Elsevier

Catalysis Today

Volume 249, 1 July 2015, Pages 236-243
Catalysis Today

Influence of the reaction temperature on the oxygen reduction reaction on nitrogen-doped carbon nanotube catalysts

https://doi.org/10.1016/j.cattod.2014.11.020Get rights and content

Highlights

  • N-doped carbon nanotubes prepared by CVD method with iron as growth catalyst.

  • Influence of iron on the oxygen reduction reaction activity accessed by the RRD electrode.

  • Influence of the temperature on the ORR activity and stability.

  • Comparison of the ORR stability between N-CNT and Pt/C catalysts.

Abstract

Nitrogen-doped carbon nanotubes (N-CNT) were synthesized at 700 °C via the chemical vapour deposition (CVD) method and were used as catalysts in the oxygen reduction reaction (ORR) in 0.1 M KOH. The activity toward the ORR and the stability of these N-CNTs in alkaline solution were studied as a function of the reaction temperature and of the chemical treatment applied to the catalyst. The kinetic analysis of these catalysts was also carried out and compared to the ORR performance of the commercial Pt/C Vulcan XC72 catalyst. N-CNT-700BW catalyst without any chemical treatment after the CVD synthesis, possesses a half-wave potential E1/2 of approximately 0.82 V vs. RHE, 50 mV lower than the E1/2 value of Pt/C catalyst and a specific current density Jk at 0.9 V = 5.46 mA/mg at T = 25 °C. Removal of the major part of the iron growth catalyst by a chemical treatment resulted in a strongly decreased but still measurable activity. The activation energy of the N-CNT-based catalyst was calculated and is around 38 kJ mol−1 at an ORR overpotential of 300 mV. Increasing the temperature of the electrolyte up to 75 °C leads to a positive shift of the half-wave potential of the reaction as well as an increase of the H2O2 escape. The long-term stability test has also been conducted and indicates a good stability of the activity of the N-CNT-based catalysts under operation in alkaline media.

Introduction

The oxygen reduction reaction (ORR) is of critical importance to support industrial development of fuel cells and metal-air batteries for the future energy mix infrastructure [1], [2], [3]. The slow kinetics of the ORR compared to that of the hydrogen oxidation at the anode severely limits the performance of low temperature fuel cells. To date, platinum-based materials are used as state-of-the art ORR catalysts due to their higher, compared to other materials, catalytic activity. However, they suffer from high cost, low tolerance to poisons such as methanol and CO, and low stability mostly due to the Pt particle agglomeration, Pt dissolution and to the corrosion of the carbon support under fuel cell operation conditions [4], [5]. A large number of investigations have been devoted to the decrease of the amount and to the replacement of platinum by other catalysts, including Pt-based alloys [6], [7], [8], transition metal–nitrogen–carbon M–N–C catalysts [9], [10], [11], [12], [13], [14], perovskite-type oxide catalysts [15], [16], [17] and carbon-based materials doped with various elements [18].

Application of M–N–C-type materials as the ORR catalysts dates back to the 1960–1970s when it was discovered that metal (e.g. Fe) porphyrins and Phthalocyanines can be pyrolyzed to produce highly active catalysts [19], [20]. The last decades saw a remarkable rise in the interest toward the M–N–C ORR materials, a diversification of their methods of preparation by using various transition metal and nitrogen precursors [10], [12], [21] and a significant progress in the understanding of the nature of the active sites and the mechanism of electrocatalysis [13], [14], [22].

Nitrogen-doped carbon composites such as nitrogen-doped carbon nanotubes/nanofibers and/or mesoporous carbon have received an increasing academic and industrial interest, as catalysts or as catalyst support with enhanced surface properties, in several catalytic applications during the last decades [23], [24], [25], [26], [27], [28]. These composites, either in a bulk or supported forms, are mostly synthesized via chemical vapor deposition (CVD) process using different sources of carbon and nitrogen precursors and iron as the growth catalyst [29], [30], [31], [32], [33], [34], [35] or synthesized by pyrolysis of a precursor containing nitrogen, carbon in the presence of a transition metal catalyst [36], [37]. Beside their use as catalyst support in several reactions, nitrogen-doped carbon nanotubes (N-CNTs) have also been considered as catalysts for replacing platinum in the cathode oxygen reduction reaction (ORR) for fuel cells application [38], [39], [40], [41], [42], [43], [44]. The issue on whether metal-free N-containing materials might act as catalysts in the ORR attracted much attention. It is widely accepted that while in alkaline media metal-free carbon materials possess the ORR activity, in acid the activity of metal-free materials is small. In recent studies, Singh et al. [45] and Masa et al. [46] compared N-containing carbon nanostructures and N-coordinated iron carbon catalysts and observed a significant positive effect of transition metal ions on the ORR activity. On the other hand, Singh et al. [45] reported that an initially a much higher activity of the iron-containing catalyst degraded more rapidly than that of iron-free catalyst in the fuel cell environment.

