Carbon-Based Metal-Free Electrocatalysis for Energy Conversion, Energy Storage, and Environmental Protection

Abstract

Carbon-based metal-free catalysts possess desirable properties such as high earth abundance, low cost, high electrical conductivity, structural tunability, good selectivity, strong stability in acidic/alkaline conditions, and environmental friendliness. Because of these properties, these catalysts have recently received increasing attention in energy and environmental applications. Subsequently, various carbon-based electrocatalysts have been developed to replace noble metal catalysts for low-cost renewable generation and storage of clean energy and environmental protection through metal-free electrocatalysis. This article provides an up-to-date review of this rapidly developing field by critically assessing recent advances in the mechanistic understanding, structure design, and material/device fabrication of metal-free carbon-based electrocatalysts for clean energy conversion/storage and environmental protection, along with discussions on current challenges and perspectives.

Keywords

Metal-free electrocatalysis / Carbon-based catalysts / Energy conversion and storage / Environmental protection

References

[1] Dunn B, Kamath H, Tarascon JM Electrical energy storage for the grid: a battery of choices. Science, 2011, 334: 928-935.

[2] Lewis NS, Nocera DG Powering the planet: chemical challenges in solar energy utilization. Proc. Natl. Acad. Sci. USA, 2006, 103: 15729-15735.

[3] Zhang J, Xia Z, Dai L Carbon-based electrocatalysts for advanced energy conversion and storage. Sci. Adv., 2015, 1: e1500564.

[4] Dai L, Xue Y, Qu L, et al. Metal-free catalysts for oxygen reduction reaction. Chem. Rev., 2015, 115: 4823-4892.

[5] Hu C, Xiao Y, Zhao Y, et al. Highly nitrogen-doped carbon capsules: scalable preparation and high-performance applications in fuel cells and lithium ion batteries. Nanoscale, 2013, 5: 2726-2733.

[6] Xue Y, Ding Y, Niu J, et al. Rationally designed graphene-nanotube 3D architectures with a seamless nodal junction for efficient energy conversion and storage. Sci. Adv., 2015, 1: 1400198.

[7] Kumar B, Asadi M, Pisasale D, et al. Renewable and metal-free carbon nanofibre catalysts for carbon dioxide reduction. Nat. Commun., 2013, 4: 2819.

[8] Zhang J, Qu L, Shi G, et al. N, P-codoped carbon networks as efficient metal-free bifunctional catalysts for oxygen reduction and hydrogen evolution reactions. Angew. Chem. Int. Ed., 2016, 55: 2230-2234.

[9] Shui J, Lin Y, Connell J, et al. Nitrogen-doped holey graphene for high-performance rechargeable Li-O₂ batteries. ACS Energy Lett., 2016, 1: 260-265.

[10] Liu X, Dai L Carbon-based metal-free catalysts. Nat. Rev. Mater., 2016, 1: 16064.

[11] Hu C, Dai L Carbon-based metal-free catalysts for electrocatalysis beyond the ORR. Angew. Chem. Int. Ed., 2016, 55: 11736-11758.

[12] Dai L Carbon-based catalysts for metal-free electrocatalysis. Curr. Opin. Electrochem., 2017, 4: 18-25.

[13] Lai LF, Potts JR, Zhan D, et al. Exploration of the active center structure of nitrogen-doped graphene-based catalysts for oxygen reduction reaction. Energy Environ. Sci., 2012, 5: 7936-7942.

[14] Li QF, He RH, Jensen JO, et al. Approaches and recent development of polymer electrolyte membranes for fuel cells operating above 100 C. Chem. Mater., 2003, 15: 4896-4915.

[15] Zhang HW, Shen PK Recent development of polymer electrolyte membranes for fuel cells. Chem. Rev., 2012, 112: 2780-2832.

[16] Shui J, Wang M, Du F, et al. N-doped carbon nanomaterials are durable catalysts for oxygen reduction reaction in acidic fuel cells. Sci. Adv., 2015, 1: e1400129.

[17] Pham C, Klingele M, Britton B, et al. Tridoped reduced graphene oxide as a metal-free catalyst for oxygen reduction reaction demonstrated in acidic and alkaline polymer electrolyte fuel cells. Adv. Sustain. Syst., 2017, 1: 1600038-1600047.

[18] Han JH, Guo XW, Tto Y, et al. Effect of chemical doping on cathodic performance of bicontinuous nanoporous graphene for Li-O₂ batteries. Adv. Energy Mater., 2016, 6: 1501870.

[19] Ren X, Zhu J, Du F, et al. B-doped graphene as catalyst to improve charge rate of lithium-air battery. J. Phys. Chem. C, 2014, 118: 22412-22418.

[20] Xiao J, Mei D, Li X, et al. Hierarchically porous graphene as a lithium-air battery electrode. Nano Lett., 2011, 11: 5071-5078.

[21] Zhang Z, Bao J, He C, et al. Hierarchical carbon-nitrogen architectures with both mesopores and macrochannels as excellent cathodes for rechargeable Li-O₂ batteries. Adv. Funct. Mater., 2014, 24: 6826-6833.

[22] Park JB, Lee J, Yoon CS, et al. Ordered mesoporous carbon electrodes for Li-O₂ batteries. ACS Appl. Mater. Interfaces, 2013, 5: 13426-13431.

[23] Guo Z, Zhou D, Dong XL, et al. Ordered hierarchical mesoporous/macroporous carbon: a high-performance catalyst for rechargeable Li-O₂ batteries. Adv. Mater., 2013, 25: 5668-5672.

[24] Zhao C, Yu C, Liu S, et al. 3D porous N-doped graphene frameworks made of interconnected nanocages for ultrahigh-rate and long-life Li-O₂ batteries. Adv. Funct. Mater., 2015, 25: 6913-6920.

[25] Zhang J, Zhao Z, Xia Z, et al. A metal-free bifunctional electrocatalyst for oxygen reduction and oxygen evolution reactions. Nat. Nanotechnol., 2015, 10: 444-452.

