6 research outputs found

    Single-Layer Graphene Membranes Withstand Ultrahigh Applied Pressure

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    High mechanical strength is essential for pressure-driven membrane separations with nanoporous single-layer graphene, but its ability to withstand high pressures remains to be demonstrated. We monitored failure of centimeter-scale single-layer graphene membranes on porous supports subjected to high pressures. Consistent with theory, the membranes were found to withstand higher pressures when placed on porous supports with smaller pore diameters, but failure occurred over a surprisingly broad range of pressures, attributed to heterogeneous susceptibility to failure at wrinkles, defects, and slack in the suspended graphene. Remarkably, nonwrinkled areas withstood pressure exceeding 100 bar at which many kinds of membrane suffer from compaction. Our study shows that single-layer graphene membranes can sustain ultrahigh pressure especially if the effect of wrinkles is isolated using supports with small pores and suggests the potential for the use of single-layer graphene in high-pressure membrane separations

    Molecular Sieving Across Centimeter-Scale Single-Layer Nanoporous Graphene Membranes

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    Molecular sieving across atomically thin nanoporous graphene is predicted to enable superior gas separation performance compared to conventional membranes. Although molecular sieving has been demonstrated across a few pores in microscale graphene membranes, leakage through nonselective defects presents a major challenge toward realizing selective membranes with high densities of pores over macroscopic areas. Guided by multiscale gas transport modeling of nanoporous graphene membranes, we designed the porous support beneath the graphene to isolate small defects and minimize leakage through larger defects. Ion bombardment followed by oxygen plasma etching was used to produce subnanometer pores in graphene at a density of ∼10<sup>11</sup> cm<sup>–2</sup>. Gas permeance measurements demonstrate selectivity that exceeds the Knudsen effusion ratio and scales with the kinetic diameter of the gas molecules, providing evidence of molecular sieving across centimeter-scale nanoporous graphene. The extracted nanoporous graphene performance is comparable to or exceeds the Robeson limit for polymeric gas separation membranes, confirming the potential of nanoporous graphene membranes for gas separations

    A Scalable Route to Nanoporous Large-Area Atomically Thin Graphene Membranes by Roll-to-Roll Chemical Vapor Deposition and Polymer Support Casting

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    Scalable, cost-effective synthesis and integration of graphene is imperative to realize large-area applications such as nanoporous atomically thin membranes (NATMs). Here, we report a scalable route to the production of NATMs via high-speed, continuous synthesis of large-area graphene by roll-to-roll chemical vapor deposition (CVD), combined with casting of a hierarchically porous polymer support. To begin, we designed and built a two zone roll-to-roll graphene CVD reactor, which sequentially exposes the moving foil substrate to annealing and growth atmospheres, with a sharp, isothermal transition between the zones. The configurational flexibility of the reactor design allows for a detailed evaluation of key parameters affecting graphene quality and trade-offs to be considered for high-rate roll-to-roll graphene manufacturing. With this system, we achieve synthesis of uniform high-quality monolayer graphene (<i>I</i><sub>D</sub>/<i>I</i><sub>G</sub> < 0.065) at speeds ≥5 cm/min. NATMs fabricated from the optimized graphene, via polymer casting and postprocessing, show size-selective molecular transport with performance comparable to that of membranes made from conventionally synthesized graphene. Therefore, this work establishes the feasibility of a scalable manufacturing process of NATMs, for applications including protein desalting and small-molecule separations

    Kinetic Control of Angstrom-Scale Porosity in 2D Lattices for Direct Scalable Synthesis of Atomically Thin Proton Exchange Membranes

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    Angstrom-scale pores introduced into atomically thin 2D materials offer transformative advances for proton exchange membranes in several energy applications. Here, we show that facile kinetic control of scalable chemical vapor deposition (CVD) can allow for direct formation of angstrom-scale proton-selective pores in monolayer graphene with significant hindrance to even small, hydrated ions (K+ diameter ∼6.6 Å) and gas molecules (H2 kinetic diameter ∼2.9 Å). We demonstrate centimeter-scale Nafion|Graphene|Nafion membranes with proton conductance ∼3.3–3.8 S cm–2 (graphene ∼12.7–24.6 S cm–2) and H+/K+ selectivity ∼6.2–44.2 with liquid electrolytes. The same membranes show proton conductance ∼4.6–4.8 S cm–2 (graphene ∼39.9–57.5 S cm–2) and extremely low H2 crossover ∼1.7 × 10–1 – 2.2 × 10–1 mA cm–2 (∼0.4 V, ∼25 °C) with H2 gas feed. We rationalize our findings via a resistance-based transport model and introduce a stacking approach that leverages combinatorial effects of interdefect distance and interlayer transport to allow for Nafion|Graphene|Graphene|Nafion membranes with H+/K+ selectivity ∼86.1 (at 1 M) and record low H2 crossover current density ∼2.5 × 10–2 mA cm–2, up to ∼90% lower than state-of-the-art ionomer Nafion membranes ∼2.7 × 10–1 mA cm–2 under identical conditions, while still maintaining proton conductance ∼4.2 S cm–2 (graphene stack ∼20.8 S cm–2) comparable to that for Nafion of ∼5.2 S cm–2. Our experimental insights enable functional atomically thin high flux proton exchange membranes with minimal crossover

    Introducing Carbon Diffusion Barriers for Uniform, High-Quality Graphene Growth from Solid Sources

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    Carbon diffusion barriers are introduced as a general and simple method to prevent premature carbon dissolution and thereby to significantly improve graphene formation from the catalytic transformation of solid carbon sources. A thin Al<sub>2</sub>O<sub>3</sub> barrier inserted into an amorphous-C/Ni bilayer stack is demonstrated to enable growth of uniform monolayer graphene at 600 °C with domain sizes exceeding 50 μm, and an average Raman D/G ratio of <0.07. A detailed growth rationale is established via in situ measurements, relevant to solid-state growth of a wide range of layered materials, as well as layer-by-layer control in these systems

    Interdependency of Subsurface Carbon Distribution and Graphene–Catalyst Interaction

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    The dynamics of the graphene–catalyst interaction during chemical vapor deposition are investigated using in situ, time- and depth-resolved X-ray photoelectron spectroscopy, and complementary grand canonical Monte Carlo simulations coupled to a tight-binding model. We thereby reveal the interdependency of the distribution of carbon close to the catalyst surface and the strength of the graphene–catalyst interaction. The strong interaction of epitaxial graphene with Ni(111) causes a depletion of dissolved carbon close to the catalyst surface, which prevents additional layer formation leading to a self-limiting graphene growth behavior for low exposure pressures (10<sup>–6</sup>–10<sup>–3</sup> mbar). A further hydrocarbon pressure increase (to ∼10<sup>–1</sup> mbar) leads to weakening of the graphene–Ni(111) interaction accompanied by additional graphene layer formation, mediated by an increased concentration of near-surface dissolved carbon. We show that growth of more weakly adhered, rotated graphene on Ni(111) is linked to an initially higher level of near-surface carbon compared to the case of epitaxial graphene growth. The key implications of these results for graphene growth control and their relevance to carbon nanotube growth are highlighted in the context of existing literature