Fluid dynamics: an emerging route for the scalable production of graphene in the last five years

Bulk applications of graphene in fields such as advanced composites, conductive ink, and energy storage require cheap and scalable graphene. Fortunately, in the last decade, liquid-phase exfoliation of graphite to give pristine graphene has been thought as a promising way to massive production of graphene at high efficiency and low cost, in terms of the cheap and abundant graphite source and a variety of cost-effective exfoliation techniques. Though many exfoliation techniques are available so far, this article will highlight the recent progress of fluid dynamics route which emerges as a promising scalable and efficient way for graphene production in the last five years. The emphasis is set on vortex fluidic devices and pressure- and mixer-driven fluid dynamics, with our perspectives on the latest progress, exfoliation mechanism, and some key issues that require further study in order to realize industrial applications.Comment: 18 figure

Direct Evidence of the Exfoliation Efficiency and Graphene Dispersibility of Green Solvents toward Sustainable Graphene Production

Achieving a sustainable production of pristine high-quality graphene and other layered materials at a low cost is one of the bottlenecks that needs to be overcome for reaching 2D material applications at a large scale. Liquid phase exfoliation in conjunction with N-methyl-2-pyrrolidone (NMP) is recognized as the most efficient method for both the exfoliation and dispersion of graphene. Unfortunately, NMP is neither sustainable nor suitable for up-scaling production due to its adverse impact on the environment. Here, we show the real potential of green solvents by revealing the independent contributions of their exfoliation efficiency and graphene dispersibility to the graphene yield. By experimentally separating these two factors, we demonstrate that the exfoliation efficiency of a given solvent is independent of its dispersibility. Our studies revealed that isopropanol can be used to exfoliate graphite as efficiently as NMP. Our finding is corroborated by the matching ratio between the polar and dispersive energies of graphite and that of the solvent surface tension. This direct evidence of exfoliation efficiency and dispersibility of solvents paves the way to developing a deeper understanding of the real potential of sustainable graphene manufacturing at a large scale

Polyoxometalate (POM)-layered double hydroxides (LDH) composite materials: design and catalytic applications

Layered double hydroxides (LDHs) are an important large class of two-dimensional (2D) anionic lamellar materials that possess flexible modular structure, facile exchangeability of inter-lamellar guest anions and uniform distribution of metal cations in the layer. Owing to the modular accessible gallery and unique inter-lamellar chemical environment, polyoxometalates (POMs) intercalated with LDHs has shown a vast array of physical properties with applications in environment, energy, catalysis, etc. Here we describe how polyoxometalate clusters can be used as building components for the construction of systems with important catalytic properties. This review article mainly focuses on the discussion of new synthetic approaches developed recently that allow the incorporation of the element of design in the construction of a fundamentally new class of materials with pre-defined functionalities in catalytic applications. Introducing the element of design and taking control over the finally observed functionality we demonstrate the unique opportunity for engineering materials with modular properties for specific catalytic applications

A lithium-ion battery based on a graphene nanoflakes ink anode and a lithium iron phosphate cathode

Li-ion rechargeable batteries have enabled the wireless revolution transforming global communication. Future challenges, however, demands distributed energy supply at a level that is not feasible with the current energy-storage technology. New materials, capable of providing higher energy density are needed. Here we report a new class of lithium-ion batteries based on a graphene ink anode and a lithium iron phosphate cathode. By carefully balancing the cell composition and suppressing the initial irreversible capacity of the anode, we demonstrate an optimal battery performance in terms of specific capacity, i.e. 165 mAhg-1, estimated energy density of about 190 Whkg-1 and life, with a stable operation for over 80 charge-discharge cycles. We link these unique properties to the graphene nanoflake anode displaying crystalline order and high uptake of lithium at the edges, as well as to its structural and morphological optimization in relation to the overall battery composition. Our approach, compatible with any printing technologies, is cheap and scalable and opens up new opportunities for the development of high-capacity Li-ion batteries.Comment: 17 pages, 10 figure

Stability and Thermal Properties Study of Metal Chalcogenide-Based Nanofluids for Concentrating Solar Power

Nanofluids are colloidal suspensions of nanomaterials in a fluid which exhibit enhanced thermophysical properties compared to conventional fluids. The addition of nanomaterials to a fluid can increase the thermal conductivity, isobaric-specific heat, diffusivity, and the convective heat transfer coefficient of the original fluid. For this reason, nanofluids have been studied over the last decades in many fields such as biomedicine, industrial cooling, nuclear reactors, and also in solar thermal applications. In this paper, we report the preparation and characterization of nanofluids based on one-dimensional MoS2 and WS2 nanosheets to improve the thermal properties of the heat transfer fluid currently used in concentrating solar plants (CSP). A comparative study of both types of nanofluids was performed for explaining the influence of nanostructure morphologies on nanofluid stability and thermal properties. The nanofluids prepared in this work present a high stability over time and thermal conductivity enhancements of up to 46% for MoS2-based nanofluid and up to 35% for WS2-based nanofluid. These results led to an increase in the efficiency of the solar collectors of 21.3% and 16.8% when the nanofluids based on MoS2 nanowires or WS2 nanosheets were used instead of the typical thermal oil

Scalable production of graphene inks via wet-jet milling exfoliation for screen-printed micro-supercapacitors

The miniaturization of energy storage units is pivotal for the development of next-generation portable electronic devices. Micro-supercapacitors (MSCs) hold a great potential to work as on-chip micro-power sources and energy storage units complementing batteries and energy harvester systems. The scalable production of supercapacitor materials with cost-effective and high-throughput processing methods is crucial for the widespread application of MSCs. Here, we report wet-jet milling exfoliation of graphite to scale-up the production of graphene as supercapacitor material. The formulation of aqueous/alcohol-based graphene inks allows metal-free, flexible MSCs to be screen-printed. These MSCs exhibit areal capacitance (Careal) values up to 1.324 mF cm-2 (5.296 mF cm-2 for a single electrode), corresponding to an outstanding volumetric capacitance (Cvol) of 0.490 F cm-3 (1.961 F cm-3 for a single electrode). The screen-printed MSCs can operate up to power density above 20 mW cm-2 at energy density of 0.064 uWh cm-2. The devices exhibit excellent cycling stability over charge-discharge cycling (10000 cycles), bending cycling (100 cycles at bending radius of 1 cm) and folding (up to angles of 180{\deg}). Moreover, ethylene vinyl acetate-encapsulated MSCs retain their electrochemical properties after a home-laundry cycle, providing waterproof and washable properties for prospective application in wearable electronics