Elsevier

Electrochimica Acta

Volume 303, 20 April 2019, Pages 167-175
Electrochimica Acta

Electrochemical oxidation of ordered mesoporous carbons and the influence of graphitization

https://doi.org/10.1016/j.electacta.2019.02.065Get rights and content

Highlights

  • The electrochemical oxidation of ordered mesoporous carbons (OMC) has been studied.

  • OMC were graphitized to improve the carbon ordering and degradation resistance.

  • Graphitization led to a significant reduction of the oxidation associated charge.

  • The materials exhibited a large electrochemical surface area after graphitization.

  • An increase of the relative oxygen amount upon electrooxidation was evidenced by XPS.

Abstract

Ordered mesoporous carbon materials (OMC), obtained by the template carbonization pathway from silica templates (sacrificial method), exhibit promising features for many applications mainly due to their large surface area. Graphitization is a common approach to improve the electrical conductivity and degradation resistance. We have investigated the graphitization of two different OMC at 1500 °C and the electrochemical oxidation by potential holding at 1.4 V vs. reversible hydrogen electrode (RHE) in acidic electrolyte. Graphitization conducts to a significant reduction of the electrooxidation associated charge, between 50 and 90% depending on the carbon properties, together with a decrease of surface area of 35–48%. The materials still exhibit a large electrochemical surface area, according to electrochemical impedance and cyclic voltammetry experiments. Upon electrooxidation, the relative amount of oxygen increases according to a comparative analysis of X-ray photoelectron spectroscopy test of the electrodes before and after potential holding. The results are of interest to define strategies towards the amelioration of carbon degradation by electrooxidation in electrochemical devices.

Introduction

Ordered mesoporous carbon (OMC) materials obtained by the template carbonization pathway from silica templates (hard-templating or sacrificial methodology) exhibit tunable nanostructures and developed mesoporosity with widely open interconnected pores, making them promising materials for many applications, such as sensors and biosensors [1], electrochemistry [2], adsorption and catalysis [3], or electrochemical energy storage [[4], [5], [6], [7]] and conversion [8,9]. Among them, OMC have attracted special attention for their application at the catalytic layers of low temperature fuel cells (e.g. polymer electrolyte membrane fuel cells, PEMFC and direct alcohol fuel cells, DAFC). Their large surface area and ordered structure facilitate the dispersion of the active phase for OMC-supported Pt-based nanoparticles, thus favoring the performance of these electrochemical devices [[10], [11], [12], [13], [14], [15], [16], [17], [18]]. Open-frame porous carbons obtained by the sacrificial methodology from silica templates have also been recently investigated as a hosting structure for metal-nitrogen-carbon coordinates to be applied as platinum-free catalysts [[19], [20], [21], [22], [23], [24], [25], [26]].

One drawback of OMC is their low electrical conductivity due to their amorphous character, and consequently high ohmic resistances can be found in electrochemical applications, leading to a decrease of the performance of the device (fuel cells, capacitors, etc.). Furthermore, carbon materials tend to undergo electrooxidation at highly positive potentials [27], which is considered to be one of the main problems facing the lifetime of positive electrodes in electrochemical devices. In order to address these limitations, different graphitization methodologies of templated mesoporous carbons have been proposed, such as heat treatments at high temperature [[27], [28], [29], [30], [31]] or catalytic approaches [[32], [33], [34]]. Catalytic approaches involve the use of metals (e.g. Fe or Ni), which need to be removed in a final step using oxidizing agents and increasing the cost of the final catalyst. Whereas, heat treatments at high temperature have been used to increase the graphitization degree of OMC supports and successfully deposit metal nanoparticles on the surface despite the decrease of the support oxygen content upon annealing [27,35].

Carbon electrooxidation is a complex multi-step process involving both the formation of oxygen species and the complete oxidation to CO2 at elevated potentials through the reaction in equation (1) [36]:C + 2H2O → CO2 + 4H+ + 4e (E0 = 0.207 V vs. RHE)

Although many works have been devoted to study carbon electrooxidation using different nanostructured carbon materials [[37], [38], [39], [40], [41], [42], [43], [44], [45], [46], [47], [48], [49]], the exact mechanism is not completely clear. Additionally, the influence of OMC graphitization on carbon electrooxidation needs to be further studied.

In this work, two different OMC with adjustable textural and morphological properties have been synthesized and heat treated at 1500 °C to increase their crystallinity and their electrical conductivity. The influence of graphitization on the electrochemical oxidation of carbon was evaluated by potential holding at 1.4 V vs RHE in aqueous acid medium (0.5 M H2SO4). Additionally, cyclic voltammetry and electrochemical impedance spectroscopy have been used to study the effect of heat treatment on the electrochemical behavior, together with chemical analysis to elucidate changes in the electrode composition.

