Graphene Production and Application

Graphene is a super thin and strong material with potential to revolutionize the field of technology. As such, graphene is quickly attracting attention from researchers seeking to identify new concepts and applications of this “supermaterial.” Graphene Production and Application is a comprehensive and easy-to-understand source of information on the advances in the growing research on graphene. Written by experts in the field, this book covers the topics of synthetic approaches, characterization techniques, and applications of graphene. It is ideally suited for a broad range of readers including students, instructors, and professionals

Uudsed nanostruktuursed korrosioonivastased komposiitkatted

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Jay Mondali doktoritöös uuriti grafeenoksiidi ja redutseeritud grafeenoksiidi nanoliistakute valmistamise tehnoloogiat ja valmistati nende ainete baasil lihtkatted, hübriidkatted koos elektrit juhtiva polümeeri polüpürrooliga ning komposiitkatted koos metalloksiidide Al2O3 ja TiO2 nanokiledega. Katted kanti roostevaba terase või Ti-sulamist valmistatud katseobjektide pindadele, kasutades vurrkatmise, elektrokeemilise sadestamise ja aatomkihtsadestamise meetodeid. Katete omaduste uurimiseks kasutades laia hulka tahkisobjektide karakteriseerimise vahendeid, mis on saadaval TÜ Füüsika ja Keemia instituutides. Samuti määrati elektrokeemiliste mõõtmiste ja standarttestidega nende katete võime kaitsta alusmaterjale korrosiooni eest. Töö tulemusena näidati ära, et kuigi nii valmistatud liht- kui hübriidkatted aitavad teatud määral pidurdada korrosiooniprotsesse metallalustel, ei suuda need katted tõhusalt pidurdada punktkorrosiooni nimetatud aluste pikaajalisel hoidmisel tugevasti korrodeeruvates soolalahustes. Seevastu uudsed, submikromeetrilise paksusega grafeeni baasil loodud komposiitkatted näitasid üles väga head korrosioonikaitset mõlema sulami pinnal, ületades paljude tänapäeva tööstuses kasutatavate kümneid kuni sadu kordi paksemate kaitsekatete näitajaid. Töö tulemused on avaldatud eriala juhtivates ajakirjades ja tutvustatud rahvusvahelistel konverentsidel. Antud doktoritöö valmis prof. Väino Sammelselja juhendamisel. Tööd oponeerima on kutsutud prof. M. Ferreira Aveiro Ülikoolist ja dr. M. Krunks TTÜ-st.In this thesis corrosion inhibition performance of graphene and graphene oxide based composite/hybrid coatings was studied. Graphene is a two-dimensional one-atom-thick sheet of carbon having hexagonal lattice, and it is a basic structural unit of graphite. Graphene has proven to be one of the most popular advanced materials in recent developments. This carbon material is widely studied for advanced applications starting from energy harvesting to nanoelectronics and finishing with drug delivery because of many extraordinary properties of it. Among all of the properties the atom/ion barrier property was one of the most interesting for this work. Some studies to use graphene or graphene-based materials as a barrier sheet were published before starting this work and some appeared during the run of this investigation. Lately, the development of graphene and graphene oxide based functionalized biocompatible barrier coatings attracts a great attention among scientists and probably industrialists as well. But the use of graphene oxide/reduced graphene oxide nanoplatelets for corrosion protection of metal alloys was practically not studied before this work, despite the facts that the ideas of preparation the materials were known already decades, and as row material relatively cheap powder of natural graphite can be used. In this thesis the barrier properties of graphene/graphene oxide based nanostructured coatings, including composite and hybrid coatings were investigated towards corrosion protection. Investigations were carried through using different strategies: for the preparation of thin protective coatings spin-coating, electrochemical deposition and atomic layer deposition (ALD) techniques were used. For the corrosion inhibition performance studies of synthesized graphene oxide and reduced graphene oxide the hybrid coatings of graphene oxide-polypyrrole and the composite coatings of graphene-metal oxide laminates were prepared. The extent of protection ability of the coatings deposited onto AISI type 304 stainless steel and Ti-6Al-4V alloy substrates was studied thoroughly by electrochemical methods, as open circuit potential and Tafel plots, voltammetry and electrochemical impedance spectrometry, and tested by standard ASTM G48 A and long-time immersion tests in salt solutions. The studies revealed that prepared graphene and graphene oxide based hybrid and especially composite coatings well inhibit corrosion of the metal substrates. This definitely increases lifetime and stability of the metal details and equipment made from these materials, helping to preserve the materials and energy, thus helping to develop also a more sustainable society.

