Metal Oxide Nanosheet: Synthesis Approaches and Applications in Energy Storage Devices (Batteries, Fuel Cells, and Supercapacitors)

Abstract

In recent years, the increasing energy requirement and consumption necessitates further improvement in energy storage technologies to obtain high cycling stability, power and energy density, and specific capacitance. Two-dimensional metal oxide nanosheets have gained much interest due to their attractive features, such as composition, tunable structure, and large surface area which make them potential materials for energy storage applications. This review focuses on the establishment of synthesis approaches of metal oxide nanosheets (MO nanosheets) and their advancements over time, as well as their applicability in several electrochemical energy storage systems, such as fuel cells, batteries, and supercapacitors. This review provides a comprehensive comparison of different synthesis approaches of MO nanosheets, as well their suitability in several energy storage applications. Among recent improvements in energy storage systems, micro-supercapacitors, and several hybrid storage systems are rapidly emerging. MO nanosheets can be employed as electrode and catalyst material to improve the performance parameters of energy storage devices. Finally, this review outlines and discusses the prospects, future challenges, and further direction for research and applications of metal oxide nanosheets.

Keywords: batteries; energy storage; fuel cells; metal oxide nanosheets; molecular-scale integration; supercapacitors.

Figure 1

Number of publications on “metal oxide nanosheets” from 2010–2022.

Figure 2

Illustration of the Mn₃O₄ characterization process. (a) XRD patterns, (b) SEM image of the precursor Mn₃O₄, and (c) of the ball-milled Mn₃O₄, respectively. Reprinted with permission from [36]. Copyright 2018 American Chemical Society.

Figure 3

(A) Illustration of the synthesis approaches of the Ti0_0.87O₂/N-doped graphene superlattice. (B) XRD patterns of (i) Ti_0.87O₂/PDDA-graphene superlattices and (ii) Ti_0.87O₂/N-doped graphene superlattices. (C) SEM and (D) HRTEM images of Ti0_0.87O₂/PDDA-graphene superlattices. (E) SEM and (F) HRTEM images of Ti_0.87O₂/N-doped graphene superlattices. (G) High-resolution spectrum of N 1s in Ti_0.87O₂/N-doped graphene superlattices. Reprinted with permission from [42]. Copyright 2018 American Chemical Society.

Figure 4

Schematic illustration of the common soft chemical exfoliation approach for synthesizing metal oxide nanosheets. Reprinted with permission from [49]. Copyright 2018 Elsevier.

Figure 5

Schematic showing the surface coating process of LAO on LACO. Reprinted with permission from [64]. Copyright 2021 Elsevier.

Figure 6

Electrochemical performance of the Zn/ε-MnO₂ coin cells. (a) Cyclic voltametric (CV) curves of the Zn/ε-MnO₂ cell at a scan rate of 0.1 mV s⁻¹. (b) The discharge/charge voltage profiles at various current densities between 0.6 and 1.9 V. (c) Rate capability. (d) Long-term cyclic performance and the corresponding Coulombic efficiency at 500 mA g⁻¹. Reprinted with permission from [35]. Copyright 2018 American Chemical Society.

Figure 7

The synthesis process of SnO₂/MG nanosheets. Reprinted with permission from [96]. Copyright 2019 Elsevier.

Figure 8

(A) Diagram of the sodium diffusion path towards the [100] directions between the TiO₂/graphene bilayers. (B) The energy of sodium diffusion along the [100] direction in TiO₂ bilayers and TiO₂/graphene bilayers. (C) Illustration of the Na diffusion path along the [001] directions between the TiO₂/graphene bilayers. (D) The energy of Na diffusion along the [001] direction in TiO₂ bilayers and TiO₂/graphene bilayers. (E) Illustration of a possible Na diffusion path in Ti_0.87O₂/graphene bilayers. (F) The energy of Na diffusion in Ti_0.87O₂ bilayers and Ti_0.87O₂/graphene bilayers. Reprinted with permission from [41]. Copyright 2018 American Chemical Society.

Figure 9

Ragone plots of various rechargeable batteries and EDLC, and the comparison with BSHs. Reprinted with permission from [110]. Copyright 2017 Willey online library.

Figure 10

(a) A typical hybrid energy storage device with a working process. (b) Different types of hybrid devices and their electrolyte and electrode materials. Reprinted with permission from [110]. Copyright 2017 Willey online library.

Figure 11

The current-potential curves for (a) the anodes and cathodes, (b) the current-potential curves measured using several potential windows, (c) different scan rates, (d) the GC/D plots measured using several potential windows, (e) different current densities, and (f) the Ragone plot of the BSH. Reprinted with permission from [111]. Copyright 2018 American Chemical Society.

Figure 12

Schematic of the step-wise synthesis process of the catalyst and corresponding SEM images. Reprinted with permission from Ref. [134]. Copyright 2021 Elsevier.

Figure 13

Synthesis flow diagram of NiO. Reprinted with permission from [134]. Copyright 2021 Elsevier.

Figure 14

Schematic representation of a PEM fuel cell [140]. Copyright permission 2020, Elsevier.

Figure 15

Schematic illustration of the preparation of Pt–TiO_{2 − x} NS. Reprinted with permission from [140]. Copyright 2020 Elsevier.

Figure 16

Schematic diagram of a microbial fuel cell. Reprinted with permission from [147]. Copyright 2021 Elsevier.

Figure 17

Schematic of MoO₃/NiCo₂O₄-NSs, α-FeOOH/rGO synthesis (hydrothermal) process, and asymmetric supercapacitor. Reprinted with permission from [157]. Copyright 2019 Elsevier.