Mechanochemical synthesis of ZIF(Zn, Co)/NixCoyAlz-LDH composite by solid state ion exchange as advanced materials for pseudocapacitor electrode

Abstract

Metal-organic frameworks (MOFs), and layered double hydroxides (LDHs) as worthy hot-spot materials have gained substantial attention for electrochemical energy storage and conversion applications as a result of their structural diversities, excellent physical properties, and promising electrochemical performance. In this work, we synthesized composite materials comprised of ZIF-8 and NiCoAl-LDHs via a mechanochemical method and in-situ solid state ion exchange. The findings have shown that the synergetic effects between ZIF-8 and LDHs in composite materials and tuning of the percentages of Ni and Co in LDHs have a positive contribution to enhancing electrochemical performance in supercapacitors. In this regard, among pure LDHs and ZIF-8\\NixCoyAl0.33 LDHs, ZIF-8\\Ni(17%)Co(50%)Al(33%)-LDH indicated higher specific capacitance of 256 F g−1 and higher rate of performance. In ZIF-8/Ni(17%)Co(50%)Al(33%)-LDH, LDH nanosheets’ structure improves the conductivity of ZIF-8, and optimized bimetal Ni-Co provides more active sites. In addition, the asymmetric supercapacitor (ASC) assembled by ZIF-8/Ni(17%)Co(50%)Al(33%)-LDH as the cathode and activated carbon (AC) as the anode achieved a good performance in terms of specific capacity, energy density, and cyclic stability. For instance, the ASC delivered a maximum energy density of 184 Wh kg−1 at 1291 W kg−1 and outstanding capacitance retention of 91% after 5000 cycles. This study demonstrates that the interaction between different element ratios in LDHs and the composition of LDHs with ZIFs (porous and redox-active MOFs) has significant effects on using ZIFs/LDHs electrode materials in advanced supercapacitor applications.