Metal Free Catalysts for Water Splitting

$28.50

Metal Free Catalysts for Water Splitting

Paramita Karfa, Kartick Chandra Majhi, Rashmi Madhuri

Water splitting through electrolysis with the use of renewable sources is a highly versatile method of energy conversion producing hydrogen, which is a very clean energy carrier. Development of earth abundant catalyst with long term stability and high efficiency is of current research interest which can replace noble metal catalyst like Pt, Ir. Catalyst prepared through metal precursors like metal oxides, metal selenides, metal phosphides suffer from high expenses, poor durability, vulnerability to gas poisoning, limitations in electrolytic medium, formation of by-product which are not environmental friendly, low selectivity. Researcher have synthesized a new class of material i.e., metal free catalyst which acquires some of the best properties like large surface area, variety of shape and size and high robustness. Among the metal free catalysts, the carbon based catalyst was studied and researched more expansively. Research is going on full steam to overcome different key challenges like catalyst stability, high Faradaic efficiency and to explore further future opportunities in this exhilarating field.

Keywords
Water Splitting, Oxygen Evolution Reaction (OER), Hydrogen Evolution Reaction (HER), Metal Free Catalyst, Graphene, Carbon Nanotube, Graphitic Carbon Nitride

Published online 10/5/2019, 28 pages

Citation: Paramita Karfa, Kartick Chandra Majhi, Rashmi Madhuri, Metal Free Catalysts for Water Splitting, Materials Research Foundations, Vol. 59, pp 97-124, 2019

DOI: https://doi.org/10.21741/9781644900451-4

Part of the book on Electrochemical Water Splitting

References
[1] M. K. Hubbert, Energy from fossil fuels, Science 109 (1949) 103-109. https://doi.org/10.1126/science.109.2823.103
[2] J.A Turner, A realizable renewable energy future, Science 285 (1999) 687-689. https://doi.org/10.1126/science.285.5428.687
[3] K. Mazloomi, C. Gomes, Hydrogen as an energy carrier: Prospects and challenges, Renew. Sust. Energ. Rev. 16 (2012) 3024-3033. https://doi.org/10.1016/j.rser.2012.02.028
[4] A. Züttel, A. Remhof, A. Borgschulte, O. Friedrichs, Hydrogen: the future energy carrier, ‎Philos. Trans. Royal Soc. A 368, (2010) 3329-3342. https://doi.org/10.1098/rsta.2010.0113
[5] S.U.M Khan, M. Al-Shahry, W.B. Ingler, Efficient photochemical water splitting by a chemically modified n-TiO2, Science 297 (2002) 2243-2245. https://doi.org/10.1126/science.1075035
[6] T. Hisatomi, J. Kubota, K. Domen, Recent advances in semiconductors for photocatalytic and photoelectrochemical water splitting, Chem. Soc. Rev. 43 (2014) 7520-7535. https://doi.org/10.1039/C3CS60378D
[7] J. Wang, W. Cui, Q. Liu, Z. Xing, A.M. Asiri, X. Sun, Recent progress in cobalt‐based heterogeneous catalysts for electrochemical water splitting. Adv. Mater. 28 (2016) 215-230. https://doi.org/10.1002/adma.201502696
[8] X. Li, X. Hao, A. Abudula, G. Guan, Nanostructured catalysts for electrochemical water splitting: Current state and prospects, J. Mater. Chem. A (2016) 11973-12000. https://doi.org/10.1039/C6TA02334G
