메뉴 건너뛰기




Volumn 7, Issue 7, 2014, Pages 1054-1064

Active catalysts based on cobalt oxide@cobalt/N-C nanocomposites for oxygen reduction reaction in alkaline solutions

Author keywords

Co N C; CoO; electrocatalysis; oxygen reduction reaction

Indexed keywords


EID: 84904575105     PISSN: 19980124     EISSN: 19980000     Source Type: Journal    
DOI: 10.1007/s12274-014-0468-1     Document Type: Article
Times cited : (75)

References (53)
  • 1
    • 84882580139 scopus 로고    scopus 로고
    • Nanostructured nonprecious metal catalysts for oxygen reduction reaction
    • Wu, G.; Zelenay, P. Nanostructured nonprecious metal catalysts for oxygen reduction reaction. Acc. Chem. Res. 2013, 46, 1878-1889.
    • (2013) Acc. Chem. Res. , vol.46 , pp. 1878-1889
    • Wu, G.1    Zelenay, P.2
  • 3
    • 33645389077 scopus 로고    scopus 로고
    • Oxygen reduction electrodes for electrolysis in chlor-alkali cells
    • Kiros, Y.; Pirjamali, M.; Bursell, M. Oxygen reduction electrodes for electrolysis in chlor-alkali cells. Electrochim. Acta. 2006, 51, 3346-3350.
    • (2006) Electrochim. Acta. , vol.51 , pp. 3346-3350
    • Kiros, Y.1    Pirjamali, M.2    Bursell, M.3
  • 4
    • 84881498481 scopus 로고    scopus 로고
    • Recent progress in the development of anode and cathode catalysts for direct methanol fuel cells
    • Tiwari, J.; Tiwari, R.; Singh, G.; Kim, K. Recent progress in the development of anode and cathode catalysts for direct methanol fuel cells. Nano Energy2013, 2, 553-578.
    • (2013) Nano Energy , vol.2 , pp. 553-578
    • Tiwari, J.1    Tiwari, R.2    Singh, G.3    Kim, K.4
  • 5
    • 84887049834 scopus 로고    scopus 로고
    • Mesoporous metal-nitrogen-doped carbon electrocatalysts for highly efficient oxygen reduction reaction
    • Liang, H.; Wei, W.; Wu, Z.; Feng, X.; Müllen, K. Mesoporous metal-nitrogen-doped carbon electrocatalysts for highly efficient oxygen reduction reaction. J. Am. Chem. Soc. 2013, 135, 16002-16005.
    • (2013) J. Am. Chem. Soc. , vol.135 , pp. 16002-16005
    • Liang, H.1    Wei, W.2    Wu, Z.3    Feng, X.4    Müllen, K.5
  • 6
    • 84883598629 scopus 로고    scopus 로고
    • Superior capacitive and electrocatalytic properties of carbonized nanostructured polyaniline upon a low-temperature hydrothermal treatment
    • Vujković, M.; Gavrilov, N.; Pašti, I.; Krstić, J.; Travas-Sejdic, J.; Ćirić-Marjanović, G.; Mentus, S. Superior capacitive and electrocatalytic properties of carbonized nanostructured polyaniline upon a low-temperature hydrothermal treatment. Carbon2013, 64, 472-486.
    • (2013) Carbon , vol.64 , pp. 472-486
    • Vujković, M.1    Gavrilov, N.2    Pašti, I.3    Krstić, J.4    Travas-Sejdic, J.5    Ćirić-Marjanović, G.6    Mentus, S.7
  • 9
    • 84882587286 scopus 로고    scopus 로고
    • Platinum-based oxygen reduction electrocatalysts
    • Wu, J.; Yang, H. Platinum-based oxygen reduction electrocatalysts. Acc. Chem. Res. 2013, 46, 1848-1857.
    • (2013) Acc. Chem. Res. , vol.46 , pp. 1848-1857
    • Wu, J.1    Yang, H.2
  • 10
    • 84892767762 scopus 로고    scopus 로고
    • Computational design of core/shell nanoparticles for oxygen reduction reactions
    • Zhang, X.; Lu, G. Computational design of core/shell nanoparticles for oxygen reduction reactions. J. Phys. Chem. Lett. 2014, 5, 292-297.
