Anion-exchange Membrane Direct Ethanol Research Articles

A novel electrocatalyst based on Fe-ZIF-PPY nanocomposite for oxygen reduction reaction in air-breathing direct-ethanol fuel cell

The development of alcohol tolerance electrocatalysts to reduce expensive electrocatalysts has been the prospect of widespread use of alcoholic fuel cells. Therefore, the production of favorable electrocatalysts with the optimized percentage of metals and heteroatoms, enables control of electrocatalytic properties to enhance activity in the alkaline medium. In this work, Fe-ZIF-polypyrrole composite (Fe-ZIF-PPY) was carbonized under argon atmosphere, and finally, S,N-codoped carbon nanotubes containing iron nanoparticles nanocomposite (Fe-NC/S,N-CNT) was obtained. The electrocatalytic property, structure, and morphology of Fe-NC/S,N-CNT were explored via various characterization techniques (Fe-SEM, TEM, HRTEM, TGA, Raman, XRD, BET, XPS, ICP, element mapping and EDAX). Applicability of the S-doped Fe-N-C catalyst in alkaline media shows high ORR activity with sharp half-wave potential at 0.93 V (vs. RHE) and the Tafel slope of 53 mV/dec. Also, in an anion-exchange membrane direct ethanol fuel cell (AEM-DEFC) under the same conditions, two cathodes are made with the optimized electrocatalyst as MEA-1 and commercial 10 wt% Pt/C as MEA-2. The power density of 20 and 9 mW cm−2 were obtained at 0.6 V in an air-breathing, respectively. The performance of Fe-NC/S,N-CNT catalyst was assessed optimum in DEFC. In examining the effective factors to boost the activity of the catalyst, the prominent roles of specific surface area (SSA), porosity, conductivity, and high density of active sites can be note.

Comprehensive Analysis on the Highly Active and Stable PdAu/C Electrocatalyst for Ethanol Oxidation Reaction in Alkaline Media

Both the catalytic activity and stability of palladium toward the ethanol oxidation reaction (EOR) in alkaline media are urgently required to be enhanced for the practical application of anion exchange membrane direct ethanol fuel cells (AEM DEFCs). The considerable improvement in the stability induced by the Au element has been well demonstrated; however, the catalytic activity from combining Pd with Au remains unsatisfied. Here, we successfully synthesize a series of PdxAuy/C electrocatalysts with different Pd/Au atomic ratios by a coreduction method, and in contrast to normal acknowledgments, the optimal PdAu/C sample not only possesses good stability but also has strikingly improved activity toward the EOR in alkaline media. Results show that the peak current density and degradation percentage for PdAu/C are, respectively, 84.16 mA/cm2 and 12% and 59.73 mA/cm2 and 67% for the pure Pd/C sample. It is anticipated that the striking activity toward the EOR can be attributed to an antipoisoning effect elec...

A passive anion-exchange membrane direct ethanol fuel cell stack and its applications

We report a passive anion-exchange membrane direct ethanol fuel cell (AEM DEFC) stack that consists of two back-to-back independent-tank single cells. This particular design not only enables a reduction in the weight and volume of the stack, but also avoids the cross reaction of the liquid alkali occurring between two single cells. Experimental results indicate that the passive dual-cell stack that uses a non-Pt anode catalyst and a non-precious metal cathode catalyst yields a peak power density of as high as 38 mW cm−2 at room temperature, a figure which is about 22 times higher than that of the conventional proton-exchange membrane DEFC stack. The improved performance is ascribed to: i) the accelerated electrochemical kinetics for the both anode and cathode reactions, and ii) the use of the ethanol-tolerant cathode catalyst that eliminates the cathode mixed overpotential. Finally, a power pack consisting of two series-connected stacks is applied to power a toy car, which is demonstrated to continuously run for one hour at a high constant speed of 0.52 m s−1 with on each fueling of a fuel tank with a volume of 4.5 mL.