[9] X. Zou, Z. Xiaoxin, Y. Zhang, Noble metal-free hydrogen evolution catalysts for water splitting. Chem. Soc. Rev. 44 (2015) 5148-5180. https://doi.org/10.1039/C4CS00448E
[10] D. Kong, J.J. Cha, H. Wang, H.R. Lee, Y. Cui, First-row transition metal dichalcogenide catalysts for hydrogen evolution reaction, Energy. Environ. Sci. 6 (2013) 3553-3558. https://doi.org/10.1039/c3ee42413h
[11] D.R. Gamelin, Water splitting: Catalyst or spectator, Nat Chem. 4 (2012) 965. https://doi.org/10.1038/nchem.1514
[12] J.D Benck, T.R. Hellstern, J. Kibsgaard, P. Chakthranont, T.F. Jaramillo, Catalyzing the hydrogen evolution reaction (HER) with molybdenum sulfide nanomaterials, ACS Catal. 4, (2014) 3957-3971. https://doi.org/10.1021/cs500923c
[13] N-T Suen, S-F Hung, Q. Quan, N. Zhang, Y-J. Xu, H.M. Chen, Electrocatalysis for the oxygen evolution reaction: recent development and future perspectives, Chem. Soc. Rev. 46 (2017) 337-365. https://doi.org/10.1039/C6CS00328A
[14] C.C.L McCrory, S. Jung, J.C. Peters, T.F. Jaramillo. Benchmarking heterogeneous electrocatalysts for the oxygen evolution reaction. J. Am. Chem. Soc. 135 (2013) 16977-16987. https://doi.org/10.1021/ja407115p
[15] T. Reier, M. Oezaslan, P. Strasser, Electrocatalytic oxygen evolution reaction (OER) on Ru, Ir, and Pt catalysts: a comparative study of nanoparticles and bulk materials, ACS Catal. 2 (2012) 1765-1772. https://doi.org/10.1021/cs3003098
[16] A.T. Swesi, J. Masud, M. Nath, Nickel selenide as a high-efficiency catalyst for oxygen evolution reaction, Energy. Environ. Sci. Science 9 (2016) 1771-1782. https://doi.org/10.1039/C5EE02463C
[17] E. Fabbri, A. Habereder, K. Waltar, R. Kötz, T.J. Schmidt, Developments and perspectives of oxide-based catalysts for the oxygen evolution reaction, Catal. Sci. Technol.4 (2014) 3800-3821. https://doi.org/10.1039/C4CY00669K
[18] M.S. Burke, L.J. Enman, A.S. Batchellor, S. Zou, S.W. Boettcher, Oxygen evolution reaction electrocatalysis on transition metal oxides and (oxy) hydroxides: activity trends and design principles, Chem. Mater. 27 (2015) 7549-7558. https://doi.org/10.1021/acs.chemmater.5b03148
[19] Y. Zheng, Y. Jiao, L.H. Li, T. Xing, Y. Chen, M. Jaroniec, S.Z. Qiao, Toward design of synergistically active carbon-based catalysts for electrocatalytic hydrogen evolution, ACS nano 8 (2014) 5290-5296. https://doi.org/10.1021/nn501434a
[20] M.T.M. Koper, Hydrogen electrocatalysis: A basic solution, Nat. Chem. 5 (2013): 255. https://doi.org/10.1038/nchem.1600
[21] J.A. Turner, Sustainable hydrogen production, Science 305 (2004) 972-974. https://doi.org/10.1126/science.1103197
[22] J.D. Holladay, J. Hu, D.L. King, Y. Wang, An overview of hydrogen production technologies, Catal. Today 139 (2009) 244-260. https://doi.org/10.1016/j.cattod.2008.08.039
[23] I.K. Kapdan, F.Kargi, Bio-hydrogen production from waste materials, Enzyme Microb. Technol. 38 (2006) 569-582. https://doi.org/10.1016/j.enzmictec.2005.09.015
[24] Y. Shi, B. Zhang, Recent advances in transition metal phosphide nanomaterials: synthesis and applications in hydrogen evolution reaction, Chem. Soc. Rev. 45 (2016) 1529-1541. https://doi.org/10.1039/C5CS00434A
[25] J.D. Benck, T.R. Hellstern, J. Kibsgaard, P. Chakthranont, T.F. Jaramillo, Catalyzing the hydrogen evolution reaction (HER) with molybdenum sulfide nanomaterials, ACS Catal. 4 (2014) 3957-3971. https://doi.org/10.1021/cs500923c
