MH电极中氢扩散系数的测定及其应用

利用恒流放电法测定了金属氢化物(MH)电极中氢原子扩散系数的平均值. 通过恒电位法测定了MH电极中氢原子的扩散系数与其荷电态(SOC)的关系. 根据MH电极模型可知, 增大氢原子扩散系数或减小储氢合金粒径均能提高MH电极的快速充电性能, 并能计算出MH电极在不同的初始荷电态、不同充电倍率下, 表面氢原子浓度达到最大值所需的时间.     

瞬态光电导谱研究Pt的负载对TiO2光生载流子寿命的影响

采用瞬态光电导谱研究了TiO₂的光电导衰减曲线,通过计算机拟合得到光生载流子的寿命,并考察了Pt的负载量对TiO₂光生载流子有效寿命的影响.结果表明,增大Pt的负载量,可延缓光电导的衰减趋势,从而延长TiO₂光生载流子的有效寿命,有效地降低了光生载流子的复合率.     

Rare earth hydrogen storage alloy used in borohydride fuel cells

Fuel cell using the borohydride as the fuel has attracted much attentions because of high energy density and working potential. In this work, LaNi_4.5Al_0.5 hydrogen storage alloy used as the anodic material to replace noble metals has been investigated. Experimental results showed that H₂ evolution was unavoidable during discharge process because of the hydrolysis of , but the utilization of the fuel increased with the increasing current densities. At high discharge current, the alloy electrode showed the lowest hydrogen generation rate and higher utilization of the fuel because, the generated hydrogen was absorbed and oxidized to produce electric energy similar to the behavior of hydrogen storage alloy in nickel–metal hydride batteries. The reaction mechanism of borohydride on the surface of electrode made of hydrogen storage alloy also has been discussed. Hydrogen storage alloy would be a promising material as the anodic catalyst in borohydride fuel cell.     

Platinum alloying effects on the behavior of a metal hydride electrode

This is a study of the alloy structure, cycling life, and reaction kinetics of LaNi_4.7–x Sn_0.3Pt _x (x=0 and 0.1) metal hydride electrodes, using X-ray diffraction, X-ray absorption spectroscopy, electrochemical charge/discharge cycling, and electrochemical impedance spectroscopy. It is seen that the presence of platinum in the alloy causes an increase of the cycle life and a decrease in the hydrogen equilibrium pressure, activation time, charge storage capacity, and the rate of capacity decay during multicycling. XANES results are consistent with a decrease in the Ni oxidation in the Pt-containing alloy after the electrode cycling, indicating a protection introduced by Pt against Ni oxidation. It was also found that the catalytic activity of charge/discharge is improved with Pt alloying, a factor exclusively related to an increase of the active area due to higher alloy pulverization.     

Self-discharge behavior of LaNi5-based hydrogen storage electrodes in different electrolytes

Nickel–metal hydride (Ni–MH) batteries using hydrogen storage alloys as negative electrode materials have been developed and commercialized because of their high energy density, high rate capability and long cycle life, without causing environmental pollution (Song et al. J Alloys Comp 298:254, 2000; Jang et al. J Alloys Comp 268:290, 1998). However, the self-discharge rate is relatively higher than that of the Ni–Cd batteries, which would certainly be disadvantageous in practical applications. The capacity loss of a battery during storage is often related to self-discharge in the cells. Self-discharge takes place from a highly charged state of a cell to a lower state of charge (SOC) and is typically caused by the highly oxidizing or reducing characteristic of one or both of the electrodes in the cell. This self-discharge behavior may be affected by various factors such as gases, impurities, temperature, type of alloy electrode, electrolytes, or charge/discharge methods. The loss of capacity can be permanent or recoverable, depending on the nature of the mechanism (chemical or electrochemical) and aging condition. In this paper, the effects of electrolyte composition and temperature on self-discharge behavior of LaNi₅-based hydrogen storage alloy electrodes for Ni–MH batteries have been investigated. It was found that both reversible and irreversible capacity loss of MH electrode tested at 333 K were higher than that at 298 K. When tested at 298 K and 333 K, reversible capacity loss was mainly affected by the electrolyte, while the irreversible capacity loss was not affected. The dissolution of Al from the electrode can be reduced more effectively in an electrolyte with Al addition, compared with that in normal electrolyte. This resulted in a lower reversible capacity loss for the electrode exposed in the Al³⁺-rich electrolyte. SEM analysis has shown that some needle shape and hexagonal corrosion products were formed on the surface of the alloy electrodes, especially after storage at high temperature.     