[26] Li B, Geng D, Lee XS, et al. Eggplant-derived microporous carbon sheets: towards mass production of efficient bifunctional oxygen electrocatalysts at low cost for rechargeable Zn-air batteries. Chem. Commun., 2015, 51: 8841-8844.

[27] Hadidi L, Davari E, Iqbal M, et al. Spherical nitrogen-doped hollow mesoporous carbon as an efficient bifunctional electrocatalyst for Zn-air batteries. Nanoscale, 2015, 7: 20547-20556.

[28] Shinde SS, Lee CH, Sami A, et al. Scalable 3-D carbon nitride sponge as an efficient metal-free bifunctional oxygen electrocatalyst for rechargeable Zn-air batteries. ACS Nano, 2017, 11: 347-357.

[29] Hu C, Dai L Multifunctional carbon-based metal-free electrocatalysts for simultaneous oxygen reduction, oxygen evolution, and hydrogen evolution. Adv. Mater., 2017, 29: 1604942.

[30] Davodi F, Tavakkoli M, Lahtinen J, et al. Straightforward synthesis of nitrogen-doped carbon nanotubes as highly active bifunctional electrocatalysts for full water splitting. J. Catal., 2017, 353: 19-27.

[31] Yue X, Huang SL, Cai JJ, et al. Heteroatoms dual doped porous graphene nanosheets as efficient bifunctional metal-free electrocatalysts for overall water-splitting. J. Mater. Chem. A, 2017, 5: 7784-7790.

[32] Roy-Mayhew JD, Bozym DJ, Punckt C, et al. Functionalized graphene as a catalytic counter electrode in dye-sensitized solar cells. ACS Nano, 2010, 4: 6203-6211.

[33] Xue Y, Liu J, Chen H, Wang R, et al. Nitrogen-doped graphene foams as metal-free counter electrodes in high-performance dye-sensitized solar cells. Angew. Chem. Int. Ed., 2012, 51: 12124-12127.

[34] Seo SH, Kim SY, Koo BK, et al. Influence of electrolyte composition on the photovoltaic performance and stability of dye-sensitized solar cells with multiwalled carbon nanotube catalysts. Langmuir, 2010, 26: 10341-10346.

[35] Cha SI, Koo BK, Seo SH, et al. Pt-free transparent counter electrodes for dye-sensitized solar cells prepared from carbon nanotube micro-balls. J. Mater. Chem., 2010, 20: 659-662.

[36] Kumar B, Asadi M, Pisasale D, et al. Renewable and metal-free carbon nanofibre catalysts for carbon dioxide reduction. Nat. Commun., 2013, 4: 2819.

[37] Sharma PP, Wu JJ, Yadav RM, et al. Nitrogen-doped carbon nanotube arrays for high-efficiency electrochemical reduction of CO₂: on the understanding of defects, defect density, and selectivity. Angew. Chem. Int. Ed., 2015, 54: 13701-13705.

[38] Wu JJ, Liu MJ, Sharma PP, et al. Incorporation of nitrogen defects for efficient reduction of CO₂ via two-electron pathway on three-dimensional graphene foam. Nano Lett., 2016, 16: 466-470.

[39] Xu J, Kan Y, Huang R, et al. Revealing the origin of activity in nitrogen-doped nanocarbons towards electrocatalytic reduction of carbon dioxide. ChemSusChem, 2016, 9: 1085-1089.

[40] Zhang S, Kang P, Ubnoske S, et al. Polyethylenimine-enhanced electrocatalytic reduction of CO₂ to formate at nitrogen-doped carbon nanomaterial. J. Am. Chem. Soc., 2014, 136: 7845-7848.

[41] Qie L, Lin Y, Connell J, et al. Highly rechargeable lithium-CO₂ batteries with a boron-and nitrogen-codoped holey-graphene cathode. Angew. Chem. Int. Ed., 2017, 56: 6970-6974.

[42] Hu X, Li Z, Chen J Flexible Li-CO₂ batteries with liquid-free electrolyte. Angew. Chem. Int. Ed., 2017, 56: 5785-5789.

[43] Kroto HW, Heath JR, Obrien SC, et al. C60: buckminsterfullerene. Nature, 1985, 318: 162-163.

[44] Dai L Carbon Nanotechnology: Recent Developments in Chemistry, Physics, Materials Science and Device Applications 2006 Amsterdam Elsevier

[45] Zhu Z, Wei N, Xie H, et al. Acoustic-assisted assembly of an individual monochromatic ultralong carbon nanotube for high on-current transistors. Sci. Adv., 2016, 2: e1601572.

[46] Zhang RF, Zhang YY, Zhang Q, et al. Growth of half-meter long carbon nanotubes based on Schulz–Flory distribution. ACS Nano, 2013, 7: 6156-6161.

[47] Dresselhaus M Carbon connections promise nanoelectronics. Phys. World, 1996, 9: 18.

[48] Peigney A, Laurent C, Flahaut E, et al. Specific surface area of carbon nanotubes and bundles of carbon nanotubes. Carbon, 2001, 39: 507-514.

[49] Lu X, Chen ZF Curved pi-conjugation, aromaticity, and the related chemistry of small fullerenes. Chem. Rev., 2005, 105: 3643-3696.

[50] Tasis D, Tagmatarchis N, Bianco A, et al. Chemistry of carbon nanotubes. Chem. Rev., 2006, 106: 1105-1136.

[51] Karousis N, Tagmatarchis N, Tasis D Current progress on the chemical modification of carbon nanotubes. Chem. Rev., 2010, 110: 5366-5397.

[52] Qu L, Du F, Dai L Preferential syntheses of semiconducting vertically aligned single-walled carbon nanotubes for direct use in FETs. Nano Lett., 2008, 8: 2682-2687.

[53] Planeix JM, Coustel N, Coq B, et al. Application of carbon nanotubes as supports in heterogeneous catalysis. J. Am. Chem. Soc., 1994, 116: 7935-7936.

