Electrochemically reduced Pt oxide thin film as a highly active electrocatalyst for direct ethanol alkaline fuel cell

The Pt oxide thin film and Pt thin film were prepared by reactive sputtering and the electrocatalytic activity of the ethanol oxidation reaction was investigated in a KOH solution for developing the alkaline direct ethanol fuel cells. After electrochemical reduction by passing a cathodic electric charge, the Pt oxide thin film showed 29 times larger ethanol oxidation current than the Pt thin film. This superior activity was caused by an increase in the electrochemical active surface area and the existence of residual oxygen, which was confirmed by cyclic voltammetry and XPS measurement. Due to the contribution of the residual oxygen, the rate-determining step of the ethanol oxidation reaction might change, because the Tafel slope of the Pt oxide thin film during the ethanol oxidation reaction was changed by electrochemical reduction. Despite the total Pt amount in the Pt oxide thin film being smaller than that in the Pt thin film, the Pt oxide thin film showed excellent ethanol oxidation activity. Therefore, the Pt oxide treated by electrochemical reduction may be a promising anode catalyst for the direct ethanol fuel cells.     

直接乙醇燃料电池研究面临的挑战

从热力学、动力学及乙醇渗透等方面,综述了直接乙醇燃料电池(DEFC)研究面临的挑战.从热力学角度看,在低温(＜100℃)时,乙醇的最大热力学转化效率低于14%,降低了DEFC的效率;从动力学角度看,目前对乙醇氧化活性最高的Pt-Sn催化剂仍不能使乙醇完全氧化,降低了DEFC的法拉第效率;乙醇渗透可能带来的后果,加大了研究的困难性.     

Ni添加对直接乙醇燃料电池Pt基催化剂催化性能的影响

本文通过水热法制备出孔径分布范围3.1~4.2nm,比表面积为174.72m₂/g的CeO₂作为助催化剂,以碳纳米管为载体,采用微波辅助乙二醇法制备PtNiCeO₂/C催化剂,探究Ni添加对Pt基催化剂电催化性能的影响。利用X射线衍射仪(XRD)、比表面积及孔径分析仪(BET)、扫描电镜(SEM)和电子能谱(EDAX)对所制备的CeO₂及催化剂进行微观表征,利用电化学工作站对所制备的催化剂进行电化学性能测试。结果表明,添加CeO₂且催化剂中Pt与Ni的比例为5:1时,制备的催化剂电催化性能最优,其电化学活性表面积为90.41m₂/g,对乙醇催化氧化的峰电流密度值为837.67A/g,1100s的稳态电流密度值为178.33A/g,说明添加一定量的Ni,可提高催化剂的抗中毒能力和电催化性能。     

石墨烯载体上直接合成具有Pt(100)择优取向的催化剂及其电催化性能研究

以石墨烯为载体,乙二醇为还原剂,采用油浴法,通过加入不同添加剂作为形状导向剂合成了Pt(100)晶面择优取向的催化剂,并探讨了催化剂的性能。利用X射线衍射仪(XRD)、透射电镜(TEM)、感应耦合等离子原子发射光谱 (ICP-AES)及扫描电镜(SEM)对所合成的催化剂进行微观表征,利用电化学工作站对所合成的催化剂进行电化学性能测试。结果表明,添加KBr参与合成的Pt(100)晶面取向的催化剂,其微观粒子的立方体形貌最为规整,且形成最彻底。同时,其电催化性能最优,电化学活性表面积为42.43m2/g,对乙醇氧化的峰值电流密度为417.67A/g,1100s的稳态电流密度值为149.50A/g,对乙醇催化氧化反应的活化能最低,对乙醇氧化峰电流密度保持率为82.26%。     

Modified SPEEK membranes for direct ethanol fuel cell

Membranes with low ethanol crossover were prepared aiming their application for direct ethanol fuel cell (DEFC). They were based on (1) sulfonated poly(ether ether ketone) (SPEEK) coated with carbon molecular sieves (CMS) and (2) on SPEEK/PI homogeneous blends. The membranes were characterized concerning their water and ethanol solution uptake, water and ethanol permeability in pervaporation experiments and their performance in DEFC tests. The ethanol permeabilities for the CMS-coated (180 nm and 400 nm thick layers) SPEEK were 8.5 and 3.1 × 10⁻¹⁰ kg m s⁻¹ m⁻² and for the homogeneous SPEEK/PI blends membranes with 10, 20 and 30 wt.% of PI were 4.4, 1.0 and 0.4 × 10⁻¹⁰ kg m s⁻¹ m⁻² respectively, which is 2- to 50-fold lower than that for plain SPEEK (19 × 10⁻¹⁰ kg m s⁻¹ m⁻²). Particularly the SPEEK/PI membranes had substantially better performance than Nafion 117^® membranes in DEFC tests at 60 °C and 90 °C.     

In situ spectroscopy studies of ethanol oxidation reaction using a single fuel cell/ATR-FTIR setup

This work presents a new method to study the ethanol oxidation reaction in a functional fuel cell adapting the single cell on an ATR-FTIR accessory. Using this configuration it was possible to observe the formation of the main products — acetaldehyde and acetic acid — and also measure the decay of the ethanol concentration at various temperatures. Furthermore, it was ascertained that the increment of power density with the temperature increase in the Pt/C anode fuel cell favors the acetaldehyde production. The proposed setup is a very promising characterization technique for studies of in situ electrochemical oxidation of small organic molecules.     

