Suchergebnisse

We report on the modification of graphene oxide (GO) with poly(vinyl alcohol) (PVA) leading to the mechanical improvement of GO based materials. First, GO was covalently functionalised with PVA by esterification of carboxylic groups on GO with hydroxyl groups of PVA resulting in functionalised f-(PVA)GO. This was carried out for PVA of six different molecular weights. This functionalised graphene oxide could be formed into a paper-like material by vacuum filtration. Papers prepared from f-(PVA)GO showed significant increases in mechanical properties compared to those prepared with GO or with simple mixtures of GO and PVA. The best performance was achieved for PVA functional groups with molecular weights between 50 and 150 kg/mol. Improvements in Young's moduli of 60% and tensile strength of 400% were observed relative to GO-only paper. The improved mechanical properties are attributed to enhanced inter-flake stress transfer due to the covalently bonded PVA. Second, functionalised f-(PVA)GO was used as filler in * Corresponding author. Tel/Fax: +34 976 73-3977 / -3318. E-mail address: wmaser@icb.csic.es (W.K. Maser) 2 PVA-based composites. The application of a pre-selection method allowed the use of only the largest functionalised f-(PVA)GO flakes. This resulted in substantially reinforced PVA-f-(PVA)GO composites. Both modulus and strength increased by 40% relative to the pure polymer for f- (PVA)GO loadings below 0.3 vol.%. ; The authors would like to acknowledge Science Foundation Ireland, (grant number 07/IN.7/I1772), Spanish Ministry of Science and Innovation (MICINN) under project MAT2010-15026, Spanish Research Council CSIC under project 201080E124 and the Government of Aragon (DGA) under Project DGA-T66 CNN. M.C. thanks MICINN for her PhD contract and funding for research stay at TCD under FPI Programme BES-2008-003503. ; Peer reviewed

Integrated approaches that expedite the production and processing of graphene into useful structures and devices, particularly through simple and environmentally friendly strategies, are highly desirable in the efforts to implement this two-dimensional material in state-of-the-art electrochemical energy storage technologies. Here, we introduce natural nucleotides (e.g., adenosine monophosphate) as bifunctional agents for the electrochemical exfoliation and dispersion of graphene nanosheets in water. Acting both as exfoliating electrolytes and colloidal stabilizers, these biomolecules facilitated access to aqueous graphene bio-inks that could be readily processed into aerogels and inkjet-printed interdigitated patterns. Na-O2 batteries assembled with the graphene-derived aerogels as the cathode and a glyme-based electrolyte exhibited a full discharge capacity of ∼3.8 mAh cm–2 at a current density of 0.2 mA cm–2. Moreover, shallow cycling experiments (0.5 mAh cm–2) boasted a capacity retention of 94% after 50 cycles, which outperformed the cycle life of prior graphene-based cathodes for this type of battery. The positive effect of the nucleotide-adsorbed nanosheets on the battery performance is discussed and related to the presence of the phosphate group in these biomolecules. Microsupercapacitors made from the interdigitated graphene patterns as the electrodes also displayed a competitive performance, affording areal and volumetric energy densities of 0.03 μWh cm–2 and 1.2 mWh cm–3 at power densities of 0.003 mW cm–2 and 0.1 W cm–3, respectively. Taken together, by offering a green and straightforward route to different types of functional graphene-based materials, the present results are expected to ease the development of novel energy storage technologies that exploit the attractions of graphene. ; Funding by the Spanish Ministerio de Economía y Competitividad (MINECO) and the European Regional Development Fund (ERDF) through project MAT2015-69844-R and by the Spanish Ministerio de Ciencia, Innovación y Universidades and ERDF through project RTI2018-100832-B-I00 is gratefully acknowledged. Partial funding by Plan de Ciencia, Tecnología e Innovación (PCTI) 2013-2017 del Principado de Asturias and the ERDF through project IDI/2018/000233 is also acknowledged. J.M.M. is grateful to the Spanish Ministerio de Educación, Cultura y Deporte (MECD) for his pre-doctoral contract (FPU14/00792). J.N.C. acknowledges the ERC Adv. Gr. FUTUREPRINT. This work was also financially supported by the European Union (Graphene Flagship, Core 2, Grant number 785219). ; Peer reviewed