Nanofluidic electric generators constructed from boron nitride nanosheet membranes

doi:10.1016/j.nanoen.2018.03.030

Nano Energy

Volume 47, May 2018, Pages 368-373

https://doi.org/10.1016/j.nanoen.2018.03.030 Get rights and content

Highlights

•
Membrane fabricated from novel 2D nanomaterial (BN nanosheets) for energy generation.
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A working device that converts hydraulic pressure into electric current.
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Structural analysis of the BN membrane reveals the ionic channels presented in the hydrated BN membrane.
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Formation mechanism of ionic channels in the BN conduits and the origin of the electric current.

Abstract

Harvesting clean energy through artificial devices has attracted tremendous interest in the past few decades. More specifically, electricity generated by electrokinetic effects has received much attention recently due to the development of microfluidic and nanofluidic device. In this paper, we have developed a novel power-generating device based on membranes made of boron nitride (BN) nanosheets. The hydrated BN membrane contains intra-layer spacing between individual BN nanosheets, which can form nanofluidic channels to accommodate water molecules and ions. This novel device with a membrane area of 5 mm² generates a large current of 12.1 nA in 0.1 M NaCl solution with a pressure gradient of 5 kPa, and reaching a maximum output power of 3.2 pW. Furthermore, multiple devices can be connected and operated simultaneously to increase the current output, which is promising for future clean energy harvesting devices.

Graphical abstract

Introduction

Electric eels can generate bioelectricity with voltage over 600 V through their cell membrane as a mean of self-defence [1], [2]. This phenomenon has inspired mimicry of clean energy harvesting through artificial systems, which includes power generation from electrokinetic devices [3]. In such a device, when ions move through nanoscale fluidic channels, an electric field is formed due to the surface charges of the channel walls and their interaction with ions. Ion transport in nanoscale channels differs significantly from that in the bulk solution [4], [5] and is greatly affected by the surface charge when the channel size is close to the Debye screening length [6], [7], [8], [9], [10]. In order to harvest mechanical energy and convert into electrokinetic energy through this mechanism, a great amount of efforts have been made on the fabrication of intricate nanofluidic channels. Method including conventional methods like lithography has been widely used to construct these devices [11], [12], [13]. While lithography can precisely control the diameter, shape and length of a one-dimensional nanofluidic channel, it requires costly equipment, complicated processing procedure, and has limited scalability i.e. the number of channel production is limited to only one or a few during each fabrication [11], [12]. Facile preparation of nanoscale channels by the self-assembly of two-dimensional (2D) layered materials emerges as a promising and effective alternative for this application [13], [14], [15], [16], [17].

Nanofluidic channels have been observed in membranes based on a number of 2D nanomaterials such as graphene oxide (GO) [9], [18], [19], [20], [21] and nano-clays [14], [22]. Compared to conventional nanofabrication methods such as lithography [8], [23] and soft templating [24], [25], the fabrication of nanofluidic channels from 2D nanomaterials dispersion provides advantages in terms low cost, simplicity in processing and scalability [14], [15], [16], [26], [27], [28], [29]. The highly charged surface and the water permeability of 2D capillaries between closely spaced nanosheets provide a large number of nanofluidic channels for ion transportation [30]. Boron nitride (BN) nanosheet is a 2D layered nanomaterial that consist of boron and nitrogen atoms in a hexagonal plane arrangement similar to carbon atoms in graphene, while having very different properties such as wide band gap, higher thermal and chemical stability. BN nanosheets are ideal candidate in many applications that require higher thermal and chemical stability, or insulating properties. BN membrane with highly ordered lamellar microstructure can be fabricated from BN colloidal dispersion [29] and contains highly charged surface [31]. Therefore BN membrane is a highly promising candidate for making electrokinetic device for harvesting clean energy.

In this paper, we report preparation of a novel power generation device based on ion transport through BN nanosheets conduits. The BN membrane provides a large number of nanofluidic channels, which can be utilized to convert hydraulic pressure into streaming ionic current. The current generated on the device reached 12.1 nA with a pressure difference of 5 kPa. In addition, alternating current response can be observed when an alternating pressure was applied, meaning that the device can work bi-directionally. Moreover, multiple devices can be connected to generate greater current. Because of its small footprint, it could possibly be integrated into other devices to harvest energy from mechanical forces and movements such as tide, door opening and closing, or even body movements.

