Reduced Graphene Oxide for Room Temperature Hydrogen Storage Application
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Abstract:
Graphene oxide (GO) is extracted from graphite oxide synthesized using modified Hummers method. The extracted GO solution is then drop casted onto a p type silicon substrate and dried in hot air oven. The dried solution is annealed at a temperature of about 200 degree Celsius for about one hour to obtain thermally reduced graphene oxide (RGO). Such thermally synthesized RGO usually have a lot of structural defects which can act as a binding site for hydrogen. The binding efficiency of hydrogen to defect centers can be increased by applying electric field to RGO as it changes the carrier concentration (doping) on the surface. This induces more polarization in the hydrogen molecule resulting in strong binding force, thereby increasing its hydrogen storage efficiency. In our experiment we have demonstrated room temperature electric field doping in RGO films by modulating the channel current by changing the back gate voltage which is a precursor for employing RGO in hydrogen storage applications. Keywords Graphene oxide, Reduced graphene oxide, Field effect, Hydrogen storage, and DefectsKeywords:
Graphite oxide
Based on the Hummers method, graphite oxide and oxidation activated carbon were prepared from graphite and activated carbon. The differences in the structure and property of graphite and activated carbon before and after the liquid-phase oxidation were analyzed. The analysis showed that there were surface oxidation and internal oxidation for natural graphite flakes, but there was only surface oxidation for activated carbon of coconut shells. Surface oxidation took place because the natural graphite flakes and activated carbon possessed many polarity groups, which gave them strong polar and chemical activity. Internal oxidation increased the distance between the layers of graphite flakes from 0.335 4 nm to 0.898 1 nm, which was induced by the polarity groups and H2O between the layers of graphite flakes. In alkaline solution, graphite oxide delaminated into needle-like and spherical nano-particles, some of which coalesced. The oxidation activated carbon was in the form of spherical nano-particles, which coalesced into chain structure.
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Graphene oxide was synthesized from graphite flakes using modified Hummers' method. The interlayer spacings of graphite, graphite oxide and graphene oxide were measured using X-ray diffraction technique. The C/O atomic ratios of graphite oxide and graphene oxide were calculated from XPS measurements. The transformation of graphite to graphite oxide and finally to graphene oxide was clearly observed from the micro-Raman spectroscopy data and was confirmed from the FESEM micrographs. UV-VIS-NIR spectrophotometer was used to study the absorbance of graphene oxide and reduced graphene oxide samples. Finally, the chemically reduced graphene oxide was heat-treated in air to obtain chemically modified graphene.
Graphite oxide
Absorbance
Graphene foam
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A new method to separate graphite oxide (GO) modified by polyethylene oxide (PEO) by the aid of ultrasonic radiation was developed. Modified GO (graphene oxide or single layer of graphite oxide) did not show not appear crystalline peak (d002) on the X-Ray and took the form of a single layer graphene oxide on the image AFM and TEM. The exfoliated graphene oxide was reduced (RGO) to graphene by the reducing agent system HI – Acetic acid (HI-AcOH). The sheet resistance of RGOHI-AcOH is about 120 Ω/sq in the form graphene paper. In addition, FTIR, UV-Vis and Raman spectra showed more clearly about characteristics of graphite oxide, graphene oxide and RGOHI-AcOH.
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Graphite was chemically cleaved to graphene by Billups Reaction,and the morphologies and microstructures of graphene were characterized by SEM,Raman and AFM.The results show that the graphite was first functionalized by 1-iodododecane,which led to the cleavage of the graphene layer in the graphite.The second decoration cleaved the graphite further and graphene was obtained.The heights of the graphene layer were larger than 1 nm due to the organic decoration.
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Graphite oxide
Carbon fibers
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Based on the Hummers method,the graphite oxide (GO) was prepared from the flake graphite through liquid oxidation;and then the graphene was prepared by using hydrazine hydrate to reduce the exfoliated graphite oxide nanosheets in the aqueous colloidal suspension.The structure and the thermal stability of graphite,graphite oxide and graphene were characterized by Fourier transform infrared spectroscopy (FT-IR),Raman spectroscopy (RS),X-ray diffraction analysis (XRD) and thermo-gravimetric analysis (TG),respectively.The results show that part of sp3-hybridized carbons in graphite oxide are reduced to sp2-hybridized carbons in graphene,and the average size of sp2-hybridized carbon layer surface of graphene is larger than that of graphite oxide,while the intensity of crystallization and the regularity of graphene are lower than that of graphite.Under our experimental conditions,the structure of the reduced graphite oxide can not be fully recovered to the original structure of the graphite before it forms graphite oxide;it means that the structure of graphene is different from that of graphite.The thermal analysis results indicate that the heat stability of graphene is much better than that of graphite oxide.
