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Carbon 195 (2022) 57e68 Contents lists available at ScienceDirect Carbon journal homepage: www.elsevier.com/locate/carbon An electrochemical route to holey graphene nanosheets for charge storage applications D.F. Carrasco , J.I. Paredes **, S. Villar-Rodil *, F. Suarez-García , A. Martínez-Alonso , J.M.D. Tascon Instituto de Ciencia y Tecnología del Carbono, INCAR-CSIC, C/Francisco Pintado Fe 26, 33011 Oviedo, Spain articleinfo abstract Article history: Received 26 December 2021 Received in revised form 26 March 2022 Accepted 1 April 2022 Keywords: Holey graphene Anodic exfoliation Capacitive energy storage Holey graphene nanosheets are potentially useful in several relevant technological applications, including electrochemical energy storage and molecular separation. Access to this material is mostly accomplished by resorting to standard graphene oxides obtained by common routes (e.g., the Hummers method). However, such a type of highly oxidized graphenes may not be the best option as a precursor to holey graphene on account of their chemical/structural heterogeneity and harsh synthesis conditions. Here, we report the use of highly oxidized graphene nanosheets derived by an electrochemical exfoli- ation/oxidation strategy as an alternative precursor to holey graphene. Compared to a standard graphene oxide with the same extent of oxidation, the electrochemically derived precursor exhibited larger aro- matic domains, which provided a structural basis for its higher electrical conductivity, as well as smaller and denser oxidized regions, associated to a higher chemical homogeneity and lability of its oxygen- containing functional groups. Through selective chemical etching of the oxidized domains, the latter feature was exploited to afford holey graphene nanosheets having smaller and more uniform holes. When used as an electrode material for electrochemical charge storage, the electrochemically derived holey graphene outperformed its standard graphene oxide-based counterpart in terms of capacity and energy density. Overall, boasting distinct structural and chemical characteristics, highly oxidized gra- phene obtained by electrochemical means can be regarded as a prospective advantageous precursor to many graphene-based materials whose preparation has traditionally relied on the processing of gra- phene oxides. © 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 1. Introduction The advent of graphene and its derivatives, more than a decade ago, as experimentally available two-dimensional (2D) materials has fueled intensive research efforts worldwide aimed at exploiting their many appealing characteristics in a variety of technological applications [1,2]. One such application realm is that of electro- chemical energy storage, where different types of graphenes can be used either as the active material or in a supporting role (e.g., as a conductive additive) for electrodes of supercapacitors and batteries [3e7]. The main rationale for the attraction of graphene in elec- trochemical energy storage lies in a number of relevant features * Corresponding author. ** Corresponding author. E-mail addresses: paredes@incar.csic.es (J.I. Paredes), silvia@incar.csic.es (S. Villar-Rodil). that this 2D carbon material exhibits, including high electrical conductivity, chemical and mechanical stability, and large specific surface area [3,5]. However, these attributes are mostly associated to stand-alone graphene nanosheets (NSs) in pristine form, but in practice they tend to be degraded to some extent during the fabrication and/or processing of the 2D material. Particularly, the reduction of accessible surface area due to NS re-stacking is a serious issue that can readily occur when initially well-exfoliated graphenes are processed into electrodes. Such a re-stacking inevi- tably leads to a much impeded transport of ions within the elec- trode and, therefore, to a poor charge storage performance of the latter [3,8]. Over the years, different strategies have been devised to directly prevent nanosheet re-stacking or to counteract its negative con- sequences in graphene electrodes. These strategies mostly rely on the generation of some kind of porosity in the electrodes, which can be categorized as interlayer and in-plane porosity [8e10]. The https://doi.org/10.1016/j.carbon.2022.04.003 0008-6223/© 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).PDF Image | electrochemical route to holey graphene nanosheets
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