    • (2014) J. Phys. Chem. Lett. , vol.5 , pp. 292-297
    • Zhang, X.1    Lu, G.2
  • 11
    • 84870428956 scopus 로고    scopus 로고
    • Nitrogen-doped graphene and its iron-based composite as efficient electrocatalysts for oxygen reduction reaction
    • Parvez, K.; Yang, S.; Hernandez, Y.; Winter, A.; Turchanin, A.; Feng, X.; Müllen, K. Nitrogen-doped graphene and its iron-based composite as efficient electrocatalysts for oxygen reduction reaction. ACS Nano2012, 6, 9541-9550.
    • (2012) ACS Nano , vol.6 , pp. 9541-9550
    • Parvez, K.1    Yang, S.2    Hernandez, Y.3    Winter, A.4    Turchanin, A.5    Feng, X.6    Müllen, K.7
  • 13
    • 84865280791 scopus 로고    scopus 로고
    • Electrocatalysis of oxygen reduction reaction on polyaniline-derived nitrogen-doped carbon nanoparticle surfaces in alkaline media
    • Gavrilov, N.; Pašti, I.; Mitrić, M.; Travas-Sejdic, J.; Ćirić-Marjanović, G.; Mentus, S. Electrocatalysis of oxygen reduction reaction on polyaniline-derived nitrogen-doped carbon nanoparticle surfaces in alkaline media. J. Power Sources2012, 220, 306-316.
    • (2012) J. Power Sources , vol.220 , pp. 306-316
    • Gavrilov, N.1    Pašti, I.2    Mitrić, M.3    Travas-Sejdic, J.4    Ćirić-Marjanović, G.5    Mentus, S.6
  • 15
    • 84879369994 scopus 로고    scopus 로고
    • Optimized synthesis of Fe/N/C cathode catalysts for PEM fuel cells: A matter of iron-ligand coordination strength
    • Tian, J.; Morozan, A.; Sougrati, M.; Lefevre, M.; Chenitz, R.; Dodelet, J.; Jones, D.; Jaouen, F. Optimized synthesis of Fe/N/C cathode catalysts for PEM fuel cells: A matter of iron-ligand coordination strength. Angew. Chem. Int. Ed. 2013, 52, 6867-6870.
    • (2013) Angew. Chem. Int. Ed. , vol.52 , pp. 6867-6870
    • Tian, J.1    Morozan, A.2    Sougrati, M.3    Lefevre, M.4    Chenitz, R.5    Dodelet, J.6    Jones, D.7    Jaouen, F.8
  • 16
    • 84884341217 scopus 로고    scopus 로고
    • Hierarchical interconnected macro-/mesoporous Co-containing N-doped carbon for efficient oxygen reduction reactions
    • Jiang, H.; Su, Y.; Zhu, Y.; Shen, J.; Yang, X.; Feng, Q.; Li, C. Hierarchical interconnected macro-/mesoporous Co-containing N-doped carbon for efficient oxygen reduction reactions. J. Mater. Chem. A2013, 1, 12074-12081.
    • (2013) J. Mater. Chem. A , vol.1 , pp. 12074-12081
    • Jiang, H.1    Su, Y.2    Zhu, Y.3    Shen, J.4    Yang, X.5    Feng, Q.6    Li, C.7
  • 17
    • 84870595063 scopus 로고    scopus 로고
    • Coupling effect between cobalt oxides and carbon for oxygen reduction reaction
    • Liu, J.; Jiang, L.; Tang, Q.; Zhang, B.; Su, D.; Wang, S.; Sun, G. Coupling effect between cobalt oxides and carbon for oxygen reduction reaction. ChemSusChem2012, 5, 2315-2318.
    • (2012) ChemSusChem , vol.5 , pp. 2315-2318
    • Liu, J.1    Jiang, L.2    Tang, Q.3    Zhang, B.4    Su, D.5    Wang, S.6    Sun, G.7
  • 18
    • 84864139376 scopus 로고    scopus 로고
    • Nanocomposites of CoO and a mesoporous carbon (CMK-3) as a high performance cathode catalyst for lithium-oxygen batteries
    • Sun, B.; Liu, H.; Munroe, P.; Ahn, H.; Wang, G. Nanocomposites of CoO and a mesoporous carbon (CMK-3) as a high performance cathode catalyst for lithium-oxygen batteries. Nano Res. 2012, 5, 460-469.
