View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Open Archive Toulouse Archive Ouverte Open Archive TOULOUSE Archive Ouverte ( OATAO ) OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao.univ-toulouse.fr/ Eprints ID : 16795 To link to this article : DOI : 10.1016/j.jpowsour.2015.12.036 URL : http://dx.doi.org/10.1016/j.jpowsour.2015.12.036 To cite this version : Dall’Agnese, Yohan and Rozier, Patrick and Taberna, Pierre-Louis and Gogotsi, Yury and Simon, Patrice Capacitance of two-dimensional titanium carbide (MXene) and MXene/carbon nanotube composites in organic electrolytes . (2016) Journal of Power Sources, vol. 306. pp. 510-515. ISSN 0378-7753 Any correspondence concerning this service should be sent to the repository administrator: [email protected] Capacitance of two-dimensional titanium carbide (MXene) and MXene/carbon nanotube composites in organic electrolytes Yohan Dall’Agnese a, b, c, Patrick Rozier a, b, Pierre-Louis Taberna a, b, Yury Gogotsi c, Patrice Simon a, b, * a Universite Paul Sabatier, CIRIMAT UMR CNRS 5085, 118 Route de Narbonne, 31062 Toulouse, France b Reseau sur le Stockage Electrochimique de l’Energie (RS2E), FR CNRS 3459, France c Department of Materials Science and Engineering, A. J. Drexel Nanomaterials Institute, Drexel University, Philadelphia, PA 19104, USA h i g h l i g h t s graphical abstract 3 types of Ti3C2 electrodes were prepared: clay, delaminated and CNT composite. Capacitance up to 245 F cmÀ3 in 1 M EMITFSI solution in acetonitrile was achieved. Imidazolium (EMIþ) ions intercala- tion was demonstrated by in situ XRD. a b s t r a c t Pseudocapacitive materials that store charges by fast redox reactions are promising candidates for designing high energy density electrochemical capacitors. MXenes e recently discovered two- dimensional carbides, have shown excellent capacitance in aqueous electrolytes, but in a narrow po- tential window, which limits both the energy and power density. Here, we investigated the electro- chemical behavior of Ti3C2 MXene in 1M solution of 1-ethly-3-methylimidazolium bis- (trifluoromethylsulfonyl)-imide (EMITFSI) in acetonitrile and two other common organic electrolytes. This paper describes the use of clay, delaminated and composite Ti C electrodes with carbon nanotubes Keywords: 3 2 Electrochemical capacitors in order to understand the effect of the electrode architecture and composition on the electrochemical À1 À3 À1 Two-dimensional materials performance. Capacitance values of 85 F g and 245 F cm were obtained at 2 mV s , with a high rate þ MXene capability and good cyclability. In situ X-ray diffraction study reveals the intercalation of large EMI X-ray diffraction cations into MXene, which leads to increased capacitance, but may also be the rate limiting factor that Carbon nanotube, titanium carbide determines the device performance. 1. Introduction either porous carbon materials or pseudocapacitive materials for electrostatic or redox energy storage, respectively [3,4]. In the Electrochemical capacitors (ECs) are commercial devices used latter, the charge is stored by fast redox reactions at the surface of for high power delivery applications [1,2]. They typically utilize materials such as MnO2, RuO2, Nb2O5 or MoO3 [5e8]. Recently, energy storage based on ion intercalation into two-dimensional (2D) materials has attracted much attention because of promising * Corresponding author. Universite Paul Sabatier, CIRIMAT UMR CNRS 5085, 118 results with up to 375 F gÀ1 in KOH or 200 F gÀ1 in organic elec- route de Narbonne, 31062 Toulouse, France. trolyte for functionalized graphene [9,10]. E-mail address: [email protected] (P. Simon). http://dx.doi.org/10.1016/j.jpowsour.2015.12.036 A new family of two-dimensional materials called MXenes has working electrode, an Ag wire as a pseudo-reference electrode and emerged as promising electrodes for energy storage devices such as a commercial activated carbon (YP17 Kuraray, Japan) overcapacitive batteries [11 e15], metal ion (Liþ, Naþ) capacitors [16 e18] and ECs counter electrode prepared by mixing 5 wt.% polytetrafluoro- [19e22]. MXenes are synthetized by selective etching of the A layer ethylene binder (60 wt.% in H2O, Aldrich) to 95 wt.% of YP17. A from the conductive ternary carbide family of MAX phases [23]. Of polypropylene membrane (GH Polypro, Pall) was used as a sepa- the MXene family, Ti3C2 was the first discovered and is the most rator. The electrolyte was a 1 M solution of EMITFSI (1-ethyl-3- studied to date. First studies of Ti3C2 as electrode material in methylimidazolium bis(trifluoromethylsulfonyl)imide, Solvionic) supercapacitors showed capacities up to 100 F gÀ1 for intercalation in acetonitrile (Acros Organics). For comparison purposes, 1 M þ 2þ 3þ of cations such as Li , Mg or Al in aqueous electrolytes [19]. EMIBF4 (1-ethyl-3-methylimidazolium tetrafluoroborate, Fluka) Aside, MXene performance can be greatly improved by tuning the and 1 M TEABF4 (tetraethylammonium tetrafluoroborate, Acros surface functional groups, delamination or addition of carbon Organics) in acetonitrile were tested. The cells were assembled in nanoparticles [14,21,22]. Delaminated Ti3C2 electrodes containing an argon-filled glovebox. A VMP3 potentiostat (Biologic SA, France) carbon nanotubes have also shown noteworthy performance in was used for electrochemical testing. Cyclic voltammetry (CV) was lithium ion batteries, as well as in aqueous supercapacitors with performed at scan rates from 2 to 100 mV sÀ1; capacitance values capacity up to 430 mAh gÀ1 and capacitance of 140 F gÀ1, respec- were calculated by integrating the reduction current. Galvanostatic tively [14,22]. The modification of the chemistry of the surface chargeedischarge measurements were performed at 1 A gÀ1 and groups through a new “clay” synthesis route led to a 2-fold increase corresponding capacitances were calculated from the slopes of the in volumetric capacitance (up to 900 F cmÀ3) in sulfuric acid elec- curves. Gravimetric capacitances were calculated from the total trolyte due to dense packing of 2D MXene sheets combined with mass of the composite electrode; associated volumetric capaci- their accessibility due to pre-intercalation of ions during the syn- tances were obtained using the density of the respective electrodes. thesis [20]. The role of pseudocapacitance in these high values was Electrochemical impedance spectroscopy (EIS) was performed be- confirmed by showing a reversible change in the oxidation state of tween 100 mHz and 200 kHz in two-electrode configuration after titanium atoms in MXene [24]. polarization at 0.5 V vs. Ag using a three-electrode setup. However, MXene has been investigated as electrode material for ECs mainly in aqueous electrolytes, which show a limited potential 2.3. Material characterization window due to water electrolysis. Moreover, oxidation of Ti3C2 under high anodic potentials in aqueous electrolytes further limits A scanning electron microscope (SEM, JSM-6700F, JEOL) was its use to cathodes of asymmetric devices. As both the energy and used to investigate the electrodes' morphology and structure. X-ray the power density increase with the square of the potential win- diffraction (XRD) patterns of the CNT-Ti3C2 electrodes were dow, its expansion is one of the key challenges for designing SCs collected by a Brucker D8 diffractometer using a Cu Ka radiation with improved performance and organic electrolyte may expand (l ¼ 1.5406 Å) in the range 2q ¼ 5e50 with a step of 0.016. The the voltage window beyond 2e2.5 V. samples were polarized at different potentials using a 2-electrode In this work, we report on the electrochemical performance of cell (LRCS, University de Picardie Jules Verne, Amiens, France) Ti3C2 in organic supercapacitor electrolytes for supercapacitor ap- covered with a beryllium window served as the current collector, plications. The energy storage mechanism was studied by in situ X- avoiding electrolyte evaporation and allowing in situ electro- ray diffraction (XRD). chemical XRD. Nitrogen sorption analysis at 77 K using Micro- meritics ASAP 2020 apparatus was carried out for calculating the 2. Experimental specific surface area (SSA) using the BrunauereEmmeteTeller (BET) equation after outgassing under vacuum at 300 C for 12 h. 2.1. Electrode preparation 3. Results and discussion Ti3C2 was synthesized by selectively etching the aluminum layer out of the Ti3AlC2 MAX phase in a 6M HCl/LiF solution at 35 C for Fig. 1 shows cross-section SEM images of electrode materials. 24 h [20]. The obtained material was then washed with distilled The as-prepared MXene clay, denoted as Ti3C2TX, is shown in Fig.1a. water. MXene samples after synthesis were terminated with OH, O MXene layers can be rolled and sheared, forming a freestanding and F and we add Tx to the Ti3C2 formula to show those surface flexible electrode [20,21]. Fully delaminated MXene electrodes, terminations. Full delamination of Ti3C2Tx was obtained by ultra- denoted as d-Ti3C2TX (Fig. 1b), were prepared for improving the sonication for 1 h in distilled water. A composite material was electrochemical performance by taking advantage of a higher prepared by mixing the colloidal solution of delaminated Ti3C2 with specific surface area (SSA) resulting from delamination. The SSA 2 À1 2 À1 20 wt. % of multiwalled carbon nanotubes (MWCNT C100, Graph- values were 23 m g for multilayered Ti3C2 and 98 m g for 2 À1 istrength) which have specific surface area of 175 m g . The as- delaminated Ti3C2 measured elsewhere by nitrogen gas sorption synthetized Ti3C2Tx, the delaminated Ti3C2Tx and the CNT/Ti3C2Tx analysis [12]. However, previous studies demonstrated that composite were filtered on polypropylene membranes then rolled restacking of delaminated MXene layers forming a dense MXene into film electrodes on Teflon membranes using a glass tube. Once “paper” with in-plane alignment of MXene sheets limits the dried, the films were easily removed from the membrane to obtain accessibility of electrolyte ions.