氢气催化氧化法冷启动对PEMFC电堆衰减的影响

利用氢气催化氧化法对质子交换膜燃料电池(PEMFC)电堆进行-32℃的低温启动,结果表明在经过10次冷启动后,电堆整体输出性能没有明显衰减。然而通过对该短堆进行解析发现膜电极组件(MEA)存在局部衰减,主要是电堆出口和入口处对应区域的MEA发生了衰减,其中出口处的衰减更为明显。通过对电堆入口、中间和出口区域的电极进行循环伏安、电化学阻抗和线性扫描伏安测试,结果表明:入口处的电极衰减主要来自于催化剂的团聚或者流失以及水结冰导致的膜的氢气透过性增加;出口处的电极衰减主要来自于催化剂的团聚或者流失。

高温质子交换膜燃料电池的复合催化层电极

高温质子交换膜燃料电池具有耐毒化,稳定性好的优势,是具有较强应用前景的一种能源转换装置。本文制备了具有复合催化层结构的气体扩散电极,用于增强燃料电池阳极的催化性能。在气体扩散电极中,将偏氟乙烯-六氟丙烯共聚物和聚苯基咪唑聚合物作为催化剂的粘结材料,调节了电极界面的浸润结构。通过对电极表面形貌和润湿性的表征,发现该种结构的催化层孔隙率和粗糙度更高,双层结构的润湿性差别明显(接触角分别为149°和19°),这有利于形成稳定的三相反应界面。测试结果表明,该种结构的催化层能够有效提高催化材料的利用效率,燃料电池对氢气燃料的峰值功率密度提高约22%。与此同时,使用含一氧化碳质量浓度为10000和30000 mg/m^3的氢气燃料,电池峰值功率密度能够分别保持82.1%和71.4%,证明该燃料电池对一氧化碳杂质保持了良好的耐毒性。

High activity of a Pt decorated Ni/C nanocatalyst for hydrogen oxidation

The Pt decorated Ni/C nanocatalysts were prepared for hydrogen oxidation reaction（HOR） in fuel cell.By regulating the contents of Pt and Ni in the catalyst,both the composition and the structure affected the electrochemical catalytic characteristics of the Pt-Ni/C catalysts.When the Pt mass content was 3.1% percent and that of Ni was 13.9% percent,the Pt-Ni/C-3 catalyst exhibited a larger electrochemically active surface area and a higher exchange current density toward HOR than those of pure supported platinum sample.Our study demonstrates a feasible approach for designing the more efficient catalysts with lower content of noble metal for HOR in fuel cell.

The effect of ethanol on the performance of CrO_x/SiO_2 catalysts during propane dehydrogenation

The effects of ethanol vapor pretreatment on the performance of CrOx/SiO2 catalysts during the dehydrogenation of propane to propylene were studied with and without the presence of CO2.The catalyst pretreated with ethanol vapor exhibited better catalytic activity than the pristine CrOx/SiO2,generating 41.4% propane conversion and 84.8% propylene selectivity.The various catalyst samples prepared were characterized by X-ray diffraction,transmission electron microscopy,temperature-programmed reduction,X-ray photoelectron spectroscopy and reflectance UV-Vis spectroscopy.The data show that coordinative Cr^3＋ species represent the active sites during the dehydrogenation of propane and that these species serve as precursors for the generation of Cr^3＋.Cr^3＋ is reduced during the reaction,leading to a decrease in catalytic activity.Following ethanol vapor pretreatment,the reduced CrOx in the catalyst is readily re-oxidized to Cr^6＋ by CO2.The pretreated catalyst thus exhibits high activity during the propane dehydrogenation reaction by maintaining the active Cr^3＋ states.

Simultaneous hydrogen and peroxide production by photocatalytic water splitting

Photocatalytic oxidation of water is a promising method to realize large-scale H2O2 production without a hazardous and energy-intensive process. In this study, we introduce a Pt/TiO2(anatase) photocatalyst to construct a simple and environmentally friendly system to achieve simultaneous H2 and H2O2 production. Both H2 and H2O2 are high-value chemicals, and their separation is automatic. Even without the assistance of a sacrificial agent, the system can reach an efficiency of 7410 and 5096 μmol g^-1 h^–1 (first 1 h) for H2 and H2O2, respectively, which is much higher than that of a commercial Pt/TiO2(anatase) system that has a similar morphology. This exceptional activity is attributed to the more favorable two-electron oxidation of water to H2O2, compared with the four-electron oxidation of water to O2.

