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Carbon-based electrocatalysts for advanced energy conversion and storage.

Zhang J, Xia Z, Dai L - Sci Adv (2015)

Bottom Line: Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play curial roles in electrochemical energy conversion and storage, including fuel cells and metal-air batteries.Having rich multidimensional nanoarchitectures [for example, zero-dimensional (0D) fullerenes, 1D carbon nanotubes, 2D graphene, and 3D graphite] with tunable electronic and surface characteristics, various carbon nanomaterials have been demonstrated to act as efficient metal-free electrocatalysts for ORR and OER in fuel cells and batteries.We present a critical review on the recent advances in carbon-based metal-free catalysts for fuel cells and metal-air batteries, and discuss the perspectives and challenges in this rapidly developing field of practical significance.

View Article: PubMed Central - PubMed

Affiliation: Center of Advanced Science and Engineering for Carbon (Case4Carbon), Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, OH 44106, USA.

ABSTRACT
Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play curial roles in electrochemical energy conversion and storage, including fuel cells and metal-air batteries. Having rich multidimensional nanoarchitectures [for example, zero-dimensional (0D) fullerenes, 1D carbon nanotubes, 2D graphene, and 3D graphite] with tunable electronic and surface characteristics, various carbon nanomaterials have been demonstrated to act as efficient metal-free electrocatalysts for ORR and OER in fuel cells and batteries. We present a critical review on the recent advances in carbon-based metal-free catalysts for fuel cells and metal-air batteries, and discuss the perspectives and challenges in this rapidly developing field of practical significance.

No MeSH data available.


Related in: MedlinePlus

Comparison of a conventional air electrode and a CNT/ionic liquid–based air electrode.(A) Schematic illustration of a conventional air electrode. (B) Weight variation of the SWNT/[C2] salt and [C2C1im][NTf2] for 1 week. (C and D) Schematic illustration of the SWNT/[C2C1im][NTf2] CNG air electrode, in which SWNTs are untangled through π-π interaction with the imidazolium cation of [C2C1im] (green), whereas [NTf2] ions (purple) are anchored in the gel through electric neutrality (C) and the tricontinuous passage of electrons, ions, and oxygen in SWNT/[C2C1im][NTf2] CNG (D). Electrons conduct along the CNTs, whereas lithium ions transferred from the ionic liquid electrolyte outside into the cross-linked network gel become coordinated by the inside-anchored [NTf2] ion. Oxygen in the cross-linked network gel is incorporated with the lithium ions and electrons along the SWNTs, thereby turning into the discharge products. [From T. Zhang, H. Zhou, From Li–O2 to Li–air batteries: Carbon nanotubes/ionic liquid gels with a tricontinuous passage of electrons, ions, and oxygen. Angew. Chem. Int. Ed.51, 11062–11067 (2012). Reprinted with permission from Wiley.]
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Figure 9: Comparison of a conventional air electrode and a CNT/ionic liquid–based air electrode.(A) Schematic illustration of a conventional air electrode. (B) Weight variation of the SWNT/[C2] salt and [C2C1im][NTf2] for 1 week. (C and D) Schematic illustration of the SWNT/[C2C1im][NTf2] CNG air electrode, in which SWNTs are untangled through π-π interaction with the imidazolium cation of [C2C1im] (green), whereas [NTf2] ions (purple) are anchored in the gel through electric neutrality (C) and the tricontinuous passage of electrons, ions, and oxygen in SWNT/[C2C1im][NTf2] CNG (D). Electrons conduct along the CNTs, whereas lithium ions transferred from the ionic liquid electrolyte outside into the cross-linked network gel become coordinated by the inside-anchored [NTf2] ion. Oxygen in the cross-linked network gel is incorporated with the lithium ions and electrons along the SWNTs, thereby turning into the discharge products. [From T. Zhang, H. Zhou, From Li–O2 to Li–air batteries: Carbon nanotubes/ionic liquid gels with a tricontinuous passage of electrons, ions, and oxygen. Angew. Chem. Int. Ed.51, 11062–11067 (2012). Reprinted with permission from Wiley.]

