Full paperNitrogen and sulfur co-doped porous carbon sheets for energy storage and pH-universal oxygen reduction reaction
Graphical abstract
Introduction
High cost, together with the drawback of methanol crossover and carbon mono-oxide poisoning effects of platinum [1], have prompted intensive research efforts on developing more durable, efficient, and less expensive alternative catalysts for the oxygen reduction reaction (ORR) in fuel cells. The report of cobalt based ORR catalysts [2] has sparked a tremendous interests in the study of nonprecious metal catalysts (NPMCs) [3], [4], [5], [6]. Problems associated with existing NPMCs include the fast degradation of metal components by peroxide intermediates, leading to low stability and insufficient activity [7]. Therefore, identifying the true catalytic sites in atomic level and guiding the design of new types of catalysts with outstanding activity and stability for ORR become quite urgent.
After extensive and in-depth searching, heteroatom (e.g. N, P, S, B) doped carbon materials [8], [9], [10], [11], [12], [13], [14], [15], [16], [17] have been identified as a promising new class of metal-free catalysts for ORR, where excellent electrocatalytic activity and stability have been achieved. A representative example is Dai's work, in which nitrogen doped carbon nanotube arrays were successfully designed, exhibiting a much better ORR performance than Pt/C catalysts in alkaline media [18]. Coupled with improved electron transportation along the aligned carbon nanotubes, the strong electronic affinity of N atoms is counterbalanced by the adjacent C atoms, favoring the adsorption of O2 and effectively weakening O-O bonds for efficient ORR performance via a four electron transfer pathway [19], [20], [21].
Recent worldwide research in this exciting field does not only confirm that electrocatalytic activities of heteroatom-doped carbon materials originate from the changes in charge and spin densities of carbon atoms adjacent to these doping heteroatoms [22], [23], but also reveals that the doping level as well as the type of bonds formed between dopants and carbon atoms have great impacts on oxygen charge transfer [24], [25], [26], [27]. Many studies have followed the above guidelines to carefully tune the active sites via controlling the heteroatom doping types and balancing the doping contents, such as N/S, N/P and N/S/P doped CNTs [28], [29], [30], [31], graphene [11], [32], [33], [34], [35], and graphite [36] for fuel cells and other applications. Even better ORR performance than commercial Pt/C catalysts, from excellent durability to methanol crossover effects, have been demonstrated by those co-/tri-doped carbon based metal-free ORR catalysts in alkaline electrolytes [37], [38], [39], [40].
However, there are only limited success in the design of heteroatom-doped metal-free catalysts in practical acidic polymer electrolyte membrane (PEM) fuel cells, suffering from their fast degradation and low ORR performance in acidic media [41], [42], [43], [44]. This is indicative that the optimal active sites for the ORR in alkaline and acidic environments are likely dissimilar. Therefore, it would be advantageous to design a class of materials which contain different types of ORR catalytic sites, while retaining the favorable 3-dimensional structure for electrolyte transportation and high electrical conductivity for electron transfer. In this work, we developed a new doping strategy for incorporating both nitrogen and sulfur doping types and contents, and rationally designed N/S co-doped porous carbon sheet (NSPCS) cathodes that may potentially work in both acidic and alkaline ORR electrolytes. Electrochemical experiments demonstrate that the as-prepared NSPCS has extraordinarily high onset and half-wave potential of ORR. To the best of our knowledge, its ORR activity in acidic media outperformed all the existing ORR catalysts. The anti-corrosive property of carbon-based NSPCS also provide better methanol tolerance, longer time durability, and excellent capacitance in supercapacitors, making such carbon-based metal-free catalysts as great potential candidates for replacing the commercial platinum catalysts in practical PEM fuel cells.
Section snippets
Results and discussion
The morphology and composites of N,S1,S2-CM1000-b were characterized by SEM, TEM and elemental mapping in Fig. 1. SEM image in Fig. 1a shows a carbon sheet structure, while N,S1,S2-CM1000 without ball milling exhibits a nearly spherical structure in Fig. S1c, illustrating that ball milling has destroyed the spherical structure. Elemental mapping confirms uniform distribution of S, N and O elements on the surface of porous carbon sheet, implying that the active sites arising from nitrogen and
Conclusions
We successfully synthesized a series of N,S-codoped porous carbon materials by a new doping strategy. The as-prepared N,S1,S2-CM1000-b materials composes of porous carbon sheets with high density of active sites on the surface and abundant structural defects. The synergistic effect of doped S and N results in excellent electrochemical performance. It exhibits a high onset and half-wave potential in acidic system that outperform all existing heteroatom-doped carbon based electrode materials.
