High catalytic activity of nanostructured Pd thin films electrochemically deposited on polycrystalline Pt and Au substrates towards electro-oxidation of methanol

Nanostructured Pd thin films are directly formed on polycrystalline Pt and Au substrates in the absence of hard and soft templates by using a cyclic potential sweep technique, which is confirmed by both SEM observation and their unusual cyclic voltammetric characteristics in H₂SO₄ solution. Interestingly, the bimetallic electrodes obtained after the deposition of ultrathin Pd films onto Pt and Au substrates display much higher catalytic activity towards the electro-oxidation of methanol than the bulk Pt electrode. Besides, it is found that the foreign metal substrate has great influence on the electro-catalytic behavior of the Pd films.     

Zinc underpotential deposition at Pt(111) and Pt(110) under the influence of boric acid and chloride anions

Zinc underpotential deposition (Zn UPD) was studied by cyclic voltammetry in solutions of various pH and composition, where the effects of the presence of boric acid or chloride in the solution were observed. We have found that the cyclic voltammograms of Zn UPD at Pt(111) were dependent on boric acid concentrations, zinc ion concentrations, and pH in acidic solutions. These suggest that the induced adsorption of borate by releasing of H⁺ is accompanied with Zn UPD. The preadsorbed chloride species on Pt(110) accelerate the UPD process by their removal just before the UPD, making the surface sites available for the process, and the UPD remains at identical electrode potentials, while the chloride ions do not take part in the induced adsorption on UPD Zn at Pt, as clearly found by the radiotracer method. These show that the anions play versatile roles in the process of adlayer formation by their different but essential chemical characteristics. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 6, pp. 745–751 The text was submitted by the authors in English.     

Electrochemical Designing of Au/Pt Core Shell Nanoparticles as Nanostructured Catalyst with Tunable Activity for Oxygen Reduction

Au/Pt core shell nanoparticles (NPs) have been prepared via a layer‐by‐layer growth of Pt layers on Au NPs using underpotential deposition (UPD) redox replacement technique. A single UPD Cu monolayer replacement with Pt(II) yielded a uniform Pt film on Au NPs, and the shell thickness can be tuned by controlling the number of UPD redox replacement cycles. Oxygen reduction reaction (ORR) in air‐saturated 0.1 M H₂SO₄ was used to investigate the electrocatalytic behavior of the as‐prepared core shell NPs. Cyclic voltammograms of ORR show that the peak potentials shift positively from 0.32 V to 0.48 V with the number of Pt layers increasing from one to five, suggesting the electrocatalytic activity increases with increasing the thickness of Pt shell. The increase in electrocatalytic activity may originate mostly from the large decrease of electronic influence of Au cores on surface Pt atoms. Rotating ring‐disk electrode voltammetry and rotating disk electrode voltammetry demonstrate that ORR is mainly a four‐electron reduction on the as‐prepared modified electrode with 5 Pt layers and first charge transfer is the rate‐determining step.     

Investigation of ruthenium deposition onto a platinized platinum electrode in sulfuric acid media

Ruthenium deposition onto platinized Pt electrode in 0.5 M H₂SO₄ solution is investigated. The I–V profiles of the Pt electrode covered with Ru depend on the potential of Ru deposition. This phenomenon is explained by the increasing degree of oxidation of the Ru layers deposited at higher potentials. Oxidation of Ru deposited at low potentials begins with comparatively slow processes. A mechanism for Ru deposition via ionization of hydrogen adsorbed on platinized Pt electrode is proposed.     