Section snippets

Preparation of BN nanosheets and BN membranes

Colloidal dispersion of few-layer BN nanosheet was prepared as described in our previous report [29]. Briefly, h-BN (Momentive Performance Materials Inc.) and urea (Sigma-Aldrich) powders with a weight ratio of 1:20 and total weight of 10 g were milled for 20 h by using a planetary ball mill (Pulverisette 7, Fritsch) at a speed of 500 rpm at room temperature under nitrogen atmosphere. The BN/urea mixture was dispersed in 200 ml water and dialyzed (membrane cut-off: 14000 kDa) for around 1 week

Results and discussion

The BN membrane is fabricated by vacuum filtration of few-layer BN nanosheets colloidal dispersion, as shown in Fig. 1a–c [18], [33], [34], [35]. The few-layer BN (3–8 layers with average around 5 layers) was prepared by a one-step exfoliation and functionalization ball-milling method reported previously [29]. After filtration, the BN membrane on the membrane filter is white, highly glossy, as shown in Fig. 1c. A typical scanning electron microscopy (SEM) image of the cross-section view of the

Conclusion

In this paper, an electric generation device based on BN nanosheets membrane has been developed. The hydrated BN membrane contains intra-layer spacing between the individual BN nanosheets which can accommodate two or three layers of water molecules and form nanofluidic channels within the membrane. The BN membrane provides thousands of nanofluidic channels, which can convert hydraulic pressure into streaming ionic current. The current generated on the device is the highest among all the 2D

Acknowledgements

S. Qin and D. Liu contributed equally to this work. This work was financially supported by the Australian Research Council Discovery Early Career Researcher Award scheme (DE150101617 and DE140100716), Australian Research Council Discovery Project scheme (DP150102346), Deakin University Postgraduate Research Scholarship (DUPR) and Deakin University Central Research Grant Scheme. This research was undertaken on the SAXS/WAXS beamline (Beam time ID: M10395) at the Australian Synchrotron. We thank

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Citation Excerpt :
Although the power density of a single nanopore was high, it is hard to expand for large–area preparation with low cost [21]. The ion-selective lamellar membrane constructed with two-dimension (2D) nanosheets was more suitable for large scale application, owned to the advantages of simplicity and strong expansibility [22–26]. Uniform and continuous nanofluidic channels could be easily formed by superposing of 2D nanosheets [27,28].
Ion-selective membrane based technologies, such as electrodialysis and reverse electrodialysis technology, show great potential in addressing challenge of the water-energy nexus. However, the ion-selective membrane usually suffers from the trade-off between ionic selectivity and ion transport capacity. Here, we prove that mesoporous structure in lamellar ion-selective membrane can increase the transmembrane ionic transport with no loss of ionic selectivity. The mesoporous structure is constructed via adjusting the pH of graphene oxide/ionic polymer solution and self-assembly of flocculating solution. Negatively or positively charged graphene oxide based membrane with a thickness of 4 μm was used in a three-compartment electrochemical cell for osmosis energy conversion and desalination. An output power density of 5.87 W m⁻² is achieved by mixing artificial seawater (0.5 M NaCl) and river water (0.01 M NaCl). The conductivity of seawater can quickly decrease from 12.3 mS cm⁻¹ to 36 μS cm⁻¹ in typical electrodialysis process, showing the excellent desalination ability. This work proves a new strategy of enhancing transmembrane ionic transport in ion-selective membrane and provides new opportunities for 2D nanomaterials.

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¹: These authors contributed equally to this work.

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Full paperNanofluidic electric generators constructed from boron nitride nanosheet membranes

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Preparation of BN nanosheets and BN membranes

Results and discussion

Conclusion

Acknowledgements

Sep. Purif. Technol.

J. Cell. Comp. Physiol.

Nat. Nanotechnol.

J. Appl. Mech.

Phys. Fluids

Microfluid. Nanofluid.

Nat. Nanotechnol.

Nano Lett.

Phys. Rev. Lett.

J. Am. Chem. Soc.

Appl. Phys. Lett.

Nano Lett.

Nano Lett.

Adv. Mater.

Adv. Mater.

Adv. Funct. Mater.

Nat. Commun.

ACS Energy Lett.

Science

J. Am. Chem. Soc.

Full paper
Nanofluidic electric generators constructed from boron nitride nanosheet membranes