    • (2012) Nano Res. , vol.5 , pp. 460-469
    • Sun, B.1    Liu, H.2    Munroe, P.3    Ahn, H.4    Wang, G.5
  • 19
    • 79959379132 scopus 로고    scopus 로고
    • Chelating agent assisted heat treatment of carbon supported cobalt oxide nanoparticle for use as cathode catalyst of polymer electrolyte membrane fuel cell (PEMFC)
    • Huang, C.; Liu, S.; Hwang, W. Chelating agent assisted heat treatment of carbon supported cobalt oxide nanoparticle for use as cathode catalyst of polymer electrolyte membrane fuel cell (PEMFC). Energy2011, 36, 4410-4414.
    • (2011) Energy , vol.36 , pp. 4410-4414
    • Huang, C.1    Liu, S.2    Hwang, W.3
  • 20
    • 84885150712 scopus 로고    scopus 로고
    • Electrocatalytic activity and stability of Co and Mn-based oxides for the oxygen reduction reaction in alkaline electrolyte
    • Queiroz, A.; Lima, F. Electrocatalytic activity and stability of Co and Mn-based oxides for the oxygen reduction reaction in alkaline electrolyte. J. Electroanal. Chem. 2013, 707, 142-150.
    • (2013) J. Electroanal. Chem. , vol.707 , pp. 142-150
    • Queiroz, A.1    Lima, F.2
  • 22
    • 84866696454 scopus 로고    scopus 로고
    • Oxygen reduction electrocatalyst based on strongly coupled cobalt oxide nanocrystals and carbon nanotubes
    • Liang, Y.; Wang, H.; Diao, P.; Chang, W.; Hong, G.; Li, Y.; Gong, M.; Xie, L.; Zhou, J.; Wang, J. et al. Oxygen reduction electrocatalyst based on strongly coupled cobalt oxide nanocrystals and carbon nanotubes. J. Am. Chem. Soc. 2012, 134, 15849-15857.
    • (2012) J. Am. Chem. Soc. , vol.134 , pp. 15849-15857
    • Liang, Y.1    Wang, H.2    Diao, P.3    Chang, W.4    Hong, G.5    Li, Y.6    Gong, M.7    Xie, L.8    Zhou, J.9    Wang, J.10
  • 24
    • 79953667003 scopus 로고    scopus 로고
    • Low-platinum and platinum-free catalysts for the oxygen reduction reaction at fuel cell cathodes
    • Morozan, A.; Jousselme, B.; Palacin, S. Low-platinum and platinum-free catalysts for the oxygen reduction reaction at fuel cell cathodes. Energy Environ. Sci. 2011, 4, 1238-1254.
    • (2011) Energy Environ. Sci. , vol.4 , pp. 1238-1254
    • Morozan, A.1    Jousselme, B.2    Palacin, S.3
  • 25
    • 84878644154 scopus 로고    scopus 로고
    • High performance Fe- and N-doped carbon catalyst with graphene structure for oxygen reduction
    • Peng, H.; Mo, Z.; Liao, S.; Liang, H.; Yang, L.; Luo, F.; Song, H.; Zhong, Y.; Zhang, B. High performance Fe- and N-doped carbon catalyst with graphene structure for oxygen reduction. Sci. Rep. 2013, 3, 1765.
    • (2013) Sci. Rep. , vol.3 , pp. 1765
    • Peng, H.1    Mo, Z.2    Liao, S.3    Liang, H.4    Yang, L.5    Luo, F.6    Song, H.7    Zhong, Y.8    Zhang, B.9
  • 26
    • 79955405239 scopus 로고    scopus 로고
    • High-performance electrocatalysts for oxygen reduction derived from polyaniline, iron, and cobalt
    • Wu, G.; More, K.; Johnston, C.; Zelenay, P. High-performance electrocatalysts for oxygen reduction derived from polyaniline, iron, and cobalt. Science2011, 332, 443-447.