In general, the ORR is operated at temperature close to the maximum affordable temperature of the fuel cell membrane, ca. 80 °C for Nafion®. For the state-of-the-art anion exchange membranes the operating temperature is usually lower due to their so far insufficient thermal stability. It is thus of interest to compare the electrocatalytic activities of Pt and non-PGM (platinum group metal) catalysts as a function of the operation temperature. Furthermore, it is expected that an increase of the reaction temperature increases the materials corrosion which could directly impact the ORR performance during the operation. It is thus of interest to be able to correlate the stability of the N-doped carbon catalysts, after and before leaching of the iron catalyst with that of the Pt/C, not only at room temperature, but also at higher operating temperature. Deactivation of the Pt/C catalyst as a result of cycling was reported in a number of publications [5], [43], [44], [47], [48]. Herein, we report on the ORR activity and stability of the N-CNTs catalysts as a function of the reaction temperature (25–75 °C) and their comparison to a benchmark Pt-20 wt%/C catalyst. It is expected that such investigation will be of interest for the future development of non-PGM catalysts for fuel cell applications where the long-term stability is a prerequisite.

Section snippets

N-CNTs synthesis

The N-CNT sample was synthesized using the chemical vapor deposition (CVD) method with iron supported on alumina as a growth catalyst [23], [24], [49]. The Fe/Al2O3 catalyst was synthesized by impregnating the gamma alumina support with an aqueous solution containing Fe(NO3)3 and contained 20 wt% of Fe. The solid was dried at room temperature overnight and oven-dried at 110 °C for 24 h. It was then calcined in air at 350 °C for 2 h in order to transform the nitrate precursor into Fe2O3 oxide. The Fe2

Characterization of N-CNTs

Representative SEM and TEM micrographs of N-CNTs synthesized at 700 °C are presented in Fig. 1. SEM micrographs indicate the relatively high homogeneity of the diameter of the as-synthesized N-CNTs which is centered around 80 nm and length up to several tens of micrometers (Fig. 1A and B). According to the SEM analysis the N-CNTs are highly entangled forming bundles. In agreement with the recent TEM tomography analysis [52], TEM micrograph of the as-synthesized sample (Fig. 1C) shows the

Conclusions

Nitrogen-doped carbon nanotube (N-CNT) catalysts have been synthesized via the chemical vapor deposition (CVD) method at 700 °C using an Fe growth catalyst and their catalytic activity toward the oxygen reduction reaction (ORR) has been studied in alkaline electrolyte. The removal of the iron growth catalyst by a chemical treatment resulted in a significant decrease of the ORR currents as well as an increase up to 30% of the H2O2 amount escaping the catalytic layer during the ORR confirming that

Acknowledgements

The present work is financially supported by a European project (FREECATS) under a contract number NMP3-SL-2012-280658. LTP would like to thank the EU for the grant during his postdoctoral stay at the ICPEES. DVC would like to thank the Vietnamese government for the grant during his stay at the ICPEES. Dr. W. Baaziz and T. Romero (ICPEES) are gratefully acknowledged for performing TEM and SEM analysis of the sample. The SEM and TEM experiments were carried out at the facilities of IPCMS (UMR

References (68)

  • L. Dubau et al.

    Electrochim. Acta

    (2013)
  • A. Serov et al.

    Appl. Catal. B

    (2014)
  • T. Poux et al.

    Catal. Today

    (2012)
  • A. Serov et al.

    Electrochem. Commun.

    (2012)
  • J. Amadou et al.

    Catal. Today

    (2008)
  • K. Chizari et al.

    Carbon

    (2014)
  • C.Y. He et al.

    Electrochem. Commun.

    (2013)
  • Q. Liu et al.

    Electrochem. Commun.

    (2013)
  • Z. Lin et al.

    Carbon

    (2013)
  • R. Othman et al.