Monolithic Carbon Foam-Supported Pd-Ni Catalysts for Ethanol Electro-Oxidation in Alkaline Media

Anion-exchange membrane direct ethanol fuel cells are attractive owing to the fact that: i) the alkaline media speeds up the electro-kinetics of both the ethanol oxidation reaction (EOR) and oxygen reduction reaction (ORR), ii) low-cost Pd catalyst presents better catalytic activity for the EOR than Pt in alkaline environment, and iii) the ethanol possesses the advantages of high-specific energy and producing from cellulosic biomass. Carbon foam promises to be a better monolithic catalyst support due to its three-dimensional honeycomb-type open cell structure, resulting in the high porosity and the large specific surface area [1]. In this work, the carbon foam-supported PdNi nanocatalysts (PdNi/CF) were synthesized by the layer-reduction method using NaBH4 as a reductant [2], and characterized by different physicochemical methods. The experimental results indicated that the PdNi nanocatalysts were evenly dispersed on the surface of the skeleton of the carbon foam, facilitating the mass and charge transfer. The electrocatalytic activity of PdNi/CF was optimized by testing different Pd/Ni atomic ratios. It has been demonstrated that the electrocatalytic activity of PdNi/CF was higher than that of Pd/CF, suggesting promising application in alkaline direct ethanol fuel cells.

A liquid-electrolyte-free anion-exchange membrane direct formate-peroxide fuel cell

Conventionally, two critical issues that limit the steady-state discharge of alkaline liquid fuel cells are the pH-dependant problem at anode and the carbonation problem at cathode. The present work addresses these two issues by reporting an anion-exchange membrane direct liquid fuel cell that uses a pH-insensitive fuel, formate, as the reductant, and a CO2-free reactant, hydrogen peroxide, as the oxidant, referred to as anion-exchange membrane direct formate-peroxide fuel cell (AEM DFPFC). Theoretically, the cell voltage of the AEM DFPFC can be as high as 1.92 V. It has been experimentally demonstrated that a conceptual half-hour constant-current discharge of the AEM DFPFC almost remains unchanged, even eliminating the supporting electrolytes at both anode and cathode. In contrast, an anion-exchange membrane direct ethanol fuel cell (AEM DEFC) shows a sharp decline in constant discharge within a few seconds.

Layer reduction method for fabricating Pd-coated Ni foams as high-performance ethanol electrode for anion-exchange membrane fuel cells

An ideal electrode architecture that boosts the performance of anion-exchange membrane direct liquid fuel cells needs the electrode design to meet all the requirements of electrochemical kinetics and mass and charge transport characteristics. In this regard, here we propose a facile, well-controlled, and binder-free layer reduction method for preparing a three-dimensional foam electrode, which enables the catalytic particles to be directly reduced on the surface of the metal foam. This innovative layer reduction method not only avoids the formation of large catalytic aggregation, but also promises a thin and porous catalyst film that presents a sponge-like morphology uniformly coated onto the skeleton, thus both improving the electrochemical kinetics and enhancing the mass and charge transport of species. The results demonstrate that the application of the layer-reduced Pd/Ni foam electrode in an anion-exchange membrane direct ethanol fuel cell enables a peak power density and the maximum current density as high as 164 mW cm−2 and 1.34 A cm−2 at 60 °C, respectively, which are 1.03 and 1.16 times higher than those of the conventional design.

Performance of PdRu/C Anode Catalyst for Anion-Exchange Membrane Direct Ethanol Fuel Cell

Carbon supported PdRu catalysts with various Pd:Ru atomic ratios were studied by using X-ray diffraction (XRD), transmission electron microscopy (TEM), electrochemical half-cell tests, and the anion-exchange membrane direct ethanol fuel cell (AEM-DEFC) tests. Lower onset potential and peak potential and much higher steady state current for ethanol oxidation in alkaline media were observed on the bimetallic catalysts (PdxRuy/C) than on the Pd/C, while the activity for ethanol oxidation on the pure Ru/C was not noticeable. By using Pd/C anode catalysts and MnO2 cathode catalysts, AEM-DEFCs free from the expensive Pt catalyst were assembled. The AEM DEFC using the bimetallic Pd3Ru/C anode catalyst showed a peak power density as high as 176 mW cm-2 at 80 °C, about 1.8 times higher than that using the single metal Pd/C catalyst.