Oxidation of Electrodeposited Copper on Boron Doped Diamond in Acidic Solution: Manipulating the Size of Copper Nanoparticles Using Voltammetry

The in situ deposition of copper, in acidic solution onto a Boron Doped Diamond electrode, using cyclic voltammetry is explored and produced surfaces are imaged using Atomic Force Microscopy. A uniformly dense covering of copper nanoparticles is produced when the potential of a freshly polished BDD electrode is swept from 0 V in a negative direction. For example, in 1 M H₂SO₄ with a Cu(II) concentration of 1 mM, nanoparticles of height 10.1 nm, diameter 74.6 nm and a density of 16.1 particles per μm² are created when the potential is swept to ?0.35 V. The higher the concentration of Cu(II) in solution or the larger the magnitude of the end potential the larger the nanoparticles are and the more densely they are spread. When the direction of the scan is reversed and a positive potential sweep carried out evidence from the observed cyclic voltammograms and AFM images shows that copper is being incompletely stripped from the electrode surface. If the potential is then cycled continuously ten times, as would happen when the process is used for electroanalytical purposes, then an irregular and irreproducible deposit is observed. One can infer from this evidence that the incompletely stripped copper is electrochemically active and therefore adversely affecting subsequent deposition processes. Comparison to existing literature shows that the discrete application of particular deposition and stripping potentials is a much better way to produce a deposit of copper nanoparticles than application of potential through cyclic voltammetry.     

铅在铜上电沉积的原位椭圆偏振法

采用循环伏安法(CV)和原位椭圆偏振法(SE)研究铅在铜电极上的电沉积行为。 原位椭圆偏振参数Ψ和Δ值的变化率在CV图峰电位处同时出现极值。 通过建立单层膜模型描述“电极-溶液”界面的结构并对椭圆偏振光谱数据进行拟合得到铅沉积层厚度随电位的变化规律。 拟合结果显示,铅在铜电极上的电沉积有3个不同的沉积速率,-0.20～-0.35 V之间沉积速率为0.003 nm/mV,-0.35～-0.48 V之间沉积速率为0.025 nm/mV,-0.48～-0.60 V之间沉积速率为0.116 nm/mV,由此表明铅的电沉积分为3个不同阶段：欠电位沉积阶段、欠电位沉积向本体沉积的过渡阶段和本体沉积阶段。     

Pd/Pt二元合金电极的制备及氧还原性能

本文利用欠电位沉积亚单层的Cu及Pt置换取代Cu的方法, 制备了具有不同表面元素组成的Pd/Pt二元合金电极(用Pd/Ptx表示, x指欠电位沉积Cu-Pt置换取代Cu过程的次数),并对其表面元素组成、氧还原性能进行了表征. 在控制欠电位沉积Cu的下限电位恒定(0.34 V)的前提下, 表面Pt/Pd的元素组成比通过重复欠电位沉积Cu及Pt置换取代Cu的次数(1~5次)来可控地调变. 光电子能谱(XPS) 以及红外光谱实验表明,Pd/Ptx电极表层区的Pt：Pd元素组成比随着Pt沉积次数增加而增加, 对Pd/Pt4电极, 在电极表层区约2~3 nm内的Pt/Pd的原子比大约是1:4,而最表层裸露Pd原子的比例仍在20%以上。循环伏安结果显示, 随着Pt沉积次数的增加(1-5次), Pd/Ptx电极表面越不易被氧化。氧还原测试结果显示随着Pt沉积次数的增加(1~4次), Pd/Ptx二元金属电极的氧还原活性依次增加, 经过第3次沉积后其氧还原活性已优于纯Pt,而经4次以上沉积,其氧还原活性基本不变。在其它反应条件相同条件的前提下, Pd/Pt4电极上氧还原的半波电位与纯Pt相比右移约25 mV。结合本文与文献的实验结果,我们初步认为Pd/Ptx二元金属体系氧还原性能改善主要源自表层Pd原子导致其邻近的Pt原子上含氧物种吸附能的降低.     

次亚磷酸根离子在多晶铂电极上氧化的原位红外光谱研究

次亚磷酸根离子在多晶铂电极上氧化的原位红外光谱研究;电氧化;电催化;SNIFTIRS     

Site-selective Cu deposition on Pt dendrimer-encapsulated nanoparticles: correlation of theory and experiment

The voltammetry of Cu underpotential deposition (UPD) onto Pt dendrimer-encapsulated nanoparticles (DENs) containing an average of 147 Pt atoms (Pt(147)) is correlated to density functional theory (DFT) calculations. Specifically, the voltammetric peak positions are in good agreement with the calculated energies for Cu deposition and stripping on the Pt(100) and Pt(111) facets of the DENs. Partial Cu shells on Pt(147) are more stable on the Pt(100) facets, compared to the Pt(111) facets, and therefore, Cu UPD occurs on the 4-fold hollow sites of Pt(100) first. Finally, the structures of Pt DENs having full and partial monolayers of Cu were characterized in situ by X-ray absorption spectroscopy (XAS). The results of XAS studies are also in good agreement with the DFT-optimized models.     

