1. Schematics of thermal desorption method
EXFOLIATED GRAPHENE-LIKE NANOSHEETS AS INTERCALATED MATERIAL FOR HYDROGEN AND LITHIUM IONS
Gunars Bajars1, Janis Zemitis2, Peteris Lesnicenoks2, Gints Kucinskis1, Janis Kleperis1, Galina Dobele3,
1 - Institute of Solid State Physics of University of Latvia, Kengaraga Street 8, Riga LV1063, Latvia;
2 - Faculty of Materials Science and Applied Chemistry, Riga Technical University, Riga, Latvia;
3 – Latvian State Institute of Wood Chemistry, Dzerbenes str. 27 Riga LV-1006, Latvia
Introduction:
Increasing demand of energy is fuelling the research for more efficient and less polluting way to manufacture, store and use energy. Hydrogen is considered as ecologically friendly energy carrier with high energy density. To fully integrate it in energy circulation, it is important to find efficient enough and safe hydrogen storage system. So far high pressure storage tanks, liquefied hydrogen storage tanks, metal hydrides, some metal-organic frameworks and mesoporous materials are being investigated [1–4]. The aim established by DOE (USA) is to develop material that reaches at least 10 wt% of stored hydrogen until 2015 [5]. Graphene was discovered in 2004 by Geim and Novoselov [6] - the one atom thick layer of carbon atoms tightly packed into a graphite two-dimensional structure, having many extraordinary properties, also high surface specific area, a decisive factor for hydrogen storage applications - to 2630 m2/g.
Experimental: Sample preparation: To obtain graphene, the electrochemical exfoliation and water-plasma methods were used, taking graphite industrial waste road as working electrode. Different pulse sequence, amplitude, filling is used to find optimal parameters of exfoliation process. Important step is purification – single sheet material is lightest and can be easy separated with centrifuge.
Sample characterization: The initial samples were characterized by X-ray diffraction, SEM, BET method; elemental composition of zeolite samples was determined by EDAX analysis, hydrogen adsorption was used to follow hydrogen adsorptionon self-made equipment.
Schematics of thermal desorption method
Graphene sheet stacks obtained with electrochemical exfoliation.
Graphene: Obtained multistacks of graphene sheets. Raman scattering was used to identify the presence of graphene. As it is seen, Raman spectra confirm the presence of graphene sheets in collected powdered sample (left – reference, right – our sample):
Preliminary experiments were done to test hydrogen absorption capability in graphene sheet stacks, using thermal absorption/desorption methods. Two different samples were collected from both – exfoliation and plasma methods – the light fraction of material that floated on the top of solution, and heavy fraction which sank at the bottom of the solution. The test conditions were next – chamber with sample is evacuated, heated up to 160 oC, then hydrogen is introduced (2 bars) and chamber is cooled to room temperature. From observed pressure decrease the absorbed hydrogen is calculated – for light fraction ~2wt% and for heavy fraction - ~1,3wt%. In next step the chamber with sample is washed with Ar gas and heated up to 80oC and released gas analyzed with masspectrometer. Ar, H2 and CO were main registered gas components.
Graphene sheet stacks obtained with water-plasma discharge.
Discussion:. With graphene hydrogen can interact using physisorption and chemisorption forces; another possibility is to exploit intercalation of hydrogen between graphene sheets (distance between sheets is important) [7].
Our first results show that the method of exfoliation is useful to obtain graphene multi-sheet stacks from ordinary industrial waste graphite. Attention should be paid to post-treatment of exfoliated material, starting with centrifugation (the best is the lightest material), and multiple rinsing. Even better graphene material appearing when the resulting powder is heated in a reducing atmosphere (Ar : H2, 95:5). Further experiments are carried out for various ion intercalation between graphene sheets, using ultrasonic and the electrochemical methods. In this way it was possible in this way to manage a LixCy graphene material that will be studied by electrochemical and structure/composition/morphology methods. To increase amount of adsorbed hydrogen between graphene sheets, preferably firstly entering the light metals - lithium, magnesium, which forms hydrides. The first experiments in this direction are being made and results soon will be announced.
Energy level diagram for the graphene–hydrogen system. The energy is in eV per H atom [7],
References: [1] Ahluwalia RK, et all 2010 Int. J. Hydrogen Energy ; [2] Sakintuna B, Lamaridarkrim F, Hirscher M 2007 Int. J. Hydrogen Energy ; [3] Yu Y, Zhao N, Shi C, He C, Liu E, Li J 2012 Int. J. of Hydrogen Energy ; [4] Zheng J, Liu X, Xu P, Liu P, Zhao Y, Yang J 2012 Int. J. Hydrogen En ; [5] Tzimas E, et all 2003 Hydrogen Storage. The Netherlands, Institute for Energy – JRC IE. [6] Novoselov KS,Geim AK et all, Science, 306, 666 (2004); [[7] Spyrou K et al. ECS J. Solid State Sci. Technol. 2013;2:M3160-M3169
Acknowledgment : Authors acknowledge Latvian Council of Science Cooperation Project No. 666/2014 for financial support.
Contacts: PhD Peteris Lesničenoks: