Separately from direct dimethyl ether (DME) fuel cells (DDFC), in DME-fueled solid oxide fuel cell (SOFC) and DME reforming hydrogen for fuel cell and other research, introduced the DME in the fuel cell in the application status.

    Dimethyl ether (DME); fuel cells; catalyst; Reforming

    Dimethyl ether (DME) is a simple ethers material, physical nature and propane, butane and other liquefied petroleum gases is similar to normal temperature and ibm thinkpad t21 laptop battery is a kind of mild flavor ether colorless gas. DME under normal pressure of the boiling point of -24 · 9 ℃, easily compressed into a liquid at room temperature (0.6 MPa), storage and transportation convenient. The toxicity of DME is very low, not on the air and groundwater pollution; sources of wealth can be obtained from coal, oil, gas and biological variety of sources [1].

    At present, DME application in fuel cells has become a research hotspot. The author reviewed the direct DME fuel cell (DDFC), in DME-fueled solid oxide fuel cell (SOFC) and DME reforming hydrogen for fuel cells, etc. are reviewed.

    A direct dimethyl ether fuel cell (DDFC)

    DDFC through the DME and oxygen electro-catalytic reaction occurs directly emit energy. J · T · Müller et al [2] with the same battery modules to DME and methanol as fuels for comparison and found that the performance is better than DDFC direct methanol fuel cell (DMFC), particularly in the current density is lower. DDFC similar to the proton exchange membrane fuel cell (PEMFC) and DMFC, also use conductive polymer electrolyte membrane, the working temperature below 120 ℃, belonging to low-temperature fuel cells. DDFC theoretical electromotive force of 1.20 V, and DMFC (1.21 V) very; DME large molecules than methanol, and the molecular polarity is small, so DME in the proton exchange membrane penetration of an order of magnitude smaller than methanol, and the a small amount of penetration into the cathode catalyst on the DME adsorption on Pt is weak, not compete with oxygen, and therefore will not be oxidized in the cathode to prevent the cathode potential loss as well as the cathode catalyst poisoning, is expected to improve battery efficiency and longevity. Using the same battery module, only the fuel change, DDFC the open circuit voltage higher than the DMFC, that the penetration of DME is small, a small loss of cathodic polarization; DDFC Faraday efficient than DMFC, especially in the low current density; current density low at 100 mA/cm2, when, DDFC the battery voltage is higher than the DMFC, so DDFC suitable for portable power. M · M · Mench et al [3] studied the portable DDFC, that the CO adsorption on the anode catalyst is the key obstacle to DDFC technology, so the catalyst selection and design of DDFC particularly important.

    Y · Tsutsumi et al [4] the use of ordinary hydrogen PEMFC module to DME as a fuel, studied DDFC performance. In the same electrolyte membranes, DME than methanol and through an order of magnitude smaller; DME intermediate product after the oxidation of formic acid is generated, but no methanol and formaldehyde, they accordingly infer that the electro-oxidation mechanism of DME.

