【作者】 陈述；

【导师】 李则林；

【作者基本信息】 湖南师范大学 ， 分析化学， 2009， 博士

【摘要】 金属阳极/溶液界面过程呈现丰富而复杂的动力学行为,诸如依赖阳极电位的表面膜相的生成与演变、物种的表面吸脱附、金属络合反应、溶解与返沉积、气体析出、电化学振荡、表面纳米化等等。对纯金属与合金的阳极/溶液界面物理化学过程进行充分的研究,有助于揭示电极反应机理,理解界面过程,从而有可能更有效地控制电极反应方向或利用阳极过程构筑各种金属纳米材料。采用现场拉曼光谱电化学手段监测金属阳极/溶液界面的微区信息,配以时间分辨和电位调制,可同步获得电极表面物种的第一手信息,有助于从分子水平上深入认识电氧化界面动力学过程。本文利用现场拉曼光谱电化学成功研究了几种金属或合金体系的阳极电氧化过程,通过分析其电化学行为和现场光谱检测结果,为各种不同类型的电氧化机理给出了直接的证据和合理的解释。并在此基础上,选择控制合适的条件用于制备纳米材料,应用于表面增强拉曼散射（SERS）光谱分析或电化学催化过程。本学位论文主要内容分为以下几部分:1.简要介绍了现场拉曼光谱电化学技术,综述了金属/合金阳极电氧化和相关表面纳米结构的近期研究进展。2.利用现场电位调制拉曼光谱和时间分辨拉曼光谱详细研究了不同比例的Au-Sn合金在盐酸溶液中的阳极电氧化过程。包括处于不同电位区间的两种不同的去合金模式:一是在较低电位区间的经典去合金,Au-Sn合金中的Sn组分选择性溶出;二是在较高的电位下的“准去合金”,Au-Sn合金二种组分共同电溶出后,Au又通过随后的氧化—还原反应自动返沉积。同时,通过控制不同的电位条件利用经典去合金和准去合金可以简便地制备出不同形式的金纳米材料,如多孔金、金纳米粒子薄层和分散在溶液中的金溶胶。3.利用紫外可见吸收光谱和现场拉曼散射光谱分析了Pt-Ni合金在盐酸溶液中的阳极电氧化行为。结果表明,随电位逐渐升高,该合金可发生Ni的选择性溶解与Pt的共同溶解,发现并确认了Pt-Ni合金共溶解区涉及的电位加速化学置换反应现象。利用扫描电子显微镜—能谱（SEM-EDX）、原子力显微镜（AFM）和X—射线衍射（XRD）考察了特征电位下合金表面的形貌和成份演化,观察到应力腐蚀裂纹、选择性溶解产生的纳米多孔、共溶解形成的纳米多孔薄片状物等多种表面形貌结构,同时合金表面发生不同程度的Pt组分富积。所获得的纳米多孔材料对甲醇电氧化具有较高的电催化活性。4.首次利用电位调制的现场拉曼光谱对纯Pd和Au-Pd合金在含氯介质中的阳极电氧化行为进行了研究。随着电位的升高,纯Pd在盐酸溶液中表面氧化物种的特征拉曼峰依次呈现:Pd与Cl^-的络合溶解反应、二价和四价络合物种(PdCl₄^2-、PdCl₆^2-)的转变、Cl^-的氧化和Cl₂气的析出、Cl₂与Pd的化学浸蚀反应都逐一得到澄清。纯Pd在KCl溶液中,表面可生成对应的络合物种的难溶钾盐膜层（K₂PdCl₄、K₂PdCl₆）。根据上述光谱电化学结果,得出了Pd在含氯介质中的阳极氧化反应机理。此外,进一步研究了Au-Pd合金在盐酸中的阳极电氧化行为,利用现场拉曼光谱成功监测了电极表面的多种氧化物种的产生过程,并利用SEM-EDX表征了合金在特征阳极电位下的形貌与成份变化,结果表明Au-Pd合金在盐酸中电氧化主要以共同溶解形式进行。5.将准去合金化机理发展成为一种制备SERS基底的新方法:以纯金属电极（Au）为基底,通过电化学方法阴极沉积获得Au|Sn层,再借助控制阳极电位共同电化学溶解和溶解物种间的氧化—还原反应构建表面金纳米粒子堆积层,获得了具有很好表面增强拉曼效应的电极材料。另外,在强酸环境中直接利用Sn（Ⅱ）还原HAuCl₄制备了纳米金溶胶。溶胶粒子表面存在Sn（Ⅱ）络合物保护,在除氧环境下能稳定存放数月。更有趣的是,空气中的氧可诱导该溶胶发生缓慢聚沉,进而自发组装获得了纳米金的有序超晶格结构,可作为一种长效的SERS活性基底材料。6.研究了Cu-Zn和Cu-Ni两种合金在不同介质中的新的非线性阳极电氧化行为。Cu-Zn合金在氢氧化钠溶液中,在不同的电位区间可发生两种不同类型的电位和电流振荡,分别对应于循环伏安图中的两个交叉环区域。并利用拉曼光谱初步推测了表面氧化物种的变化过程和可能的振荡机理。发现了Cu-Ni合金在硫酸溶液中的析氧区间可发生电位和电流振荡,与纯Ni的振荡有明显区别。7.首次报道了在碱性溶液介质中静止铂电极上碘化物电氧化时的电化学振荡行为,其中电极/溶液界面相变过程是振荡的关键。导电性较差的固相碘膜的生成构成该体系非线性过程的负反馈,这导致碘化物氧化减缓;氧气的析出构成相应的正反馈,氧气泡机械破坏了碘膜,同时也加速了对流传质,促进了碘膜相主要通过歧化反应而发生溶解。基于电化学控制实验和现场拉曼光谱证据,给出了涉及两种不同的界面相变和歧化反应的振荡机理。更多还原

【Abstract】 There have been abundant information and complex dynamic behaviors present at the metal anode/solution interface,which depend on the anode potentials,such as formation and evolvement of surface film phases,surface adsorption and desorption,complexation,dissolution or re-deposition of metals,gas evolution,electrochemical oscillations, production of surface nanostructures and etc.Profound study on these interfacial characters of pure metal and alloy anodes/solution contributes to reveal of electrode reaction mechanism,to understand the interface process,consequently to direct the electrode reactions and to construct kinds of metal nanomaterials.In situ Raman spectroscopy has been used for inspecting the micro-zone at metal anode/solution interface.The first-hand information of the species present on electrode surface can be obtained by fitted with the