【作者】 黄钊；

【导师】 姚守拙； 谢青季；

【作者基本信息】 湖南师范大学 ， 分析化学， 2013， 博士

【摘要】 因具有特殊的结构和独特的理化性质,贵金属(亚)纳米材料的基础和应用研究备受关注。创新贵金属(亚)纳米材料的合成和分析表征方法,对促进贵金属(亚)纳米材料在电催化和电分析等方面的研究具有重要意义。本学位论文中,我们简要综述了石英晶体微天平(QCM)技术、贵金属(亚)纳米材料及其修饰电极的制备与应用的近期进展,开展了数种贵金属(亚)纳米材料及其修饰电极应用于电催化和电分析的研究。‘主要内容如下：1.通过在Au电极表面欠电位沉积(UPD)Cu、再与Pt源(H2PtCl6或K2PtCl4)进行原电池置换反应(GRR),制得单层级Pt原子修饰的金电极(对H2PtCl6或K2PtCl4,所制电极分别记为Pt(CuUPD-Pt4+)n/Au或Pt(CuUPD-Pt2+)n/Au,n表示欠电位沉积—置换过程的重复次数)。首次用电化学石英晶体微天平(EQCM)技术定量研究了所制电极,评估了其在碱性环境中催化甲醇氧化的质量比活性(SECAm)。结果表明,以H2PtCl6为Pt源所制电极(Pt(CuUPD-Pt4+)3/Au)的活性更高,最大SECAm高达35.7mAμgPt-1。根据EQCM结果计算了置换效率,籍此讨论了Pt原子在Au电极表面的层层组装结构,发现所制电极表面的裸Au位点分布百分数与实验结果(由AuOx还原峰电量测算)吻合。2.通过在Au电极表面UPD Cu、再在H2PtCl6+HAuCl4的混合溶液中进行GRR,制得Pt-Au混合原子单层修饰的金电极(PtxAuy(CuUPD-Pt4+)/Au, x和y为混合溶液中H2PtCl6和HAuCl4的摩尔浓度比),并用QCM技术计算了CUUPD与Pt(或Au)原子之间的置换效率。通过建立电极表面Pt原子的电化学性质(电化学技术测定)与其负载量(QCM测定)之间的相关性,提出了一种测定Pt-Au混合原子单层中Pt负载量的新方法。同时,考察了Pt-Au混合原子单层催化剂在酸性介质中对甲酸的电催化氧化性能,评估了Pt的活性面积比活性(SECAa)和SECAm,并比较了Pt-Au混合原子单层与其他Pt-M(M=Ir、Rh、Pd、Ru、Os)混合原子单层对甲酸的催化活性。结果表明,Pt-Au混合原子单层催化剂的催化活性最好,最大SECAa和SECAm分别为124mA·cmpt-2和102mA·μgpt-1(Pt4Au1(cuuPD-Pt4+)/Au),为迄今的比活性最高的Pt基甲酸电催化剂。3.GRR通常为较活泼金属(还原剂)和相对不活泼金属的盐(氧化剂)之间的化学氧化还原反应,UPD是指单层级金属分子(如Cu或Pb)在异种金属基底(如Pt)上的电沉积电位正于其能斯特本体沉积电位的电沉积现象,两者在基础与应用研究中均受到广泛关注。尽管目前已有许多关于GRR和UPD的报道,但GRR过程中是否会发生UPD以及UPD对GRR的影响还不清楚。作为一个新概念研究,我们在双舱室原电池(DCGC)装置中,利用QCM技术和其他相关技术,探究了较活泼金属(如Cu或Pb)在相对不活泼金属(如Pt)表面的UPD。我们发现,GRR过程中模板金属离子或其他加入的有适当活性的金属离子均可自动发生UPD。基于GRR-UPD一体化的新概念,我们提出了一种简单、便利而有效的方法(特别是DCGC法)来制备性能增强的功能纳米复合物。本章对GRR过程中UPD行为的揭示,有助于更好地理解GRR过程和探索新应用。4.采用DCGC装置,以金属Cu为阳极,以金属Pd为阴极,利用QCM和电化学噪声(ECN)技术研究了Pb在Pd表面的UPD及本体Cu的溶出。同时,以Cu为阳极,以HClO4为阳极液,以多壁碳纳米管(MWCNTs)修饰的玻碳电极(GCE)为阴极,以K2PtCl4+PdCl2+Pb(C104)2为阴极液,利用GRR-UPD概念调控Cu与Pt+Pd混合盐(K2PtCl4+PdCl2)之间的GRR,在阴极(MWCNTs/GCE)制备含Pb的Pt-Pd电催化剂,在碱性环境中考察了其对乙醇的电催化氧化性能,并藉此发展了一种高灵敏的乙醇电化学传感器。所得修饰电极对乙醇的检测灵敏度为138μAmM-1cm-2,检测限为6.6μM(S/N=3),线性范围为0.05～10mM。5.采用DCGC装置,以活泼金属Cu为阳极,以金属Au为阴极,利用QCM和ECN技术研究了Pb在Au表面UPD及本体Cu的溶出。同时,以Cu为阳极,以HClO4为阳极液,以MWCNTs/GCE为阴极,以H2PtCl6+HAuCl4+Pb(ClO4)2为阴极液,利用GRR-UPD概念调控Cu与Pt+Au混合盐(H2PtCl6+HAuCl4)之间的GRR,在MWCNTs/GCE(阴极)表面制备含Pb的Pt-Au电催化剂,在碱性环境中考察了其对甲醇的电催化氧化性能。6.采用DCGC装置,以金属Cu为阳极,以HC104为阳极液,以MWCNTs/GCE为阴极,以PdCl2+HAuCl4+Pb(ClO4)2为阴极液,利用GRR-UPD概念调控Cu与Pd+Au混合盐(PdCl2+HAuCl4)之间的GRR,在MWCNTs/GCE(阴极)表面制备含Pb的Pd-Au电催化剂,在碱性环境中考察了其对甲醛的电催化氧化性能,并藉此发展了一种高灵敏的甲醛电化学传感器。所得修饰电极对甲醛的检测灵敏度为666μAmM-1cm2,检测限为0.89μM(S/N=3),线性范围为O.01～5.0mM。更多还原

【Abstract】 Basic and applied researches of noble metal (sub-)nanomaterials have received wide attentions in diverse fields due to their unique structures and unique physicochemical properties. It is of significance to innovate the synthesis and analysis/characterization methods to stimulate the electrocatalysis and electroanalysis studies of noble metal (sub-)nanomaterials. In this dissertation, we briefly review the recent advances of quartz crystal microbalance (QCM) technology and the preparation and application of noble metal (sub-)nanomaterials, and then conduct electrocatalysis and electroanalysis