Rational Design of Metal‐Organic Framework Derived Hollow NiCo₂O₄ Arrays for Flexible Supercapacitor and Electrocatalysis

Abstract

Metal‐organic frameworks (MOFs) are promising porous precursors for the construction of various functional materials for high‐performance electrochemical energy storage and conversion. Herein, a facile two‐step solution method to rational design of a novel electrode of hollow NiCo2O4 nanowall arrays on flexible carbon cloth substrate is reported. Uniform 2D cobalt‐based wall‐like MOFs are first synthesized via a solution reaction, and then the 2D solid nanowall arrays are converted into hollow and porous NiCo2O4 nanostructures through an ion‐exchange and etching process with an additional annealing treatment. The as‐obtained NiCo2O4 nanostructure arrays can provide rich reaction sites and short ion diffusion path. When evaluated as a flexible electrode material for supercapacitor, the as‐fabricated NiCo2O4 nanowall electrode shows remarkable electrochemical performance with excellent rate capability and long cycle life. In addition, the hollow NiCo2O4 nanowall electrode exhibits promising electrocatalytic activity for oxygen evolution reaction. This work provides an example of rational design of hollow nanostructured metal oxide arrays with high electrochemical performance and mechanical flexibility, holding great potential for future flexible multifunctional electronic devices.

Rational Design of Nickel Hydroxide‐Based Nanocrystals on Graphene for Ultrafast Energy Storage

“…The broadening of the redox peak is attributed to the combination of a capacitive electrode and a batterytype Faradaic electrode. [70] Moreover, compared to the energy/ power densities of advanced hybrid/asymmetric supercapacitors reported recently [22,43,[51][52][53][54][55][56][57][58][59] (Figure 6d, Figure S10, and Table S3, Supporting Information), the Ni-Co-Mn-OH/rGO//PPD/rGO hybrid device has demonstrated reasonably superior gravimetric energy/power densities. The energy and power densities of the Ni-Co-Mn-OH/rGO//PPD/ rGO hybrid device were calculated from galvanostatic discharge curves ( Figure S9, Supporting Information) with the Ragone plot shown in Figure 6d.…”

“…[47] This finding enables us to design, predict, and validate the charge storage properties of Ni hydroxide-based electrodes by analyzing the deprotonation (i.e., OH bond breaking) barriers. [22,43,[51][52][53][54][55][56][57][58][59] Here, we report our findings in rational design, synthesis, and characterization of a series of Ni hydroxide-based nanocrystals/reduced graphene oxide (rGO) composites as electrodes in an alkaline electrolyte for fast energy storage.…”

Structural Engineering of Low‐Dimensional Metal–Organic Frameworks: Synthesis, Properties, and Applications

“…[251][252][253][254] Up to now, various 2D MOF-derived nanostructure arrays have been reported, such as Ni-doped Co-Co 2 N nanosheet/carbon cloth, [255] N-doped carbon-Co 3 O 4 sheet/ carbon cloth, [256] Co 3 O 4 @N-doped carbon nanosheet/nickel foam, [257] and CoSe 2 sheets/carbon cloth. [259] Furthermore, 2D MOF-derivatives can be also obtained through hydrothermal/ solvothermal reaction. [61] For example, Wang and co-workers reported a two-step strategy, i.e., ion exchange and etching process followed by thermal treatment in air, to prepare hollow NiCo 2 O 4 nanowall arrays on carbon cloth.…”

“…Moreover, the authors proposed that the coordinatively unsaturated metal sites and the coupling effect of Co and Ni species in bimetallic MOF nanosheets are responsible for their high electrocatalytic activity in OER (Figure 15c). [258] Similarly, Co 3 O 4 /C nanowire arrays [231,233] and hollow NiCo 2 O 4 nanostructure [259] have been also prepared via thermally conversion of their corresponding LD MOF precursors, and then used as efficient OER electrocatalysts. [90] can be also converted to active materials for OER via heat treatment, such as metal oxides, metal phosphates, and porous carbon-based materials.…”

“…Zheng and co-workers further prepared oriented Co/Ni-BDC MOF nanosheets on carbon fiber paper (CFP). [73,140,169,175,239,241,258,259] LD MOF-based materials and their derivatives have also been used in other electrochemical energy storage devices, such as sodium-ion batteries (SIBs), lithium sulfur batteries, and battery-supercapacitor hybrid devices. Similarly, the conductive MOF nanowire arrays of Cu-CAT grown on carbon paper showed a high areal capacitance of about 22 µF cm −2 , when used as electrodes for solid-state supercapacitor, which is owing to the high porosity and excellent conductivity of electrode material.…”