Comparative studies of cobalt hydroxide and nickel hydroxide designed using novel metal tetrafluoroborate as active materials of battery supercapacitor hybrids

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Author list: You X.-Y.; Lee P.-Y.; Wang S.-C.; Kongvarhodom C.; Saukani M.; Yougbaré S.; Chen H.-M.; Ho K.-C.; Wu Y.-F.; Lin L.-Y.

Publisher: Elsevier

Publication year: 2024

Volume number: 100

ISSN: 2352-152X

eISSN: 2352-1538

URL: https://www.scopus.com/inward/record.uri?eid=2-s2.0-85203294239&doi=10.1016%2fj.est.2024.113678&partnerID=40&md5=28f2cbdf390a44a18d7812cc8d74034d

Languages: English-Great Britain (EN-GB)

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Abstract

Structure directing agent (SDA) can tailor morphology of active materials with preferable surface properties. Ammonium fluoroborate has been proposed as an effective SDA to synthesize metal organic framework (MOF) derivatives in previous reports, where fluoroborate ions play as morphology regulators by providing steric hindrance. Nickel and cobalt hydroxides are intensively used as active materials in battery supercapacitor hybrids (BSHs), owing to high theoretical capacitances and durability. However, previous studies rarely investigate metal specie effects on energy storage and compare electrochemical performance of nickel and cobalt hydroxides particularly in unique synthesis environments. In this study, nickel tetrafluoroborate (Ni(BF4)2) and cobalt tetrafluoroborate (Co(BF4)2) are respectively used as nickel and cobalt sources to synthesize hydroxides as active materials of BSHs. Tetrafluoroborate ions act as SDAs to design favorable morphologies, while 2-methylimidazole is incorporated to control the pH value for facilitating precipitations. The Ni(OH)2 and Co(OH)2 electrodes respectively show specific capacitances (CF) of 1118.5 and 334.3 F/g at 20 mV/s, owing to the preferable alpha-type hydroxide and larger pore volume/width for Ni(OH)2. A BSH consisted of a Ni(OH)2 positive electrode shows a maximum energy density of 64.0 Wh/kg at 700.0 W/kg, and the CF retention of 116% and Coulombic efficiency of 94% after 5000 cycles. © 2024 Elsevier Ltd

Keywords

Metal organic framework derivative, Nickel tetrafluoroborate