    Int. J. Hydrogen Energy

    (2012)
  • D. Singh et al.

    J. Catal.

    (2014)
  • J. Masa et al.

    Electrochim. Acta

    (2014)
  • C. Grolleau et al.

    Electrochim. Acta

    (2008)
  • K. Chizari et al.

    Appl. Catal. A: Gen.

    (2010)
  • S. Biniak et al.

    Carbon

    (1997)
  • V.V. Strelko et al.

    Surf. Sci.

    (2004)
  • T. Sharifi et al.

    Carbon

    (2012)
  • M. Rouhet et al.

    Electrochem. Commun.

    (2013)
  • W.Y. Wong et al.

    Electrochim. Acta

    (2014)
  • P.D. Beattie et al.

    J. Electroanal. Chem.

    (1999)
  • N.M. Markovic et al.

    Surf. Sci. Rep.

    (2002)
  • R. Schlögl
  • M. Winter et al.

    Chem. Rev.

    (2004)
  • N.M. Marković et al.

    Fuel Cell

    (2001)
  • V.M.V. Lebedeva et al.

    Electrochim. Acta

    (2013)
  • J. Greeley et al.

    Nat. Chem.

    (2009)
  • V.R. Stamenkovic et al.

    Science

    (2007)
  • G. Wu et al.

    Acc. Chem. Res.

    (2013)
  • M. Lefèvre et al.

    Science

    (2009)
  • T.S. Olson et al.

    J. Phys. Chem. C

    (2010)
  • G. Wu et al.

    Science

    (2011)
  • U. Tylus et al.

    J. Phys. Chem. C

    (2014)
  • J. Suntivich et al.

    Nat. Chem.

    (2011)
  • Cited by (22)

    • Preliminary study on the electrocatalytic performance of an iron biochar catalyst prepared from iron-enriched plants

      2020, Journal of Environmental Sciences (China)
      Citation Excerpt :

      To verify this, an iron-impregnated biochar (Fe-BC) catalyst was prepared by pyrolyzing E. crassipes roots grown hydroponically in solutions with different concentrations of Fe(III). The catalytic activity of the different Fe-BC preparations was tested using electrocatalytic reduction of hydrogen peroxide (H2O2), a technique widely used in materials science, chemical analysis, environment assessment and clinical diagnostics (Muthukrishnan et al., 2015; Sitnikova et al., 2014; Truong et al., 2015). This study explores the feasibility of reuse of hyperaccumulating plants used for phytoremediation.

    • Role of phosphorus in nitrogen, phosphorus dual-doped ordered mesoporous carbon electrocatalyst for oxygen reduction reaction in alkaline media

      2018, International Journal of Hydrogen Energy
      Citation Excerpt :

      Recent studies have shown that nitrogen (N)-doped carbon nanomaterials (such as ordered mesoporous carbons, carbon nanotubes, graphene, etc.) could be an efficient and metal-free alternative to platinum (Pt) for oxygen reduction reaction (ORR), which enables a significant cost reduction while maintaining high efficiency with economic viability for applications in fuel cells and other energy devices [1–7].

    • Controllable synthesis of three-dimensional nitrogen-doped graphene as a high performance electrocatalyst for oxygen reduction reaction

      2017, International Journal of Hydrogen Energy
      Citation Excerpt :

      Given that metal macrocycles become metal–nitrogen–carbon (M–N–C) cluster after the pyrolysis, the complexes of organic compounds and transition metal are used to prepare M–N–C cluster catalysts [13–16]. Non-precious metal catalysts also contain carbon-based metal-free materials, such as heteroatom-doped (N, P, B) graphene [17–20], carbon nanotubes [21–24], carbon nanofibers [25], and porous carbon [26,27]. Among these non-precious metal catalysts, N-doped graphene materials become one of the hot topics in the fuel cell research [28].

    • One-step synthesis of nitrogen-doped carbon nanofibers from melamine over nickel alloy in a closed system

      2017, Chemical Physics Letters
      Citation Excerpt :

      The catalysts, as usual, also contain a support or textural promoter, which is aimed to stabilize the metal particles in disperse state. The synthesis of CNF is performed in a flow regime, while the doping with nitrogen is achieved by addition of nitrogen precursor (ammonia, pyridine, melamine, methylimidazoles, etc.) into the reaction mixture [21–24]. In present work, a new approach for the synthesis of N-CNF is proposed.

    View all citing articles on Scopus
    View full text