[26] Y. Li, H. Wang, L. Xie, Y. Liang, G. Hong, H. Dai, MoS2 nanoparticles grown on graphene: an advanced catalyst for the hydrogen evolution reaction, J. Am. Chem. Soc. 133 (2011) 7296-7299. https://doi.org/10.1021/ja201269b
[27] P. Xiao, M. AlamSk, L. Thia, X. Ge, R.J. Lim, J-Y Wang, K.H. Lim, X. Wang, Molybdenum phosphide as an efficient electrocatalyst for the hydrogen evolution reaction,Energy. Environ. Sci. 7 (2014) 2624-2629. https://doi.org/10.1039/C4EE00957F
[28] Y. Ito, W. Cong, T. Fujita, Z. Tang, M. Chen, High catalytic activity of nitrogen and sulfur co‐doped nanoporous graphene in the hydrogen evolution reaction, Angew. Chem. Int. Ed. 127 (2015) 2159-2164. https://doi.org/10.1002/ange.201410050
[29] Y. Shi, B. Zhang, Recent advances in transition metal phosphide nanomaterials: Synthesis and applications in hydrogen evolution reaction, Chem. Soc. Rev. 45 (2016) 1529-1541. https://doi.org/10.1039/C5CS00434A
[30] S. Lu, Z. Zhuang, Electrocatalysts for hydrogen oxidation and evolution reactions, Sci. China Mater. 59 (2016) 217-238. https://doi.org/10.1007/s40843-016-0127-9
[31] D. Chialvo, MR Gennero, A. C. Chialvo, Hydrogen evolution reaction: analysis of the Volmer-Heyrovsky-Tafel mechanism with a generalized adsorption model,‎ J. Electroanal. Chem. 372 (1994) 209-223. https://doi.org/10.1016/0022-0728(93)03043-O
[32] A. Xie, N. Xuan, K. Ba, Z. Sun, Pristine graphene electrode in hydrogen evolution reaction, ACS Appl. Mater. Interfaces 9 (2017) 4643-4648. https://doi.org/10.1021/acsami.6b14732
[33] Z. Sun, W. Fan, T. Liu, Graphene/graphene nanoribbon aerogels as tunable three-dimensional framework for efficient hydrogen evolution reaction, Electrochim. Acta 250 (2017) 91-98. https://doi.org/10.1016/j.electacta.2017.08.009
[34] Y. Tian, Z. Wei, X. Wang, S. Peng, X. Zhang, W-M Liu, Plasma-etched, S-doped graphene for effective hydrogen evolution reaction, Int. J. Hydrog. Energy 42 (2017) 4184-4192. https://doi.org/10.1016/j.ijhydene.2016.09.142
[35] B. Deng, D. Wang, Z. Jiang, J. Zhang, S. Shi, Z-J. Jiang, M. Liu, Amine group induced high activity of highly torn amine functionalized nitrogen doped graphene as the metal-free catalyst for hydrogen evolution reaction, Carbon 138 (2018) 169-178. https://doi.org/10.1016/j.carbon.2018.06.008
[36] K. Chu, F. Wang, X-L. Zhao, X-P Wei, Xin-wei Wang, Y. Tian, One-step and low-temperature synthesis of iodine-doped graphene and its multifunctional applications for hydrogen evolution reaction and electrochemical sensing, Electrochim. Acta 246 (2017) 1155-1162. https://doi.org/10.1016/j.electacta.2017.07.001
[37] Y. Liu, H. Yu, X. Quan, S. Chen, H. Zhao, Y. Zhang, Efficient and durable hydrogen evolution electrocatalyst based on nonmetallic nitrogen doped hexagonal carbon, Sci. Rep. 4 (2014) 6843. https://doi.org/10.1038/srep06843
[38] X. Liu, W. Zhou, L. Yang, L. Li, Z. Zhang, Y. Ke, S. Chen, Nitrogen and sulfur co-doped porous carbon derived from human hair as highly efficient metal-free electrocatalysts for hydrogen evolution reactions, ‎J. Mater. Chem. A 3 (2015)10135-10135. https://doi.org/10.1039/C5TA90086G
