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

Dye-sensitized solar cells (DSCs) have gained widespread interest because of their potential for low-cost solar energy conversion. Currently, the certified record efficiency of these solar cells is 11.1%, and measurements of their durability and stability suggest lifetimes exceeding 10 years under operational conditions. The DSC is a photoelectrochemical system: a monolayer of sensitizing dye is adsorbed onto a mesoporous TiO2 electrode, and the electrode is sandwiched together with a counter electrode. An electrolyte containing a redox couple fills the gap between the electrodes. The redox couple is a key component of the DSC. The reduced part of the couple regenerates the photo-oxidized dye. The formed oxidized species diffuses to the counter electrode, where it is reduced. The photovoltage of the device depends on the redox couple because it sets the electrochemical potential at the counter electrode. The redox couple also affects the electrochemical potential of the TiO2 electrode through the recombin...

Characteristics of the Iodide/Triiodide Redox Mediator in Dye-Sensitized Solar Cells

The same equation was derived from two different impedance models based on the quite different physical descriptions proposed by Kern et al.(1) and by Bisquert.(2,3) Reliable values of the parameters relating to electron transport in dye-sensitized solar cells can be determined from measured spectra by electrochemical impedance spectroscopy when careful analysis of the measured spectra is done based on the classification and clarification of the same impedance equation consequent from the two models. The requisites for making highly efficient dye-sensitized solar cells were proposed.

Determination of parameters of electron transport in dye-sensitized solar cells using electrochemical impedance spectroscopy.

Synthesis and catalytic properties of metal nanoparticles: Size, shape, support, composition, and oxidation state effects

Catalysts for direct ethanol fuel cells

The present investigation is based on a study of electro-oxidation of ethanol in alkaline medium over the carbon supported PdxNiy catalyst formulations synthesized by simultaneous reduction of the precursors using sodium borohydride as the reducing agent. X-ray diffraction studies of the PdNi/C nano-particles reveal formation of the face-centered cubic crystalline Pd, NiO and Ni(OH)2 on a meso porous carbon support whereas XPS confirmed the presence of metallic Ni and the oxide phases NiO, Ni(OH)2, NiOOH in the catalyst matrix. The structure and morphology of the binary matrix and the role of Ni and its oxide as a catalytically contributing entity in the oxidation process was ascertained by the help of respective analytical techniques like transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), voltammetry and chronoamperometry. Sequential oxidation steps were suggested involving dimeric (NiO)2 as one of the intermediate species during the oxidation reaction proceeding towards aldehyde formation and further to carbonate production via the intermediate formation of a six member ring, thereby increasing the reaction rates. This phenomenon has been discussed at molecular level using the results obtained from XPS analysis. The observations were further accomplished by extending the work to ion chromatography for quantitative analysis of the products formed during oxidation of ethanol. All the above results are congruent with the mechanistic interpretation and reflect the paramount significance of NiO existing in the binary catalyst matrix for accelerating ethanol oxidation reaction kinetics at a temperature 40 °C and above.

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Energy efficient role of Ni/NiO in PdNi nano catalyst used in alkaline DEFC

A comparative study on ethanol oxidation behavior at Pt and PtRh electrodeposits

Electrochemical investigations have been carried out to study the oxidation kinetics of ethanol in alkaline solution on carbon-supported ternary alloy catalysts Pt–Pd–Au within the temperature range of 20–80 °C. To derive a better understanding of the contribution of each of the metallic components toward the catalytic oxidation of ethanol, some of the investigations were extended to the individual noble metals for comparison, however, at a single temperature (20 °C). The individual metals could barely show their catalytic efficiency toward ethanol oxidations when compared to the alloyed catalyst. The ternary catalyst exhibited much lower values and a larger temperature dependence of onset potential for ethanol oxidation. With the rise of potential, the apparent activation energy (Ea(app)) for ethanol oxidation on the Pt/C electrode increased, whereas a decreasing trend was observed with the Pt30Pd38Au32/C electrode. It was suggested that the Pt30Pd38Au32/C electrode bears an excellent tolerance toward et...

The Beneficial Role of the Cometals Pd and Au in the Carbon-Supported PtPdAu Catalyst Toward Promoting Ethanol Oxidation Kinetics in Alkaline Fuel Cells: Temperature Effect and Reaction Mechanism

The Pt-Pd/C electrocatalyst was synthesized on graphite substrate by the electrochemical codeposition technique. The physicochemical characterization of the catalyst was done by SEM, XRD, and EDX. The electrochemical characterization of the Pt-Pd/C catalyst for methanol electro-oxidation was studied over a range of NaOH and methanol concentrations using cyclic voltammetry, quasisteady-state polarization, chronoamperometry, and electrochemical impedance spectroscopy. The activity of methanol oxidation increased with pH due to better OH species coverage on the electrode surface. At methanol concentration (>1.0 M), there is no change in the oxidation peak current density because of excess methanol at the electrode surface and/or depletion of OH− at the electrode surface. The Pt-Pd/C catalyst shows good stability and the low value of Tafel slope and charge transfer resistance. The enhanced electrocatalytic activity of the electrodes is ascribed to the synergistic effect of higher electrochemical surface area, preferred OH− adsorption, and ad-atom contribution on the alloyed surface.

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Jayati Datta

Papers

Energy efficient role of Ni/NiO in PdNi nano catalyst used in alkaline DEFC

A comparative study on ethanol oxidation behavior at Pt and PtRh electrodeposits

The Beneficial Role of the Cometals Pd and Au in the Carbon-Supported PtPdAu Catalyst Toward Promoting Ethanol Oxidation Kinetics in Alkaline Fuel Cells: Temperature Effect and Reaction Mechanism

Characterization of Pt-Pd/C Electrocatalyst for Methanol Oxidation in Alkaline Medium

High performance PtPdAu nano-catalyst for ethanol oxidation in alkaline media for fuel cell applications