Mentions: 3D carbon foam with bimodal mesopores of narrow pore size distributions (~4.3 and 30.4 nm), prepared by using a mesocellular silica foam as the hard template, was demonstrated to show an approximately 40% higher discharge capacity in a Li-O2 battery than the commercial carbon blacks (such as XC-72, Super P), as the ultra-large surface area of mesoporous carbon with a large pore volume could allow a high uptake of lithium oxide during the discharge process (142). Template-synthesized porous honeycomb-like carbon with hierarchical pores has also been used as an air electrode in Li-O2 batteries to yield a significantly higher specific capacity of 3233 mAh g−1 and an improved cycle efficiency with a higher discharge voltage plateau (2.75 versus 2.50 V) than that of a conventional carbon electrode (143). These results indicate that carbon with an optimal pore structure, a large surface area, and a high pore volume is a desirable air cathode for a high rate and large discharge capacity. Indeed, hierarchical carbon electrodes composed of highly aligned CNT fibrils with a well-defined pore structure, which renders good accessibility of oxygen to the inner electrode and a uniform deposition of discharge products on the individual CNTs, have been demonstrated to significantly enhance both the cycling stability and rate capability for Li-O2 batteries (144). Similarly, NCNTs synthesized on nickel foams by a floating catalyst CVD method were shown to deliver a specific capacity of 1814 mAh g−1 (normalized to the weight of the air electrode) in Li-O2 batteries. These 3D network structures could not only facilitate the O2 diffusion but also provide sufficient void volume for product deposition during a discharge process. The intimate contact between the NCNTs and the Ni current collector is an additional advantage for suppressing the volume expansion, leading to less polarization and good cycling performance (143). On the other hand, Zhang and Zhou (145) have designed, along with a conventional air electrode (Fig. 9A), a network gel consisting of SWNTs and ionic liquid [that is, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) ([C2C1im][NTf2])] as the oxygen electrode (Fig. 9, B and C) for a Li-O2 battery. The use of ionic liquid with excellent nonvolatility, high hydrophobicity, high thermal stability, and a broad electrochemical window, in conjunction with the 3D physically cross-linked SWNTs for efficient electron transfer and high uptake of discharge products (Fig. 9C), ensured an efficient tricontinuous pathway for electron, ion, and oxygen transfers (Fig. 9D), leading to a pronounced specific energy density and robust cycling stability without decomposition of the electrolyte (145).


Carbon-based electrocatalysts for advanced energy conversion and storage.

Zhang J, Xia Z, Dai L - Sci Adv (2015)