time-resolved and potential-dependent spectra, which will be very helpful to deep recognize the interfacial dynamic of anodic processes at the molecular level.In this thesis,several anodic processes of metals and alloys have been investigated by in situ Raman spectroelectrochemistry.From the analysis of electrochemical behaviors and in situ spectral results,direct identification and reasonable explanations were provided for various types of electrooxidation mechanism.Meanwhile,nano-structured materials for surface-enhanced Raman spectroscopy and electrocatalysis have been fabricated by utilizing the anodic processes.The main contents are summarized as follows:1.The in situ Raman spectroelectrochemical technique has been briefly introduced.The recent research progress of the anodic electrooxidation for pure metals/alloys and correlative nanostructures have been reviewed.2.The electrochemical processes in dealloying of Au-Sn alloys with different ratios in an HCl solution have been first investigated in detail by means of in situ potential-dependent and time-resolved Raman spectra.Two dealloying modes were found occurring within different potential regions in the electrooxidation of Au-Sn alloys. One is the mode known as classical dealloying,where Sn is selectively dissolved;and the other a so-called quasi-dealloying mode found here,in which Au re-deposits automatically after simultaneous dissolution with Sn.Meanwhile,nanoporous gold,thin layers of gold nanoparticles stacked on the surface,and colloidal gold in the solution can be prepared from the Au-Sn alloys simply by an electrochemical control of potential.3.Investigation on the potential-dependent anodic oxidation of a Pt-Ni alloy electrode has been performed in an HCl solution.Spectroscopic information of UV-vis absorption and in situ Raman scattering shows that the alloy undergoes selective Ni dissolution and simultaneous Pt dissolution successively with the increase of the applied potential. The measurements of SEM-EDX,AFM and XRD at selected potentials reveal that Pt enrichment occurs in the alloy degradation accompanying diversiform morphological evolution such as cracks from stress corrosion,ultrafine pores by selective dissolution,and flaky nanoporous films involving simultaneous dissolution and potential accelerated replacement reaction between Ni in the alloy and dissolved PtCl₆^2-.Moreover,the nanoporous films display high electrocatalytic activity toward the methanol oxidation.4.The surface oxidation processes of Pd and Au-Pd alloy electrode in chloride containing solutions have been investigated in detail by means of in situ potential-dependent Raman spectroscopy for the first time.In the HCl solution,characteristic Raman bands such as for the oxidative coordination of Pd with Cl^-,the transformation of soluble Pd（Ⅱ） to Pd（Ⅳ） complexes,the electrooxidation of Cl^- into Cl₂,and the redox between Cl₂ and Pd were all detected unambiguously during the potential ascending.While in the KCl solution,insoluble salt films of K₂PdCl₄ and K₂PdCl₆ were found on the electrode surface due to their poor solubility.A mechanism scheme is given on the basis of spectroelectrochemical results.Moreover,the electrooxidation of Au-Pd alloy in HCl solution has been further studied.Several species from anodic oxidation were detected by in situ Raman spectra,and the morphomogies at typical anodic potentials were also characterized. It can be concluded that the Au-Pd alloy electrooxidation follows simultaneous dissolution procedure in the HCl medium.5.The quasi-dealloying manner has been grafted onto a pure Au electrode to construct the SERS substrate conveniently.Firstly, electrodeposite a tin overlayer on the substrate as Au|Sn layer,and then co-dissolve the Sn overlayer with Au underneath by controlling the potential at the simultaneous dissolving region.A thin layer of gold nanoparticles（GNPs） sticking to the gold electrode surface can be obtained and it performs good surface Raman enhancement. Besides,we described the synthesis of Sn（Ⅱ） complex stabilized GNPs by Sn（Ⅱ） reduction of HAuCl₄ in high acid aqueous solution. This gold colloid was stable for months in oxygen-free surrounding. More interestingly,the GNPs in the colloid were futher assembled into uniform supperlattice by slow sedimentation,which was induced by the oxygen bit by bit.The supperlattice can be served as a long-lived acive SERS substrate.6.Nonliner behaviours for anodic electrooxidation of Cu-Zn and Cu-Ni alloy have been studied in different medium.Two different types of potential and current oscillations were found during the anodic electrooxidation of Cu-Zn alloy in NaOH solution,corresponding to the two crossing cycles in the cyclic voltammograms,respectively. With the help of Raman spectra,the oxide species on the alloy electrode were discussed and possible oscillatory mechanism was given.A new electrochemical oscillatory system was found for the electrodissolution of copper-nickel alloy in sulfuric acid in the region of oxygen evolution,which is different from the oscillatory system for pure Ni electrooxidation.7.Oscillations have been first observed during iodide oxidation in an alkaline solution on a static platinum electrode,where phase transitions at the interface of electrode/solution are essential.The film formation of solid iodine acts as a negative nonlinear feedback slowing down the iodide oxidation due to its poor conductivity,and oxygen gas evolution as a positive nonlinear feedback by destroying the iodine film mechanically and by promoting its dissolution through convection mainly via disproportional reaction.Based on the results of electrochemical experiments and in situ Raman spectroscopy,a tentative mechanism is given concerning the interfacial phase transition and the disproportional reaction.更多还原