Measuring the proton selectivity of graphene membranes

Walker, Michael I.; Braeuninger‐Weimer, Philipp; Weatherup, Robert S.; Hofmann, Stephan; Keyser, Ulrich F.

doi:10.1063/1.4936335

Cited by 65 publications

(98 citation statements)

References 26 publications

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“…The substantial power generated in our experiments can be attributed mainly to the atomic-scale thickness of the MoS 2 membrane. Our results also provide new avenues for studying other membrane-based processes, such as water desalination 7 or proton transport 29 . Furthermore, the nanopore generator may see application in other ultralow-power devices, such as in electronics.…”

Section: Letter Researchmentioning

confidence: 75%

Single-layer MoS2 nanopores as nanopower generators

Feng

Gräf

Liu

et al. 2016

Nature

978

855

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Making use of the osmotic pressure difference between fresh water and seawater is an attractive, renewable and clean way to generate power and is known as 'blue energy' 1-3 . Another electrokinetic phenomenon, called the streaming potential, occurs when an electrolyte is driven through narrow pores either by a pressure gradient 4 or by an osmotic potential resulting from a salt concentration gradient 5 . For this task, membranes made of two-dimensional materials are expected to be the most efficient, because water transport through a membrane scales inversely with membrane thickness 5-7 . Here we demonstrate the use of single-layer molybdenum disulfide (MoS 2 ) nanopores as osmotic nanopower generators. We observe a large, osmotically induced current produced from a salt gradient with an estimated power density of up to 10 6 watts per square metre-a current that can be attributed mainly to the atomically thin membrane of MoS 2 . Low power requirements for nanoelectronic and optoelectric devices can be provided by a neighbouring nanogenerator that harvests energy from the local environment 8-11 -for example, a piezoelectric zinc oxide nanowire array 8 or single-layer MoS 2 (ref. 12). We use our MoS 2 nanopore generator to power a MoS 2 transistor, thus demonstrating a self-powered nanosystem.MoS 2 nanopores have already demonstrated better water-transport behaviour than graphene 13,14 owing to the enriched hydrophilic surface sites (provided by the molybdenum) that are produced following either irradiation with transmission electron microscopy (TEM) 15 or electrochemical oxidation 16 . The osmotic power is generated by separating two reservoirs containing potassium chloride (KCl) solutions of different concentrations with a freestanding MoS 2 membrane, into which a single nanopore has been introduced 13 . A chemical potential gradient arises at the interface of these two liquids at a nanopore in a 0.65-nm-thick, single-layer MoS 2 membrane, and drives ions spontaneously across the nanopore, forming an osmotic ion flux towards the equilibrium state (Fig. 1a). The presence of surface charges on the pore screens the passing ions according to their charge polarity, and thus results in a net measurable osmotic current, known as reverse electrodialysis 1 . This cation selectivity can be better understood by analysing the concentration of each ion type (potassium and chloride) as a function of the radial distance from the centre of the pore, as we show here through molecular-dynamics simulations (Fig. 1b).We fabricated MoS 2 nanopores either by TEM 13 (Fig. 1c) Distance from the centre of the pore (Å)C max /C min = 1,000C max /C min = 500C max /C min = 100 LETTER RESEARCHosmotic current can be expected, owing to the long time required for the system to reach equilibrium. We measured the osmotic current and voltage across the pore by using a pair of Ag/AgCl electrodes to characterize the current-voltage (I-V) response of the nanopore.To gain a better insight into the performance of the MoS 2 nanopore power generator, ...

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Section: Letter Researchmentioning

confidence: 75%

Single-layer MoS2 nanopores as nanopower generators

Feng

Gräf

Liu

et al. 2016

Nature

978

855

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“…In this scenario,wesuggest that protons are prone to passage through these atomic defect sites in accordance with previous reports. [31] However,wecould not experimentally identify the relative contribution of these two pathways (via intact form or defect sites). Both pathways may contribute simultaneously in our system, taking into account the effect of the strong electric field in the electrochemical double layer (EDL, ca.…”

Section: Angewandte Chemiementioning

confidence: 99%

Single Graphene Layer on Pt(111) Creates Confined Electrochemical Environment via Selective Ion Transport

Rudnev

Wiberg

et al. 2017

Angew Chem Int Ed

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Graphene is a promising candidate for an ideal membrane material. Its ultralow (one-atomic) thickness potentially provides high permeation and at the same time high selectivity. Here, it is shown that these properties can be used to create a confined, two-dimensional electrochemical environment between a graphene layer and a single-crystal Pt(111) surface. The well-defined fingerprint voltammetric characteristics of Pt(111) provide an immediate information about the penetration and intercalation of ions into the confined space. These processes are shown to be highly selective.

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“…From the chemisorption site, our calculations yield a proton penetration barrier of 3.60 eV. As noted, in previous experiments, the 2D layers were surrounded by proton conducting polymers or aqueous solutions [1,2,9,20,22]. In the current study, we do not aim to model such an aqueous environment.…”

mentioning

confidence: 99%

“…Considerable theoretical effort has been devoted towards understanding the microscopic details of how protons penetrate 2D materials [9,17,18,[20][21][22]. It has been established on the basis of density-functional theory (DFT) calculations that the barriers to proton penetration through pristine graphene and h-BN in vacuum can be excessively high.…”

mentioning

confidence: 99%

Hydrogenation Facilitates Proton Transfer through Two-Dimensional Honeycomb Crystals

Feng

Chen

Fang

et al. 2017

J. Phys. Chem. Lett.

100

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Recent experiments have triggered a debate about the ability of protons to transfer through individual layers of graphene and hexagonal boron nitride (h-BN). However, calculations have shown that the barriers to proton penetration can, at more than 3 eV, be excessively high. Here, on the basis of first principles calculations, we show that the barrier for proton penetration is significantly reduced, to less than 1 eV, upon hydrogenation even in the absence of pinholes in the lattice. Analysis reveals that the barrier is reduced because hydrogenation destabilises the initial state (a deep-lying chemisorption state) and expands the honeycomb lattice through which the protons penetrate. This study offers a rationalization of the fast proton transfer observed in experiments, and highlights the ability of proton transport through single-layer materials in hydrogen rich solutions.

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Measuring the proton selectivity of graphene membranes

Cited by 65 publications

References 26 publications

Single-layer MoS2 nanopores as nanopower generators

Single-layer MoS2 nanopores as nanopower generators

Single Graphene Layer on Pt(111) Creates Confined Electrochemical Environment via Selective Ion Transport

Hydrogenation Facilitates Proton Transfer through Two-Dimensional Honeycomb Crystals

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