NbSe₂ Nanosheets/Nanorolls Obtained via Fast and Direct Aqueous Electrochemical Exfoliation for High-Capacity Lithium Storage

Layered transition-metaldichalcogenides (LTMDs) in two-dimensional(2D) form are attractive for electrochemical energy storage, but researchefforts in this realm have so far largely focused on the best-knownmembers of such a family of materials, mainly MoS2, MoSe2, and WS2. To exploit the potential of further,currently less-studied 2D LTMDs, targeted methods for their production,preferably by cost-effective and sustainable means, as well as controlover their nanomorphology, are highly desirable. Here, we report aquick and straightforward route for the preparation of 2D NbSe2 and other metallic 2D LTMDs that relies on delaminating theirbulk parent solid under aqueous cathodic conditions. Unlike typicalelectrochemical exfoliation methods for 2D materials, which generallyrequire an additional processing step (e.g., sonication) to completedelamination, the present electrolytic strategy yielded directly exfoliatednano-objects in a very short time (1-2 min) and with significantyields (& SIM;16 wt %). Moreover, the dominant morphology of theexfoliated 2D NbSe2 products could be tuned between rolled-upnanosheets (nanorolls) and unfolded nanosheets, depending on the solventwhere the nano-objects were dispersed (water or isopropanol). Thisrather unusual delamination behavior of NbSe2 was exploredand concluded to occur via a redox mechanism that involves some degreeof hydrolytic oxidation of the material triggered by the cathodictreatment. The delamination strategy could be extended to other metallicLTMDs, such as NbS2 and VSe2. When tested towardelectrochemical lithium storage, electrodes based on the exfoliatedNbSe(2) products delivered very high capacity values, upto 750-800 mA h g(-1) at 0.5 A g(-1), where the positive effect of the nanoroll morphology, associatedto increased accessibility of the lithium storage sites, was madeapparent. Overall, these results are expected to expand the availabilityof fit-for-purpose 2D LTMDs by resorting to simple and expeditiousproduction strategies of low environmental impact.