Mechanical Property Enhancement of PVP-PVA Nanocomposite by Graphene Oxide

Graphene, is the building block of many carbon forms, including graphite, carbon nanotubes and Buck-minster fullerenes. It has honey-comb lattice structre with an atomic layer of sp2bonded carbon atoms. Its excellent properties for example, like Youngs modulus is about 1 TPa, breaking strength is about 140 GPa, thermal conductivity is about 5000 Wm-1K-1, and high specific surface area of about 2650 m2g-1.One of the most important application of graphene is in the fabrication of layered polymer nano-composites. Its unique two dimensional morphology provides high available surface area with very small thickness(in nano size) which can be exploited in load bearing, electrical, and barrier applications. However, the reinforcing agents and their types, considerably enhance crystallinity, microstructure, and glass transition of the composites. Therefore, underpinning the processing-microstructure-property relationship in these materials is very important. The easier route of graphene production is through the top-bottom approach, where graphene oxide (GO) is synthesized by chemical exfoliation method followed by suitable reduction of GO to graphene. GO can hold various oxygen containing functional groups that make it easily mixed in nonpolar solvents. Subsequently, by different chemical treatments, few of those functional groups can be removed, and few others can be added/created, and the layer-matrix attachment can be done. The current work focus on the approaches to strengthen the matrix-reinforcement interface by various types of amines, resulting in unbelievably ultra-strong and ultra-tough PVA and PVP nanocomposites. The enhanced mechanical properties were investigated by tensile testing of different graphene oxide samples and chemically reduced graphene samples(reduced by TEA and TEOA).It has been confirmed that the reduced graphene sample shows better elastic properties compare to GO based polymer composites

Molecular sorption of carbon-based porous structures: a study on water harvesting and carbon dioxide capture

Carbon (CO2) capture using regenerable sorbents is an effective means of mitigating green-house gas emission to the environment. The first-generation sorbents, based on liquid amines, suffer from instability, toxicity and high-energy penalty for regeneration. Solid sorbents, e.g. based on porous silica or active carbon, offer the potential of long cyclability and low cost. However, the sorption capacity is limited due to low surface area and pore volume, particularly if only physisorption mechanism dominates. The challenge and main aim of this study is to identify an effective porous carbon-based solid sorbent that can possess high capacity and low regeneration energy (hence cost) penalty. The structures should offer enhanced physisorption (e.g. van der Waals binding at slit pores, with a binding energy ~-10-20 kJ mol-1) and moderate chemisorption (e.g. binding at graphene edges, point defects or carbon-supported amine-groups, with a binding energy ~-20-50 kJ mol-1) so that adsorption and desorption “window” for CO2 can be narrow and at relatively low temperature. The porous structure must show high specific surface area and well-connected pores, so that the capacity can be maximised. To achieve such goals, the project first studied graphene oxide (GO) with various degrees of oxidation, ranging from 30 at% oxygen content, to enhance surface area and defect density; secondly, highly hierarchical porous graphene networks were derived through GO via moderate temperature thermal shock (300 °C), thermal annealing (600 °C) and/or KOH activation, to promote micro-pores and porosity hierarchy; and finally, for comparison and porosity improvement, another type of porous carbon structures were derived from carbonised metal-organic frameworks (MOFs), namely MOF-5 and MOF-74. The chemical and structural properties of synthesized materials were characterised by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption-desorption isotherms (the BET method) and Raman spectroscopy. Sorption capacity and kinetics were assessed by CO2 adsorption isotherms, thermogravimetric-differential scanning calorimetry (TG-DSC) and in-house water saturation apparatus. GO demonstrated a stacked layered structure with oxygenated functional groups such as hydroxyl, epoxy and carbonyl groups on its basal planes and edges, resulting in a hybrid structure comprising a mixture of sp2 and sp3 hybridized carbon atoms. GO is hydrophilic due to the presence of the oxygenated functional groups and the laminated structure can allow slow water diffusion into the layers. As water exist in practical cases of CO2 capture, the sorption of water was studied separately and together with CO2. From the study of highly porous GO derived exfoliated GO (exfGO), it was identified that the resulting materials possessed ultrahigh surface area and total pore volume up to 853 m2 g-1 and 6.68 cm3 g-1. The structures were applied as solid sorbents with chemical modification by TEPA and PEHA polyamines wet impregnation to incorporate amine-based sorption sites. The solid-amine system exhibited ultrahigh selective flue-gas CO2 capture of 6.16 mmol g-1 at 75 °C. The desorption occurred at 100 °C, giving a desirable narrow temperature-swing window. Further testing showed the cycling stability under simulated flue-gas stream conditions had moderate decay of ~7 wt% over 40 adsorption-desorption cycles and demonstrated stable CO2 uptake ~25 wt%. From the study on MOF carbons, it was found that the carbonisation process of MOF precursors led to loss of local metal centres and produced defective carbon structures with mainly sp2 bonding. By varying the synthesis conditions and solvents, micrometre to millimetre-sized MOF-5 crystals can be synthesized. Carbonisation process retained both meso- and macro-pores and yielded MOF carbons with high surface area up to 2237 m2 g-1 and total pore volume up to 4.6 cm3 g-1. The resulting amine-impregnated MOF carbons achieved CO2 adsorption of 4.37 mmol g-1. In summary, the project has developed highly porous carbon-based solid sorbents, which are stable and environmentally benign, with high specific surface area to offer a CO2 adsorption capacity > 6 mmol g-1. The binding energy is typically controlled at -50 kJ mol-1, which allows CO2 adsorption and desorption to be carried out between 25 °C and 100 °C. The developed sorbents have met the identified challenges of flue-gas conditions CO2 capture (>50 °C, humid), high thermal stability, chemical resistance and potential for large-scale production at low-cost, as well as offering great potential for practical applications in industry. The results also show great potential for the development of high capacity carbon-based sorbents for effective pre-combustion CO2 capture and energy storage applications