[54] Serp P, Corrias M, Kalck P Carbon nanotubes and nanofibers in catalysis. Appl. Catal. A Gen., 2003, 253: 337-358.

[55] An KH, Kim WS, Park YS, et al. Electrochemical properties of high-power supercapacitors using single-walled carbon nanotube electrodes. Adv. Funct. Mater., 2001, 11: 387-392.

[56] Welna D, Qu L, Taylor B, et al. Vertically aligned carbon nanotube electrodes for lithium-ion batteries. J. Power Sources, 2011, 196: 1455-1460.

[57] Zhang S, Kang L, Wang X, et al. Arrays of horizontal carbon nanotubes of controlled chirality grown using designed catalysts. Nature, 2017, 543: 234-238.

[58] Yu D, Nagelli E, Du F, et al. Metal-free carbon nanomaterials become more active than metal catalysts and last longer. J. Phys. Chem. Lett., 2010, 1: 2165-2173.

[59] Novoselov KS, Geim AK, Morozov SV, et al. Electric field effect in atomically thin carbon films. Science, 2004, 306: 666-669.

[60] Geim AK, Novoselov KS The rise of graphene. Nat. Mater., 2007, 6: 183-191.

[61] Balandin AA, Ghosh S, Bao WZ, et al. Superior thermal conductivity of single-layer graphene. Nano Lett., 2008, 8: 902-907.

[62] Lee C, Wei XD, Kysar JW, et al. Measurement of the elastic properties and intrinsic strength of monolayer graphene. Science, 2008, 321: 385-388.

[63] Novoselov KS Positive and negative oxygen vacancies in amorphous silica. ECS Trans., 2009, 19: 3-17.

[64] Qu L, Liu Y, Baek J, et al. Nitrogen-doped graphene as efficient metal-free electrocatalyst for oxygen reduction in fuel cells. ACS Nano, 2010, 4: 1321-1326.

[65] Yu D, Nagelli E, Du F, et al. Carbon nanomaterials in biosensors: should you use nanotubes or graphene?. Angew. Chem. Int. Ed., 2010, 49: 2114-2138.

[66] Xie X, Qu L, Zhou C, et al. An asymmetrically surface-modified graphene film electrochemical actuator. ACS Nano, 2010, 4: 6050-6054.

[67] Orimo S, Majer G, Fukunaga T, et al. Hydrogen in the mechanically prepared nanostructured graphite. Appl. Phys. Lett., 1999, 75: 3093-3095.

[68] Muto S, Kimura T, Tanabe T, et al. Transmission electron microscopy and electron energy-loss spectroscopy analysis of hydrogenated nanostructured graphite prepared by mechanical milling. Jpn. J. Appl. Phys., 2005, 44: 2061.

[69] Ali M, Urgen M Simultaneous growth of diamond and nanostructured graphite thin films by hot-filament chemical vapor deposition. Solid State Sci., 2012, 14: 150-154.

[70] McCauley TG, Corrigan TD, Krauss AR, et al. Electron emission properties of Si field emitter arrays coated with nanocrystalline diamond from fullerene precursors. Mater. Res. Soc. Symp. Proc., 1998, 498: 227.

[71] Xing Yun, Dai Liming Nanodiamonds for nanomedicine. Nanomedicine, 2009, 4(2): 2009-207.

[72] Mochalin VN, Shenderova O, Ho D, et al. The properties and applications of nanodiamonds. Nat. Nanotechnol., 2012, 7: 11-23.

[73] Liu YM, Chen S, Quan X, et al. Boron and nitrogen codoped nanodiamond as an efficient metal-free catalyst for oxygen reduction reaction. J. Phys. Chem. C, 2013, 117: 14992-14998.

[74] Gu WT, Peters N, Yushin G Functionalized carbon onions, detonation nanodiamond and mesoporous carbon as cathodes in Li-ion electrochemical energy storage devices. Carbon, 2013, 53: 292-301.

[75] Shenderova OA, Zhirnov VV, Brenner DW Carbon nanostructures. Crit. Rev. Solid State Mater. Sci. 2002 27 227 356 (references cited therein)

[76] Kruger A, Kataoka F, Ozawa M, et al. Unusually tight aggregation in detonation nanodiamond: identification and disintegration. Carbon, 2005, 43: 1722-1730.

[77] Gruen D Osawa E Ultrananocrystalline diamond films from fullerene precursors. Perspectives of Fullerene Nanotechnology 2002 Dortrecht Springer

[78] Krauss AR, Auciello O, Gruen DM, et al. Ultrananocrystalline diamond thin films for MEMS and moving mechanical assembly devices. Diam. Relat. Mater., 2001, 10: 1952-1961.

[79] Swain GM, Anderson AB, Angus JC Applications of diamond thin films in electrochemistry. MRS Bull., 1998, 23: 56-60.

[80] Chen ZP, Ren WC, Gao LB, et al. Three-dimensional flexible and conductive interconnected graphene networks grown by chemical vapour deposition. Nat. Mater., 2011, 10: 424-428.

[81] Du F, Yu D, Dai L, et al. Preparation of tunable 3D pillared carbon nanotube-graphene networks for high-performance capacitance. Chem. Mater., 2011, 23: 4810-4816.

[82] Wang DW, Su DS Heterogeneous nanocarbon materials for oxygen reduction reaction. Energy Environ. Sci., 2014, 7: 576-591.

[83] Daems N, Sheng X, Vankelecom IFJ, et al. Metal-free doped carbon materials as electrocatalysts for the oxygen reduction reaction. J. Mater. Chem. A, 2014, 2: 4085-4110.

[84] Zheng Y, Jiao Y, Jaroniec M, et al. Nanostructured metal-free electrochemical catalysts for highly efficient oxygen reduction. Small, 2012, 8: 3550-3566.

[85] Gong K, Du F, Xia Z, et al. Nitrogen-doped carbon nanotube arrays with high electrocatalytic activity for oxygen reduction. Science, 2009, 323: 760-764.