Cu + Au alloy particles formed in the underpotential deposition region of copper in acid solutions

Cu + Au alloy particles electrodeposited on an amorphous carbon electrode at the underpotential region of Cu in both perchloric acid and sulfuric acid solutions were investigated by means of transmission electron microscopy. The fraction of Cu in the Cu + Au alloy particles grown in both acid solutions with a concentration of 1 mM Au ion increased while the underpotential deposition (UPD) potential was decreased. However, it was independent of the concentration of Cu ion in solution. It is inferred that the composition of the Cu + Au alloy particles is dependent on the UPD potential. The fraction of Cu in the Cu + Au alloy particles grown at around the reversible Nernst potential of Cu in 0.1 mM HAuCl₄ + 50 mM Cu(ClO₄)₂ containing perchloric acid solution was 505. This result suggests a layer-by-layer formation of the Cu + Au alloy particles. The fraction of Cu in the Cu + Au alloy particles formed in the presence of sulfate was lower than that in the perchloric acid solution as the UPD potential and the concentration of Cu ion were the same. This is attributed to an influence of coadsorbed sulfate ions.     

Underpotential deposition of cobalt onto polycrystalline platinum

An electrochemical study of cobalt electrodeposition onto a polycrystalline platinum electrode from an aqueous solution (10⁻² M CoCl₂ + 1 M NH₄Cl (pH 9.5)) was carried out through cyclic voltammetry and potential step techniques. Analysis of the voltammetric data clearly showed that a cobalt adlayer is formed during the application of potential in the underpotential deposition (upd) region. Formation of this cobalt adlayer involved the simultaneous presence of both adsorption and 2D nucleation processes. Cobalt adlayers obtained by linear voltammetry in upd region were analyzed employing diffuse reflectance spectroscopy (DRS). By using theoretical quantum studies at PM6//HF/LANL1MB level, it was possible to assign the peaks obtained by DRS at 328 and 337 nm to the cobalt adsorption on Pt(111) and Pt(100), respectively, while the signals recorded at 355 and 362 nm were related with the clean platinum surfaces Pt(100) and Pt(111). Also, quantum calculations at the PM6 level indicated that the energy formation order is Co-Pt(100) > Co-Pt(111) > Co-Pt(110) > Co-Co(surface).     

高序石墨电极上单分散纳米铜粒子的电结

Mechanism of copper electrocrystallization on highly oriented pyrolytic graphite electrode from a solution of 1 mmol/L CuSO4 and 1.0 mol/L H2SO4 has been studied using cyclic voltammogram and chronoamperometry. The results show that in copper electrodeposition the charge-transfer step is fast and the rate of growth is controlled by the rate of mass transfer of copper ions to the growing centers. Reduction of Cu(Ⅱ) ions did not undergo underpotential deposition. The initial deposition kinetics of Cu electrocrystallization corresponds to a model including progressive nucleation and diffusion controlled growth. Copper nanocrystals with size of 75.6 nm and relative standard deviation of 9% can be obtained by modulation potential electrodeposition.     

