2D inorganic nanosheets as versatile building blocks for hybrid electrode materials for supercapacitor

Among many classes of nanostructured inorganic solids, two-dimensional (2D) inorganic nanosheets (NSs) have attracted intense research activities because of their unique advantages as versatile building blocks for efficient hybrid electrodes for energy storage technologies like supercapacitors and secondary batteries. The highly anisotropic morphology, greatly expanded surface area with presence of many active sites, and tunable chemical composition with large concentration of redoxable component ions provide 2D inorganic NSs with high electrochemical activity. The hybridization with 2D inorganic NSs can provide effective synthetic ways to explore high-performance supercapacitor electrode materials with expanded surface area, enlarged voltage window, improved electrical conductivity, and enhanced specific capacitance. In this review, wide spectrum of 2D inorganic NS-based electrodes are presented with respect to their synthetic strategies and chemical compositions. The 2D inorganic NS-based electrodes can be synthesized by several synthetic strategies like intercalative hybridization, stacking control, core-shell architecture, surface anchoring, and defect control. Lots of promising supercapacitor electrodes are developed with diverse 2D inorganic NS including metal oxide, metal chalcogenide, metal hydroxide, metal carbide, metal pnictogenide, metal-organic framework, and carbonaceous compounds. The in-depth discussions about advanced approaches for elucidating the operation mechanism of supercapacitor electrodes are discussed on the basis of up-to-date characterization techniques such as spectroscopic and diffraction analyses, theoretical calculation, and in-situ characterization techniques. The great diversity and controllability of the chemical composition, surface property, and defect structure of inorganic NSs can offer valuable opportunity to optimize the supercapacitor electrode performance of 2D NS-based hybrid materials via the fine-tuning of conductivity, electrochemical kinetics, ion absorption affinity, and interfacial electronic interaction. Future directions and challenges in the researches for 2D inorganic NS-based hybrid electrodes for supercapacitors are discussed to offer insight for the exploration of next-generation supercapacitor electrode materials. (C) 2020 Elsevier B.V. All rights reserved.