Aqueous Cathodic Exfoliation Strategy toward Solution-Processable and Phase-Preserved MoS2 Nanosheets for Energy Storage and Catalytic Applications

Abstract

This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Applied Materials and Interfaces, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acsami.9b13484 ; The production of MoS2 nanosheets by electrochemical exfoliation routes holds great promise as a means to access this two-dimensional material in large quantities for different practical applications. However, the use of electrolytes based on synthetic organic salts and solvents, as well as issues related to the unwanted oxidation and/or phase transformation of the exfoliated nanosheets, constitute significant obstacles that hinder the industrial adoption of the electrochemical approach. Here, we introduce a safe and sustainable method for the cathodic delamination of MoS2 that makes use of aqueous solutions of very simple and widely available salts, mainly KCl, as the electrolyte. Combined with an appropriate biomolecule-based solvent transfer protocol, such an electrolytic exfoliation route is shown to afford colloidally dispersed, oxide-free, and phase-preserved MoS2 nanosheets of high structural quality in considerable yields. The mechanisms behind the efficient aqueous delamination of the bulk MoS2 cathode are also discussed and rationalized on the basis of the penetration of hydrated cations from the electrolyte between its layers and the immediate reduction of the accompanying water molecules. An asymmetric supercapacitor assembled with a cathodic MoS2 nanosheet–single walled carbon nanotube hybrid as the positive electrode and activated carbon as the negative electrode delivered energy densities (e.g., 26 W h kg–1 at 750 W kg–1 in 6 M KOH) that were competitive with those of other MoS2-based asymmetric devices. When used as a catalyst for the reduction of nitroarenes, the present cathodically exfoliated nanosheets exhibited one of the highest activities reported so far with MoS2 nanostructures, the origin of which is accounted for as well. Overall, by facilitating access to this two-dimensional material through a particularly simple, efficient, and cost-effective technique, these results should expedite the practical implementation of MoS2 nanosheets in energy storage, catalysis, and beyond. ; Funding by the Spanish Ministerio de Economía y Competitividad (MINECO) and the European Regional Development Fund (ERDF) through project MAT2015-69844-R, the Spanish Ministerio de Ciencia, Innovación y Universidades and the ERDF through project RTI2018-100832-B-I00, and Plan de Ciencia, Tecnología e Innovación (PCTI) 2013-2017 del Principado de Asturias and the ERDF (project IDI/2018/000233) is gratefully acknowledged. S.G-D. and J.M.M. are grateful to Spanish MINECO and Ministerio de Educación, Cultura y Deporte (MECD), respectively, for their respective pre-doctoral contracts (BES/2016 077830 and FPU14/00792). The University of Oviedo acknowledges the financial support from Spanish MINECO (MAT2016-78155-C2-1-R) and the Government of the Principality of Asturias (GRUPIN-IDI/2018/170) ; Peer reviewed