This article provides an up-to-date perspective on the use of anion-exchange membranes in fuel cells, electrolysers, redox flow batteries, reverse electrodialysis cells, and bioelectrochemical systems (e.g. microbial fuel cells). The aim is to highlight key concepts, misconceptions, the current state-of-the-art, technological and scientific limitations, and the future challenges (research priorities) related to the use of anion-exchange membranes in these energy technologies. All the references that the authors deemed relevant, and were available on the web by the manuscript submission date (30th April 2014), are included.

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Anion-exchange membranes in electrochemical energy systems

Microbial fuel cells: From fundamentals to applications. A review

Emerging desalination technologies for water treatment: a critical review.

A comprehensive review of microbial electrochemical systems as a platform technology.

Unlike flat sheets, crumpled paper balls have both high free volume and high compressive strength, and can tightly pack without significantly reducing the area of accessible surface. Such properties would be highly desirable for sheet-like materials such as graphene, since they tend to aggregate in solution and restack in the solid state, making their properties highly dependent on the material processing history. Here we report the synthesis of crumpled graphene balls by capillary compression in rapidly evaporating aerosol droplets. The crumpled particles are stabilized by locally folded, π–π stacked ridges as a result of plastic deformation, and do not unfold or collapse during common processing steps. In addition, they are remarkably aggregation-resistant in either solution or solid state, and remain largely intact and redispersible after chemical treatments, wet processing, annealing, and even pelletizing at high pressure. For example, upon compression at 55 MPa, the regular flat graphene sheets turn ...

Compression and aggregation-resistant particles of crumpled soft sheets.

Efficient salt removal in a continuously operated upflow microbial desalination cell with an air cathode

Bioelectrochemical desalination is potentially advantageous because of bioenergy production and integrated wastewater treatment and desalination. In this work, the performance and energy benefits of a liter-scale upflow microbial desalination cell (UMDC) were evaluated. The UMDC desalinated both salt solution (NaCl) and artificial seawater, and the removal rate of total dissolved solid (TDS) increased with an increased hydraulic retention time, although TDS reduction in artificial seawater was lower than that in salt solution. Our analysis suggested that electricity generation was a predominant factor in removing TDS (more than 70%), and that other factors, like water osmosis and unknown processes, also contributed to TDS reduction. It was more favorable given the high energy efficiency, when treating salt solution, to operate the UMDC under the condition of high power output compared with that of high current generation because of the amount of energy production; while high current generation was more desired with seawater desalination because of lower salinity in the effluent. Under the condition of the high power output and the assumption of the UMDC as a predesalination in connection with a reversal osmosis (RO) system, the UMDC could produce electrical energy that might potentially account for 58.1% (salt solution) and 16.5% (artificial seawater) of the energy required by the downstream RO system. Our results demonstrated the great potential of bioelectrochemical desalination.

Use of a liter-scale microbial desalination cell as a platform to study bioelectrochemical desalination with salt solution or artificial seawater.

Microbial fuel cells (MFCs) are an attractive technology for simultaneous bioenergy recovery and organic removal; however, the lack of studies conducted with large-scale MFCs, especially those larger than 1 L, obstructs further development of this technology. In this paper, we built and operated a 4.9 L upflow microbial fuel cell (UMFC) with a liquid volume of 2.4 L. Its electricity generation and organic removal performance were examined under different operating conditions. The UMFC produced an open-circuit potential of 1.00 V with an acidified catholyte. Changing the recirculation of the anolyte did not significantly affect the power output in a short period, but a long-term test demonstrated improved electricity production at higher recirculation rates. The water produced via oxygen reduction or diffused from the anode was not sufficient for the cathode reaction; thus, an external supply of water is necessary. Lowering the pH of the catholyte benefited the cathode reaction and increased power production; however, pH is not the only factor affecting the cathode reaction and if organic matters were contained in the catholyte, for instance using the anode effluent as a catholyte, electricity generation decreased. The results and experiences gained from this study will help to further develop pilot-scale MFCs for practical applications.

Effects of anolyte recirculation rates and catholytes on electricity generation in a litre-scale upflow microbial fuel cell

Energy recovery and consumption in a microbial fuel cell (MFC) can be significantly affected by the operating conditions. This study investigated the effects of electrolyte recirculation and operation mode (continuous vs sequence batch reactor) on the energy balance in a tubular MFC. It was found that decreasing the anolyte recirculation also decreased the energy recovery. Because of the open environment of the cathode electrode, the catholyte recirculation consumed 10 to 50 times more energy than the anolyte recirculation, and resulted in negative energy balances despite the reduction of the anolyte recirculation. Reducing the catholyte recirculation to 20% led to a positive energy balance of 0.0288 kWh m(-3). The MFC operated as a sequence batch reactor generated less energy and had a lower energy balance than the one with continuous operation. Those results encourage the further development of MFC technology to achieve neutral or even positive energy output.

Kyle S. Jacobson

Papers

Efficient salt removal in a continuously operated upflow microbial desalination cell with an air cathode

Use of a liter-scale microbial desalination cell as a platform to study bioelectrochemical desalination with salt solution or artificial seawater.

Effects of anolyte recirculation rates and catholytes on electricity generation in a litre-scale upflow microbial fuel cell

Energy Balance Affected by Electrolyte Recirculation and Operating Modes in Microbial Fuel Cells