Graphite oxide
Thermogravimetric analysis
Thermal Stability
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As a novel two‐dimensional carbon material, graphene has fine potential applications in the fields of electron transfer agent and supercapacitor material for its excellent electronic and optical property. However, the challenge is to synthesize graphene in a bulk quantity. In this paper, graphite oxide was prepared from natural flake graphite by Hummers’ method through liquid oxidization, and the reduced graphene oxide was obtained by chemical reduction of graphene oxide using NH 3 ·H 2 O aqueous solution and hydrazine hydrate. The raw material graphite, graphite oxide, and reduced graphene oxide were characterized by X‐ray diffraction (XRD), attenuated total reflectance‐infrared spectroscopy (ATR‐IR), and field emission scanning electron microscope (SEM). The results indicated that the distance spacing of graphite oxide was longer than that of graphite and the crystal structure of graphite was changed. The flake graphite was oxidized to graphite oxide and lots of oxygen‐containing groups were found in the graphite oxide. In the morphologies of samples, fold structure was found on both the surface and the edge of reduced graphene oxide.
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Coaly graphite is an important natural graphite resource that derived from coal under a natural process that associated with igneous intrusion. Flake graphite is usually used for the chemical synthesis of graphene oxide (GO), the main precursor for preparation of graphene, but few papers pay attention to preparing GO using coaly graphite. In this paper, four kinds of natural coaly graphite with different graphitization degrees were exposed to a modified Hummer's oxidation method to prepare GO. The flake graphite sample was also used for comparison. The results showed that the structural change process from graphite to GO were significantly affected by the graphitization degree of the original coaly graphite. The relationship between yields of GO and graphitization degrees of the coaly graphite was explored. The mechanism of why the graphite with low graphitization degrees cannot be totally oxidized was proposed. Coaly graphite with a graphitization degree of higher than 80% was easier to be oxidized and yielded the same amount of GO as the flake graphite did, suggesting it is the potential substitute for the flake graphite to produce GO in bulk quantities.
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Expanded graphite 산화물과 자성 나노입자의 복합화는 화학적 방법을 이용하였으며, Ni과 Co 나노입자를 사용하여 간단한 방법으로 자기적 특성을 가지는 graphite 산화물을 합성하였다. $H_2SO_4$ 에 $(NH_4)SO_4$ 을 첨가한 혼합 용액을 제조하여, natural graphite와 반응시키고, 1차 열처리하여 expanded graphite를 제조하였다. $1050^{\circ}C$ 에서 30초간 급속 2차 열처리와 화학적 산화 과정을 거쳐 expanded graphite oxide로 변화시킨 뒤에 $Ni(acac)_2$ , $Co(acac)_3$ 과 화학적 반응을 통하여 Expanded graphite 산화물자성 나노입자 복합체를 제조하였다. 결정 구조 분석을 위하여 x-선 회절 측정을 수행하였으며, Raman 분광 측정으로 graphite 산화물의 층상 구조를 분석하였다. 미세구조 분석을 위하여 투과전자현미경 측정을 수행하였으며, 진동시료형 자화율측정기를 이용하여 복합체의 자기적 특성을 연구하였다. 이러한 연구 결과는 graphite 화합물과 자성 물질의 복합화를 위한 기저 기술로 활용될 수 있을 것이다. The composites of expanded graphite oxide and magnetic nanoparticle (Ni and Co) were synthesized by using simple chemical method. From the raw material natural graphite, the expanded graphite was fabricated using sulfuric acid and $1^{st}$ heat treatment at $600^{\circ}C$ for 1 hour. The expanded graphite was changed to expanded graphite oxide by 2nd heat treatment at $1050^{\circ}C$ for 15 sec and chemical oxidation. The expanded graphite oxide/1-methyl-2-pyrrolidone solution reacts with the magnetic nanoparticle to form a magnetic graphite oxide composite. These graphite-based materials were characterized by x-ray diffractometer, Raman spectroscopy, transmission electron microscope, and vibration sample magnetometer. We expect that these results of this paper were become basis research of graphite oxide composite.
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Diffractometer
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