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Carbon-based electrocatalysts for advanced energy conversion and storage

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Science Advances  28 Aug 2015:
Vol. 1, no. 7, e1500564
DOI: 10.1126/sciadv.1500564

Figures

  • Scheme 1 The process of oxygen reduction reaction.

    The oxygen reduction reaction in acid and alkaline media, respectively.

  • Fig. 1 Evaluation of electrocatalytic activities toward ORR and OER.

    (A) LSV curves of electrocatalysts in oxygen-saturated electrolyte with different rotating rates. (B) Oxygen reduction curves on the disc and ring electrodes of RRDE at 5 mV s−1 scan rate at 1600 rpm, respectively. (C) Exemplary OER currents of La1−xCaxCoO3 and LaCoO3 thin films on a glassy carbon electrode (GCE) in O2-saturated 0.1 M KOH at 10 mV s−1 scan rate at 1600 rpm, capacitance-corrected by taking an average of the positive and negative scans. The contributions from AB (acetylene black) and binder (Nafion) in the thin film and GCE are shown for comparison. (D) Evidence of O2 generated from Ba0.5Sr0.5Co0.8Fe0.2O3−d (BSCF) using RRDE measurements (schematic shown as an inset). The O2 gas generated from BSCF on a GCE disc (OER current given as idisc) is reduced at the Pt ring at a constant potential of 0.4 V versus reversible hydrogen electrode (RHE). The collecting efficiency of RRED is 0.2. [From J. Suntivich, K. J. May, H. A. Gasteiger, J. B. Goodenough, Y. Shao-Horn, A perovskite oxide optimized for oxygen evolution catalysis from molecular orbital principles. Science 334, 1383–1385 (2011). Reprinted with permission from AAAS.]

  • Fig. 2 Polarization curve of PEMFC.

    The typical polarization curve describes the relationship between cell voltage and current density used to evaluate cell performance. The various losses are shown in the same figure, indicating different overpotential sources. [From V. Ramani, H. R. Kunz, J. M. Fenton, The polymer electrolyte fuel cell. Electrochem. Soc. Interface 13, 17 (2004). Reprinted with permission from the Electrochemical Society.]

  • Fig. 3 Scheme illustration of nitrogen species in nitrogen-containing graphitic carbons.

    The commonly doped nitrogen species in graphitic carbons with the corresponding reported XPS binding energies.

  • Fig. 4 Morphology characterization and catalytic performance of VA-NCNTs.

    (A) Scanning electron microscopy image of the as-synthesized VA-NCNTs on a quartz substrate. Scale bar, 2 μm. (B) Digital photograph of the VA-NCNT array after having been transferred onto a polystyrene (PS) and nonaligned CNT conductive composite film. (C) RDE voltammograms for oxygen reduction in air-saturated 0.1 M KOH at the Pt/C (curve 1), VA-CCNT (curve 2), and VA-NCNT (curve 3) electrodes. (D) Cyclic voltammograms for the ORR at the Pt/C (top) and VA-NCNT (bottom) electrodes before (solid curves) and after (dotted curves) a continuous potentiodynamic sweep for about 100,000 cycles in air-saturated 0.1 M KOH at room temperature (25 ± 1°C). Scan rate: 100 mV s−1. (E) The CO poisoning effect on the i-t chronoamperometric response for the Pt/C (black curve) and VA-NCNT (red line) electrodes. CO gas (55 ml/min) was first added into the 550 ml/min O2 flow, and then the mixture gas of ~9% CO (v/v) was introduced into the electrochemical cell at about 1700s. (F) Calculated charge density distribution for the NCNTs. (G) Schematic representations of possible adsorption modes of an oxygen molecule at the CCNTs (top) and NCNTs (bottom). [From K. Gong, F. Du, Z. Xia, M. Durstock, L. Dai, Nitrogen-doped carbon nanotube arrays with high electrocatalytic activity for oxygen reduction. Science 323, 760–764 (2009). Reprinted with permission from AAAS.]

  • Fig. 5 Scheme illustration of methods for mass production of graphene.

    The various methods for graphene production allowing a wide choice in terms of size, quality, and price for specific applications. [From K. S. Novoselov, V. I. Fal’ko, L. Colombo, P. R. Gellert, M. G. Schwab, K. Kim, A roadmap for graphene. Nature 490, 192–200 (2012). Reprinted with permission from the Nature Publishing Group.]

  • Fig. 6 Schematic illustration of the preparation of EFGnPs through the ball-milling method for ORR.