Atomically Dispersed Main Group Magnesium on Cadmium Sul-fide as the Active Site for Promoting Photocatalytic Hydrogen Evolution Catalysis

Photoabsorption charge separation/transfer and surface reaction are the three main factors influencing the efficiency of photocatalysis.Band structure engineering has been extensively applied to improve the light absorption of photocatalysts,however,most of the developed photocatalysts still suffer from low photocatalytic performance due to the limited active site(s)and fast recombination of photogenerated charge carriers.In this work,atomically dispersed main group magnesium(Mg)is introduced onto CdS monodispersed nanospheres,which greatly enhances the photocatalytic hydrogen evolution reaction.The photocatalytic hydrogen evolution reaction rate reaches 30.6 mmol·gcatalyst^-1·h^-1,which is about 11.8 and 2.5 times that of pure CdS and Pt(2 wt.%)-CdS.The atomically dispersed Mg on CdS acts as an electron sink to trap photogenerated electrons,and at the same time,greatly reduces the Gibbs free energy of hydrogen evolution reaction(HER)and accelerates HER.     

磷钼酸修饰铂电极的电化学行为及对甲醇氧化的电催化作用

通过循环伏安扫描法制备了PMo₁₂修饰Pt/Pt电极,并研究了该修饰电极在硫酸溶液中的电化学行为。研究结果表明:虽然磷钼酸具有较大的分子尺寸,但在Pt/Pt电极上仍能发生吸附作用,并且由于PMo₁₂在电极上的吸附,降低了Pt/Pt电极上氢区和氧区的荷电量,另外在0.02V左右还观察到磷钼酸的氧化-还原峰。通过稳态极化曲线和循环伏安曲线研究了PMo₁₂修饰Pt/Pt电极对甲醇氧化的电催化作用。测试结果表明:PMo₁₂修饰铂基电极不但对甲醇的电氧化具有较高的活性,而且还有一定的抗CO中毒性。该修饰电极还具有较高的稳定性。     

Potential-dependent recombination kinetics of photogenerated electrons in n- and p-type GaN photoelectrodes studied by time-resolved IR absorption spectroscopy

Recombination kinetics of photogenerated electrons in n-type and p-type GaN photoelectrodes active for H(2) and O(2) evolution, respectively, from water was examined by time-resolved IR absorption (TR-IR) spectroscopy. Illumination of a GaN film with UV pulse (355 nm and 6 ns in duration) gives transient interference spectra in both transmittance and reflection modes. Simulation shows that the interference spectra are caused by photogenerated electrons. We observed that recombination in the microsecond region is greatly affected by the applied potentials, the lifetime becoming longer at negative and positive potentials for n- and p-type GaN electrodes, respectively. There is a good correlation between potential dependence of the steady-state reaction efficiency and that of the number of surviving electrons in the millisecond region. We also performed potential jump measurement to examine the shift in Fermi level by photogenerated charge carriers. In the case of n-type GaN, the electrode potential jumps to the negative side by accumulation of electrons in the bulk. However, in the case of p-type GaN, the electrode potential first jumps to the negative side within 20 μs and gradually shifts to the positive side in a few milliseconds, while the number of charge carriers is constant at >0.2 ms. This two-step process is ascribed to electron transport from the bulk to the surface of GaN, because the electrode potential is sensitive to the number of electrons in the bulk. The results confirm that TR-IR combined with potential jump measurement provides useful information for understanding the behavior of charge carriers in photoelectrochemical systems.     