[39] B.R Sathe, X. Zou, T. Asefa, Metal-free B-doped graphene with efficient electrocatalytic activity for hydrogen evolution reaction, Catal. Sci. Technol. 4 (2014) 2023-2030. https://doi.org/10.1039/C4CY00075G
[40] W. Cui, Q. Liu, N. Cheng, A. M. Asiri, X. Sun, Activated carbon nanotubes: a highly-active metal-free electrocatalyst for hydrogen evolution reaction, Chem. Commun. 50 (2014) 9340-9342. https://doi.org/10.1039/C4CC02713B
[41] L Wei, H.E.Karahan, K. Goh, W. Jiang, D. Yu, Ö. Birer, R. Jiang, Y. Chen, A high-performance metal-free hydrogen-evolution reaction electrocatalyst from bacterium derived carbon, J. Mater. Chem. A 3 (2015) 7210-7214. https://doi.org/10.1039/C5TA00966A
[42] M. Tahir, L. Pan, F. Idrees, X. Zhang, L. Wang, J-J Zou, Z.L Wang, Electrocatalytic oxygen evolution reaction for energy conversion and storage: a comprehensive review, Nano Energy 37 (2017)136-157. https://doi.org/10.1016/j.nanoen.2017.05.022
[43] J.A. Koza, Z. He, A.S. Miller, J.A. Switzer, Electrodeposition of crystalline Co3O4. A catalyst for the oxygen evolution reaction, Chem. Mater. 24 (2012) 3567-3573. https://doi.org/10.1021/cm3012205
[44] N. Mamaca, E. Mayousse, S. Arrii-Clacens, T. W. Napporn, K. Servat, N. Guillet, K. B. Kokoh, Electrochemical activity of ruthenium and iridium based catalysts for oxygen evolution reaction, Appl. Catal. B. 111 (2012)376-380. https://doi.org/10.1016/j.apcatb.2011.10.020
[45] I.C. Man, H.Y. Su, F.C. Vallejo, H.A. Hansen, J.I. Martínez, N.G. Inoglu, J. Kitchin, T.F. Jaramillo, J.K. Norskov, J. Rossmeisl, Universality in oxygen evolution electrocatalysis on oxide surfaces, Chem. Cat. Chem. 3 (2011) 1159-1165. https://doi.org/10.1002/cctc.201000397
[46] V. Vij, S. Sultan, A.M. Harzandi, A. Meena, J.N. Tiwari, W.G. Lee, T. Yoon, K.S. Kim, Nickel-based electrocatalysts for energy-related applications: oxygen reduction, oxygen evolution, and hydrogen evolution reactions, ACS Catal.7 (2017) 7196-7225. https://doi.org/10.1021/acscatal.7b01800
[47] M. Tuckerman, K. Laasonen, M. Sprik, M. Parrinello, Ab initio molecular dynamics simulation of the solvation and transport of hydronium and hydroxyl ions in water. J. Chem. Phys. 103(1995) 150-161. https://doi.org/10.1063/1.469654
[48] X. Shen, Y.A. Small, J. Wang, P.B. Allen, M.V. Fernandez-Serra, M.S. Hybertsen, J.T.Muckerman, Photocatalytic water oxidation at the GaN (1010) – water interface, J. Phys. Chem. C114(2010) 13695-13704. https://doi.org/10.1021/jp102958s
[49] J. Yang, D. Wang, X. Zhou, C. Li, A theoretical study on the mechanism of photocatalytic oxygen evolution on BiVO4 in aqueous solution, ‎Chem. Eur. J 19(2013) 1320-1326. https://doi.org/10.1002/chem.201202365
[50] J. Zhang, X. Song, P. Li, Z. Wu, Y. Wu, S. Wang, X. Liu, Sulfur, nitrogen co-doped nanocomposite of graphene and carbon nanotube as an efficient bifunctional electrocatalyst for oxygen reduction and evolution reactions, J. Taiwan Inst. Chem. Eng. 93 (2018) 336-341. https://doi.org/10.1016/j.jtice.2018.07.040
[51] J-C. Li, P.X. Hou, M. Cheng, C. Liu, H.M. Cheng, M. Shao, Carbon nanotube encapsulated in nitrogen and phosphorus co-doped carbon as a bifunctional electrocatalyst for oxygen reduction and evolution reactions, Carbon 139 (2018) 156-163. https://doi.org/10.1016/j.carbon.2018.06.023