Performance characteristics of air-breathing anion-exchange membrane direct ethanol fuel cells

An air-breathing direct ethanol fuel cell (DEFC) with an anion-exchange membrane (AEM) and Pt-free electrodes is designed and investigated. Particular attention is paid to studying the performance characteristics of the air-breathing AEM DEFC. Experimental results reveal that this air-breathing AEM DEFC yields a peak power density as high as 38 mW cm−2 at room temperature, which is comparable to the conventional Pt-based proton exchange membrane direct methanol fuel cells (PEM DMFCs). The overshoot/undershoot behaviors of both the cell voltage and cell temperature are avoided in the air-breathing AEM DEFC due to the use of ethanol-tolerant cathode catalyst. It is also found that the cathode water flooding behavior occurs in this air-breathing AEM DEFC, thus lowering the cell performance.

PdRu/C catalysts for ethanol oxidation in anion-exchange membrane direct ethanol fuel cells

Carbon supported PdRu catalysts with various Pd:Ru atomic ratios were synthesized by impregnation method, and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), electrochemical half-cell tests, and the anion-exchange membrane direct ethanol fuel cell (AEM-DEFC) tests. XRD results suggest that the PdRu metal exists on carbon support in an alloy form. TEM study shows that the bimetallic PdRu/C catalysts have slightly smaller average particle size than the single metal Pd/C catalyst. Lower onset potential and peak potential and much higher steady state current for ethanol oxidation in alkaline media were observed on the bimetallic catalysts (PdxRuy/C) than on the Pd/C, while the activity for ethanol oxidation on the pure Ru/C was not noticeable. By using Pd/C anode catalysts and MnO2 cathode catalysts, AEM-DEFCs free from the expensive Pt catalyst were assembled. The AEM DEFC using the bimetallic Pd3Ru/C anode catalyst showed a peak power density as high as 176 mW cm−2 at 80 °C, about 1.8 times higher than that using the single metal Pd/C catalyst. The role of Ru for enhancing the EOR activity of Pd/C catalysts is discussed.

PEMFCs and AEMFCs directly fed with ethanol: a current status comparative review

The last decade’s research on the performance of proton-exchange membrane direct ethanol fuel cells (PEM-DEFCs) and anion exchange membrane direct ethanol fuel cells (AEM-DEFCs) is included in the present review. Future research challenges are identified along with potential strategies to overcome them. Pt-containing or Pt-free PEM-DEFCs that use acid proton-exchange membranes (typically Nafion type) exhibit relatively low performance (i.e., the state-of-the-art peak power density is 110 mW cm−2 at 145 °C over 4 mg of total Pt loading), while Pt-containing or Pt-free AEM-DEFCs that use low-cost anion-exchange membrane have recently exhibited better performance values (i.e., the state-of-the-art peak power density is about 185 mW cm−2 at 80 °C over Au-modified Pd catalysts supported on carbon nanotubes. The required faster kinetics of the ethanol oxidation and especially for the oxygen reduction reaction seem to be satisfied from one side by the AEM-DEFCs and from the other by PEM-DEFCs only if working at intermediate temperature values (>150 °C). Moreover, new possibilities of using less expensive metal catalysts (as silver, nickel, and palladium) are opening mainly for AEM-DEFCs and the last years for PEM-DEFCs too. Finally, it is worth to be noticed that the best value ever reported (peak power density is 360 mW cm−2 at 60 °C) has been obtained in a very promising alkaline-acid direct ethanol fuel cell (AA-DEFC).

Understanding the performance degradation of anion-exchange membrane direct ethanol fuel cells

It has recently been demonstrated that anion-exchange membrane direct ethanol fuel cells (AEM DEFCs) can yield a high power density. The operating stability and durability of this type of fuel cell is, however, a concern. In this work, we report the durability test of an AEM DEFC that is composed of a Pd/C anode, an A201 membrane, and a Fe-Co cathode and show that the major voltage loss occurs in the initial discharge stage, but the loss becomes smaller and more stable with the discharge time. It is also found that the irreversible degradation rate of the fuel cell is around 0.02 mV h−1, which is similar to the degradation rate of conventional acid direct methanol fuel cells (DMFCs). The experimental results also reveal that the performance loss of the AEM DEFC is mainly attributed to the anode degradation, while the performance of the cathode and the membrane remains relatively stable. The TEM results indicate that the particle size of the anode catalyst increases from 2.3 to 3.5 nm after the long-term discharge, which reduces the electrochemical active surface area and hence causes a decrease in the anode performance.