Graphene Oxide Mixed Matrix Membranes for Improved Desalination Performance

abstract: Reverse osmosis (RO) membranes are considered the most effective treatment to remove salt from water. Specifically, thin film composite (TFC) membranes are considered the gold standard for RO. Despite TFC membranes good performance, there are drawbacks to consider including: permeability-selectivity tradeoff, chlorine damage, and biofouling potential. In order to counter these drawbacks, polyamide matrixes were embedded with various nanomaterials called mixed matrix membranes (MMMs) or thin film nanocomposites (TFNs). This research investigates the use of graphene oxide (GO) and reduced graphene oxide (RGO) into the polyamide matrix of a TFC membrane. GO and RGO have the potential to alter the permeability-selectivity trade off by offering nanochannels for water molecules to sieve through, protect polyamide from trace amounts of chlorine, as well as increase the hydrophilicity of the membrane thereby reducing biofouling potential. This project focuses on the impacts of GO on the permeability selectivity tradeoff. The hypothesis of this work is that the permeability and selectivity of GO can be tuned by controlling the oxidation level of the material. To test this hypothesis, a range of GO materials were produced in the lab using different graphite oxidation methods. The synthesized GOs were characterized by X-ray diffraction and X-ray photoelectron microscopy to show that the spacing is a function of the GO oxygen content. From these materials, two were selected due to their optimal sheet spacing between 3.4 and 7 angstroms and embedded into desalination MMM. This work reveals that the water permeability coefficient of MMM embedded with GO and RGO increased significantly; however, that the salt permeability coefficient of the membrane also increased. Future research directions are proposed to overcome this limitation.Dissertation/ThesisMasters Thesis Civil and Environmental Engineering 201

