Defect-Engineered Nanostructured Ni/MOF-Derived Carbons for an Efficient Aqueous Battery-Type Energy Storage Device

Thapelo Prince Mofokeng; Adewale Kabir Ipadeola; Zikhona Nobuntu Tetana; Kenneth Ikechukwu Ozoemena

doi:10.1021/acsomega.0c02563

Defect-Engineered Nanostructured Ni/MOF-Derived Carbons for an Efficient Aqueous Battery-Type Energy Storage Device

ACS Omega. 2020 Aug 7;5(32):20461-20472. doi: 10.1021/acsomega.0c02563. eCollection 2020 Aug 18.

Authors

Thapelo Prince Mofokeng^{1

2}, Adewale Kabir Ipadeola¹, Zikhona Nobuntu Tetana^{1

2}, Kenneth Ikechukwu Ozoemena^{1

2}

Affiliations

¹ Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Private Bag 3, PO Wits, Johannesburg 2050, South Africa.
² DSI-NRF Centre of Excellence in Strong Materials, School of Chemistry, University of the Witwatersrand, Private Bag 3, PO Wits, Johannesburg 2050, South Africa.

Abstract

A Ni-based metal-organic framework (Ni-MOF) has been synthesized using a microwave-assisted strategy and converted to nanostructured Ni/MOF-derived mesoporous carbon (Ni/MOFDC) by carbonization and acid treatment (AT-Ni/MOFDC). The materials are well characterized with Raman, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and Brunauer-Emmett-Teller (BET), revealing that chemical etching confers on the AT-Ni/MOFDC-reduced average nanoparticle size (high surface area) and structural defects including oxygen vacancies. AT-Ni/MOFDC displays low series resistances and a higher specific capacity (C _s) of 199 mAh g^-1 compared to Ni/MOFDC (92 mAh g^-1). This study shows that the storage mechanism of the Ni-based electrode as a battery-type energy storage (BTES) system can be controlled by both non-faradic and faradic processes and dependent on the sweep rate or current density. AT-Ni/MOFDC reveals mixed contributions at different rates: 75.2% faradic and 24.8% non-faradic contributions at 5 mV s^-1, and 34.1% faradic and 65.9% non-faradic at 50 mV s^-1. The full BTES device was assembled with AT-Ni/MOFDC as the cathode and acetylene black (AB) as the anode. Compared to recent literature, the AT-Ni/MOFDC//AB BTES device exhibits high energy (33 Wh kg^-1) and high power (983 W kg^-1) with excellent cycling performance (about 88% capacity retention over 2000 cycles). This new finding opens a window of opportunity for the rational designing of next-generation energy storage devices, supercapatteries, that combine the characteristics of batteries (high energy) and supercapacitors (high power).