Product analysis of the ethanol oxidation reaction on palladium-based catalysts in an anion-exchange membrane fuel cell environment

We report a quantitative product analysis of the oxidation of ethanol in an anion-exchange membrane direct ethanol fuel cell (AEM DEFC) that consists of a Pd/C (or Pd 2Ni 3/C) anode, an AEM, and a Fe–Co cathode. The effects of the operating conditions including temperature, discharging current density, and fuel concentration, on the selectivity of each product of ethanol oxidation are investigated. It is found that incomplete ethanol oxidation to acetate prevails over complete oxidation to CO 2 in the range of testing conditions. Experimental results show that the change in the anode catalyst from Pd/C to Pd 2Ni 3/C leads to a significant increase in the cell performance, but does not help improve the CO 2 selectivity of ethanol oxidation. It is also shown that among the operating conditions tested, the operating temperature is the most significant parameter that affects the CO 2 selectivity: increasing the temperature from 60 to 100 °C enables the CO 2 current efficiency to increase from 6.0% to 30.6% with the Pd/C anode.

A high-performance integrated electrode for anion-exchange membrane direct ethanol fuel cells

We propose a new anode electrode structure that is composed of a nickel foam layer with thin catalyst films coated onto the skeleton of the foam. This innovative design of the anode electrode enables the integration of the catalyst and diffusion layers, thereby extending the electrochemical active surface area and facilitating the transport of species. The experimental results indicate that the use of the integrated electrode in an anion-exchange membrane direct ethanol fuel cell can significantly improve the cell performance as compared with the use of the conventional electrode that has separated catalyst and diffusion layers; a peak power density of 130 mW cm −2 and a maximum current density of 1060 mA cm −2 are achieved at 80 °C.

High performance of a carbon supported ternary PdIrNi catalyst for ethanol electro-oxidation in anion-exchange membrane direct ethanol fuel cells

In this paper, we report the synthesis of a carbon supported ternary PdIrNi catalyst for the ethanol oxidation reaction in anion-exchange membrane direct ethanol fuel cells (AEM DEFCs). We demonstrate that the use of the ternary PdIrNi catalyst at the anode of an AEM DEFC can increase the peak power density by more than 122% as compared with the use of the monometallic Pd catalyst, 69% as compared with the use of the bimetallic PdIr catalyst, and 44% as compared with the use of the bimetallic PdNi catalyst. Cyclic voltammetry and chronopotentiometry analyses prove that the ternary PdIrNi catalyst is catalytically much more active and more stable than the monometallic Pd catalyst and the bimetallic PdIr and PdNi catalysts.

Anion-exchange membrane direct ethanol fuel cells: Status and perspective

Direct ethanol fuel cells (DEFCs) are a promising carbon-neutral and sustainable power source for portable, mobile, and stationary applications. However, conventional DEFCs that use acid proton-exchange membranes (typically Nafion type) and platinum-based catalysts exhibit low performance (i.e., the state-of-the-art peak power density is 79.5 mW/cm2 at 90°C). Anionexchange membrane (AEM) DEFCs that use low-cost AEM and non-platinum catalysts have recently been demonstrated to yield a much better performance (i.e., the state-of-the-art peak power density is 160 mW/cm2 at 80°C). This paper provides a comprehensive review of past research on the development of AEM DEFCs, including the aspects of catalysts, AEMs, and single-cell design and performance. Current and future research challenges are identified along with potential strategies to overcome them.

Effect of cathode micro-porous layer on performance of anion-exchange membrane direct ethanol fuel cells

The effect of a cathode micro-porous layer that is composed of carbon powder or carbon nanotubes on cell performance is investigated. Polarization curves, together with the respective anode and cathode potentials, are measured. The results show that the cathode potential can be significantly improved with adding a hydrophobic micro-porous layer between the cathode catalyst layer and the gas-diffusion layer. The increased performance with the cathode micro-porous layer is mainly attributed to the fact that the cathode water flooding can be alleviated as a result of the reduced water crossover, which consequently facilitates the transport of oxygen to the catalyst layer. It is also found that a crack-free micro-porous layer made of carbon nanotubes gives a much higher cathode potential compared with a micro-porous layer composed of carbon powder.