    • (2011) Science , vol.332 , pp. 443-447
    • Wu, G.1    More, K.2    Johnston, C.3    Zelenay, P.4
  • 27
    • 79961183037 scopus 로고    scopus 로고
    • Iron-based cathode catalyst with enhanced power density in polymer electrolyte membrane fuel cells
    • Proietti, E.; Jaouen, F.; Lefèvre, M.; Larouche, N.; Tian, J.; Herranz, J.; Dodelet, J. Iron-based cathode catalyst with enhanced power density in polymer electrolyte membrane fuel cells. Nat. Commun. 2011, 2, 416.
    • (2011) Nat. Commun. , vol.2 , pp. 416
    • Proietti, E.1    Jaouen, F.2    Lefèvre, M.3    Larouche, N.4    Tian, J.5    Herranz, J.6    Dodelet, J.7
  • 28
    • 84886888923 scopus 로고    scopus 로고
    • Activity descriptor identification for oxygen reduction on nonprecious electrocatalysts: Linking surface science to coordination chemistry
    • Ramaswamy, N.; Tylus, U.; Jia, Q.; Mukerjee, S. Activity descriptor identification for oxygen reduction on nonprecious electrocatalysts: Linking surface science to coordination chemistry. J. Am. Chem. Soc. 2013, 135, 15443-15449.
    • (2013) J. Am. Chem. Soc. , vol.135 , pp. 15443-15449
    • Ramaswamy, N.1    Tylus, U.2    Jia, Q.3    Mukerjee, S.4
  • 31
    • 84875792844 scopus 로고    scopus 로고
    • Electrochemically reduced graphene oxide multilayer films as metal-free electrocatalysts for oxygen reduction
    • Huang, D.; Zhang, B.; Zhang, Y.; Zhan, F.; Xu, X.; Shen, Y.; Wang, M. Electrochemically reduced graphene oxide multilayer films as metal-free electrocatalysts for oxygen reduction. J. Mater. Chem. A2013, 1, 1415-1420.
    • (2013) J. Mater. Chem. A , vol.1 , pp. 1415-1420
    • Huang, D.1    Zhang, B.2    Zhang, Y.3    Zhan, F.4    Xu, X.5    Shen, Y.6    Wang, M.7
  • 32
    • 33947410026 scopus 로고    scopus 로고
    • Solvothermal in situ metal/ligand reactions: A new bridge between coordination chemistry and organic synthetic chemistry
    • Chen, X.; Tong, M. Solvothermal in situ metal/ligand reactions: A new bridge between coordination chemistry and organic synthetic chemistry. Acc. Chem. Res., 2007, 40, 162-170.
    • (2007) Acc. Chem. Res. , vol.40 , pp. 162-170
    • Chen, X.1    Tong, M.2
  • 33
    • 84877663410 scopus 로고    scopus 로고
    • Nitrogen-doped mesoporous carbons originated from ionic liquids as electrode materials for supercapacitors
    • Qiu, B.; Pan, C.; Qian, W.; Peng, Y.; Qiu, L.; Yan, F. Nitrogen-doped mesoporous carbons originated from ionic liquids as electrode materials for supercapacitors. J. Mater. Chem. A2013, 1, 6373-6378.
    • (2013) J. Mater. Chem. A , vol.1 , pp. 6373-6378
    • Qiu, B.1    Pan, C.2    Qian, W.3    Peng, Y.4    Qiu, L.5    Yan, F.6
  • 35
    • 50049098553 scopus 로고    scopus 로고
    • Non-platinum oxygen reduction electrocatalysts based on pyrolyzed transition metal macrocycles
    • Pylypenko, S.; Mukherjee, S.; Olson, T.; Atanassov, P. Non-platinum oxygen reduction electrocatalysts based on pyrolyzed transition metal macrocycles. Electrochim. Acta2008, 53, 7875-7883.
    • (2008) Electrochim. Acta , vol.53 , pp. 7875-7883
    • Pylypenko, S.1    Mukherjee, S.2    Olson, T.3    Atanassov, P.4
  • 36
    • 84869456969 scopus 로고    scopus 로고
    • Co/CoO Nanoparticles assembled on graphene for electrochemical reduction of oxygen
    • Guo, S.; Zhang, S.; Wu, L.; Sun, S. Co/CoO Nanoparticles assembled on graphene for electrochemical reduction of oxygen. Angew. Chem. Int. Ed. 2012, 51, 11770-11773.