Spontaneous deposition of Pt‐nanoparticles on HOPG surfaces

Pt nanoparticles were spontaneously generated by immersion of a highly ordered pyrolytic graphite substrate in a 1 mM H₂PtCl₆ + 0.05 M H₂SO₄ plating solution using different immersion times, modifying both size and density of the deposits. Atomic force microscopy images show Pt particles distributed preferentially on surface defects of the electrode, increasing their size and density with deposition time. Scanning electronic microscopy/energy‐dispersive X‐ray spectroscopy images confirmed the formation of Pt deposits after 2 h immersion, forming irregular agglomerates with different sizes distributed over the surface. The open circuit potential studies showed potentials close to the corresponding PtCl₆^2?/Pt and PtCl₄^2?/Pt couples, which would indicate that some of these processes took place at the interface. The voltammetric response of the supported Pt nanoparticles showed an increase in current density towards the hydrogen evolution reaction being more pronounced for deposits formed after an immersion time of 2 h. In this case, the voltammetric behavior was similar to polycrystalline Pt. Copyright © 2015 John Wiley & Sons, Ltd.     

Underpotential Deposition‐Induced Synthesis of Composition‐Tunable Pt?Cu Nanocrystals and Their Catalytic Properties

Pt? Cu alloy octahedral nanocrystals (NCs) have been synthesized successfully by using N,N‐dimethylformamide as both the solvent and the reducing agent in the presence of cetyltrimethylammonium chloride. Cu underpotential deposition (UPD) is found to play a key role in the formation of the Pt? Cu alloy NCs. The composition in the Pt? Cu alloy can be tuned by adjusting the ratio of metal precursors in solution. However, the Cu content in the Pt? Cu alloy NCs cannot exceed 50 %. Due to the fact that Cu precursor cannot be reduced to metallic copper and the Cu content cannot exceed 50 %, we achieved the formation of the Pt? Cu alloy by using Cu UPD on the Pt surface. In addition, the catalytic activities of Pt? Cu alloy NCs with different composition were investigated in electrocatalytic oxidation of formic acid. The results reveal that the catalytic performance is strongly dependent on Pt? Cu alloy composition. The sample of Pt₅₀Cu₅₀ exhibits excellent activity in electrocatalytic oxidation of formic acid.     

Monolayer deposition of silver and copper onto platinum electrodes at non-equilibrium conditions

Ag and Cu were deposited in submonolayer amounts onto Pt electrodes at constant cathodic potentials within the hydrogen adsorption region. Rectangular pulses of Cu²⁺ or Ag⁺ fluxes to the Pt surface were generated by a Cu or Ag generator electrode using the twin electrode thin-layer technique. The analysis of the response currents of the Pt electrode yields in formation about the metal deposition process at non-equilibrium conditions. Cu and Ag were found to deposit directly as monolayers and not at random. The displacement of adsorbed hydrogen was measured as a function of the quantity of metal deposited.     

Electrochemical systems for galvanic cells in organic aprotic solvents: V. Electrochemical behaviour of gamma-butyrolactone

Gamma-butyrolactone (GBL) was shown to decompose on the clean surface of Li, Na, K, and their amalgams. Polarization curves were obtained on Pt and “Kovar” electrodes at potentials from 4 to ?4 V vs. Li?Hg in 0.5 M LiClO₄ or vs. K?Hg in 0.5 M KPF₆. GBL was found to reduce electrochemically at potentials more positive than 1 V. Various passivation phenomena provoked by the decomposition of the solvent were observed, hindering cathodic deposition of the alkali metals from solutions of their salts in GBL. The presence of a high-molecular surfactant in the electrolyte suppresses the decomposition of GBL and suggests a path to the deposition of Li on the electrode.     

Nucleation and growth of Cu onto polycrystalline Pt electrode from acidic CuSO4 solution in the presence of H2SeO3

The early stages of Cu electrodeposition onto Pt(poly) have been investigated in 0.5 M H₂SO₄ + 0.01 M CuSO₄ solution without or with H₂SeO₃ when a molar concentration ratio [Cu(II)]/[Se(IV)] ≥ 2×10² using electrochemical and ex situ AFM techniques. The overpotential deposition of Cu has been performed onto a Pt surface precovered independently with Cu in amount close to an equivalent monolayer. Chronoamperometric results have been shown to follow an instantaneous 3D nucleation and diffusion-controlled growth model. The values of diffusion coefficient D for Cu²⁺, number of nuclei N and average nuclei radius r _av have been calculated. In the local regions of the surface, the separate large agglomerates composed of the different diameter clusters have been revealed in both cases, but, in the presence of the H₂SeO₃, they attained a distinct chain-like configuration. Some morphological characteristics have been reported.     

