Graphene and molybdenum disulphide hybrids for energy applications: an update

Graphene and its analog, two-dimensional (2D) layered molybdenum disulphide (MoS2), have been used for 'clean energy' applications in the last several years because of their remarkable electrochemical, optical, and magnetic properties. Their huge success and application potential in various fields has led to the investigation of new 2D nanomaterials which cross the boundaries of existing graphene-based devices. The combination of chemically inert graphene and redox-active MoS2 in a single electrode is providing new opportunities to improve the performance of energy devices and circumvent existing limitations. This article updates our previous review on advances in graphene-MoS2 hybrids for energy-oriented applications. In particular, a summary of recent developments in the synthesis of the graphene-MoS2 hybrids, with an emphasis on energy storage and hydrogen production, is provided. Future challenges and opportunities associated with the development of 2D hybrid materials, and their applications in energy storage systems, are discussed. (C) 2019 The Authors. Published by Elsevier Ltd

Large interspaced layered potassium niobate nanosheet arrays as an ultrastable anode for potassium ion capacitor

Available online 16 October 2020Potassium-ion battery (KIB) is a promising technology for large-scale energy storage applications due to their low cost, theoretically high energy density and abundant resources. However, the development of KIBs is hin- dered by the sluggish K + transport kinetics and the structural instability of the electrode materials during K + intercalation/de-intercalation. In the present investigation, we have designed a potassium-ion capacitor (KIC) using layered potassium niobate (K 4 Nb 6 O 17 , KNO) nanosheet arrays as anode and orange-peel derived activated carbons (OPAC) as fast capacitive cathode materials. The systematic electrochemical analysis with the ex-situ characterizations demonstrates that KNO-anode exhibits highly stable layered structure with excellent reversibil- ity during K + insertion/de-insertion. After optimization, the fabricated KNO//OPAC delivers both a high energy density of 116 Wh/kg and high power density of 10,808 W/kg, which is significantly higher than other similar hybrid devices. The cell also displays long term cycling stability over 5000 cycles, with 87 % of capacity reten- tion. This study highlights the utilization of layered nanosheet arrays of niobates to achieve superior K ‐storage for KICs, paving the way towards the development of high ‐performance anodes for post lithium ‐ion batteries.Hong Duc Pham, Nilesh R. Chodankar, Sagar D. Jadhav, Kolleboyina Jayaramulu, Ashok Kumar Nanjundan, Deepak P. Duba

True meaning of pseudocapacitors and their performance metrics: asymmetric versus hybrid supercapacitors

First published: 06 August 2020The development of pseudocapacitive materials for energy-oriented applications has stimulated considerable interest in recent years due to their high energy-storing capacity with high power outputs. Nevertheless, the utilization of nanosized active materials in batteries leads to fast redox kinetics due to the improved surface area and short diffusion pathways, which shifts their electrochemical signatures from battery-like to the pseudocapacitive-like behavior. As a result, it becomes challenging to distinguish "pseudocapacitive" and "battery" materials. Such misconceptions have further impacted on the final device configurations. This Review is an earnest effort to clarify the confusion between the battery and pseudocapacitive materials by providing their true meanings and correct performance metrics. A method to distinguish battery-type and pseudocapacitive materials using the electrochemical signatures and quantitative kinetics analysis is outlined. Taking solid-state supercapacitors (SSCs, only polymer gel electrolytes) as an example, the distinction between asymmetric and hybrid supercapacitors is discussed. The state-of-the-art progress in the engineering of active materials is summarized, which will guide for the development of real-pseudocapacitive energy storage systems.Nilesh R. Chodankar, Hong Duc Pham, Ashok Kumar Nanjundan, Joseph F. S. Fernando, Kolleboyina Jayaramulu ... Deepak P. Dubal ... et al