Dihydrogenimidazole modified silica-sulfonated poly(ether ether ketone) hybrid materials as electrolyte membranes for direct ethanol fuel cells

The present study reports on dihydrogenimidazole modified inorganic-organic mixed matrix membranes for possible application as a proton exchange membrane in direct ethanol fuel cells. The polymeric phase consisted mainly of sulfonated poly(ether ether ketone) (sPEEK) with a sulfonation degree of 55%. The inorganic phase was built up from hydrophilic fumed silica particles interconnected with partially hydrolyzed and condensed tetraethoxysilane with a total inorganic loading of 27.3%. This inorganic phase was further modified with N-(3-triethoxysilylpropyl)-4,5-dihydroimidazole (DHIM), which consists of an hydrolyzable inorganic part and a functional organic group. The influence of the modifier on the mixed matrix system was studied by means of various modifier concentrations in various aqueous-ethanolic systems (water, 2 M and 4 M ethanol). Modifier concentration and ethanol concentration of the ethanol-water mixture exhibited significant but opposite effects on the liquid uptake of the mixed matrix membranes. The proton conductivity as well as the proton diffusion coefficient as a function of modifier content showed a linear decrease. The proton conductivity as a function of temperature showed Arrhenius behavior and the activation energy of the mixed matrix membranes was 43.9 ± 2.6 kJ mol⁻¹. High selectivity of proton diffusion coefficient to ethanol permeability coefficient was obtained with high modifier concentrations. At low modifier concentrations, this selectivity was dominated by ethanol permeation and at high modifier concentrations by proton diffusion. The main electrolyte properties can be optimized by setting the DHIM content in mixed matrix membrane. With this approach, tailor-made membranes can be prepared for possible application in direct ethanol fuel cells.     

Direct Ethanol Fuel Cells: The influence of structural and electronic effects on Pt–Sn/C electrocatalysts

Carbon-supported platinum-tin electrocatalysts (Pt–Sn/C) are known to be the most efficient fuel cell anode material to oxidize ethanol in the so-called Direct Ethanol Fuel Cells (DEFC). However, the platinum-tin binary system presents distinct phases depending on the amount of Sn (i.e., the Pt:Sn ratio) and on the thermal annealing temperatures, as well as the presence of oxides (e.g. SnO₂) whose influence on the performance of DEFCs is not well understood. In this work, Pt–Sn catalysts presenting distinct Pt:Sn ratios were prepared, characterized and tested in a single DEFC. The combined results from DEFC tests and structural characterization techniques showed that increasing the amount of Sn dissolved into the Pt structure enhances DEFC performance but also that Sn content alone does not explain the overall behavior. Microstructural effects on the DEFC response was further investigated by performing a comprehensive study using high intensity X-ray Diffraction and in situ–X-Ray Absorption Spectroscopy provided by synchrotron light on Pt₃Sn₁/C samples subjected to thermal treatments in a reducing H₂ atmosphere at temperatures of 100, 200, 300, 400, and 500 °C. The results showed that best DEFC performance depends on a balance between the amount of Sn dissolved in Pt, the formation of a new phase (PtSn) and also on the presence of tin oxides, yielding a material with an optimized modified 5d-band electronic structure, which was obtained with a thermal treatment at 200 °C.     

Ethanol and CO electro-oxidation with amorphous alloys as electrodes

In recent years the interest in the use of ethanol as fuel in direct ethanol fuel cells (DEFCs) has increased. Ethanol is less toxic than methanol and the bigger size of the molecule reduces the permeability through the electrolytic membrane. But, the use of this fuel with platinum catalysts leads to the acetaldehyde and acetic acid formation as main reaction products, so the electrical efficiency decreases. Furthermore, platinum shows an important susceptibility to CO poisoning which is formed during the ethanol electro-oxidation.The aim of this work is the study of the electro-catalytic behaviour of ethanol and CO electro-oxidation reaction with amorphous alloys, obtained by mechanical alloying technique. Ni₅₉Nb₄₀Pt_0.6Pd_0.4, Ni₅₉Nb₄₀Pt_0.6Rh_0.4 and Ni₅₉Nb₄₀Pt_0.6Rh_0.2Ru_0.2 compositions were studied. The bi-catalytic alloys show a similar behaviour for the ethanol electro-oxidation. In comparison to these, the current density towards ethanol oxidation decreases with the presence of Ru, although the tri-catalytic electrode shows the best tolerance to CO, with a lower surface coverage compared to other studied.     

直接乙醇燃料电池阳极电催化剂的研究进展

介绍了直接乙醇燃料电池(DEFC)具有无毒,来源丰富的优点,分析了DEFC在Pt上的电催化氧化机理,讨论了DEFC的阳极电催化剂的重要作用;探讨了具有高电催化活性的新型Pt基催化剂、新型非贵金属催化剂、新型催化剂载体、新型的催化剂制备方法等的研究现状;指明了阳极催化剂将是今后DEFC研究和发展的重要方向之一。