title: Mussel-inspired one-pot synthesis of transition metal and nitrogen co-doped carbon (M/N-C) as efficient oxygen catalysts for Zn-air batteries.
abstract: Transition metal and nitrogen co-doping into carbon is an effective approach to promote the catalytic activities towards the oxygen reduction reaction (ORR) and/or oxygen evolution reaction (OER) in the resultant electrocatalysts, M/N-C. The preparation of such catalysts, however, is often complicated and in low yield. Herein we report a robust approach for easy synthesis of M/N-C hybrids in high yield, which includes a mussel-inspired polymerization reaction at room temperature and a subsequent carbonization process. With the introduction of selected transition metal salts into an aqueous solution of dopamine (DA), the obtained mixture self-polymerizes to form metal-containing polydopamine (M-PDA) composites, e.g. Co-PDA, Ni-PDA and Fe-PDA. Upon carbonization at elevated temperatures, these metal-containing composites were converted into M/N-C, i.e. Co-PDA-C, Ni-PDA-C and Fe-PDA-C, respectively, whose morphologies, chemical compositions, and electrochemical performances were fully studied. Enhanced ORR activities were found in all the obtained hybrids, with Co-PDA-C standing out as the most promising catalyst with excellent stability and catalytic activities towards both ORR and OER. This was further proven in Zn-air batteries (ZnABs) in terms of discharge voltage stability and cycling performance. At a discharge-charge current density of 2 mA cm(-2) and 1 h per cycle, the Co-PDA-C based ZnABs were able to steadily cycle up to 500 cycles with only a small increase in the discharge-charge voltage gap which notably outperformed Pt/C; at a discharge current density of 5 mA cm(-2), the battery continuously discharged for more than 540 h with the discharge voltage above 1 V and a voltage drop rate of merely 0.37 mV h(-1). With the simplicity and scalability of the synthetic approach and remarkable battery performances, the Co-PDA-C hybrid catalyst is anticipated to play an important role in practical ZnABs.
authors: Institute of Materials Research and Engineering (IMRE), A*STAR (Agency for Science, Technology and Research), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore. zl-liu@imre.a-star.edu.sg y-zong@imre.a-star.edu.sg.
authors: Bing
authors: B
authors: Li
authors: Center for Programmable Materials, School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Republic of Singapore. hzhang@ntu.edu.sg.
authors: Ye
authors: Y
authors: Chen
authors: Institute of Materials Research and Engineering (IMRE), A*STAR (Agency for Science, Technology and Research), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore. zl-liu@imre.a-star.edu.sg y-zong@imre.a-star.edu.sg.
authors: Xiaoming
authors: X
authors: Ge
authors: Institute of Materials Research and Engineering (IMRE), A*STAR (Agency for Science, Technology and Research), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore. zl-liu@imre.a-star.edu.sg y-zong@imre.a-star.edu.sg.
authors: Jianwei
authors: J
authors: Chai
authors: Center for Programmable Materials, School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Republic of Singapore. hzhang@ntu.edu.sg.
authors: Xiao
authors: X
authors: Zhang
authors: Institute of Materials Research and Engineering (IMRE), A*STAR (Agency for Science, Technology and Research), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore. zl-liu@imre.a-star.edu.sg y-zong@imre.a-star.edu.sg and Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Republic of Singapore.
authors: T S Andy
authors: TS
authors: Hor
authors: Institute of Materials Research and Engineering (IMRE), A*STAR (Agency for Science, Technology and Research), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore. zl-liu@imre.a-star.edu.sg y-zong@imre.a-star.edu.sg.
authors: Guojun
authors: G
authors: Du
authors: Institute of Materials Research and Engineering (IMRE), A*STAR (Agency for Science, Technology and Research), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore. zl-liu@imre.a-star.edu.sg y-zong@imre.a-star.edu.sg.
authors: Zhaolin
authors: Z
authors: Liu
authors: Center for Programmable Materials, School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Republic of Singapore. hzhang@ntu.edu.sg.
authors: Hua
authors: H
authors: Zhang
authors: Institute of Materials Research and Engineering (IMRE), A*STAR (Agency for Science, Technology and Research), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore. zl-liu@imre.a-star.edu.sg y-zong@imre.a-star.edu.sg.
authors: Yun
authors: Y
authors: Zong