Enhanced Metal–Semiconductor Interaction for Photocatalytic Hydrogen-Evolution Reaction

The selective immobilization of noble metals right at the place where photogenerated electrons migrate through the photodeposition approach is a unique strategy to load cocatalysts on semiconductors for solar hydrogen production. However, a poor metal–semiconductor interaction is often formed, which not only hinders the interfacial charge transfer, but also results in the easy aggregation and shedding of cocatalysts during photocatalytic reactions. Herein, it is demonstrated that the photodeposited ultrafine metals, such as nanosized Au, can be well stabilized on TiO₂ nanocrystallines without sintering by employing a sacrificial carbon coating annealing strategy to strengthen the metal-support interaction. Benefiting from the improved interfacial contact between Au and TiO₂ for fast charge transfer and the well-preserved size-dependent catalytic behavior of Au nanoparticles toward hydrogen evolution reaction, the annealed Au/TiO₂ exhibits a significant enhanced activity toward photocatalytic H₂ production with good durability.     

Br?nsted酸性离子液体活化电极催化制氢性能研究

分别采用玻碳( GC)、铂( Pt)和金( Au)电极研究了在Br?nsted酸性离子液体[ HMIm] HSO4中电解水制氢的催化活性,活性大小为Pt > Au >> GC。水中离子液体的含量对析氢电流影响很大,当[ HMIm] HSO4含量为30%(V/V)时,Pt电极催化电解水产氢的阈值电位高达-0.3 V (Ag丝为准参比电极, Ag QRE),在-0.5 V (Ag QRE)处电流密度高达110.52 mA/cm2,为相同条件下Au电极的15倍,GC电极的650倍。计算结果表明,Pt电极在该电解液中的反应活化能为5.68 kJ/mol。电极的高催化活性与[ HMIm] HSO4电离产生的质子有关,使水以H3 O+的形式捕集电子,效率更高。     

石墨二炔及其电子转移增强特性

石墨二炔是由sp和sp²杂化的碳原子构成的新的碳同素异形体。由于石墨二炔具有独特的拓扑结构和电子结构、较高的电荷迁移率及优异的电子传输性能,使其与其他材料相互作用,可表现出独特的电子转移增强特性。本文基于石墨二炔的电子转移增强特性,概述了石墨二炔及其电子转移增强特性的最新研究进展,包括金属氧化物/石墨二炔、金属纳米颗粒/石墨二炔、聚合物/石墨二炔以及染料分子/石墨二炔等多种石墨二炔基材料。本文从理论和实验研究两个方面详细阐述了石墨二炔的电子转移增强特性、石墨二炔与不同材料的相互作用以及相关的应用。希望该综述能对石墨炔化学的发展起到一定的积极作用。     

光催化全解水助催化剂的设计与构建

能源和环境危机是当今社会面临的两大关键课题,利用太阳光驱动化学反应、将太阳能转化为化学能是解决上述问题的重要措施。通过光催化分解水是直接利用太阳能生产氢燃料的有效策略。光催化水分解过程可以分为三个基元步骤:光吸收、电荷分离与迁移、以及表面氧化还原反应。助催化剂可有效提高电荷分离效率、提供反应活性位点并抑制催化剂光腐蚀的发生,进而提高水分解效率。助催化剂也可以通过活化水分子以提高表面氧化还原动力学,进而提升整体光催化反应的太阳能转换效率。本文综述了助催化剂在光催化反应中的重要作用以及目前常用的助催化剂类型,详细说明了在光催化全解水过程中双助催化剂体系的构建及作用机理,并根据限制全解水的关键因素提出了新型助催化剂的设计策略。     

Exfoliated and reorganized graphite oxide on titania nanoparticles as an auxiliary co-catalyst for photocatalytic solar conversion

The hybrid of graphite oxide (GO)/TiO(2) was prepared through the spontaneous exfoliation of bulky graphite oxide and reorganization with TiO(2) nanoparticles as a solar conversion and hydrogen-generating photocatalyst. GO/TiO(2) showed enhanced activities for both photocurrent generation (in an electrode form) and hydrogen production (in a slurry form) than those of bare TiO(2) under UV light irradiation. The enhanced photocatalytic activity of GO/TiO(2) is ascribed to the ability of graphitic layers in accepting and transporting electrons from excited TiO(2), promoting the charge separation. When GO was hybridized with platinized TiO(2) (Pt/TiO(2)), it showed a marked synergistic effect for the photocatalytic hydrogen production compared with GO/TiO(2) and Pt/TiO(2). This indicates that the cheap and abundant carbon material can be a good candidate for an electron attracting reservoir and an auxiliary co-catalyst for the photocatalytic hydrogen production.     