studies of some noble metal (sub)nanomaterials and their modified electrodes. The main contents are summarized below.1. Underpotential deposition (UPD) of Cu on an Au electrode followed by galvanic replacement reaction (GRR) of CuUPD with a Pt source (H2PtCl6or K2PtCl4) yielded Au-supported Pt adlayers (for short, Pt(CuUPD-Pt4+)n/Au for H2PtCl6, or Pt(CuUPD-Pt2+)n/Au for K2PtCl4, where n denotes the number of UPD-replacement cycles). The electrochemical quartz crystal microbalance (EQCM) technique was used for the first time to quantitatively study the fabricated electrodes and estimate their mass-normalized specific activity (SECAm) for methanol oxidation in alkaline solution. In comparison with Pt(CuUPD-Pt2+)n/Au, Pt(CuUPD-Pt4+)n/Au exhibited a higher electrocatalytic activity, and the maximum SECAm was obtained to be as high as35.7mAμgpt-1at Pt(cuUPD-Pt4+)3/Au. The layer-by-layer architecture of Pt atoms on Au is briefly discussed based on the EQCM-revealed replacement efficiency, and the calculated distribution percentages of bare Au agree well with the experimental results deduced from the charge under the AuOx-reduction peaks.2. UPD of Cu on an Au electrode followed by GRR of CuUPD in the mixture of Pt source and Au source (H2PtCl6+HAuCl4) yielded Au-supported Pt-Au mixed atomic monolayer (PtxAuy(CuUPD-Pt4+)/Au, where x and y denote the ratio of molar concentration of H2PtCl6to HAuCl4in the mixture). The replacement efficiency between CuUPD atoms and Pt (or Au) atoms was calculated by QCM. By establishing the correlation between the electrochemical properties of Pt atom (determined by the electrochemistry) and the Pt loading (determined by QCM), a new method was proposed to calculate the Pt loading in the Pt-Au mixed atomic monolayer. Meanwhile, the Pt active area-normalized specific activity (SECAa) and the SECAm of Pt-Au mixed atomic monolayer toward the electrocatalytic oxidation of formic acid in acid solution were examined. In comparison with the performance of other Pt-M(M=Ir, Rh, Pd, Ru and Os) mixed atomic monolayer, the Pt-Au mixed atomic monolayer exhibited the best performance among the examined catalysts, with the highest SECAa (124mA·cmpt-2) and SECAm (102mA·μgPt-1) on the optimal electrode (Pt4Au1(CuUPD-Pt4+/Au) reported to date.3. GRR is the redox reaction betweem relatively active metal (reductant) and the salt of less active metal (oxidant), and UPD of metals refers to their (sub-)monolayer deposition at potentials more positive than the Nernstian potential for bulk deposition, both of which have attracted great academic and industrial interests in many areas. However, little is known about the possible occurrence and effect of UPD during GRR to date. As demonstration-of-concept examples here, we explore the co-occurrence of UPD of Cu or Pb on Pt during the corresponding GRR, mainly using a double cabin galvanic cell (DCGC) device, QCM, and relevent techniques. It is found that the UPD of either the ions of the template metals used in GRR or other added metal ions of appropriate electroactivities can spontaneously and universally occur during the GRR, and a simple, flexible (especially in the DCGC mode) and efficient protocol is thus recommended based on the integrated GRR-UPD concept for preparation of functional metal nanocomposites with improved electrocatalysis performance. The insights obtained here emphasize that the GRR involve the occurrence and effect of UPD, which should help the better understanding of various GRR for application explorations.4. The QCM and electrochemical noise (ECN) device technologies were employed to examine the UPD of Pb on Pd and the bulk stripping of Cu in the DCGC with a Cu anode and a Pd cathode. In addition, we used the concept of GRR-UPD to turn the GRR between Cu and Pt+Pd mixed salts (K2PtCl4+PdCl2) for synthesizing Pb-containing Pt-Pd nanoparticles on the cathode in a DCGC with a Cu anode, a multiwalled carbon nanotubes (MWCNTs) modified glassy electrode (GCE) cathode, a HC104anolyte, and a K2PtCl4+PdCl2+Pb(C104)2catholyte. The catalytic performance of the resultant Pb-containing Pt-Pd nanoparticles toward electrocatalytic oxidation of ethanol was examined in alkaline solution, and the Pb-containing Pt-Pd nanoparticles modified MWCNTs/GC electrode was used to construct an amperometric sensor for ethanol detection. The sensor exhibited a linear amperometric response to ethanol concentration from0.05to10mM with a sensitivity of138μAmM-1cm-2, a limit of detection (S/N=3) of6.6μM.5. The QCM and ECN technologies were employed to examine the UPD of Pb on Au and the bulk stripping of Cu in the DCGC with a Cu anode and a Au cathode. In addition, we used the concept of GRR-UPD to turn the GRR between Cu and Pt+Au mixed salts (H2PtCl6+HAuCl4) for synthesizing Pb-containing Pt-Au nanoparticles on the cathode in a DCGC with a Cu anode, a MWCNTs/GCE cathode, a HClO4anolyte, and a H2PtCl6+HAuCl4+Pb(C104)2catholyte. The catalytic performance of the resultant Pb-containing Pt-Au nanoparticles toward electrocatalytic oxidation of methanol was examined in alkaline solution.6. Here, we used the concept of GRR-UPD to turn the GRR between Cu and Pd+Au mixed salts (PdCl2+HAuCl4) for synthesizing Pb-containing Pd-Au nanoparticles on the cathode in a DCGC with a Cu anode, a MWCNTs/GCE cathode, a HClO4anolyte, and a PdCl2+HAuCl4+Pb(ClO4)2catholyte. The catalytic performance of the resultant Pb-containing PdAu nanoparticles toward electrocatalytic oxidation of formaldehyde was examined in alkaline solution, and the Pb-containing Pd-Au nanoparticles modified MWCNTs/GC electrode was used to construct an amperometric sesnor for formaldehyde detection. The sensor exhibited a linear amperometric response to formaldehyde concentration from0.01to5.0mM with a sensitivity of666μA mM-1cm-2, a limit of detection (S7N=3)of0.89μM.更多还原