Section snippets

Synthesis of ordered mesoporous carbons

OMC were obtained from SBA-15 silica (template) following the hard-templating methodology using different mass ratio (R) of the silica precursor (Tetraethyl Orthosilicate, TEOS, 98 wt %, Aldrich) and the surfactant (P123) (R = TEOS/P123). A furan resin/acetone mixture was used as carbon precursor. Further details can be found in Ref. [50]. Following this procedure, two different materials were obtained: OMC-R2 and OMC-R5, with R = 2 and 5, respectively. Previous works of our group showed that

Physicochemical characterization of ordered mesoporous carbons

TEM images evidence the typical ordered honeycomb structure of OMC, consisting of carbon nanorods with uniform mesopores (Fig. 1). Comparing the bare (or untreated) materials (OMC-R2 and OMC-R5), an increase of the TEOS/P123 mass ratio from 2 to 5 led to a decrease of the ordering degree of mesoporous carbons, due to a decrease of the copolymer amount (P123). In acid media, P123 surfactant forms structures of interconnected liquid crystals, which drive the silica structuration and generate the

Conclusions

Two different ordered mesoporous carbons have been synthesized and thermally treated at 1500 °C to induce graphitization. These materials have been investigated for the electrooxidation of carbon at room temperature and 1.4 V vs. RHE in 0.5 M H2SO4. The main physicochemical properties, including surface area, pore volume and chemical composition have been evaluated in order to establish a correlation with the electrochemical behavior. Graphitization resulted in an important decrease of the

Acknowledgments

The authors gratefully acknowledge financial support given by Spanish Ministry of Science, Innovation and Universities MICINN (ENE2017-83976-C2-1-R) and to the Aragón Government to the Fuel Conversion Group (T06_17R). DS acknowledges also MICINN for his Ramón y Cajal contract (RyC-2016-20944). Furthermore, the authors wish to thank Dra. Ana Beatriz García (INCAR-CSIC) for the graphitization treatment of OMC.

References (60)

  • G. Chai et al.

    Ordered uniform porous carbons as a catalyst support in a direct methanol fuel cell

    Electrochim. Acta

    (2004)
  • J. Zeng et al.

    Hybrid ordered mesoporous carbons doped with tungsten trioxide as supports for Pt electrocatalysts for methanol oxidation reaction

    Electrochim. Acta

    (2013)
  • A.H.A. Monteverde Videla et al.

    Varying the morphology of Fe-N-C electrocatalysts by templating Iron Phthalocyanine precursor with different porous SiO<inf>2</inf> to promote the Oxygen Reduction Reaction

    Electrochim. Acta

    (2015)
  • L. Osmieri et al.

    Optimization of a Fe–N–C electrocatalyst supported on mesoporous carbon functionalized with polypyrrole for oxygen reduction reaction under both alkaline and acidic conditions

    Int. J. Hydrog. Energy

    (2016)
  • L. Osmieri et al.

    Fe-N/C catalysts for oxygen reduction reaction supported on different carbonaceous materials. Performance in acidic and alkaline direct alcohol fuel cells

    Appl. Catal. B Environ.

    (2017)
  • M.M. Hossen et al.

    Synthesis and characterization of high performing Fe-N-C catalyst for oxygen reduction reaction (ORR) in Alkaline Exchange Membrane Fuel Cells

    J. Power Sources

    (2018)
  • D. Sebastián et al.

    Insights on the extraordinary tolerance to alcohols of Fe-N-C cathode catalysts in highly performing direct alcohol fuel cells

    Nanomater. Energy

    (2017)
  • V. Celorrio et al.

    Influence of thermal treatments on the stability of Pd nanoparticles supported on graphitised ordered mesoporous carbons

    Int. J. Hydrog. Energy

    (2016)
  • H. Darmstadt et al.

    Surface chemistry of ordered mesoporous carbons

    Carbon N. Y.

    (2002)
  • H. Darmstadt et al.

    Pore structure and graphitic surface nature of ordered mesoporous carbons probed by low-pressure nitrogen adsorption

    Microporous Mesoporous Mater.

    (2003)
  • M. Sevilla et al.

    Catalytic graphitization of templated mesoporous carbons

    Carbon N. Y.

    (2006)
  • S. Maass et al.

    Carbon support oxidation in PEM fuel cell cathodes

    J. Power Sources

    (2008)
  • C.-C. Hung et al.

    Corrosion of carbon support for PEM fuel cells by electrochemical quartz crystal microbalance

    J. Power Sources

    (2011)
  • S.J. Ashton et al.

    A DEMS study on the electrochemical oxidation of a high surface area carbon black

    Electrochem. Commun.

    (2011)
  • C. Alegre et al.

    Carbon xerogels electrochemical oxidation and correlation with their physico-chemical properties

    Carbon N. Y.

    (2019)
  • B. Avasarala et al.

    Surface oxidation of carbon supports due to potential cycling under PEM fuel cell conditions

    Electrochim. Acta

    (2010)
  • V.A. Golovin et al.

    New nitrogen-containing carbon supports with improved corrosion resistance for proton exchange membrane fuel cells

    Int. J. Hydrog. Energy

    (2017)
  • E.N. Gribov et al.

    A simple method for estimating the electrochemical stability of the carbon materials

    Int. J. Hydrog. Energy

    (2016)
  • R. Berenguer et al.

    Enhanced electro-oxidation resistance of carbon electrodes induced by phosphorus surface groups

    Carbon N. Y.

    (2015)
  • L. Calvillo et al.

    Control of textural properties of ordered mesoporous materials

    Microporous Mesoporous Mater.

    (2008)
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