Electrocatalysis on binary alloys: II. Oxidation of molecular hydrogen on supported Pt+Ru alloys

The electrocatalytic properties of Pt+Ru alloys supported on graphitized carbon have been studied using oxide-free metal alloys that have been well characterized for phase identification, specific metal surface area, and surface composition. The CO tolerance of the Pt+Ru alloys for the oxidation of CO contaminated hydrogen in hot concentrated H₃PO₄ increases monotonically with Ru content of the surface and is a direct result of a decreasing coverage of the alloy by adsorbed CO. Furthermore, the strength of bonding of adsorbed CO with the metal surface decreases dramatically with increasing Ru content in the surface. The absolute activity of Pt+Ru alloys for the oxidation of CO contaminated hydrogen is a complex function of temperature and electrode potential. At 160°C, pure Pt is the most active catalyst at all potentials, but at temperatures lower than 120°C the reaction-limiting current for pure Ru exceeds that of pure Pt. At any temperature from 110–160°C or any electrode potential from 0–0.3V (HE), the variation of electrocatalytic activity with alloy composition indicates only dilution of the activity of the more active component.     

Kinetic and thermodynamic studies of hydrogen storage alloys as negative electrode materials for Ni/MH batteries: a review

This paper reviews the present performances of intermetallic compound families as materials for negative electrodes of rechargeable Ni/MH batteries. The performance of the metal-hydride electrode is determined by both the kinetics of the processes occurring at the metal/solution interface and the rate of hydrogen diffusion within the bulk of the alloy. Thermodynamic and electrochemical properties for each hydride compound family will be reported. The steps of hydrogen absorption/desorption such as charge-transfer and hydrogen diffusion for evaluating the electrochemical properties of hydrogen storage alloys are discussed. Exchange current density (I ₀) and hydrogen diffusion coefficient (D _H) are the two most important parameters for evaluating the electrochemical properties of metal hydride electrode. The values of the two parameters for a number of hydrogen storage alloys are compared. The relationship between alloy composition and electrochemical properties is noted and evaluated.     

Charge storage in 40/60 TiFe alloy electrodes

Charge storage in 40/60 TiFe alloy has been investigated using electrode fabrication powder material, either of true alloy or of alloy precursor grades. The true alloy activated very reluctantly in that its maximum charge (i.e., hydrogen) capacity remained below 100 mA h g^{– 1}. In contrast, the alloy precursor could be activated to an intrinsic capacity of ~300 mA h g^–1. Charge storage of the 40/60 TiFe alloy precursor was certainly affected by the redox reactions of surface Fe, but a large amount was stored as hydrogen absorbed by the material, as indicated by a dialometric test and the poison effect. X-ray and EDAX analyses of the two materials can account for their differing abilities to store charge. Electronic Publication     

