Fe3C nanoparticle decorated Fe/N doped graphene for efficient oxygen reduction reaction electrocatalysis
Introduction
Exploring high performance electrocatalysts for sluggish oxygen reduction reaction (ORR) is crucial to promote the large-scale practical application of fuel cells and metal-air batteries [1], [2], [3]. Precious metal platinum (Pt) and its alloys have long been used as most active ORR catalysts, but their high cost and limited durability hinder their widespread applications [4], [5]. In recent years extensive research efforts have been devoted to seeking affordable and sustainable ORR electrocatalysts to replace the expensive Pt-based catalysts in fuel cells. In this regard, non-precious (transition) metal based materials have attracted particular interest since 1964 when cobalt phthalocyanine was reported as a promising ORR electrocatalyst [6]. Various hybrid materials containing non-precious metal (Co, Fe, Mn, etc.) supported on carbon have been successfully synthesized by intentionally adding non-precious metal into the carbon matrix to form catalytic active sites. The metal, particularly Fe in the form of oxide, carbide, or hydroxide has demonstrated its magic to boost the ORR activity of the neighboring graphitic carbon [7], [8], [9], [10], [11], [12]. Further, a breakthrough was made by Zelenay et al., who successfully synthesized Fe/N/C catalysts via heat-treatment of polyaniline, FeCl3 and carbon black, and as-prepared Fe/N/C material marks the most promising candidates among various non-precious metal ORR electrocatalysts [11]. Although it is still under debate about the active sites of these materials, it is now generally accepted that the simultaneous presence of transition metal species and nitrogen in the carbon matrix is critical to maximize the ORR activity.
Recently, Fe3C nanoparticle encapsulated in N-doped carbon has been reported as a new kind of highly active ORR electrocatalyst [7], [13], [14], [15]. It is proposed that the simultaneous N-doping and Fe3C encapsulation play key role in improving the ORR catalytic performance. For example, N-enriched core-shell structured ORR catalyst (Fe/Fe3C@NC) and N-doped carbon with incorporated Fe/Fe3C-nanoparticles were separately reported by different groups with comparable performance to the state-of-the-art Pt/C catalyst [14], [15]. A versatile iron–tannin-framework ink coating strategy was developed to fabricate cellulose-derived Fe3C/FeNC catalysts [16]. Xing and coworkers reported excellent ORR activity and stability of Fe3C encapsulated in hierarchically porous nitrogen-doped carbon materials in both alkaline and acidic media [17]. In 2015, mesoporous Fe/N co-doped carbon nanofibers with encapsulated Fe3C nanoparticles was reported with catalytic activity comparable to commercial Pt/C in alkaline media [18], [19], [20], [21]. Later it was further disclosed that these Fe3C nanocrystals are able to dramatically boost the catalytic activity of the neighboring FeNC active sites for ORR, which offers a useful guidance to rationally design highly active Fe/N/C based ORR electrocatalysts [22], [23].
In this work we report a facile method to synthesize mesoporous Fe/N co-doped graphene with encapsulated Fe3C nanoparticles (Fe3C@Fe/N-graphene) as an efficient ORR electrocatalyst. The synthesis relies on the spontaneous oxidative polymerization of dopamine to form polydopamine (PDA) film on graphene oxide (GO) surface in the presence of Fe3+, followed by thermal annealing in Argon (Ar) atmosphere, as shown in Fig. 1. Some Fe3+ ions were chelated into the resultant PDA film and the rest were also hydrolyzed to from FeOOH nanoparticles on the GO surface. After annealing of the PDA-Fe-rGO precursor in an inert atmosphere, Fe3C@Fe/N-graphene catalyst was obtained. Electrochemical evaluations suggest that as-prepared catalyst shows high ORR catalytic activity with overwhelming four-electron pathway, long-term durability and high methanol tolerance in alkaline media. This work reports a facile method to synthesize promising ORR electrocatalysis with multiple components and hierarchical architecture, and may offer valuable insight into the underlying mechanism of Fe3C-boosted ORR activity of Fe/N doped carbon.
Section snippets
Chemicals
Graphite powder (99.95%) and dopamine were obtained from Aladdin. Hydrogen peroxide solution (H2O2, 30%), methanol (CH3OH, 99.5%), hydrochloric acid (HCl, 37%), sodium nitrate (NaNO3) and sulfuric acid (H2SO4, 98%) were purchased from Chongqing Chuan Dong Chemical Company. All chemicals were used as received without further purification.
Synthesis of electrocatalysts
GO was synthesized using the Hummers method with minor modification [24]. Briefly, 2 g of graphite powder and 1.2 g of sodium nitrate (NaNO3) were mixed with
Results and discussion
The Fe3C@Fe/N-graphene catalyst was synthesized via a simple oxidative polymerization process to form the PDA-Fe-rGO precursor, followed by thermal annealing of as-prepared precursor. As shown in Fig. 1, during the polymerization, a portion of Fe3+ ion was chelated by the catechol groups of dopamine (See UV-vis spectra in Fig. S1 in Supporting Information) and incorporated into the resultant PDA film; due to the slightly alkaline environment, the remaining Fe3+ was hydrolyzed to form
Conclusions
In summary, a facile strategy has been developed to prepare Fe3C@Fe/N-graphene as a highly efficient ORR electrocatalyst. As-prepared catalyst shows high ORR catalytic activity with overwhelming four-electron pathway, long-term durability and high methanol tolerance in alkaline media. Although the limited current density is lower than that of Pt/C, this Fe3C@Fe/N-graphene catalyst is still valuable if considering its excellent long-term stability, strong tolerance, and low cost synthesis. This
Acknowledgements
We would like to gratefully acknowledge the financial support from National Natural Science Foundation of China (No. 21205098, 21273173), Fundamental Research Funds for the Central Universities (XDJK2015B014), Chongqing Key Laboratory for Advanced Materials and Technologies of Clean Energies, Chongqing Engineering Research Center for Rapid Diagnosis of Dread Disease and Chongqing development and reform commission.
References (39)
Renew. Sustain. Energy Rev.
(2007)- et al.
J. Power Sources
(2015) - et al.
Int. J. Hydrogen Energy
(2014) - et al.
J. Power Sources
(2015) - et al.
Nano Energy
(2014) - et al.
J. Power Sources
(2014) - et al.
J. Power Sources
(2013) - et al.
Chem. Soc. Rev.
(2015) - et al.
Chem. Rev.
(2004) - et al.
Acc. Chem. Res.
(2013)
Nature
Angew. Chem. Int. Ed.
Science
Adv. Mater.
ACS Catal.
Science
J. Am. Chem. Soc.
Angew. Chem. Int. Ed.
Angew. Chem.
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