[86] Zhao Z, Li M, Zhang L, et al. Design principles for heteroatom-doped carbon nanomaterials as highly efficient catalysts for fuel cells and metal-air batteries. Adv. Mater., 2015, 27: 6834-6840.

[87] Zhang L, Xi Z Mechanisms of oxygen reduction reaction on nitrogen-doped graphene for fuel cells. J. Phys. Chem. C, 2011, 115: 11170-11176.

[88] Yang LJ, Jiang SJ, Zhao Y, et al. Boron-doped carbon nanotubes as metal-free electrocatalysts for the oxygen reduction reaction. Angew. Chem. Int. Ed., 2011, 50: 7132-7135.

[89] Jeon I, Zhang S, Zhang L, et al. Edge-selectively sulfurized graphene nanoplatelets as efficient metal-free electrocatalysts for oxygen reduction reaction: the electron spin effect. Adv. Mater., 2013, 25: 6138-6145.

[90] Ding W, Wei ZD, Chen SG, et al. Space-confinement-induced synthesis of pyridinic-and pyrrolic-nitrogen-doped graphene for the catalysis of oxygen reduction. Angew. Chem. Int. Ed., 2013, 52: 11755-11759.

[91] Guo DH, Shibuya R, Akiba C, et al. Active sites of nitrogen-doped carbon materials for oxygen reduction reaction clarified using model catalysts. Science, 2016, 351: 361-365.

[92] Zhang HR, Liang EJ, Ding P, et al. Production and growth mechanisms of BCN nanotubes. Acta Phys. Sin., 2002, 51: 2901-2905.

[93] Yang H, Miao J, Hung S, et al. Identification of catalytic sites for oxygen reduction and oxygen evolution in N-doped graphene materials: development of highly efficient metal-free bifunctional electrocatalyst. Sci. Adv., 2016, 2: e1501122.

[94] Xiang Z, Dai Q, Chen J, et al. Edge functionalization of graphene and two-dimensional covalent organic polymers for energy conversion and storage. Adv. Mater. 2016 28 6253 6261 and references cited therein

[95] Wang B, Hu C, Dai L Functionalized carbon nanotubes and graphene-based materials for energy storage. Chem. Commun., 2016, 52: 14350-14360.

[96] Shen A, Zou Y, Wang Q, et al. Oxygen reduction reaction in a droplet on graphite: direct evidence that the edge is more active than the basal plane. Angew. Chem. Int. Ed., 2014, 53: 10804-10808.

[97] Jeon I, Choi H, Choi M, et al. Facile, scalable synthesis of edge-halogenated graphene nanoplatelets as efficient metal-free electrocatalysts for oxygen reduction reaction. Sci. Rep., 2013, 3: 1810.

[98] Jeon I, Choi H, Jung S, et al. Large-scale production of edge-selectively functionalized graphene nanoplatelets via ball milling and their use as metal-free electrocatalysts for oxygen reduction reaction. J. Am. Chem. Soc., 2013, 135: 1386-1393.

[99] Jeon I, Bae S, Seo J, et al. Scalable production of edge-functionalized graphene nanoplatelets via mechanochemical ball-milling. Adv. Funct. Mater., 2015, 25: 6961-6975.

[100] Fan X, Chang D, Chen X, et al. Functionalized graphene nanoplatelets from ball milling for energy applications. Curr. Opin. Chem. Eng., 2016, 11: 52-58.

[101] Jeon I, Choi M, Choi H, et al. Antimony-doped graphene nanoplatelets. Nature Commun., 2015, 6: 7123.

[102] Ju M, Jeon I, Kim H, et al. Edge-selenated graphene nanoplatelets as durable metal-free catalysts for iodine reduction reaction in dye-sensitized solar cells. Sci. Adv., 2016, 56: e1501459.

[103] Kim H, Jeon I, Choi I, et al. Edge-selectively antimony-doped graphene nanoplatelets as an outstanding counter electrode with an unusual electrochemical stability for dye-sensitized solar cells employing cobalt electrolytes. J. Mater. Chem. A, 2016, 4: 9029-9037.

[104] Zhang J, Qu L, Shi G, et al. N, P-codoped carbon networks as efficient metal-free bifunctional catalysts for oxygen reduction and hydrogen evolution reactions. Angew. Chem. Int. Ed., 2016, 55: 2270-2274.

[105] Qu KG, Zheng Y, Zhang XX, et al. Promotion of electrocatalytic hydrogen evolution reaction on nitrogen-doped carbon nanosheets with secondary heteroatom. ACS Nano, 2017, 11: 7293-7300.

[106] Zhang W, Lin CT, Liu KK, et al. Opening an electrical band gap of bilayer graphene with molecular doping. ACS Nano, 2011, 5: 7517-7524.

[107] Wang S, Yu D, Dai L Polyelectrolyte functionalized carbon nanotubes as efficient metal-free electrocatalysts for oxygen reduction. J. Am. Chem. Soc., 2011, 133: 5182-5185.

[108] Wang S, Yu D, Dai L, et al. Polyelectrolyte-functionalized graphene as metal-free electrocatalysts for oxygen reduction. ACS Nano, 2011, 5: 6202-6209.

[109] Jiao MG, Song W, Li K, et al. First-principles study on nitrobenzene-doped graphene as a metal-free electrocatalyst for oxygen reduction reaction. J. Phys. Chem. C, 2016, 120: 8804-8812.

[110] Tang C, Zhang Q Nanocarbon for oxygen reduction electrocatalysis: dopants, edges, and defects. Adv. Mater., 2017, 29: 1604103-1604111.

[111] Tang C, Wang HF, Chen X, et al. Topological defects in metal-free nanocarbon for oxygen electrocatalysis. Adv. Mater., 2016, 28: 6845-6851.

[112] Yan D, Li Y, Huo J, et al. Defect chemistry of non-precious metal electrocatalysts for oxygen reactions. Adv. Mater., 2017, 29: 1606459.