Interface Strengthened Graphene Oxide Reinforced PVA Nanocomposites

Graphene, an atomic layer of sp2 bonded carbon atoms in the hexagonal lattice, is the building block of many carbon forms, including carbon nanotubes, Buckminster Fullerenes, carbon onions, and graphite. Its exceptional properties, for example, Young's modulus of 1 TPa, breaking strength of 140 GPa, thermal conductivity of 5000 Wm-1K-1, and high specific theoretical surface area of 2650 m2g-1, have warranted use in many structural and functional applications. One of the most important uses of it lies as fillers in the fabrication of polymeric nanocomposites. Its special two-dimensional morphology featuring high available surface area with a nanometric thickness of the platelets can be exploited in load bearing, electrical, and barrier applications. However, the reinforcing agents and their types, considerably influence crystallinity, microstructure, and glass transition of the composites, which in turn affect materials properties. Therefore, underpinning the processing-microstructure-property relationship in these materials is of paramount importance. The preferred route of graphene production is through the top-down approach, where graphene oxide (GO) is synthesized by chemical exfoliation method followed by suitable reduction of GO to graphene. GO possesses various oxygen-containing functional groups that make it easily dispersible in aprotic solvents. Subsequently, by various chemical treatments, some of those functional groups can be removed, and few others attached/created, and the filler-matrix interface can be engineered. The crux of the current work lies in the approaches to strengthen the matrix-reinforcement interface by various types of amines, resulting in unprecedented ultrastrong and ultra-tough PVA nanocomposites. Positron annihilation lifetime spectroscopy has been used to highlight the effect of interfaces. X-ray diffractometry and thermal analysis have been used to understand crystallinity in the samples. Raman and FTIR spectroscopy have been used to understand the disorder in carbon and the chemical functional groups, respectively. Microstructural analysis (using scanning and transmission electrons) of matrices and fractured surfaces have been performed to reveal the distribution of fillers, fracture process, formation of nematic crystals, and the in-situ formation of carbon nanoribbons for strengthening. An order of magnitude increase has been found in Young's modulus and fracture strength of the composites. Such profound increase in strength can be ascribed to the nematic ordering of the functionalized GO flakes in the polymer matrix. In another variant, the formation of carbon nanoribbons from the wrinkled GO platelets and their interpenetrating distribution in the polymer matrix led to enhancement in strength and toughness

Synthesis and characterization of new polymer electrolytes to use in fuel cells fed with bio-alcohols