    (A) Schematic representation of the mechanochemical reaction between in situ generated active carbon species and reactant gases in a sealed ball-mill crusher. The cracking of graphite by ball milling in the presence of corresponding gases and subsequent exposure to air moisture resulted in the formation of EFGnPs. The red balls stand for reactant gases such as hydrogen, carbon dioxide, sulfur trioxide, and air moisture (oxygen and moisture). [Derived from (119), Copyright 2012 National Academy of Sciences.] (B) A schematic representation for the edge expansions of XGnPs caused by the edge halogens: ClGnP, BrGnP, and IGnP. (C) The optimized O2 adsorption geometries onto XGnPs, in which halogen covalently linked to two sp2 carbons. In (C), the O-O bond length and the shortest C-O bond are shown in angstrom. [From I.-Y. Jeon, H.-J. Choi, M. Choi, J.-M. Seo, S.-M. Jung, M.-J. Kim, S. Zhang, L. Zhang, Z. Xia, L. Dai, N. Park, J.-B. Baek, Facile, scalable synthesis of edge-halogenated graphene nanoplatelets as efficient metal-free eletrocatalysts for oxygen reduction reaction. Sci. Rep. 3, 1810 (2013). Reprinted with permission from the Nature Publishing Group.]

  • Fig. 7 Power and durability performance of N-G-CNT with the addition of KB in PEM fuel cells.

    (A) Polarization curves of N-G-CNT with loadings: 2, 0.5, or 0.15 mg cm−2 plus KB (2 mg cm−2) for each cathode. Weight ratio of (N-G-CNT/KB)/Nafion, 1:1. (B) Cell polarization and power density as a function of gravimetric current for N-G-CNT/KB (0.5/2 mg cm−2) with a 1:1 weight ratio of (N-G-CNT/KB)/Nafion. (C) Durability of the metal-free N-G-CNT in a PEM fuel cell measured at 0.5 V, compared with a Fe/N/C catalyst. Catalyst loading of N-G-CNT/KB (0.5 mg cm−2) and Fe/N/C (0.5 and 2 mg cm−2). Test conditions: H2/O2; 80°C; 100% relative humidity; back pressure, 2 bar. [From J. Shui, M. Wang, F. Du, L. Dai, N-doped carbon nanomaterials are durable catalysts for oxygen reduction reaction in acidic fuel cells. Sci. Adv. 1, e1400129 (2015). Reprinted with permission from AAAS.]

  • Fig. 8 Illustrated interfaces of air electrodes and proposed electrode structures.

    (A) Gas-solid-liquid three-phase interface model in aqueous electrolytes. (B) Liquid-solid two-phase interface model in nonaqueous electrolytes. [From F. Cheng, J. Chen, Metal–air batteries: From oxygen reduction electrochemistry to cathode catalysts. Chem. Soc. Rev. 41, 2172–2192 (2012). Reprinted with permission from the Royal Society of Chemistry.]

  • Fig. 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.]

  • Fig. 10 Schematic representation of a hybrid Li-air battery.

    The enlarged image shows the basic reaction process in the air electrode based on NG. [From E. Yoo, J. Nakamura, H. Zhou, N-Doped graphene nanosheets for Li–air fuel cells under acidic conditions. Energy Environ. Sci. 5, 6928–6932 (2012). Reprinted with permission from the Royal Society of Chemistry.]

  • Fig. 11 Performance of rechargeable Zn-air batteries.

    (A) Discharge/charge cycling curves of a two-electrode rechargeable Zn-air battery at a current density of 2 mA cm−2 using the NPMC-1000 (pyrolysis at 1000°C) air electrode. Three-electrode Zn-air batteries. (B) Schematic illustration for the basic configuration of a three-electrode Zn-air battery by coupling a Zn electrode with two air electrodes to separate ORR and OER. The enlarged parts illustrate the porous structures of the air electrodes, which facilitates the gas exchange. (C) Charge and discharge polarization curves of three-electrode Zn-air batteries using the NPMC-1000, NPMC-1100, or commercial Pt/C catalyst as both of the air electrodes, along with the corresponding curve (that is, Pt/C + RuO2) for the three-electrode Zn-air battery with Pt/C and RuO2 nanoparticles as each of the air electrodes, respectively. (D) Discharge/charge cycling curves of a three-electrode Zn-air battery using NPMC-1000 as air electrodes (0.5 mg cm−2 for ORR and 1.5 mg cm−2 for OER) at a current density of 2 mA cm−2. [From J. Zhang, Z. Zhao, Z. Xia, L. Dai, A metal-free bifunctional electrocatalyst for oxygen reduction and oxygen evolution reactions. Nat. Nanotechnol. 10, 444–452 (2015). Reprinted with permission from the Nature Publishing Group.]

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