Rotating ring-disk voltammetry: Diagnosis of catalytic activity of metallic copper catalysts toward CO<Subscript>2</Subscript> electroreduction

Using the rotating ring (platinum)—disk (glassy carbon) electrode methodology, electrocatalytic activity of the microstructured copper centers (imbedded within the polyvinylpyrrolidone polymer matrix and deposited onto the glassy carbon disk electrode) has been monitored during electroreduction of carbon dioxide both in acid (HClO₄) and neutral (KHCO₃) media as well as diagnosed (at Pt ring) with respect to formation of the electroactive products. Combination of the stripping-type and rotating ring-disk voltammetric approaches has led to the observation that, regardless the overlapping reduction phenomena, the reduction of carbon dioxide at copper catalyst is, indeed, operative and coexists with hydrogen evolution reaction. Using the fundamental concepts of surface electrochemistry and analytical voltammetry, the reaction products (thrown onto the platinum ring electrode) could be considered and identified as adsorbates (on Pt) under conditions of the stripping-type oxidation experiment. Judging from the potentials at which the stripping voltammetric peaks appear in neutral CO₂-saturated KHCO₃ (pH 6.8), formic acid or carbon monoxide seem to be the most likely reaction products or intermediates. The proposed methodology also permits correlation between the CO₂ electroreduction products and the potentials applied to the disk electrode. By performing the comparative stripping-type voltammetric experiments in acid medium (HClO₄ at pH 1) with the adsorbates of formic acid, ethanol and acetaldehyde (on Pt ring), it can be rationalized that, although C₂H₅OH or CH₃CHO are very likely CO₂-reduction electroactive products, formation of some HCOOH, CH₃OH or even CO cannot be excluded.     

Enhanced Electrocatalytic Activity of Dual Template Based Pt/Cu‐zeolite A/Graphene for Methanol Electrooxidation

A novel Pt/Cu‐zeolite A/graphene based electrocatalyst was successfully prepared by chemical reduction method for methanol electrooxidation. Graphite oxide and Cu functionalized zeolite A were simultaneously reduced by NaBH₄ to prepare Cu‐zeolite A/graphene support which was used to deposit Pt nanoparticles. The nanostructure and composition of as‐prepared Pt/Cu‐zeolite A/graphene composites were characterized by X‐ray diffractometer, X‐ray fluorescence, Fourier transform infrared spectrometer and scanning electron microscopy. The electrocatalytic properties of Pt/Cu‐zeolite A/graphene modified electrode for methanol oxidation were investigated by cyclic voltammetry and chronoamperometry in 0.10 mol/L H₂SO₄ + 0.50 mol/L CH₃OH solution. Compared with Pt/zeolite A/graphene electrode and Pt/graphene electrode, Pt/Cu‐zeolite A/graphene based electrode exhibited obviously enhanced current and higher electrocatalytic activity for methanol electrooxidation. The increased electrocatalytic activity was attributed to the presence of zeolite A and reduced graphene oxide based dual template, which significantly increased the effective electrode surface and facilitated the diffusion of analytes into the electroactive catalyst.     

Electroreduction of Oxygen and Electrooxidation of Methanol at Carbon and Single Wall Carbon Nanotube Supported Platinum Electrodes

The present research aimed at investigating the electrocatalytic properties and the electrochemical deposition of Pt nanoparticles on carbon powder, carbon nanotube and preparation of carbon and single wall carbon nanotube supported platinum electrodes. The Pt nanoparticles were synthesized by electroreduction of hexachloroplatinic acid in aqueous solution at ?200 mV. Electrocatalytic properties of the modified electrodes for oxygen reduction were investigated by cyclic voltammetry in O₂ saturated solution containing 0.1 M HClO₄. Methanol electrooxidation at the modified surfaces in 0.5 M HCLO₄ was studied by cyclic voltammetry. The corresponding results showed that the Pt/SWCNT/GC electrode exhibits more improved catalytical activity than the Pt/C/GC electrode.