[113] Castro Neto AH, Guinea F, Peres NMR, et al. The electronic properties of graphene. Rev. Mod. Phys., 2009, 81: 109-162.

[114] Banhart F, Kotakoski J, Krasheninnikov AV Structural defects in graphene. ACS Nano, 2011, 5: 26-41.

[115] Liu Z, Zhao Z, Wang Y, et al. In situ exfoliated, edge-rich, oxygen-functionalized graphene from carbon fibers for oxygen electrocatalysis. Adv. Mater., 2017, 29: 1606207.

[116] Chai GL, Hou ZF, Shu DJ, et al. Active sites and mechanisms for oxygen reduction reaction on nitrogen-doped carbon alloy catalysts: Stone–Wales defect and curvature effect. J. Am. Chem. Soc., 2014, 136: 13629-13640.

[117] Zhang L, Niu J, Dai L, et al. Effect of microstructure of nitrogen-doped graphene on oxygen reduction activity in fuel cells. Langmuir, 2012, 28: 7542-7550.

[118] Zhang L, Xu Q, Niu J, et al. Role of lattice defects in catalytic activities of graphene clusters for fuel cells. Phys. Chem. Chem. Phys., 2015, 17: 16733-16743.

[119] Jin H, Huang H, He Y, et al. Graphene quantum dots supported by graphene nanoribbons with ultrahigh electrocatalytic performance for oxygen reduction. J. Am. Chem. Soc., 2015, 137: 7588-7591.

[120] Jiang Y, Yang L, Sun T, et al. Significant contribution of intrinsic carbon defects to oxygen reduction activity. ACS Catal., 2015, 5: 6707-6712.

[121] Jia Y, Zhang L, Du A, et al. Defect graphene as a trifunctional catalyst for electrochemical reactions. Adv. Mater., 2016, 28: 9532-9538.

[122] Zhao X, Zou X, Yan X, et al. Defect-driven oxygen reduction reaction (ORR) of carbon without any element doping. Inorg. Chem. Front., 2016, 3: 417-421.

[123] Su DS, Perathoner S, Centi G Nanocarbons for the development of advanced catalysts. Chem. Rev., 2013, 113: 5782-5816.

[124] Sharma R, Baik JH, Perera CJ, et al. Anomalously large reactivity of single graphene layers and edges toward electron transfer chemistries. Nano Lett., 2010, 10: 398-405.

[125] Yuan W, Zhou Y, Li Y, et al. The edge-and basal-plane-specific electrochemistry of a single-layer graphene sheet. Sci. Rep., 2013, 3: 2248.

[126] Tao L, Wang Q, Dou S, et al. Edge-rich and dopant-free graphene as a highly efficient metal-free electrocatalyst for the oxygen reduction reaction. Chem. Commun., 2016, 52: 2764-2767.

[127] Wang S, Iyyamperumal E, Roy A, et al. Vertically aligned BCN nanotubes as efficient metal-free electrocatalysts for the oxygen reduction reaction: a synergetic effect by co-doping with boron and nitrogen. Angew. Chem. Int. Ed., 2011, 50: 11756-11760.

[128] Zhao Y, Yang L, Chen S, et al. Can boron and nitrogen co-doping improve oxygen reduction reaction activity of carbon nanotubes?. J. Am. Chem. Soc., 2013, 135: 1201-1204.

[129] Zheng Y, Jiao Y, Ge L, et al. Two-step boron and nitrogen doping in graphene for enhanced synergistic catalysis. Angew. Chem., 2013, 125: 3192-3198.

[130] Tian GL, Zhang Q, Zhang BS, et al. Toward full exposure of “active sites”: nanocarbon electrocatalyst with surface enriched nitrogen for superior oxygen reduction and evolution reactivity. Adv. Funct. Mater., 2014, 24: 5956-5961.

[131] Qu KG, Zheng Y, Jiao Y, et al. Polydopamine-inspired, dual heteroatom-doped carbon nanotubes for highly efficient overall water splitting. Adv. Energy Mater., 2017, 7: 1602068.

[132] Zheng Y, Jiao Y, Zhu YH, et al. Hydrogen evolution by a metal-free electrocatalyst. Nat. Commun., 2014, 5: 3783.

[133] Shinde SS, Sami A, Lee JH Electrocatalytic hydrogen evolution using graphitic carbon nitride coupled with nanoporous graphene co-doped by S and Se. J. Mater. Chem. A, 2015, 3: 12810-12819.

[134] Xie GC, Zhang K, Guo BD, et al. Graphene-based materials for hydrogen generation from light-driven water splitting. Adv. Mater., 2013, 25: 3820-3839.

[135] Katsounaros I, Cherevko S, Zeradjanin AR, et al. Oxygen electrochemistry as a cornerstone for sustainable energy conversion. Angew. Chem. Int. Ed., 2014, 53: 102-121.

[136] Huang XD, Zhao YF, Ao ZM, et al. Micelle-template synthesis of nitrogen-doped mesoporous graphene as an efficient metal-free electrocatalyst for hydrogen production. Sci. Rep., 2014, 4: 7557.

[137] Ge JM, Zhang B, LV LB, et al. Constructing holey graphene monoliths via supramolecular assembly: enriching nitrogen heteroatoms up to the theoretical limit for hydrogen evolution reaction. Nano Energy, 2015, 15: 567-575.

[138] Chen S, Duan JJ, Jaroniec M, et al. Nitrogen and oxygen dual-doped carbon hydrogel film as a substrate-free electrode for highly efficient oxygen evolution reaction. Adv. Mater., 2014, 26: 2925-2930.

[139] Othman R, Dicks AL, Zhu ZH Non precious metal catalysts for the PEM fuel cell cathode. Int. J. Hydrogen Energy, 2012, 37: 357-372.