Co（Ⅱ）-空穴和Pt-电子助催化剂协同作用增强P掺杂g-C3N4光催化产氢性能（英文）

石墨相氮化碳(g-C3N4)是一种新型的有机半导体材料,具有独特的层状结构、合适的能带位置、简单的制备方法以及出色的稳定性等特点,因而被广泛应用于光催化产氢领域.但是,较高的光生载流子的复合率和受限的迁移率大大地限制了g-C3N4的光催化产氢性能.目前,大量的研究证实块状g-C3N4的液相剥离、表面改性、元素掺杂、与其他半导体复合构筑异质结以及负载助催化剂等方法可以在一定程度上提高g-C3N4的光催化产氢性能.但是单一的g-C3N4改性方法往往并不能获得最理想的光催化产氢性能,因此,本文采用低温磷化法制备了二价钴(Co(II))修饰的磷(P)掺杂的g-C3N4纳米片(Co(II)/PCN),同时实现了掺杂P原子和负载空穴助催化剂Co(II),该催化剂表现出出色的光催化产氢性能.在光催化制氢过程中,铂(Pt)纳米颗粒作为电子助催化剂成功的负载在Co(II)/PCN上.光催化实验结果表明,最佳的Pt/Co(II)/PCN复合材料光催化产氢速率达到774μmol·g^?1·h^?1,比纯相的g-C3N4纳米片(89.2μmol·g^?1·h^?1)提升8.6倍.同时优化的光催化剂具有良好的光催化稳定性,并在402 nm处具有2.76%的量子产率.XRD,TEM,STEM-EDX和AFM结果证明,成功制备了纳米片状形貌的g-C3N4及其复合材料,催化剂中均匀的分布着Co和P元素.通过XPS证明了P-N的存在以及Co(II)的存在,并且Co(II)是以一种无定型的CoOOH的形式吸附在g-C3N4表面.光照后的TEM证明Pt颗粒成功的负载在Co(II)/PCN表面.UV-vis DRS表明,由于P的掺杂以及Co(II)的修饰,Co(II)/PCN相比于g-C3N4纳米片在可见光区域光吸收有了明显的增强.通过稳态和瞬态光致发光光谱分析,同时结合电化学分析表征(i-t、EIS)以及电子顺磁共振技术分析,证实了Co(II)/PCN高效光催化性能的原因可能是由于更高效的光生载流子分离效率.本文对Pt/Co(II)/PCN可能的光催化增强机理提出了设想.P的掺杂可以优化g-C3N4的电子结构,提高其光生载流子分离效率.而以Pt作为电子助催化剂,可以有效地捕获P掺杂的g-C3N4导带中的光生电子,进而发生水还原产氢反应;以Co(II)作为空穴助催化剂,可以捕获价带中的光生空穴,进而发生三乙醇胺氧化反应.通过采用不同功能的助催化剂,实现P掺杂g-C3N4光生电子空穴的定向分流,促进了P掺杂g-C3N4的光生载流子的分离,从而提高催化剂的光催化产氢性能.本文可以为设计具有空穴-电子双助催化剂的光催化产氢系统提供一个新的思路.     

Variations in the Charge and Open-Circuit Potential of a Platinum Electrode during Adsorption of Iodine and Iodide Ions

The adsorption of iodine and iodide anions on a Pt/Pt electrode (0.5 M H₂SO₄ as a supporting solution) is compared using potentiodynamic and galvanostatic charging curves, transients of the current and open-circuit potential (OCP), and analytical measurements. Variations in the charge and OCP during the adsorption obey relationships derived for strong adsorption of neutral species and ions on a hydrogen electrode with the formation of irreversibly adsorbed atoms. The main product of the I₂ and I^– chemisorption in acid solutions is adsorbed iodine atoms. However, adsorption of iodine occurs in noticeable amounts and above a monolayer in the form of species that undergo electrodesorption during a cathodic polarization to potentials of the beginning of hydrogen adsorption. In the presence of a monolayer of adsorbed iodine atoms, potential of the zero total charge of a Pt/Pt electrode is in the oxygen adsorption region.     

MgNi2添加对AB5型储氢合金电化学性能的影响

制得了含Mg的AB5型稀土合金, 研究了合金添加Mg后合金电化学性能的变化. 采用ICP, XRD对合金组成和结构进行分析, 并通过EIS、CV、SEM和阳极极化曲线研究了电化学反应机理.     

Metal–metal (hydr)oxide heterostructures for electrocatalysis of hydrogen electrode reactions

Metal/metal (hydr)oxide heterostructures have been proposed as an efficient means to enhance the kinetics of hydrogen electrode reactions (the hydrogen evolution and the hydrogen oxidation reaction) on Pt, Ni, and other electrodes in the alkaline medium. However, the reasons for the faster electrode kinetics are still not fully understood. By considering two electrode materials, namely Pt and Ni, widely studied in hydrogen electrode reactions in alkaline media, this review brings to light differences in their pH-dependent behavior and likely different genesis of the enhancement in the presence of 3d transition metal oxides.