Preparation of N,S1,S2-CM1000 materials
The preparation of N,S1,S2-CM1000 is accomplished via the pyrolysis of a homogeneous mixture consisting of polymeric materials and thiourea (see Fig. S1). To synthesize the polymer, 0.5 g thiocyanuric acid, 28.0 ml pyridine and 2.0 ml hexachlorobutadiene were mixed in a 50 ml stainless steel autoclave with a Teflon liner. The polymerization took place in an oven at 200 ℃ for 4 h, followed by naturally cooling down to the room temperature. Solid products were collected through centrifugation at
Acknowledgments
This work was supported by the National Natural Science Foundation of China (51772219, 21471116, and 21628102), the Zhejiang Provincial Natural Science Foundation of China (LZ17E020002 and LZ15E020002). Jun Lu gratefully acknowledges support from the U. S. Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Office. Argonne National Laboratory is operated for DOE Office of Science by UChicago Argonne, LLC, under contract number DE-AC02-06CH11357.
References (46)
- et al.
Low-temperature synthesis of nitrogen/sulfur co-doped three-dimensional graphene frameworks as efficient metal-free electrocatalyst for oxygen reduction reaction
Carbon
(2013) First-principles molecular dynamics simulation of O2 reduction on nitrogen-doped carbon
Appl. Surf. Sci.
(2009)- et al.
Direct anchoring of platinum nanoparticles on nitrogen and phosphorus-dual-doped carbon nanotube arrays for oxygen reduction reaction
Electrochim. Acta
(2015) - et al.
N-, P- and S-tridoped graphene as metal-free electrocatalyst for oxygen reduction reaction
J. Electroanal. Chem.
(2015) - et al.
Enhanced electrocatalytic activity due to additional phosphorous doping in nitrogen and sulfur-doped graphene: a comprehensive study
Carbon
(2014) - et al.
Nitrogen and sulfur co-doped porous carbon – is an efficient electrocatalyst as platinum or a hoax for oxygen reduction reaction in acidic environment PEM fuel cell
Energy
(2017) - et al.
Nitrogen and sulfur codoped porous carbon microsphere: a high performance electrode in supercapacitor
Electrochim. Acta
(2016) Electrocatalyst approaches and challenges for automotive fuel cells
Nature
(2012)A new fuel cell cathode catalyst
Nature
(1964)- et al.
High-performance electrocatalysts for oxygen reduction derived from polyaniline, iron, and cobalt
Science
(2011)
Iron-based catalysts with improved oxygen reduction activity in polymer electrolyte fuel cells
Science
Highly crystalline multimetallic nanoframes with three-dimensional electrocatalytic surfaces
Science
Iron-based cathode catalyst with enhanced power density in polymer electrolyte membrane fuel cells
Nat. Commun.
Recent advances in non-precious metal catalysis for oxygen-reduction reaction in polymer electrolyte fuel cells
Energy Environ. Sci.
Nitrogen-doped carbon nanosheets with size-defined mesopores as highly efficient metal-free catalyst for the oxygen reduction reaction
Angew. Chem. Int. Ed.
Nitrogen-doped nanoporous carbon nanosheets derived from plant biomass: an efficient catalyst for oxygen reduction reaction
Energy Environ. Sci.
A metal-free bifunctional electrocatalyst for oxygen reduction and oxygen evolution reactions
Nat. Nanotechnol.
N,P-codoped carbon networks as efficient metal-free bifunctional catalysts for oxygen reduction and hydrogen evolution reactions
Angew. Chem. Int. Ed.
Nitrogen-doped porous carbon nanosheets templated from g-C3N4 as metal-free electrocatalysts for efficient oxygen reduction reaction
Adv. Mater.
N-, O-, and S-tridoped nanoporous carbons as selective catalysts for oxygen reduction and alcohol oxidation reactions
J. Am. Chem. Soc.
BCN graphene as efficient metal-free electrocatalyst for the oxygen reduction reaction
Angew. Chem. Int. Ed.
Can boron and nitrogen co-doping improve oxygen reduction reaction activity of carbon nanotubes
J. Am. Chem. Soc.
Controlling the active sites of sulfur-doped carbon nanotube–graphene nanolobes for highly efficient oxygen evolution and reduction catalysis
Adv. Energy Mater.
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