Catalytic Transformation of Oxygenated Organic Compounds into Pure Hydrogen

The continual growth in transportation fuels and more strict environmental legislations have led to immense interest in developing green biomass energy. In this work, a proposed catalytic transformation of oxygenated organic compounds （related to bio-oil） into pure hydrogen was desighed, involving the catalytic reforming of oxygenated organic compounds to hydrogen- rich mixture gas followed by the conversion of CO to CO2 via the water gas reaction and the removal of CO2. The optimization of the different reforming catalyst, the reaction conditions as well as various sources of oxygenated organic compounds were investigated in detail. The production of pure hydrogen, with the H2 content up to 99.96% and the conversion of 97.1%, was achieved by the integrated catalytic transformation. The reaction pathways were addressed based on the investigation of decomposition, catalytic reforming, and the water gas reaction.

Ni-mediated Liquid Phase Reduction of Carbonyl Compounds in the Presence of Atmospheric Hydrogen

An efficient reduction system of benzaldehyde with hydrogen under ambient pressure was developed using facile NiO catalyst. The non-aromatic solvents such as cyclohexane, tetrahydrofuran (THF) and n-hexane, and the addi-tive with strong basicity e.g. KOH, were necessary for smooth conversion of the substrate. That the catalyst can be recov-ered and reused for nine times without loss of catalytic activity indicates that this catalyst is a recyclable one for benzal-dehyde reduction.

Blocking backward reaction on hydrogen evolution cocatalyst in a photosystem Ⅱ hybrid Z-scheme water splitting system

Photocatalytic Z-scheme water splitting is considered as a promising approach to produce solar hydrogen.However,the forward hydrogen production reaction is often impeded by backward reactions.In the present study,in a photosystem Ⅱ-integrated hybrid Z-scheme water splitting system,the backward hydrogen oxidation reaction was significantly suppressed by loading a PtCrOx cocatalyst on a ZrO2/TaON photocatalyst.Due to the weak chemisorption and activation of molecular hydrogen on PtCrOx,where Pt is stabilized in the oxidized forms,Pt^Ⅱ and Pt^Ⅳ,hydrogen oxidation is inhibited.However,it is remarkably well-catalyzed by the metallic Pt cocatalyst,thereby rapidly consuming the produced hydrogen.This work describes an approach to inhibit the backward reaction in the photosystem Ⅱ-integrated hybrid Z-scheme water splitting system using Fe(CN)6^3-/Fe(CN)6^4-redox couple as an electron shuttle.

Selective catalytic reduction of NO_x by H_2 over Pd/TiO_2 catalyst

Pd/TiO2 catalysts prepared by three different methods(impregnation,deposition-precipitation,and polyethylene glycol reduction)were investigated in the selective catalytic reduction of NOx by H2(H2-SCR).It was found that the preparation method exerted a significant effect on the activity of the Pd/TiO2 catalyst,and that the catalyst prepared by the polyethylene glycol reduction method exhibited the highest activity in the reduction of NOx.Characterization of the catalyst showed that,in the Pd/TiO2 catalyst prepared by the polyethylene glycol reduction method,the existing Pd species was Pd0,which is the desirable species for the H2-SCR of NOx.In situ DRIFTS studies demonstrated that over this catalyst,more chelating nitrite and monodentate nitrite species formed,both of which are reactive intermediates in the H2-SCR of NOx.All of these factors account for the high activity of Pd/TiO2 prepared by the polyethylene glycol reduction method.

Sustainable solid-state synthesis of uniformly distributed PdAg alloy nanoparticles for electrocatalytic hydrogen oxidation and evolution

New sustainable syntheses based on solid-state strategies have sparked enormous attention and provided novel routes for the synthesis of supported metallic alloy nanocatalysts(SMACs).Despite considerable recent progress in this field,most of the developed methods suffer from either complex operations or poorly controlled morphology,which seriously limits their practical applications.Here,we have developed a sustainable strategy for the synthesis of PdAg alloy nanoparticles(NPs)with an ultrafine size and good dispersion on various carbon matrices by directly grinding the precursors in an agate mortar at room temperature.Interestingly,no solvents or organic reagents are used in the synthesis procedure.This simple and green synthesis procedure provides alloy NPs with clean surfaces and thus an abundance of accessible active sites.Based on the combination of this property and the synergistic and alloy effects between Pd and Ag atoms,which endow the NPs with high intrinsic activity,the PdAg/C samples exhibit excellent activities as electrocatalysts for both the hydrogen oxidation and evolution reactions(HOR and HER)in a basic medium.Pd9Ag1/C showed the highest activity in the HOR with the largest j0,m value of 26.5 A g Pd^–1 and j0,s value of 0.033 mA cmPd^–2,as well as in the HER,with the lowest overpotential of 68 mV at 10 mA cm^–2.As this synthetic method can be easily adapted to other systems,the present scalable solid-state strategy may open opportunity for the general synthesis of a wide range of well-defined SMACs for diverse applications.