    Y · Liu et al [5] compared the Pt / C and Pt-Ru / C on the catalytic activity of DME. In the 50 ~ 70 ℃, when the electrode potential at 0.55 V (vs · RHE) above, Pt / C showed higher activity; when the electrode potential at 0.55 V (vs · RHE) below, Pt - Ru / C activity and better. This result is similar to the situation in the DMFC, but with the literature [4] different. They also studied several other binary alloy catalysts for DME electro-oxidation of the catalytic activity and found that Mo, Sn can significantly increase adherence to Pt / C catalytic activity, while the W, Ni, Cr and Co can not. J · H · Yu et al [6] studied the DDFC at 80 ℃ performance. As a result of lower temperature, liquid water, DME as a gas, designed a white jumbled form of flow field plate, in order to promote gas DME dissolved in water. Contrast was found, Pt-Ru catalyst in the DDFC in better capacity than Pd. DME on Pt catalyst on the electrochemical reaction activity than hydrogen, methanol, etc., especially at low temperature. They will mix of DME and methanol, the fuel supply to the fuel cell pressure of 0.45 MPa in the case, will be DME dissolved in 2 mol / L of methanol, the measured concentration of DME in mixed solution of 31%. 80 ℃, by comparing the DME solution, DME and methanol mixed solution, methanol solution as fuel cell performance when they come to DME and methanol mixed solution as a fuel, the battery the best performance (85 mW/cm2), mixed solution of DME the contribution of the battery performance is about 24%; mixed fuel can improve fuel cell performance at low temperature work. G · Kéranguéven, etc. [7] In the study of a large number of Pt electrodes on the electrochemical oxidation of DME and found that the oxidation of DME adsorption is the controlling step in the process. They use infrared reflectance spectroscopy analysis of DME adsorption at different potentials, oxidation of the intermediates and products, that the DME in addition to Pt catalyst was directly oxidized to CO2, or COOH, and partly be adsorbed on Pt, the formation of Pt -CHO or Pt-CO, when Pt was activated with water, adsorbed on Pt and Pt-CHO on the Pt-CO synergy is a result of oxidation of COOH, or CO2. Zhao et al [8] was studied by cyclic voltammetry at Pt electrode DME electro-oxidation and adsorption behavior was found at very low potentials DME began to dissociative adsorption, but the speed is very slow. L · L · Lu et al [9] studied the DME on the electrochemical behavior of Pt single crystal was found in 0.5 mol / L H2SO4 in, DME in the low potential [0.2 ~ 0.5 V (vs · RHE )], under adsorbed on Pt (111) crystal surface and decompose to produce intermediate CO, 0.8 V, when, DME oxidized generated CO2. Kedie Cai et al [10] studied the anode catalyst and electrolyte membrane on the performance of DDFC for the characteristics of DME, optimization and improvement of the membrane electrode [11], in the membrane electrode anode diffusion layer different regions of the hydrophilic and hydrophobic treatment reduces the mass transfer resistance, extending the life of the membrane electrode.

    2 to DME as fuel for SOFC

    DME is a potential alternative fuel for SOFC. DME easy compared with the hydrogen to liquefy the gas at atmospheric pressure, the actual operation, ease of storage and applications. In the SOFC working temperature, DME's response to high activity can be directly used as fuel without reforming unit, the reaction time of less NOx and carbon emissions. S · G · Masters et al [12] studied the NO carrier in the Al2O3 catalyst on the selective reduction and found that DME as reducing agent, in the 400 ~ 450 ℃ under the oxidation rate of up to 100%; γ-Al2O3, 5% MoO3 / Al2O3, 14% MoO3/Al2O3 and 6% V2O5/Al2O3 the oxidation of DME has a higher catalytic activity. Al2O3 catalyst carrier can be used as a catalyst for the use of DME in SOFC. S · Z · Wang et al [13-14] reported that in order to LaGaO3 as the electrolyte, in order to DME fueled SOFC performance. Battery at 800 ℃ when the power density of up to 0.8 W/cm2, performance and hydrogen fuels are similar, but with the temperature lowered to DME as fuel for SOFC performance was significantly lower than hydrogen-fueled SOFC. Composite anode in the Fe content HP PAVILION ZT3000 Laptop Battery, the promotion of sintering the electrodes, but also changed the electrode / electrolyte interface microstructure. Electrode electrochemical oxidation catalytic activity of DME depends on the Ni, Fe ratio, n (Ni): n (Fe) = 8:2 of the electrode, the electrochemical activity of the highest. They also found that the load on the Al2O3 and La-GaO3 series of vector a variety of metal, the partial oxidation of DME has a high catalytic activity, the reaction products strongly depends on the active metal and the carrier. Al2O3 catalyst load in the main products were CO, H2, CH4, HCHO, CO2 and H2O; in La0 · 8Sr0 · 2Ga0 · 8Mg0 · 15Co0 · 05O3 load were no HCHO generated a catalyst. They also inspected the load on the LaGaO3-based electrolyte on the Ni electrode and Ni-Sr-doped CeO2 composite electrode catalytic DME oxidation characteristics. -Doped Co, after the LaGaO3 based electrolyte, DME markedly enhanced the performance of complete oxidation, significantly inhibited the occurrence of coke. L · Yu et al [15] studied the DME in the SnO2/MgO and SnO2/CaO on the oxidation characteristics. In the 275 ~ 300 ℃, these two catalysts have a catalytic effect on the oxidation of DME, in which SnO2/CaO higher activity. Two kinds of catalytic activity at 300 ℃ the best, DME in the SnO2/CaO on the conversion rate of 21.8% for the 18.2% in the SnO2/MgO; continue to rise the temperature, two kinds of catalytic activity are declined.