    • (2012) Angew. Chem. Int. Ed. , vol.51 , pp. 11770-11773
    • Guo, S.1    Zhang, S.2    Wu, L.3    Sun, S.4
  • 37
    • 0037803446 scopus 로고    scopus 로고
    • Pore size determination in modified micro- and mesoporous materials. Pitfalls and limitations in gas adsorption data analysis
    • Groen, J.; Peffer, L.; Pérez Ramírez, J. Pore size determination in modified micro- and mesoporous materials. Pitfalls and limitations in gas adsorption data analysis. Micropor. Mesopor. Mater. 2003, 60, 1-17.
    • (2003) Micropor. Mesopor. Mater. , vol.60 , pp. 1-17
    • Groen, J.1    Peffer, L.2    Pérez Ramírez, J.3
  • 38
    • 84939775172 scopus 로고
    • Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity
    • Sing, K.; Everett, D.; Haul, R.; Moscou, L.; Pierotti, R.; Rouquerol, J.; Siemieniewska, T. Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity. Pure Appl. Chem. 1985, 57, 603-619.
    • (1985) Pure Appl. Chem. , vol.57 , pp. 603-619
    • Sing, K.1    Everett, D.2    Haul, R.3    Moscou, L.4    Pierotti, R.5    Rouquerol, J.6    Siemieniewska, T.7
  • 40
    • 84868578861 scopus 로고    scopus 로고
    • Facile synthesis of manganese-oxide-containing mesoporous nitrogen-doped carbon for efficient oxygen reduction
    • Tan, Y.; Xu, C.; Chen, G.; Fang, X.; Zheng, N.; Xie, Q. Facile synthesis of manganese-oxide-containing mesoporous nitrogen-doped carbon for efficient oxygen reduction. Adv. Funct. Mater. 2012, 22, 4584-4591.
    • (2012) Adv. Funct. Mater. , vol.22 , pp. 4584-4591
    • Tan, Y.1    Xu, C.2    Chen, G.3    Fang, X.4    Zheng, N.5    Xie, Q.6
  • 41
    • 80052192526 scopus 로고    scopus 로고
    • A review on non-precious metal electrocatalysts for PEM fuel cells
    • Chen, Z.; Higgins, D.; Yu, A.; Zhang, L.; Zhang, J. A review on non-precious metal electrocatalysts for PEM fuel cells. Energy Environ. Sci. 2011, 4, 3167-3192.
    • (2011) Energy Environ. Sci. , vol.4 , pp. 3167-3192
    • Chen, Z.1    Higgins, D.2    Yu, A.3    Zhang, L.4    Zhang, J.5
  • 42
    • 59849084114 scopus 로고    scopus 로고
    • Nitrogen-doped carbon nanotube arrays with high electrocatalytic activity for oxygen reduction
    • Gong, K.; Du, F.; Xia, Z.; Durstock, M.; Dai, L. Nitrogen-doped carbon nanotube arrays with high electrocatalytic activity for oxygen reduction. Science2009, 323, 760-764.
    • (2009) Science , vol.323 , pp. 760-764
    • Gong, K.1    Du, F.2    Xia, Z.3    Durstock, M.4    Dai, L.5
  • 43
    • 84883285826 scopus 로고    scopus 로고
    • A class of high performance metal-free oxygen reduction electrocatalysts based on cheap carbon blacks
    • Sun, X.; Song, P.; Zhang, Y.; Liu, C.; Xu, W.; Xing, W. A class of high performance metal-free oxygen reduction electrocatalysts based on cheap carbon blacks. Sci. Rep. 2013, 3, 2505.
    • (2013) Sci. Rep. , vol.3 , pp. 2505
    • Sun, X.1    Song, P.2    Zhang, Y.3    Liu, C.4    Xu, W.5    Xing, W.6
  • 44
    • 77950140364 scopus 로고    scopus 로고
    • Nitrogen-doped graphene as efficient metal-free electrocatalyst for oxygen reduction in fuel cells
    • Qu, L.; Liu, Y.; Baek, J.; Dai, L. Nitrogen-doped graphene as efficient metal-free electrocatalyst for oxygen reduction in fuel cells. ACS Nano2010, 4, 1321-1326.