Poly(vinyl alcohol) (PVA)-based membranes have gathered significant interest because of their film forming ability and low cost. These films are usually crosslinked to provide a macromolecular network with high dimensional stability. PVA can be modified by introduction of sulfonic acid groups (sPVA) contributing to increase its proton conductivity. In addition, the preparation of hybrid organic-inorganic composite membranes by the addition of graphene oxide (GO) as nano-filler not only reinforces the matrix but also decreases the permeability of solvents. All this has motivated the use of these materials for the preparation of proton exchange membranes (PEMs) for direct methanol fuel cell (DMFC) applications. Contribution I presents the chemical schemes followed for the bi-sulfonation of the PVA, the synthesis of GO and the preparation of PVA/GO and sPVA/GO composite membranes. In addition, a structural, morphological, thermal, and mechanical characterization of the starting materials and the composite membranes were performed. Finally, in order to evaluate the suitability of the prepared PEMs in fuel cells, the prot cond. was evaluated at room temperature. The results showed that the addition of GO (1 wt.%) into the sPVA matrix, 30sPVA/GO membrane, enhance by 89% the prot cond. compared to its homologue membrane, 30sPVA, free-standing of GO. In Contribution II, the proton conductive properties of the previously prepared membranes were investigated as a function of the structural (bi-sulfonation) and morphological (crosslinking and addition of GO) modifications. The bi-sulfonated membrane reinforced with GO, 30sPVA/GO, stands out over the rest. The addition of GO improves considerably its prot cond. (20.96 mS/cm at 90 °C) and its maximum power density (Pmax) in the H2-O2 fuel cell test (13.9 mW/cm2 at 25 ºC). In Contribution III was studied the effect of a new variable, the sufonation of the GO (sGO), on the functional properties of the composites PVA/sGO and sPVA/sGO for DMFC applications. In addition, the results were compared to that obtained for the previously described PVA/GO and sPVA/GO composites. The results conclude that, contrary to expectations, the multiple sulfonation of the 30sPVA/sGO composite strongly reduces the prot cond. (5.22 mS/cm at 50 °C) compared to its homologue 30sPVA/GO (8.42 mS/cm at 50 °C), despite its higher values of ion exchange capacity (IEC). Finally, the 30PVA/sGO composite (1.85 mW/cm2) shows a significant improvement of the DMFC performance (50 °C, 4M methanol solution) compared to the 30sPVA/GO composite (1.00 mW/cm2). The Layer-by-Layer (LbL) assembly method was used in Contribution IV for the preparation of composite membranes assembled via hydrogen bonding interactions. To do this, GO/PVA and GO/sPVA bilayers were deposited on the surface of 15PVA and 15sPVA substrate membranes, respectively. The composites were denoted as 15PVA(GO/PVA)n and 15sPVA(GO/sPVA)n where n is the number of deposited bilayers, in our case n ranges between 1 and 3. Finally, the potential of the composite membranes for DMFC applications were evaluated, showing the best performance the 15sPVA(GO/sPVA)1 composite. Finally, the Contribution V was focused on the preparation of composite membranes by LbL Assembly method, but in this case the assembly forces were electrostatic interactions. The GO was dispersed in a poly(allyl amine hydrochloride) solution (GO-PAH) in order to obtain a positively charged solution. The composites were assembled by alternate deposition of GO-PAH and sPVA layers on the surface of 15PVA and 15sPVA substrates, obtaining as a result the composites 15PVA(GO-PAH/sPVA)n and 15sPVA(GO-PAH/sPVA)n. The best value of prot cond. (8.26 mS/cm at 90 °C) was obtained for the 15PVA(GO-PAH/sPVA)1 composite, almost twice that the value obtained for its homologue sulfonated composite 15sPVA(GO-PAH/sPVA)1 (4.96 mS/cm a 90 °C).Membranas constituidas básicamente por alcohol polivinílico (PVA) han despertado un gran interés debido a su bajo coste y su fácil procesado para conformarlas en forma de films. Estos films frecuentemente son sometidos a entrecruzamiento para disponer de una red macromolecular con una elevada estabilidad dimensional. La modificación del PVA por introducción de grupos sulfónicos (sPVA) cambia la estructura del polímero contribuyendo a aumentar su conductividad protónica. Además, la preparación de membranas híbridas orgánico-inorgánicas (composites) mediante la adición de óxido de grafeno (GO) refuerza la matriz, a la vez que disminuye su permeabilidad frente a disolventes. Todo ello ha motivado el uso de estos materiales para la preparación de membranas de intercambio protónico (PEMs) empleadas en pilas de combustible de metanol (DMFCs). En la Contribución I se presentan los esquemas químicos conducentes a la bi-sulfonación del PVA, la síntesis del GO y la preparación de las membranas composite PVA/GO y sPVA/GO. Además, se realizó la caracterización estructural, morfológica, térmica y mecánica de cada uno de los materiales de partida y de los composite. Finalmente, con el fin de evaluar su idoneidad como PEMs en pilas de combustible, se evaluó su cond. prot a temperatura ambiente. Los resultados obtenidos mostraron que la adición de GO (1 wt.