    At present, for the use of DME in SOFC research has just started, related research focused on aspects of the catalyst.

    3 DME reforming hydrogen

    DME and methanol is similar to high energy density, easy storage and transport; advantage is the relatively inert, non-corrosive, non-carcinogenic and low cost can be well positioned to meet the requirements of PEMFC hydrogen sources. The steam reforming of DME is expected to replace steam reforming of methanol for fuel cells. DME steam reforming of the research has focused on catalysts, and in order to Ni system, Cu lines and precious metals major as [16-20], as compared with the methanol reforming, research is still in the initial stage. V · V · Galvita, etc. [16] will load in the γ-Al2O3 carrier on a 12 - silicon tungsten heteropoly acid and Cu/SiO2 mixed, as the DME steam reforming catalyst, DME conversion rate was 100%, the concentration of hydrogen-rich gas exports was 71% (volume ratio). In the 400 ~ 600 ℃, when, DME containing Ni catalyst carrier obtained under the partial oxidation of hydrogen. Is generally believed that, DME oxidation of at least two ways: ① DME decomposition, followed by decomposition of the intermediate is oxidized; ② O2 direct oxidation. S · Z · Wang et al [13] investigated different metal catalysts and the load on different carriers on the Ni catalyst for DME partial oxidation reactions, and found that DME has a high oxidation activity can be generated when the CO below 327 ℃ and H2. In the γ-Al2O3 vector product of CO, H2, CH4, HCHO, CO2 and H2O; on other carriers do not HCHO generation. Γ-Al2O3 in the carrier, the catalytic activity of the order: Ni> Rh> Co Ru> Fe> Pt Ag. DME partial oxidation catalyst Ni/LaGaO3 right to be different kinds of gas components with high activity and selectivity, in the 200 ~ 400 ℃, it can use DME steam reforming method of hydrogen production, using acidic mixture of oxides as carrier catalysts (Cu, Zn, Pd or Pt, etc.) can be catalytic steam reforming of DME. γ-Al2O3 is more suitable for methanol, DME hydration generated when the carrier; copper-based catalyst for steam reforming of methanol to obtain H2 + CO. In the Cu/γ-Al2O3 adding Pd as an additive can improve the catalytic activity and the H2 yield, the reaction temperature dropped to 250 ℃ and maintain a high conversion rate, but higher concentrations of CO; adding Zn as an aid agent, results slightly inferior to Pd, but the availability of high-yield and reduce the CO content of H2. In the Production of Hydrogen from Steam Reforming of DME, the reaction can be considered in two steps: ① DME hydrate formation of methanol; ② methanol into hydrogen. Cu/γ-Al2O3 be a more suitable catalyst, Pd as an additive to enhance activity, while Zn as an additive to reduce CO, the reaction temperature may choose at about 300 ℃, reaction time to inhibit CH4 production.

Plasma hydrogen technology [21-22] can be carried out at room temperature, with start-up and fast response, simple equipment, etc., the technology is also used to study the DME reforming hydrogen production. In the plasma discharge steam reforming process, the water vapor can eliminate carbon deposition and improve system stability. Appropriate amount of water vapor help to improve the conversion rate of DME and hydrogen selectivity, and reduce the energy consumption of hydrogen. Excessive water vapor flow rate will reduce the conversion rate of DME. DME partial oxidation in the hydrogen plasma discharge process, which leads to an appropriate amount of oxygen, but also can improve the conversion rate of DME to remove coke, while reducing power consumption.

    4 Conclusion

    DME's energy density, physical and chemical properties of a good, environmentally friendly, as the ideal fuel for fuel cells. It can be used DDFC, as a low temperature, portable power supply, but also at a relatively high temperature for the SOFC power generation unit as a fixed, but also as a convenient storage and transport of fuel through the reformer to provide hydrogen for the PEMFC . Current DME in the fuel cell research has just started to develop high-performance catalyst for carrying out catalytic reaction mechanism of DME and reaction kinetics studies, can promote the application of DME in the IBM THINKPAD R30 Laptop Battery.