    • (2010) ACS Nano , vol.4 , pp. 1321-1326
    • Qu, L.1    Liu, Y.2    Baek, J.3    Dai, L.4
  • 45
    • 77950283502 scopus 로고    scopus 로고
    • Nitrogen-doped ordered mesoporous graphitic arrays with high electrocatalytic activity for oxygen reduction
    • Liu, R.; Wu, D.; Feng, X.; Mullen, K. Nitrogen-doped ordered mesoporous graphitic arrays with high electrocatalytic activity for oxygen reduction. Angew. Chem. Int. Ed. 2010, 49, 2565-2569.
    • (2010) Angew. Chem. Int. Ed. , vol.49 , pp. 2565-2569
    • Liu, R.1    Wu, D.2    Feng, X.3    Mullen, K.4
  • 46
    • 80051917801 scopus 로고    scopus 로고
    • Theoretical study of possible active site structures in cobalt-polypyrrole catalysts for oxygen reduction reaction
    • Shi, Z.; Liu, H.; Lee, K.; Dy, E.; Chlistunoff, J.; Blair, M.; Zelenay, P.; Zhang, J.; Liu, Z. Theoretical study of possible active site structures in cobalt-polypyrrole catalysts for oxygen reduction reaction. J. Phys. Chem. C2011, 115, 16672-16680.
    • (2011) J. Phys. Chem. C , vol.115 , pp. 16672-16680
    • Shi, Z.1    Liu, H.2    Lee, K.3    Dy, E.4    Chlistunoff, J.5    Blair, M.6    Zelenay, P.7    Zhang, J.8    Liu, Z.9
  • 47
    • 84890375209 scopus 로고    scopus 로고
    • Oxygen reduction electrocatalysis using N-doped graphene quantum-dots
    • Saidi, W. A. Oxygen reduction electrocatalysis using N-doped graphene quantum-dots. J. Phys. Chem. Lett. 2013, 4, 4160-4165.
    • (2013) J. Phys. Chem. Lett. , vol.4 , pp. 4160-4165
    • Saidi, W.A.1
  • 48
    • 84890337279 scopus 로고    scopus 로고
    • The effect of metal catalyst on the electrocatalytic activity of nitrogen-doped carbon nanotubes
    • Tang, Y.; Burkert, S.; Zhao, Y.; Saidi, W. A.; Star, A. The effect of metal catalyst on the electrocatalytic activity of nitrogen-doped carbon nanotubes. J. Phys. Chem. C2013, 117, 25213-25221.
    • (2013) J. Phys. Chem. C , vol.117 , pp. 25213-25221
    • Tang, Y.1    Burkert, S.2    Zhao, Y.3    Saidi, W.A.4    Star, A.5
  • 49
    • 0024030376 scopus 로고
    • On the effect of a heat treatment on the structure of carbon-supported metalloporphyrins and phthalocyanines
    • van Veen, J.; Colijn, H.; van Baar, J. On the effect of a heat treatment on the structure of carbon-supported metalloporphyrins and phthalocyanines. Electrochim. Acta1988, 33, 801-804.
    • (1988) Electrochim. Acta , vol.33 , pp. 801-804
    • van Veen, J.1    Colijn, H.2    van Baar, J.3
  • 52
    • 84876535703 scopus 로고    scopus 로고
    • Tunable nitrogen-doped carbon aerogels as sustainable electrocatalysts in the oxygen reduction reaction
    • Wohlgemuth, S.; Fellinger, T.; Jäker, P.; Antonietti, M. Tunable nitrogen-doped carbon aerogels as sustainable electrocatalysts in the oxygen reduction reaction. J. Mater. Chem. A2013, 1, 4002-4009.
    • (2013) J. Mater. Chem. A , vol.1 , pp. 4002-4009
    • Wohlgemuth, S.1    Fellinger, T.2    Jäker, P.3    Antonietti, M.4
  • 53
    • 84892114320 scopus 로고    scopus 로고
    • 4 macrocycles and beyond
    • J. Zagal, F. Bedioui, and J. Dedelet (Eds.), New York: Springer
    • 4-macrocyclic metal complexes. Zagal, J.; Bedioui, F.; Dedelet, J., Eds.; Springer: New York, 2006; pp 83-147.
    • (2006) 4-Macrocyclic Metal Complexes , pp. 83-147
    • Dodelet, J.1


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.