Ice-templated hybrid graphene oxide—graphene nanoplatelet lamellar architectures: tuning mechanical and electrical properties

From IOP Publishing via Jisc Publications RouterHistory: received 2020-10-21, oa-requested 2021-01-07, rev-recd 2021-01-12, accepted 2021-01-25, epub 2021-02-23, open-access 2021-02-23, ppub 2021-05-14Publication status: PublishedFunder: Morgan Advanced Materials and RAEngFunder: Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Brasil (CAPES)Funder: Heilongjiang Huasheng Graphite Co., People’s Republic of ChinaAbstract: The traditional freeze-casting route for processing graphene-based aerogels is generally restricted to aqueously dispersed flakes of graphene oxide (GO) and post-processing reduction treatments, which brings restrictions to the aerogels electrical properties. In this work, we report a versatile aqueous processing route that uses the ability of GO todisperse graphene nanoplatelets (GNP) to produce rGO-GNP lamellar aerogels via unidirectional freeze-casting. In order to optimise the properties of the aerogel, GO-GNP dispersions were partially reduced by L-ascorbic acid prior to freeze-casting to tune the carbon and oxygen (C/O) ratio. The aerogels were then heat treated after casting to fully reduce the GO. The chemical reduction time was found to control the microstructure of the resulting aeorgels and thus to tune their electrical and mechanical properties. An rGO-GNP lamellar aerogel with density of 20.8 ± 0.8 mg cm−3 reducing using a reduction of 60 min achieved an electrical conductivity of 42.3 S m−1. On the other hand, an optimal reduction time of 35 min led to an aerogel with compressive modulus of 0.51 ±0.06 MPa at a density of 23.2 ± 0.7 mg cm−3, revealing a compromise between the tuning of electrical and mechanical properties. We show the present processing route can also be easily applied to produce lamellar aerogels on other graphene-based materials such as electrochemically exfoliated graphene

Producing open-porous inorganic component with layer having homogenous pore structure, comprises solidifying emulsion consisting of stabilized aqueous inorganic suspension, alkane and emulsifier to obtain basic body by freezing process

The method comprises solidifying emulsion consisting of stabilized aqueous inorganic suspension, alkane and emulsifier to obtain a basic body by a freezing process, emulsifying alkane with a volume of 45-75% related to the total volume of the emulsified suspension in an aqueous inorganic suspension, so that the developed emulsion droplets have a size of smaller than 50mu m and the formed emulsion suppresses the growth of single crystals, which are larger than 50 mu m, during freezing the aqueous phase, and freezing the produced emulsion, so that only the water freezes in the emulsion. The method comprises solidifying emulsion consisting of stabilized aqueous inorganic suspension, alkane and emulsifier to obtain a basic body by a freezing process, emulsifying alkane with a volume of 45-75% related to the total volume of the emulsified suspension in an aqueous inorganic suspension, so that the developed emulsion droplets have a size of smaller than 50mu m and the formed emulsion suppresses the growth of single crystals, which are larger than 50 mu m, during freezing the aqueous phase, freezing the produced emulsion, so that only the water freezes in the emulsion and the emulsified alkane remains liquid, drying the component, in which under maintaining the frozen state of the water, the alkane is evaporated at reduced pressure and then the water is removed from the component by sublimation or by other drying process, and subsequently sintering the obtained basic body. The inorganic powder in the stabilized aqueous suspension is ceramic powder, metal powder, mineral powder, metal carbide powder and/or metal nitride powder, and is used with an average particle size of smaller than 50 mu m. A colloidal nanosol is used as inorganic constituent in the aqueous inorganic suspension. A binder is used as further constituent in the aqueous inorganic suspension. The produced emulsion is poured as layer with a defined thickness in the form of any geometry before freezing, an upper surface layer of the emulsion is removed subsequently or after a determined wait time, a further layer of other composition is applied and the process is often repeated. The obtained basic body is coated or infiltrated in green or sintered state, so that the body has a closed porosity in the outer layer and is subsequently dried and sintered

Optimization of oxygen feed membranes in autothermal steam-reformers

In conventional concepts for autothermal steam-reformers the spatial temperature distribution is disadvantageous. The different rates of the exothermic oxidation and endothermic reforming reactions lead to the problem of temperature hot-spots, which can damage or even destroy the catalyst or other elements of the reformer. This is especially the case, when the needed oxygen is premixed to the feed gas resulting in a high temperature peak in the entrance region. In the past, some first attempts have been made to solve this hot-spot problem.. One idea is, that the oxygen is not premixed to the feed gas but injected at different positions distributed over the length of the reformer. This leads to more but much smaller temperature peaks. Expanding this idea, one can use also a continuous oxygen injection over the length of the reformer. This can for example be realized by an open porous membrane. By varying the permeability of such a membrane we can adjust the spatial oxygen flux distribution. One of our previous works 1 focused on the optimization procedure of the membrane structure to achieve an isothermal behaviour of the adiabatic autothermal steam-reformer. In the present work we investigate the use of such oxygen feed membranes with varying permeabilities, both in experiments and by simulation analysis. The simulation results show that an optimized membrane can be used for a wide range of operation conditions, i.e. mass fluxes and amounts of oxygen flux without being reduced in efficiency. The experimental results are in good agreement with the simulations and indicate the feasibility of the concept of spatial oxygen feed distribution in autothermal steam-reformers to avoid the hot-spot problem