = −0.37 to −0.33 V for FeMo Carbides/NG (Figs. S6 b-f &Table S4). The up-shift of on-set and half-wave potentials clearly indicates that N-doping can enhance catalyst performance for ORR. Moreover, the reduction peaks between −0.5 and −0.3 V become more clear and well-defined with the increasing annealing temperature from 700 to 900 degree, which is attributed to the increased N-doping level (4.2, 4.7 and 4.9% respectively in Table S2†) and thus the enhanced electric conductivity of the catalysts (see impedance data in Fig. 5e). The abovementioned results were further verified via linear sweep voltammery (LSV) measurements on a rotating disk electrode (RDE) for deferent graphene-supported FeMo carbide materials, along with the commercial Pt/C electrode, at a scan rate of 2 mV/s in O2-saturated 0.1 M KOH solution. The polarization curves of graphene-supported FeMo carbide electrodes in Fig. 5a exhibits two-step process, indicating a mixture of two-electron and four-electron reduction processes. The onset potential and half-wave potential for FeMo Carbide/G-800 are E1 = −0.20 V and E2 = −0.51 V, remarkably lower than those of FeMo Carbide/NG-800 in Fig. 5a (i.e. E1 = −0.09 V and E2 = −0.33 V). The current density for FeMo Carbide/G-800 is 1.3 mA/cm2 at −0.40 V, 2.3 mA/cm2 at −0.6 V, and 3.0 mA/cm2 at −0.8 V, respectively, much lower than 2.3 mA/cm2 (at −0.40 V), 3.0 mA/cm2 (at −0.60 V) and 3.5 mA/cm2 (at −0.80 V) for FeMo Carbide/NG-800 (see Fig. 5c & Table S4†). The enhanced ORR current density on FeMo Carbide/NG-800 appears to be attributed to the better dispersion of metal carbides and hence more active sites on NG-800 (vs. G-800). Nevertheless both FeMo Carbides on G-800 and NG-800 catalysts in Fig. 5a are still not comparable to commercial Pt/C catalysts. The polarization profile of Pt/C in Fig. 5a shows much better ORR performance with high onset potential (E1 = 0.06 V), high half-wave potential (E2 = −0.08 V) and high diffusion-limited current (4.0 mA/cm2 at −0.8 V).

Bottom Line: 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).

View Article: PubMed Central - PubMed

Affiliation: 1] School of Applied Science, Harbin University of Science and Technology, Harbin 150080, P.R. China [2] Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 637371, Singapore.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus