EQCM Investigation of the Electrodeposition of MnO2 and Its Capacitance Behavior

Electro-oxidation of Mn2+ to MnO2 by cyclic voltammetry on gold in acidic (0.1 M H2SO4) and neutral (0.1 M Na2SO4) media was studied using electrochemical quartz-crystal microbalance (EQCM). The cyclic voltammetric behavior of Au is different in these electrolytes. From EQCM data of mass variation during cycling, the rate of electrodeposition of MnO2 is higher in the neutral medium than in the acidic medium. Specific capacitance of MnO2 deposited from the neutral medium is higher than that deposited from the acidic medium owing to different crystallographic structures.

An EQCM Investigation of Electrochemical Precipitation of Mn(OH)(2) and Its Capacitance Behavior

Electrochemical quartz crystal microbalance (EQCM) has been used to study the electrochemical precipitation of Mn(OH)(2) on a Au crystal and its capacitance properties. From the EQCM data, it is inferred that NO3- ions get adsorbed on the Au crystal and then undergo reduction, resulting in an increase in pH near the electrode surface. Precipitation of Mn2+ occurs as Mn(OH)(2), with an increase in mass of the Au crystal. Mn(OH)(2) undergoes oxidation to MnO2, which exhibits electrochemical supercapacitor behavior on subjecting to electrochemical cycling in a Na2SO4 electrolyte. EQCM data indicate mass variations corresponding to surface insertion/extraction of Na+ ions during discharge/charge cycling. (C) 2010 The Electrochemical Society. DOI: 10.1149/1.3479665] All rights reserved.

An EQCM investigation of capacitance of MnO2 in electrolytes containing multivalent cations

MnO2 is electrochemically deposited on Au coated quartz crystal to study the electrochemical capacitance properties and to monitor the mass variations that accompany reversible adsorption/desorption of Na+, Mg2+ and La3+ ions during discharge/charge cycling. There is an increase in the values of specific capacitance of MnO2 with increase in charge of the cation in the electrolyte. Also, there is an increase in mass during discharge due to adsorption of cations from the electrolyte resulting from reduction of MnO2. Mass decreases during charging process due to desorption of cations. The magnitude of mass variation is approximately proportional to the atomic weight of the cationic element. (C) 2012 Elsevier B.V. All rights reserved.

EQCM investigation of electrochemical deposition and stability of Co-Pi oxygen evolution catalyst of solar energy storage

Photoassisted electrolysis of water is considered as an effective way of storing solar energy in the form of hydrogen fuel. This overall reaction involves the oxidation of water to oxygen at the anode and the reduction of protons to hydrogen at the cathode. Cobalt-phosphate-based catalyst (Co-Pi) is a potentially useful material for oxygen evolution reaction. In the present study, electrochemical deposition of Co-Pi catalyst is carried out on Au-coated quartz crystal from 0.1 M phosphate buffer (pH 7) containing 0.5 mM Co2+ ion, along with the simultaneous measurement of mass changes at the electrode surface. Cyclic voltammograms and mass variations are recorded during the course of deposition. A current peak is observed at 0.92 V vs Ag/AgCl, 3 M KCl corresponding to oxidation of Co2+ ion. The mass of the electrode starts increasing at this potential, suggesting the deposition of a Co(III)-based insoluble product on the electrode surface. The stability of the catalyst is also studied at several potentials in both buffered and nonbuffered electrolyte by monitoring the real-time mass variations.

EQCM characterization of self-assembled kinetics of 4-pyridyl hydroquinone at Pt surface and its ion transfer in electrochemical redox

The adsorbed kinetics, proton transportation in electrochemical redox process of 4-pyridyl hydroquinone (4PHQ) self-assembled monolayer (SAM) modified Pt electrode were studied by electrochemical quartz crystal microbalance (EQCM) in situ. It proved that the electrode was modified by a monolayer and underwent a rapid electron transfer. It was a slow adsorbed kinetic process. The ion transfer in the electrochemical redox at the SAM-modified electrode surface mainly involved into the hydrate hydrogen ion.

EQCM study during lithium insertion/deinsertion processes in Nb2O5 films prepared by polymeric precursor method

The electrochemical quartz crystal microbalance (EQCM) technique was used to study two chemically distinct Nb2O5 electrochromic thin films (one pure and the other lithium-doped) during the lithium electroinsertion reaction. In the initial cycles, the electrode showed an irreversible mass variation greater than expected for Li+ insertion/deinsertion processes, which was attributed to the wettability effect (allied to the porous morphology) that emerged as the dominant process in apparent electrode mass changes. As the cycles progressed, the mass variation stabilized and the changes in apparent mass became reversible, showing a good correlation with the charge variations.The results generally indicated that the Li+ insertion/deinsertion process occurred more easily in the Nb2O5-doped film, which also displayed a greater capacity for Li+ insertion. However, a total mass/charge balance analysis revealed that the stoichiometry of the Li+ solid state insertion/deinsertion reaction was similar in the two electrodes under study. © 2005 Elsevier B.V. All rights reserved.

An EQCM-D study of the influence of chloride on the lead anodic oxidation

The influence of chloride on the electrodeposition of lead films and their dissolution in anodic stripping voltammetric experiments was examined. Gold substrates were plated with lead films, and mass changes were monitored by using the electrochemical quartz crystal microbalance with dissipation factor (EQCM-D). The results showed that the amount of electrodeposited lead is slightly dependent on the chloride concentration. The charge/mass ratio data indicated the presence of Pb(I) and Pb(II) as a result of film dissolution, and the precipitation and deposition of PbCl2 onto the electrode surface. Scanning electron microscopy images revealed that the morphology of the lead film was strongly influenced by chloride present in the plating solution and that much rougher films were obtained in comparison with those obtained in the absence of chloride. The rate of the anodic dissolution was higher for lead films with higher surface areas, which lead to an increase in their stripping voltammetric currents. (C) 2012 Elsevier Ltd. All rights reserved.

Real-time monitoring of electrochemically active biofilm developing behavior on bioanode by using EQCM and ATR/FTIR

In the current study, the relationship between current and biomass and bio-adhesion mechanism of electrogenic biofilm on electrode were investigated using EQCM and ATR-SEIRAS linking electrochemistry. The results indicated that cellular biomass of biofilm on QCM-crystal surface showed maximum value of 6.0 μg/cm2 in initial batch and 11.5 μg/cm2 in the second batch on mature biofilm, producing a similar maximum current density of 110 μA/μg. Especially, the optimum cell biomass linking high electricity production ratio (110 μA/μg) occurred before maximum biomass coming, implying that over-growth mature biofilm is not an optimum state for enhancing power output of MFCs. On the other hand, the spectra using ATR-SEIRAS technique linking electrochemistry obviously exhibited water structure adsorption change at early biofilm formation and meanwhile the water adsorption accompanied the adsorbed bacteria and the bound cells population on the electrode increased with time. Meanwhile, the direct contact of bacteria and electrode via outer-membrane protein can be confirmed via a series spectra shift at amide I and amide II modes and water movement from negative bands displacing by adsorbed bacteria. Our study provided supplementary information about the interaction between the microbes and electrode beyond traditional electrochemistry.

Eletrodeposição de revestimentos funcionais compósitos Cu/partículas de óxidos de alumínio

Revestimentos funcionais compósitos são um atrativo tecnológico crescente, pois possibilitam a combinação de materiais metálicos, poliméricos ou cerâmicos, resultando em propriedades superiores as dos materiais individuais, sendo por este motivo, largamente aplicados na engenharia de materiais. Na presente dissertação, foram produzidos revestimentos compósitos por eletrodeposição através da codeposição de uma matriz metálica de cobre e de partículas de óxidos de alumínio incorporadas (g - Al2O3 ou AlO(OH)), sobre substratos de aço carbono, a partir de diferentes banhos eletrolíticos. Três etapas foram efetuadas, na primeira realizou-se o estudo da influência do modo de agitação e da presença ou não de ligantes (citrato de sódio 1,00 mol/L) nos teores de cobre e alumina nos revestimentos produzidos. Em seguida foi avaliada a ação de complexantes (citrato de sódio 1,00 mol/L e pirofosfato de potássio 0,90 mol/L) usando polarização potenciodinâmica e voltametria cíclica, em conjunto com microbalança eletroquímica de cristal de quartzo (EQCM) e a posterior produção de revestimentos compósitos a partir de banhos contendo CuSO4 0,02 mol/L + pirofosfato de potássio 0,90 mol/L + 20 g/L de alumina, variando a densidade de corrente aplicada (I), a velocidade de agitação do eletrodo rotatório (A) e o do tempo de agitação prévia (t). Por fim, na terceira etapa, fez-se a substituição de alumina por Boehmita e a produção dos revestimentos a partir de banhos contendo CuSO4 0,02 mol/L + pirofosfato de potássio 0,90 mol/L + 20 g/L de Boehmita, empregando um planejamento composto central, em que os parâmetros citados também foram variados. Os resultados mostraram que a presença de um ligante e a agitação prévia e continuada do eletrólito durante o experimento foram fundamentais para a produção dos revestimentos compósitos. Ensaios de EQCM mostraram que o citrato se adsorveu na superfície do eletrodo de ouro, diferentemente do pirofosfato. Os teores de Boehmita e cobre nos revestimentos produzidos, assim como a morfologia, resistência de polarização e densidade de corrente de corrosão dos revestimentos foram influenciados pelos parâmetros avaliados.

杂多化合物的氧化还原性质、自组装和应用

1．利用电化学和现场紫外-可见-近红外光谱电化学的方法，系统研究了一系列过渡金属取代杂多化合物ZnW_(11)M(M = Cr，Mn，Fe，Co，Ni，Cu，Zn)的电化学行为。所有的这些化合物都在相近的电位处表现出四对连续的基于W中心的氧化还原反应。研究表明，ZnW_(11)M中基于W中心的氧化还原反应可能反映了它那个未知的缺位阴离子ZnW_(11)的氧化还原反应。此外，电活性过渡会属取代杂多化合物ZnW_(11)M(M = Cu，Fe，Mn)还表现了过渡金属M的氧化还原反应。例如：ZnW_(11)Cu~(11)表现出Cu的沉积和溶出，ZnW_(11)Fe~(III)在正电位处有一特殊的源于Fe的氧化还原反应，ZnW_(11)Mn则发生一个氧化反应和两个还原反应。根据实验结果我们提出了一些基本的反应机理。选取HNO_2为底物考察了这一系列过渡金属取代杂多化合物的电催化性能。通过比较电催化还原电流的大小，我们可以定性地排出这一系列过渡金属取代杂多化合物对HNO_2还原反应的电催化性能的顺序（由高到低）：ZnW_(11)Cu > ZnW_(11)Co > ZnW_(11)Cr和ZnW_(11)Fe > ZnW_(11)Zn、ZnW_(11)Mn和ZnW_(11)Ni。这一系列过渡金属取代杂多化合物的电催化性能的差别，可能主要是来自于它们分子结构中所取代的过渡金属元素的影响。实验证明ZnW_(11)M对HNO_2还原反应的电催化过程中产生NO气体。2．采用末端带有电荷的烷基硫醇首先自组装在金电极表面形成前体膜，在此前体膜上成功地沉积出杂多阴离子和一种阳离子聚合物的多层膜。利用多种技术对这种多层膜进行了表征，包括紫外可见光谱法、X射线光电子能谱法、反射-吸收红外光谱法、电化学石英晶体微天平法等。而且我们把这种修饰方法推广应用于不同结构类型、不同组成的杂多阴离子和同多阴离子中去，制备了它们的多层膜。利用原位EQCM技术研究了杂多酸分子的吸附动力学行为及电化学反应过程中的离子传输特性。实验结果表明，在修饰膜的电化学反应过程中，HSO_4~-离子的迁移在膜的电荷补偿中是必不可少的。修正并发展了依据原位EQCM技术考察迁移物种特性的方法，并基于此详细分析了HPA分子在各种修饰条件下电化学反应中正常及反常的频率响应及离子迁移行为。3．首次开发出来一种新颖的多层膜成膜方法-电化学生长法，并应用于制备含杂多化合物的多层膜中。通过多种技术表征，证明了电化学生长法比文献中通用的浸泡法更优越，可以在含有支持电解质的溶液里成膜而没有其它离子竞争吸附的缺点，制备出的自组装多层膜生长更均匀、超薄且功能良好。电化学生长法可望在制备其它种类的多层膜中会有广泛的应用。同时，我们也比较了这两种多层膜对于底物BrO_3~-和HNO_2还原反应的电催化作用。特别地，我们详细考察了多层膜厚度和最外层种类对电催化反应的影响。我们发现电催化性能随着多层膜层数（厚度）的增加而增长，这意味着我们可以通过调节多层膜的层数来达到最有效的催化性能，这一点是多层膜修饰电极优越于其它类型修饰电极最突出的优点之一。此外，我们还发现QPVP-Os最外层对催化反应有着一定的阻碍作用。这些影响作用可以从多层膜中电催化剂沉积量的多少和QPVP-Os最外层的屏蔽作用得以解释。4．尽管SiW_(l2)O_(40)~(4-)不能直接吸附在裸金电极的表面形成单层膜，我们成功地在预先自组装有半胱氨的金电极上制备出来了SiW_(12)O_(40)~(4-)单层膜。但是，这种SiW_(12)O_(40)~(4-)单层膜化学修饰电极的稳定性较差。基于同阳离子聚合物QPVP-Os的静电相互作用，我们成功地制备了均匀的SiW_(l2)O_(40)~(4-)多层膜。SiW_(l2)O_(40)~(4-)多层膜CMEs对BrO_3~-，H_2O_2和HNO_2的还原表现出显著的催化效应。对HNO，还原的催化效应随着层数由l到3的增加而增强，而这种催化效应的增强却随着层数由3到7而趋于平缓。由于多层膜结构是建立在同QPVP-Os的强烈的静电作用上的，因此SiW_(12)O_(40)~(4-)多层膜CMEs比单层膜CMEs有更好的稳定性。我们主要利用电化学方法（循环伏安法，CV）、紫外可见光谱法(UV-vis)、X-射线光电子能谱法(XPS)、X-射线反射法(XR)和电化学交流阻抗法(EIS)，对这种杂多阴离子自组装多层膜的成膜过程、多层膜结构和组成进行了进一步地表征。5．通过氨阳离子自由基修饰方法，把4-氨基苯甲酸修饰到玻碳电极表面。研究了该单层膜对多种电活性分子的影响，膜的阻滞行为主要是由于静电相互作用所导致的。利用循环伏安和电化学交流阻抗法考察了4-氨基苯甲酸修饰电极对不同酸度条件下铁氰化钾的电子传递情况，并测得了它的表面pKa值大约为3.1。以修饰在玻碳电极表面的4-氨基苯甲酸单层膜为前体膜，成功地静电沉积了阳离 子聚合物QPVP-Os和多种杂多化合物组成的多层膜。采用循环伏安法详细研究了这种杂多化合物单层膜和多层膜的电化学行为，并且考察了这种复合膜对三种底物BrO_3~-,HNO_2及H_2O_2的还原反应的电催化性能。6．类似地，在4-氨基苯甲酸修饰的玻碳电极表面上，我们也成功地制备了SiW_(12)的多层膜。循环伏安、X-射线光电子能谱和X-射线反射的实验结果证明多层膜的生长非常均匀而且稳定。X-射线反射实验测定了多层膜中每个SiW_(12)/QPVP-Os双层的平均厚度为30.3A。这种复合膜对Br0_3~-，HNO_2和H_2O_2还原有明显的催化活性，并且在较大的浓度范围内催化电流与浓度具有良好的线性关系。更有意义的是，随着SiW_(12)多层膜层数的增加（固定在多层膜中催化剂量的增加），多层膜的催化能力具较大程度地提高。因此，我们可以通过合理地控制多层膜的厚度来改善其催化活性及分析测定的灵敏度，从而达到最佳的催化效能和优化出最适宜的实验条件。由于电极的稳定性较好，期望可以实际用于Br0_3~-，HNO_2和H_20_2的检测。7．采用电化学生长方法在4-氨基硫酚自组装膜修饰的金电极上，制备了包含杂多阴离子（SiMo_(11)VO_(40)~(5-)和Pr(SiMo_7W_4)O_(40)~(5-)）和阳离子聚合物PDDA的多层膜修饰电极。用循环伏安法研究了多层膜修饰电极的电化学行为。在多层膜生长过程中，我们发现Mo的第三个氧化还原峰随多层膜层数的增加显著增长，而前两个氧化还原峰增长缓慢甚至不增长，这可能是由于PDDA对Mo的前两个还原峰有一定的阻碍作用所导致的。多层膜修饰电极的峰电位随pH的增加而线性负移，表明有氢离子参与到杂多阴离子的氧化还原反应中。多层膜修饰电极对BrO_3~-和HNO_2的还原反应有良好的电催化作用，Mo的第三个还原峰峰电流与BrO_3~-的浓度都有良好的线性关系，并且催化电流随着多层膜层数的增加而增长。8．我们考察了首先通过静电沉积技术（离子键组装）成膜，然后经过后续光化学反应来制备一类含聚苯胺的基于共价键结合的多层膜。通过紫外光的辐照，膜的交联结构可由离子键型转变为共价键型。溶剂刻蚀的结果表明此种共价键合多层膜有更好的稳定性。电化学实验表明，以此种方式组装在多层膜中的聚苯胺仍保留了其电化学性质。

石英晶体微天平在电极表面反应研究中的应用

石英晶体微天平（QCM）具有高灵敏度检测质量变化的特点，在电化学、分析化学以及生物化学等研究领域都有广泛的应用。特别是电化学石英晶体微天平体（EQCM），已经成为电化学研究的一种有力手段。本人在工作期间应用QCM/EQCM进行了如下研究：首次提出了云母作为QCM石英晶振新型表面材料的设想，并成功地制成云母-石英晶振子，其在气相、液相中可以正党起振。在液相中，应用此云母石英晶振检测了DNA（pCAT）在云母表面的吸附过程。并与原子力显微镜（AFM）联用观察了DNA在云母表面吸附的物理图象；直接证明了二价锰离子在DNA吸附于云母表面过程中的固定作用。研究了水相中2-巯基苯并咪唑的电化学氧化过程，考察了pH值，浓度的影响。应用EQCM监测了此氧化成膜的过程。结果表明此反应为一电子过程。并结合表面光电子能谱（XPS）对此氧化膜进行了初步表征。应用EQCM研究了核黄素RF在金电极度上的吸附行为和电化学行为。考查了pH值、浓度和扫速对RF的吸附行为和电化学行为的影响。在pH ≤ 9.71下得到可逆的循环伏安图；而pH > 9.71时RF不发生电化学反应；最大电流响应在pH = 8.0。当RF浓度小于1.0 * 10~(-4)mol/L(pH = 6.92)时，电流与扫速平方根成正比关系，相反，浓度大于此值则电流与扫速成正比关系。在辅酶Q_0水溶液的电化学研究中，由伏安曲线得到Q_0的电位～pH图，并以此分析了不同pH值下的Q_0的存在形式，求算了Q_0的酸解常数。研究还表明了辅酶Q_0在金电极上的吸附行为随pH的变化而不同。另外还应用EQCM研究了多晶金电极度在盐酸中的阳极度溶解行为，证明此过程是三电子过程。并发现生物素具有抑制金电极度阳极度溶解的作用。

高稳定性安培生物传感器的研制

生物传感器已发展成为一种新型的分析手段，并被广泛应用于临床、环境、食品等领域。本论文从合成新型生物相容性固定化载体、寻找高稳定性的酶及建立新的有机相体系三方面对酶电极进行了研究。主要结果如下：1. 采用有机-无机杂化的方法，首次将无机玻璃材料同高分子水凝胶结合起来，制备了一种新的固定化载体。我们对其制备条件进行了优化，结果表明：正硅酸乙酯与水的最佳比率为1:4，而水凝胶有最佳含量为38.3%。这种掺杂材料一方面春服了两种材料各自的缺点，即溶胶-凝胶陶瓷材料的开裂和水凝胶的溶胀；另一方面保留了水凝胶的生物相容性和无机玻璃的物理刚性、高稳定性等优点。红外、电镜和QCM实验证明，膜中含有大量的羟基和氢键，且两种组分形成互穿网络。另外，当酶分子被包埋于溶胶-凝胶复合膜中后，没有发现酶的泄漏。2. 用此种杂化材料固定了葡萄糖氧化酶、辣根过氧化物酶及酷氨酸酶，制备了薄膜型生物传感器。有机-无机复合膜较薄从而具有短的扩散路径，因此传感器的响应很快。另外，由于杂化膜的高生物相容性和稳定性，这些酶固定后都保持了高的生物活性，故制备的生物传感器具有高的灵敏度和好的稳定性等优点。这些证明溶胶-凝胶掺杂法是制备高稳定的生物传感器的普适方法。3. 通过双水相萃取、Mono-Q柱层析和Butylsuperose疏水层析等纯化步骤，从商品大豆的种皮中提纯了一种高稳性的大豆过氧化物酶。该酶的活力为200 pyrogallol U/mg，大大高于Sigma公司产品（130 pyrogallol U/mg)。此过氧化物酶可在从pH3-10范围内维持其活性，并且显示了不寻常的热稳定性（60 ℃时半衰期为20小时）。我们用此酶首次制备出在酸性条件下可稳定使用的过氧化氢传感器。在低的pH值时，酶电极具有快的响应，高的灵敏度和好的长期稳定性。此酸稳定传感器的提出扩展了生物传感器的应用领域。4. 发展了一种新型的可用于监测惰性有机溶剂的安培传感器。EQCM和电化学实验阐明了其机理：注入的有机溶剂富集底物探针酚，降低了酶膜中酚的浓度，故引起传感器响应的下降。因为电流的下降正比于所加入的有机溶剂的数量，因此可以用安培传感器来定量测定电化学惰性的有机溶剂。对某有机溶剂的灵敏度和检测限依赖于酶载量及固定化载体和底物探针的憎水性。该传感器可以用于废水分析和环境临测，大大地延伸了生物传感器的适用范围。5. 将生物膜与传感器技术结合起来，制备了双层磷脂膜生物传感器。采用浸涂及浇铸等新的固定化方法，将辣根过氧化物酶分别固定到双层及多层磷脂膜中，在玻碳电极上制备了过氧化氢传感器。由于生物膜所带的负电荷能排斥抗坏血酸、尿酸等阴离子物质，从而较大的消除了杂质的干扰。另外由于生物膜在电极表面上为酶提供了生物相容的微环境，故实现了辣根过氧生物酶与玻碳电极之间的直接电子转移，为制备第三代生物传感器奠定了基础。

Charge Transport Processes of Immobilized Heteropolyanions at Self-assembled Monolayer Modified Gold Electrode by Electrochemical Quartz Crystal Microbalance Measurement

The in situ electrochemical quartz crystal microbalance(EQCM) technique was used to investigate the ion transport of immobilized heteropolyanions at a self-assembled monolayer(SAM) modified gold electrode during electrochemical redox process. A mixed transfer method was presented to analyse the abnormal change of resonant frequency based on the simultaneous insertion/extraction of different ions. The results indicate that the migration of HSO4- anions was indispensable in the redox process of the heteropolyan ions in a I mol/L H2SO4 solution and played a key role in the abnormal change of the resonant frequency. Such a change was attributed to different packing densities derived by means of differently immobilized methods.

Application of Ru(bpy)(3)(2+) in control and formation of gold surface nanostructure through oxidation-reduction cycling

It was studied that the nanostructure formed on a gold surface via a simple oxidation-reduction cycles (ORC) in 0.1 M KCl containing Ru(bpy)(3)(2+) with different concentrations. Atomic force microscopy (AFM) and energy-dispersed spectroscopy (EDS) were used to characterize the nanostructure formed on the gold surface. Sweep-step voltammetry and corresponding electroluminescence (ECL) response, in situ electrochemical quartz crystal microbalance (EQCM) measurement were used to monitor the ORC. procedure. It was found that the surface structure became more uniform in the presence of Ru(bpy)(3)(2+), and the surface roughness was decreasing with the increasing of Ru(bpY)(3)(2+) concentration, suggesting a simple and effective method to control the formation of nanostructure on the gold surface.