[52] B, Zhang, E. Zhang, S. Wang, Y. Zhang, Z. Ma, Y.Qiu, Bifunctional oxygen electrocatalyst derived from photochlorinated graphene for rechargeable solid-state Zn-air battery, J. Colloid Interface Sci. 543 (2019) 84-95. https://doi.org/10.1016/j.jcis.2019.02.044
[53] N. Jia, Q. Weng, Y. Shi, X. Shi, X. Chen, P. Chen, Z. An, Yu Chen, N-doped carbon nanocages: Bifunctional electrocatalysts for the oxygen reduction and evolution reactions, Nano Res. 11 (2018)1905-1916. https://doi.org/10.1007/s12274-017-1808-8
[54] J. Tian, Q. Liu, A.M. Asiri, K.A. Alamry, X. Sun, Ultrathin graphitic C3N4nanosheets/graphene composites: efficient organic electrocatalyst for oxygen evolution reaction, Chem. Sus. Chem. 7 (2014) 2125-2130. https://doi.org/10.1002/cssc.201402118
[55] N. Cheng, Q. Liu, J. Tian, Y. Xue, A.M. Asiri, H. Jiang, Y. He, X. Sun, Acidically oxidized carbon cloth: a novel metal-free oxygen evolution electrode with high catalytic activity, Chem. Commun. 51 (2015) 1616-1619. https://doi.org/10.1039/C4CC07120D
[56] S. Chen, J. Duan, M. Jaroniec, S.Z.Qiao, Nitrogen and oxygen dual‐doped carbon hydrogel film as a substrate‐free electrode for highly efficient oxygen evolution reaction, Adv. Mater. 26 (2014), 2925-2930. https://doi.org/10.1002/adma.201305608
[57] C. Zhang, B. Wang, X. Shen, J. Liu, X. Kong, S.S.C Chuang, D. Yang, A. Dong, Zhenmeng Peng, A nitrogen-doped ordered mesoporous carbon/graphene framework as bifunctional electrocatalyst for oxygen reduction and evolution reactions, Nano Energy 30 (2016)503-510. https://doi.org/10.1016/j.nanoen.2016.10.051
[58] J. Zhang, Z. Zhao, Z. Xia, L. Dai, A metal-free bifunctional electrocatalyst for oxygen reduction and oxygen evolution reactions, ‎Nat. Nanotechnol. 10 (2015) 444. https://doi.org/10.1038/nnano.2015.48
[59] J. Sun, S.E. Lowe, L. Zhang, Y. Wang, K. Pang, Y. Wang, Y. Zhong, Ultrathin nitrogen‐doped holey carbon@ graphene bifunctional electrocatalyst for oxygen reduction and evolution reactions in alkaline and acidic media, Angew. Chem. Int. Ed. 130(2018)16749-16753. https://doi.org/10.1016/j.jpowsour.2008.01.070
[60] W. Schmittinger, A. Vahidi, A review of the main parameters influencing long-term performance and durability of PEM fuel cells, J. Power Sources. 180 (2008) 1-14. https://doi.org/10.1016/j.jpowsour.2008.01.070
[61] A. Romo-Negreira, D.J. Cott, S.D. Gendt, K. Maex, M.M. Heyns, P.M. Vereecken, Electrochemical tailoring of catalyst nanoparticles for CNT spatial-dimension control, ‎J. Electrochem. Soc. 157 (2010) K47-K51. https://doi.org/10.1149/1.3280245
[62] T. Shinagawa, K.Takanabe, Towards versatile and sustainable hydrogen production through electrocatalytic water splitting: electrolyte engineering, Chem. Sus. Chem. 10 (2017)1318-1336. https://doi.org/10.1002/cssc.201601583
[63] J. Heyrovský, A theory of overpotential. Recueil des TravauxChimiques des Pays‐Bas 46 (1927) 582-585. https://doi.org/10.1002/recl.19270460805
[64] M. Görlin, P. Chernev, J. Ferreira de Araújo, T. Reier, S. Dresp, B. Paul, R. Krähnert, H. Dau, P.Strasser, Oxygen evolution reaction dynamics, faradaic charge efficiency, and the active metal redox states of Ni–Fe oxide water splitting electrocatalysts, J. Am. Chem. Soc. 138(2016)5603-5614. https://doi.org/10.1021/jacs.6b00332
[65] J.R. Hollenbeck, C.R. Williams, Turnover functionality versus turnover frequency: A note on work attitudes and organizational effectiveness, J. Appl. Psychol. 71 (1986) 606. https://doi.org/10.1037//0021-9010.71.4.606
[66] M. Lukaszewski, M. Soszko, A. Czerwiński, Electrochemical methods of real surface area determination of noble metal electrodes–an overview, Int. J. Electrochem. Sci. 11 (2016) 4442-4469. https://doi.org/10.20964/2016.06.71
[67] D. Astruc, ed. Nanoparticles and catalysis. John Wiley & Sons, (2008). https://doi.org/10.1002/9783527621323
[68] J.D. Benck, Z. Chen, L.Y. Kuritzky, A.J. Forman, T.F. Jaramillo, Amorphous molybdenum sulfide catalysts for electrochemical hydrogen production: insights into the origin of their catalytic activity, ACS Catal. 2 (2012) 1916-1923. https://doi.org/10.1021/cs300451q
[69] C. Hu, L. Dai, Carbon‐based metal‐free catalysts for electrocatalysis beyond the ORR, Angew. Chem. Int. Ed. 55 (2016) 11736-11758. https://doi.org/10.1002/anie.201509982
[70] L. Zhang, J. Xiao, H. Wang, M. Shao, Carbon-based electrocatalysts for hydrogen and oxygen evolution reactions, ACS Catal. 7 (2017)7855-7865. https://doi.org/10.1021/acscatal.7b02718
[71] L. Dai, D.W. Chang, J.B. Baek, W. Lu, Carbon nanomaterials for advanced energy conversion and storage, Small 8(2012)1130-1166. https://doi.org/10.1002/smll.201101594
[72] Y. Zhao, R. Nakamura, K. Kamiya, S. Nakanishi, K. Hashimoto, Nitrogen-doped carbon nanomaterials as non-metal electrocatalysts for water oxidation, Nat. Commun. 4 (2013) 2390. https://doi.org/10.1038/ncomms3390
[73] H. Chen, M.B. Müller, K.J. Gilmore, G.G. Wallace, D. Li, Mechanically strong, electrically conductive, and biocompatible graphene paper, Adv. Mater. 20(2008) 3557-3561. https://doi.org/10.1002/adma.200800757
[74] A.K. Geim, K.S. Novoselov, The rise of graphene, In Nanoscience and Technology: A Collection of Reviews from Nature Journals (2010) 11-19. https://doi.org/10.1142/9789814287005_0002
[75] A.H.C Neto, F. Guinea, N.M.R Peres, K.S. Novoselov, A.K. Geim, The electronic properties of graphene, Rev. Mod. Phys. 81 (2009) 109. https://doi.org/10.1103/RevModPhys.81.109
[76] J. Lai, S. Li, F. Wu, M.Saqib, R. Luque, G. Xu, Unprecedented metal-free 3D porous carbonaceous electrodes for full water splitting, Energy Environ. Sci. 9 (2016) 1210-1214. https://doi.org/10.1039/C5EE02996A
[77] J. Zhang, L. Dai, Nitrogen, Phosphorus, and Fluorine Tri‐doped Graphene as a Multifunctional Catalyst for Self‐Powered Electrochemical Water Splitting, Angew. Chem. Int. Ed 55 (2016)13296-13300. https://doi.org/10.1002/anie.201607405
[78] J. Zhang, C. Zhang, J. Sha, H. Fei, Y. Li, J.M. Tour, Efficient water-splitting electrodes based on laser-induced graphene, ACS Appl. Mater. Interfaces 9 (2017) 26840-26847. https://doi.org/10.1021/acsami.7b06727
[79] Y. Jia, L. Zhang, A. Du, G. Gao, J. Chen, X. Yan, C. L. Brown, X. Yao, Defect graphene as a trifunctional catalyst for electrochemical reactions, Adv. Mater. 28 (2016) 9532-9538. https://doi.org/10.1002/adma.201602912
[80] X. Yue, S. Huang, J. Cai, Y. Jin, P.K. Shen, Heteroatoms dual doped porous graphene nanosheets as efficient bifunctional metal-free electrocatalysts for overall water-splitting, ‎J. Mater. Chem. A 5 (2017) 7784-7790. https://doi.org/10.1039/C7TA01957B
[81] T.W. Ebbesen, P.M. Ajayan, Large-scale synthesis of carbon nanotubes, Nature 358 (1992) 220. https://doi.org/10.1038/358220a0
[82] S. Iijima, T. Ichihashi, Single-shell carbon nanotubes of 1-nm diameter, Nature 363(1993)603. https://doi.org/10.1038/363603a0
[83] X. Lin, X.K. Wang, V.P. Dravid, R.P.H. Chang, J.B. Ketterson, Large scale synthesis of single‐shell carbon nanotubes, Appl. Phys. Lett. 64 (1994) 181-183. https://doi.org/10.1063/1.111525
[84] A. Adam, M.H. Suliman, H. Dafalla, A.R. Al-Arfaj, M.N. Siddiqui, M. Qamar, Rationally dispersed molybdenum phosphide on carbon nanotubes for the hydrogen evolution reaction, ACS Sustain. Chem. Eng.6 (2018) 11414-11423. https://doi.org/10.1021/acssuschemeng.8b01359
[85] F. Davodi, M. Tavakkoli, J. Lahtinen, T. Kallio, Straightforward synthesis of nitrogen-doped carbon nanotubes as highly active bifunctional electrocatalysts for full water splitting, J. Catal. 353 (2017) 19-27. https://doi.org/10.1021/acssuschemeng.8b01359
[86] K. Qu, Y. Zheng, Y. Jiao, X. Zhang, S. Dai, S‐Z. Qiao, Polydopamine‐Inspired, Dual Heteroatom‐Doped Carbon Nanotubes for Highly Efficient Overall Water Splitting, Adv. Energy Mater. 7 (2017)1602068. https://doi.org/10.1002/aenm.201602068
[87] A. Ali, D. Akyüz, M. A.Asghar, A. Koca, B. Keskin, Free-standing carbon nanotubes as non-metal electrocatalyst for oxygen evolution reaction in water splitting, ‎Int. J. Hydrog. Energy 43(2018)1123-1128. https://doi.org/10.1016/j.ijhydene.2017.11.060
[88] C. Zhang, S. Bhoyate, M. Hyatt, B.L. Neria, K. Siam, P. K. Kahol, M. Ghimire, S. R. Mishra, F. Perez, R.K. Gupta, Nitrogen-doped flexible carbon cloth for durable metal free electrocatalyst for overall water splitting, Surf. Coat. Technol. 347 (2018) 407-413. https://doi.org/10.1016/j.ijhydene.2017.11.060
[89] Y. Cheng, C. Xu, L. Jia, J.D. Gale, L. Zhang, C. Liu, P.K. Shen, S.P. Jiang, Pristine carbon nanotubes as non-metal electrocatalysts for oxygen evolution reaction of water splitting, Appl. Catal. B 163 (2015) 96-104. https://doi.org/10.1016/j.apcatb.2014.07.049
[90] A. Thomas, A. Fischer, F. Goettmann, M. Antonietti, J.O. Müller, R. Schlögl, J.M. Carlsson, Graphitic carbon nitride materials: variation of structure and morphology and their use as metal-free catalysts,‎J. Mater. Chem. 18 (2008) 4893-4908. https://doi.org/10.1039/b800274f
[91] Y. Zheng, J. Liu, J. Liang, M. Jaroniec, S.Z. Qiao, Graphitic carbon nitride materials: controllable synthesis and applications in fuel cells and photocatalysis, Energy Environ. Sci. 5 (2012) 6717-6731. https://doi.org/10.1039/c2ee03479d
[92] H.X. Zhong, Q. Zhang, J. Wang, X.B. Zhang, X.L. Wei, Z.J. Wu, K. Li, F.L. Meng, D. Bao, J.M Yan, Engineering ultrathinC3N4 quantum dots on graphene as a metal-free water reduction electrocatalyst, ACS Catal. 8 (2018) 3965-3970. https://doi.org/10.1021/acscatal.8b00467
[93] Y. Zheng, Y. Jiao, Y. Zhu, L. H. Li, Y. Han, Y. Chen, A. Du, M. Jaroniec, S.Z. Qiao, Hydrogen evolution by a metal-free electrocatalyst, Nat. Commun. 5 (2014) 3783. https://doi.org/10.1038/ncomms4783