Comparison of a conventional air electrode and a CNT/ionic liquid–based air electrode.(A) Schematic illustration of a conventional air electrode. (B) Weight variation of the SWNT/[C2] salt and [C2C1im][NTf2] for 1 week. (C and D) Schematic illustration of the SWNT/[C2C1im][NTf2] CNG air electrode, in which SWNTs are untangled through π-π interaction with the imidazolium cation of [C2C1im] (green), whereas [NTf2] ions (purple) are anchored in the gel through electric neutrality (C) and the tricontinuous passage of electrons, ions, and oxygen in SWNT/[C2C1im][NTf2] CNG (D). Electrons conduct along the CNTs, whereas lithium ions transferred from the ionic liquid electrolyte outside into the cross-linked network gel become coordinated by the inside-anchored [NTf2] ion. Oxygen in the cross-linked network gel is incorporated with the lithium ions and electrons along the SWNTs, thereby turning into the discharge products. [From T. Zhang, H. Zhou, From Li–O2 to Li–air batteries: Carbon nanotubes/ionic liquid gels with a tricontinuous passage of electrons, ions, and oxygen. Angew. Chem. Int. Ed.51, 11062–11067 (2012). Reprinted with permission from Wiley.]
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Figure 9: Comparison of a conventional air electrode and a CNT/ionic liquid–based air electrode.(A) Schematic illustration of a conventional air electrode. (B) Weight variation of the SWNT/[C2] salt and [C2C1im][NTf2] for 1 week. (C and D) Schematic illustration of the SWNT/[C2C1im][NTf2] CNG air electrode, in which SWNTs are untangled through π-π interaction with the imidazolium cation of [C2C1im] (green), whereas [NTf2] ions (purple) are anchored in the gel through electric neutrality (C) and the tricontinuous passage of electrons, ions, and oxygen in SWNT/[C2C1im][NTf2] CNG (D). Electrons conduct along the CNTs, whereas lithium ions transferred from the ionic liquid electrolyte outside into the cross-linked network gel become coordinated by the inside-anchored [NTf2] ion. Oxygen in the cross-linked network gel is incorporated with the lithium ions and electrons along the SWNTs, thereby turning into the discharge products. [From T. Zhang, H. Zhou, From Li–O2 to Li–air batteries: Carbon nanotubes/ionic liquid gels with a tricontinuous passage of electrons, ions, and oxygen. Angew. Chem. Int. Ed.51, 11062–11067 (2012). Reprinted with permission from Wiley.]
Mentions: 3D carbon foam with bimodal mesopores of narrow pore size distributions (~4.3 and 30.4 nm), prepared by using a mesocellular silica foam as the hard template, was demonstrated to show an approximately 40% higher discharge capacity in a Li-O2 battery than the commercial carbon blacks (such as XC-72, Super P), as the ultra-large surface area of mesoporous carbon with a large pore volume could allow a high uptake of lithium oxide during the discharge process (142). Template-synthesized porous honeycomb-like carbon with hierarchical pores has also been used as an air electrode in Li-O2 batteries to yield a significantly higher specific capacity of 3233 mAh g−1 and an improved cycle efficiency with a higher discharge voltage plateau (2.75 versus 2.50 V) than that of a conventional carbon electrode (143). These results indicate that carbon with an optimal pore structure, a large surface area, and a high pore volume is a desirable air cathode for a high rate and large discharge capacity. Indeed, hierarchical carbon electrodes composed of highly aligned CNT fibrils with a well-defined pore structure, which renders good accessibility of oxygen to the inner electrode and a uniform deposition of discharge products on the individual CNTs, have been demonstrated to significantly enhance both the cycling stability and rate capability for Li-O2 batteries (144). Similarly, NCNTs synthesized on nickel foams by a floating catalyst CVD method were shown to deliver a specific capacity of 1814 mAh g−1 (normalized to the weight of the air electrode) in Li-O2 batteries. These 3D network structures could not only facilitate the O2 diffusion but also provide sufficient void volume for product deposition during a discharge process. The intimate contact between the NCNTs and the Ni current collector is an additional advantage for suppressing the volume expansion, leading to less polarization and good cycling performance (143). On the other hand, Zhang and Zhou (145) have designed, along with a conventional air electrode (Fig. 9A), a network gel consisting of SWNTs and ionic liquid [that is, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) ([C2C1im][NTf2])] as the oxygen electrode (Fig. 9, B and C) for a Li-O2 battery. The use of ionic liquid with excellent nonvolatility, high hydrophobicity, high thermal stability, and a broad electrochemical window, in conjunction with the 3D physically cross-linked SWNTs for efficient electron transfer and high uptake of discharge products (Fig. 9C), ensured an efficient tricontinuous pathway for electron, ion, and oxygen transfers (Fig. 9D), leading to a pronounced specific energy density and robust cycling stability without decomposition of the electrolyte (145).

Bottom Line: Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play curial roles in electrochemical energy conversion and storage, including fuel cells and metal-air batteries.Having rich multidimensional nanoarchitectures [for example, zero-dimensional (0D) fullerenes, 1D carbon nanotubes, 2D graphene, and 3D graphite] with tunable electronic and surface characteristics, various carbon nanomaterials have been demonstrated to act as efficient metal-free electrocatalysts for ORR and OER in fuel cells and batteries.We present a critical review on the recent advances in carbon-based metal-free catalysts for fuel cells and metal-air batteries, and discuss the perspectives and challenges in this rapidly developing field of practical significance.

View Article: PubMed Central - PubMed

Affiliation: Center of Advanced Science and Engineering for Carbon (Case4Carbon), Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, OH 44106, USA.

ABSTRACT
Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play curial roles in electrochemical energy conversion and storage, including fuel cells and metal-air batteries. Having rich multidimensional nanoarchitectures [for example, zero-dimensional (0D) fullerenes, 1D carbon nanotubes, 2D graphene, and 3D graphite] with tunable electronic and surface characteristics, various carbon nanomaterials have been demonstrated to act as efficient metal-free electrocatalysts for ORR and OER in fuel cells and batteries. We present a critical review on the recent advances in carbon-based metal-free catalysts for fuel cells and metal-air batteries, and discuss the perspectives and challenges in this rapidly developing field of practical significance.

No MeSH data available.


Related in: MedlinePlus