%) como nano-carga a la matriz de sPVA genera un composite, 30sPVA/GO, cuya cond. prot supera en un 89 % a la de su membrana homóloga sin carga, 30sPVA. La Contribución II trata de explorar las propiedades conductoras de las membranas preparadas previamente en función de la modificación estructural (bi-sulfonación) y la morfológica (reticulación y adición de GO). La membrana bi-sulfonada y reforzada con GO, 30sPVA/GO, destaca sobre el resto. La adición de GO mejora considerablemente tanto la cond. prot (20.96 mS/cm a 90 ºC) como la densidad de potencia máxima (Pmax) en pila de combustible de hidrógeno (13.9 mW/cm2 a temperatura ambiente). En la Contribución III se estudió el efecto de una nueva variable, la sulfonación del GO (sGO), sobre las propiedades funcionales de los composites PVA/sGO y sPVA/sGO en aplicaciones de DMFC. Además, se llevó a cabo un estudio comparativo con los composite PVA/GO y sPVA/GO previamente descritos. Los resultados concluyeron que, en contra a lo esperado, la múltiple sulfonación de la membrana 30sPVA/sGO reduce fuertemente su cond. prot (5.22 mS/cm a 50 ºC) en comparación con su homóloga 30sPVA/GO (8.42 mS/cm a 50 ºC), aun mostrando valores superiores de IEC. Finalmente, el rendimiento de la composite 30PVA/sGO (1.85 mW/cm2) en una DMFC (50 ºC, disolución de metanol 4M) mostró una mejora significativa en comparación con la composite 30sPVA/GO (1.00 mW/cm2). El método de LbL assembly se empleó en la Contribución IV para la preparación de composites ensamblados mediante enlaces por puente de hidrógeno. Para ello, se llevó a cabo la deposición de bicapas de GO/PVA y GO/sPVA sobre los substratos 15PVA y 15sPVA, respectivamente. Los composites se codificaron como 15PVA(GO/PVA)n y 15sPVA(GO/sPVA)n siendo n el número de bicapas depositadas, en nuestro caso n varía entre 1 y 3. Por último, se evaluó su potencial para aplicaciones en DMFC, presentando el mejor comportamiento el composite 15sPVA(GO/sPVA)1. Finalmente, la Contribución V va dedicada a la fabricación de composites mediante el método de LbL Assembly, pero en este caso a través de interacciones electrostáticas. El GO se dispersó en una disolución de hidrocloruro de polialilamina (GO-PAH), con el fin de dotarlo de carga positiva. El ensamblaje se realizó por deposición alterna de capas de GO-PAH y sPVA, obteniéndose los composites 15PVA(GO-PAH/sPVA)n y 15sPVA(GO-PAH/sPVA)n. El mejor valor de cond. prot (8.26 mS/cm a 90 ºC) se obtuvo para el composite 15PVA(GO-PAH/sPVA)1, siendo casi el doble que el obtenido para su homólogo sMembranes constituïdes a base PVA han despertat un gran interès a causa del seu baix cost i el seu fàcil processament per conformar-les en forma de films. Aquests films freqüentment són sotmesos a entrecreuament per disposar d'una xarxa macromolecular amb una elevada estabilitat dimensional. La modificació del PVA per introducció de grups sulfònics (sPVA) canvia l'estructura del polímer contribuint a augmentar la seua conductivitat protònica. A més, la preparació de membranes híbrides orgànic-inorgànics (composites) mitjançant addició d'òxid de grafè (GO) reforça la matriu, alhora que disminueix la seua permeabilitat enfront de dissolvents. Tot això ha motivat l'ús d'aquestos materials per a la preparació de membranes d'intercanvi protònic (PEMs) emprades en piles de combustible de metanol (DMFCs). En la Contribució I es presenten els esquemes químics conduents a la bi-sulfonació del PVA, la síntesi del GO i la preparació de les membranes composite PVA/GO i sPVA/GO. A més, es va realitzar la caracterització estructural, morfològica, tèrmica i mecànica de cada un dels materials de partida i de les membranes composite. Finalment, per tal d'avaluar la seua idoneïtat com a PEMs en piles de combustible, es va mesurar la seua cond. prot a temperatura ambient. Els resultats obtinguts van mostrar que l¿addició de GO (1 wt.%) com a nano-càrrega en la matriu de sPVA genera un composite, 30sPVA/GO, amb una cond. prot que supera en un 89% a la de la seua membrana homòloga sense càrrega, 30sPVA. La Contribució II tracta d'explorar les propietats conductores de les membranes composite preparades prèviament en funció de la modificació estructural (bi-sulfonació) i morfològica (reticulació i addició de GO). La membrana bi-sulfonada i reforçada amb GO, 30sPVA/GO, destaca sobre la resta. L'addició de GO millora considerablement tant la cond. prot (20.96 mS/cm a 90 ºC) com la densitat de potència màxima (Pmax) a la pila de combustible d'hidrogen (13.9 mW/cm2 a temperatura ambient). En la Contribució III es va estudiar l'efecte d'una nova variable, la sulfonació del GO (sGO), sobre les propietats funcionals dels composites PVA/sGO i sPVA/sGO per aplicacions en DMFC. A més, es va dur a terme un estudi comparatiu amb els composites PVA/GO i sPVA/GO prèviament descrits. Els resultats van concloure que en contra del que s'esperava, la múltiple sulfonació de la membrana 30sPVA/sGO redueix fortament la seua cond. prot (5.22 mS/cm a 50 ºC) en comparació amb la seua homòloga 30sPVA/GO (8.42 mS/cm a 50 ºC), tot i que mostra valors superiors de IEC. Finalment, el rendiment de la membrana 30PVA/sGO (1.85 mW/cm2) en una DMFC (50 ºC, dissolució de metanol 4M) va mostrar una millora significativa en comparació amb la membrana 30sPVA/GO (1.00 mW/cm2). El mètode de LBL assembly es va emprar en la Contribució IV per a la preparació de composites acoblats mitjançant enllaços per pont d'hidrogen. Amb aquest fi, es va dur a terme la deposició de bicapes de GO/PVA i GO/sPVA sobre els substrats 15PVA i 15sPVA, respectivament. Els composites es van codificar com a 15PVA(GO/PVA)n i 15sPVA(GO/sPVA)n on n és el nombre de bicapes dipositades, en el nostre cas n varia entre 1 i 3. Finalment, es va avaluar el seu potencial per a aplicacions en DMFC, presentant el millor comportament el composite 15sPVA(GO/sPVA)1. Finalment, la Contribució V va dedicada a la fabricació de composites mitjançant el mètode de LBL Assembly, però en aquest cas acoblats a través d'interaccions electrostàtiques. El GO es va dispersar en una dissolució de hidroclorur de polialilamina (GO-PAH), per tal de dotar-lo de càrrega positiva. L'acoblament es va realitzar per deposició alterna de capes de GO-PAH i sPVA, obtenint-se els composites 15PVA(GO-PAH/sPVA)n i 15sPVA(GO-PAH/sPVA)n. El millor valor de cond. prot (8.26 mS/cm a 90 ºC) es va obtenir per al composite 15PVA(GO-PAH/sPVA)1, sent gairebé el doble que l'obtingutSánchez Ballester, SC. (2017). Synthesis and characterization of new polymer electrolytes to use in fuel cells fed with bio-alcohols [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/86198TESI