[140] Hamilton PJ, Pollet BG Polymer electrolyte membrane fuel cell (PEMFC) flow field plate: design, materials and characterisation. Fuel Cells, 2010, 10: 489-509.

[141] Wang SY, Jiang SP Prospects of fuel cell technologies. Natl. Sci. Rev., 2017, 4: 163-166.

[142] Appleby AJ Electrocatalysis of aqueous dioxygen reduction. J. Electroanal. Chem., 1993, 357: 117-179.

[143] Schmidt TJ, Markovic NM Encyclopedia of Surface and Colloid Science 2006 New York Taylor & Francis

[144] Rao CV, Ishikawa Y Activity, selectivity, and anion-exchange membrane fuel cell performance of virtually metal-free nitrogen-doped carbon nanotube electrodes for oxygen reduction reaction. J. Phys. Chem. C, 2012, 116: 4340-4346.

[145] Yu D, Zhang Q, Dai L Highly efficient metal-free growth of nitrogen-doped single-walled carbon nanotubes on plasma-etched substrates for oxygen reduction. J. Am. Chem. Soc., 2010, 132: 15127-15129.

[146] Xiang Z, Xue Y, Cao D, et al. Highly efficient electrocatalysts for oxygen reduction based on 2D covalent organic polymers complexed with non-precious metals. Angew. Chem. Int. Ed., 2014, 53: 2433-2437.

[147] Kundu S, Nagaiah TC, Xia W, et al. Electrocatalytic activity and stability of nitrogen-containing carbon nanotubes in the oxygen reduction reaction. J. Phys. Chem. C, 2009, 113: 14302-14310.

[148] Wang XQ, Lee JS, Zhu Q, et al. Ammonia-treated ordered mesoporous carbons as catalytic materials for oxygen reduction reaction. Chem. Mater., 2010, 22: 2178-2180.

[149] Li YG, Zhou W, Wang HL, et al. An oxygen reduction electrocatalyst based on carbon nanotube-graphene complexes. Nat. Nanotechnol., 2012, 7: 394-400.

[150] Shi QQ, Peng F, Liao SX, et al. Sulfur and nitrogen co-doped carbon nanotubes for enhancing electrochemical oxygen reduction activity in acidic and alkaline media. J. Mater. Chem. A, 2013, 1: 14853-14857.

[151] Xiong W, Du F, Liu Y, et al. 3-D carbon nanotube structures used as high performance catalyst for oxygen reduction reaction. J. Am. Chem. Soc., 2010, 132: 15839-15841.

[152] Winther-Jensen B, Winther-Jensen O, Forsyth M, et al. High rates of oxygen reduction over a vapor phase–polymerized PEDOT electrode. Science, 2008, 321: 671-674.

[153] Choi CH, Chung MW, Kwon HC, et al. Nitrogen-doped graphene/carbon nanotube self-assembly for efficient oxygen reduction reaction in acid media. Appl. Catal. B Environ., 2014, 144: 760-766.

[154] Gouse PS, Sahu AK, Arunchander A, et al. Nitrogen and fluorine co-doped graphite nanofibers as high durable oxygen reduction catalyst in acidic media for polymer electrolyte fuel cells. Carbon, 2015, 93: 130-142.

[155] Zhang J, Dai L Nitrogen, phosphorus, and fluorine tri-doped graphene as a multifunctional catalyst for self-powered electrochemical water splitting. Angew. Chem. Int. Ed., 2016, 55: 13296-13300.

[156] Pei ZX, Gu JX, Wang YK, et al. Component matters: paving the roadmap toward enhanced electrocatalytic performance of graphitic C3N4-based catalysts via atomic tuning. ACS Nano, 2017, 11: 6004-6014.

[157] Li XH, Antonietti M Polycondensation of boron-and nitrogen-codoped holey graphene monoliths from molecules: carbocatalysts for selective oxidation. Angew. Chem. Int. Ed., 2013, 52: 457-4576.

[158] Lai JP, Li SP, Wu FX, et al. Unprecedented metal-free 3D porous carbonaceous electrodes for full water splitting. Energy Environ. Sci., 2016, 9: 1210-1214.

[159] Meng YY, Voiry D, Goswami A, et al. N-, O-, and S-tridoped nanoporous carbons as selective catalysts for oxygen reduction and alcohol oxidation reactions. J. Am. Chem. Soc., 2014, 136: 13554-13557.

[160] Li FJ, Zhang T, Zhou HS Challenges of non-aqueous Li-O₂ batteries: electrolytes, catalysts, and anodes. Energy Environ. Sci., 2013, 6: 1125-1141.

[161] Imanishi N, Yamamoto OO Rechargeable lithium-air batteries: characteristics and prospects. Mater. Today, 2014, 17: 24-30.

[162] Dou S, Li XY, Tao L, et al. Cobalt nanoparticle-embedded carbon nanotube/porous carbon hybrid derived from MOF-encapsulated Co₃O₄ for oxygen electrocatalysis. Chem. Commun., 2016, 52: 9727-9730.

[163] Kwak WJ, Jung HG, Aurbach D, et al. Optimized bicompartment two solution cells for effective and stable operation of Li-O₂ batteries. Adv. Energy Mater., 2017, 7: 1701232.

[164] Hu C, Wang L, Zhao Y, et al. Designing nitrogen-enriched echinus-like carbon capsules for highly efficient oxygen reduction reaction and lithium ion storage. Nanoscale, 2014, 6: 8002-8009.

[165] Meng W, Wen LN, Song ZH, et al. Metal-free boron-doped carbon microspheres as excellent cathode catalyst for rechargeable Li-O₂ battery. J. Solid State Electrochem., 2017, 21: 665-671.

[166] Shu CZ, Lin YM, Su DS N-doped onion-like carbon as an efficient oxygen electrode for long-life Li-O₂ battery. J. Mater. Chem. A, 2016, 4: 2128-2136.

[167] Shui J, Du F, Xue C, et al. Vertically aligned N-doped coral-like carbon fiber arrays as efficient air electrodes for high-performance nonaqueous Li-O₂ batteries. ACS Nano, 2014, 8: 3015-3022.

[168] Lim KH, Kweon HJ, Kim HS Polydopamine-derived nitrogen-doped graphitic carbon for a bifunctional oxygen electrode in a non-aqueous Li-O₂ battery. J. Electrochem. Soc., 2017, 164: A1595-A1600.

[169] Kang JW, Kim DY, Suk JD, et al. Enhanced energy and O₂ evolution efficiency using an in situ electrochemically N-doped carbon electrode in non-aqueous Li-O₂ batteries. J. Mater. Chem. A, 2015, 3: 18843-18846.

[170] Xing ZY, Luo XY, Qi YT, et al. Nitrogen-doped nanoporous graphenic carbon: an efficient conducting support for O₂ cathode. ChemNanoMat, 2016, 2: 692-697.

[171] Lin H, Liu ZX, Mao YX, et al. Effect of nitrogen-doped carbon/Ketjen black composite on the Morphology of Li₂O₂ for high-energy-density Li-air batteries. Carbon, 2016, 96: 965-971.

[172] Elia GA, Hassoun J, Kwak WJ, et al. An advanced lithium-air battery exploiting an ionic liquid-based electrolyte. Nano Lett., 2014, 14: 6572-6577.

[173] Mi R, Liu H, Wang H, et al. Effects of nitrogen-doped carbon nanotubes on the discharge performance of Li-air batteries. Carbon, 2014, 67: 744-752.

[174] Li J, Peng B, Zhou G, et al. Partially cracked carbon nanotubes as cathode materials for lithium-air batteries. ECS Electrochem. Lett., 2013, 2: A25-A27.

[175] Cao RG, Lee JS, Liu ML, et al. Recent progress in non-precious catalysts for metal-air batteries. Adv. Energy Mater., 2012, 2: 816-829.

[176] Lakes R Materials with structural hierarchy. Nature, 1993, 361: 511.

[177] Zhou W, Zhang HZ, Nie HJ, et al. Hierarchical micron-sized mesoporous/macroporous graphene with well-tuned surface oxygen chemistry for high capacity and cycling stability Li-O₂ battery. ACS Appl. Mater. Interfaces, 2015, 7: 3389-3397.

[178] Ding NS, Chien W, Hor A Influence of carbon pore size on the discharge capacity of Li-O₂ Batteries. J. Mater. Chem., 2014, 2: 12433-12441.

[179] Liu S, Wang Z, Yu C, et al. Free-standing, hierarchically porous carbon nanotube film as a binder-free electrode for high-energy Li-O₂ batteries. J. Mater. Chem. A, 2013, 1: 12033-12037.

[180] Li YG, Dai HJ Recent advances in zinc-air batteries. Chem. Soc. Rev., 2014, 43: 5257-5275.

[181] Xu M, Ivey DG, Xie Z, et al. Rechargeable Zn-air batteries: progress in electrolyte development and cell configuration advancement. J. Power Sources, 2015, 283: 358-371.

[182] Lee JS, Kim ST, Cao R, et al. Metal-air batteries with high energy density: Li-air versus Zn-air. Adv. Energy Mater., 2011, 1: 34-50.

[183] Chen S, Duan JJ, Zheng Y, et al. Ionic liquid-assisted synthesis of N/S-double doped graphene microwires for oxygen evolution and Zn-air batteries. Energy Storage Mater., 2015, 1: 17-24.

[184] Liu Q, Wang Y, Dai L, et al. Scalable fabrication of nanoporous carbon fiber films as bifunctional catalytic electrodes for flexible Zn-air batteries. Adv. Mater., 2016, 28: 3000-3006.

[185] Zhao Y, Nakamura R, Kamiya K, et al. Nitrogen-doped carbon nanomaterials as non-metal electrocatalysts for water oxidation. Nat. Commun., 2013, 4: 2390.

[186] Yu XW, Zhang M, Chen J, et al. Nitrogen and sulfur codoped graphite foam as a self-supported metal-free electrocatalytic electrode for water oxidation. Adv. Energy Mater., 2016, 6: 1501492.

[187] Lei YJ, Wei L, Zhai SL, et al. Metal-free bifunctional carbon electrocatalysts derived from zeolitic imidazolate frameworks for efficient water splitting. Mater. Chem. Front., 2018, 2: 102-111.

[188] Zhang ZY, Yi ZR, Wang J, et al. Nitrogen-enriched polydopamine analogue-derived defect-rich porous carbon as a bifunctional metal-free electrocatalyst for highly efficient overall water splitting. J. Mater. Chem. A, 2017, 5: 17064-17072.

[189] Hu C, Chen X, Dai Q Earth-abundant carbon catalysts for renewable generation of clean energy from sunlight and water. Nano Energy, 2017, 41: 367-376.

[190] Wang S, Zhang L, Xia Z, et al. BCN graphene as efficient metal-free electrocatalyst for the oxygen reduction reaction. Angew. Chem. Int. Ed., 2012, 51: 4209-4212.

[191] Liu J, Liu Y, Liu N, et al. Metal-free efficient photocatalyst for stable visible water splitting via a two-electron pathway. Science, 2015, 347: 970-974.

[192] Wu MX, Lin X, Wang TH, et al. Low-cost dye-sensitized solar cell based on nine kinds of carbon counter electrodes. Energy Environ. Sci., 2011, 4: 2308-2315.

[193] Brennan LJ, Byrne MT, Bari M, et al. Carbon nanomaterials for dye-sensitized solar cell applications: a bright future. Adv. Energy Mater., 2011, 1: 472-485.

[194] Lee KS, Lee WJ, Park NG, et al. Transferred vertically aligned N-doped carbon nanotube arrays: use in dye-sensitized solar cells as counter electrode. Chem. Commun., 2011, 47: 4264-4266.

[195] Dong P, Pint CL, Hainey M, et al. Vertically aligned single-walled carbon nanotubes as low-cost and high electrocatalytic counter electrode for dye-sensitized solar cells. ACS Appl. Mater. Interfaces, 2011, 3: 3157-3161.

[196] Li S, Luo Y, Lv W, et al. Vertically aligned carbon nanotubes grown on graphene paper as electrodes in lithium-ion batteries and dye-sensitized solar cells. Adv. Energy Mater., 2011, 1: 486-490.

[197] Lu K, Hu Z, Ma J, et al. A rechargeable iodine-carbon battery that exploits ion intercalation and iodine redox chemistry. Nat. Commun., 2017, 8: 527.

[198] Wang YL, Sun QL, Zhao QQ, et al. Rechargeable lithium/iodine battery with superior high-rate capability by using iodine-carbon composite as cathode. Energy Environ. Sci., 2011, 4: 3947-3950.

[199] Zhao Q, Lu Y, Zhu Z, et al. Rechargeable lithium-iodine batteries with iodine/nanoporous carbon cathode. Nano Lett., 2015, 15: 5982-5987.

[200] Zhao Y, Hong M, Mercier NB, et al. A 3.5 V lithium-iodine hybrid redox battery with vertically aligned carbon nanotube current collector. Nano Lett., 2014, 14: 1085-1092.

[201] Su Z, Tong CJ, He DQ, et al. Ultra-small B₂O₃ nanocrystals grown in situ on highly porous carbon microtubes for lithium-iodine and lithium-sulfur batteries. J. Mater. Chem. A, 2016, 4: 8541-8547.

[202] Zhang C, Mahmood N, Yin H, et al. Synthesis of phosphorus doped graphene and its multifunctional applications for oxygen reduction reaction and lithium ion batteries. Adv. Mater., 2013, 25: 4932-4937.

[203] Xu J, Wang M, Wickramaratne N, et al. High-performance sodium ion batteries based on a 3D anode from nitrogen-doped graphene foams. Adv. Mater., 2015, 27: 2042-2048.

[204] Duan XC, Xu JT, Wei ZX, et al. Metal-free carbon materials for CO₂ electrochemical reduction. Adv. Mater., 2017, 29: 1701784.

[205] Kuhl KP, Hatsukade T, Cave ER, et al. Electrocatalytic conversion of carbon dioxide to methane and methanol on transition metal surfaces. J. Am. Chem. Soc., 2014, 136: 14107-14113.

[206] Wu JJ, Yadav RM, Liu MJ, et al. Achieving highly efficient, selective, and stable CO₂ reduction on nitrogen-doped carbon nanotubes. ACS Nano, 2015, 9: 5364-5371.

[207] Sreekanth N, Nazrulla MA, Vineesh TV, et al. Metal-free boron-doped graphene for selective electroreduction of carbon dioxide to formic acid/formate. Chem. Commun., 2015, 51: 1606-16064.

[208] Nakata K, Ozaki T, Terashima C, et al. High-yield electrochemical production of formaldehyde from CO₂ and seawater. Angew. Chem. Int. Ed., 2014, 53: 871-874.

[209] Liu Y, Chen S, Quan X, et al. Efficient electrochemical reduction of carbon dioxide to acetate on nitrogen-doped nanodiamond. J. Am. Chem. Soc., 2015, 137: 11631-11636.

[210] Lu X, Tan TH, Ng YH, et al. Highly selective and stable reduction of CO₂ to CO by a graphitic carbon nitride/carbon nanotube composite electrocatalyst. Chem. Eur. J., 2016, 22: 11991-11996.

[211] Wu JJ, Ma SC, Sun J, et al. A metal-free electrocatalyst for carbon dioxide reduction to multi-carbon hydrocarbons and oxygenate. Nat. Commun., 2016, 7: 13869.

[212] Song YF, Chen W, Zhao CC, et al. Metal-free nitrogen-doped mesoporous carbon for electroreduction of CO₂ to ethanol. Angew. Chem. Int. Ed., 2017, 56: 10840-10844.

[213] Li W, Seredych M, Rodriguez-Castellon E, et al. Metal-free nanoporous carbon as a catalyst for electrochemical reduction of CO₂ to CO and CH₄. ChemSusChem, 2016, 9: 606-616.

[214] Liu YM, Zhang YJ, Cheng K, et al. Selective electrochemical reduction of carbon dioxide to ethanol on a boron- and nitrogen-co-doped nanodiamond. Angew. Chem. Int. Ed., 2017, 56: 15607-15611.

[215] Wang H, Chen Y, Hou X, et al. Nitrogen-doped graphenes as efficient electrocatalysts for the selective reduction of carbon dioxide to formate in aqueous solution. Green Chem., 2016, 18: 3250-3252.

[216] Sun X, Kang X, Zhu Q, et al. Very highly efficient reduction of CO₂ to CH₄ using metal-free N-doped carbon electrodes. Chem. Sci., 2016, 7: 2883-2887.

[217] Liu Y, Chen S, Quan X, et al. Tuning the electrochemical properties of a boron and nitrogen codoped nanodiamond rod array to achieve high performance for both electro-oxidation and electro-reduction. J. Mater. Chem. A, 2013, 1: 14706-14712.

[218] Yokoya T, Nakamura T, Matsushita T, et al. Origin of the metallic properties of heavily boron-doped superconducting diamond. Nature, 2005, 438: 647-650.

[219] Wang H, Jia J, Song P, et al. Efficient electrocatalytic reduction of CO₂ by nitrogen-doped nanoporous carbon/carbon nanotube membranes-A step towards the electrochemical CO₂ refinery. Angew. Chem. Int. Ed., 2017, 56: 7847-7852.

[220] Li L, Manthiram A O-and N-doped carbon nanowebs as metal-free catalysts for hybrid Li-air batteries. Adv. Energy Mater., 2014, 4: 1301795.

[221] Centi G, Perathoner S Opportunities and prospects in the chemical recycling of carbon dioxide to fuels. Catal. Today, 2009, 148: 191-205.