Electrostatic-induced assembly of graphene-encapsulated carbon@nickel-aluminum layered double hydroxide core-shell spheres hybrid structure for high-energy and high-power-density asymmetric supercapacitor

Achieving high energy density while retaining high power density is difficult in electrical double-layer capacitors and in pseudocapacitors considering the origin of different charge storage mechanisms. Rational structural design became an appealing strategy in circumventing these trade-offs between energy and power densities. A hybrid structure consists of chemically converted graphene-encapsulated carbon@nickel-aluminum layered double hydroxide core–shell spheres as spacers among graphene layers (G-CLS) used as an advanced electrode to achieve high energy density while retaining high power density for high-performance supercapacitors. The merits of the proposed architecture are as follows: (1) CLS act as spacers to avoid the close restacking of graphene; (2) highly conductive carbon sphere and graphene preserve the mechanical integrity and improve the electrical conductivity of LDHs hybrid. Thus, the proposed hybrid structure can simultaneously achieve high electrical double-layer capacitance and pseudocapacitance resulting in the overall highly active electrode. The G-CLS electrode exhibited high specific capacitance (1710.5 F g−1 at 1 A g−1) under three-electrode tests. An ASC fabricated using the G-CLS as positive electrode and reduced graphite oxide as negative electrode demonstrated remarkable electrochemical performance. The ASC device operated at 1.4 V, and delivered a high energy density of 35.5 Wh kg−1 at a 670.7 W kg−1 power density at 1 A g−1 with an excellent rate capability, as well as a robust long-term cycling stability of up to 10 000 cycles

Recent advancements of n-doped graphene for rechargeable batteries: A review

Graphene, a 2D carbon structure, due to its unique materials characteristics for energy storage applications has grasped the considerable attention of scientists. The highlighted properties of this material with a mechanically robust and highly conductive nature have opened new opportunities for different energy storage systems such as Li-S (lithium-sulfur), Li-ion batteries, and metal-air batteries. It is necessary to understand the intrinsic properties of graphene materials to widen its large-scale applications in energy storage systems. In this review, different routes of graphene synthesis were investigated using chemical, thermal, plasma, and other methods along with their advantages and disadvantages. Apart from this, the applications of N-doped graphene in energy storage devices were discussed

Carbonaceous Materials Coated Carbon Fibre Reinforced Polymer Matrix Composites

Carbon fibre reinforced polymer composites have high mechanical properties that make them exemplary engineered materials to carry loads and stresses. Coupling fibre and matrix together require good understanding of not only fibre morphology but also matrix rheology. One way of having a strongly coupled fibre and matrix interface is to size the reinforcing fibres by means of micro- or nanocarbon materials coating on the fibre surface. Common coating materials used are carbon nanotubes and nanofibres and graphene, and more recently carbon black (colloidal particles of virtually pure elemental carbon) and graphite. There are several chemical, thermal, and electrochemical processes that are used for coating the carbonous materials onto a carbon fibre surface. Sizing of fibres provides higher interfacial adhesion between fibre and matrix and allows better fibre wetting by the surrounded matrix material. This review paper goes over numerous techniques that are used for engineering the interface between both fibre and matrix systems, which is eventually the key to better mechanical properties of the composite systems