Underpotential Deposition Of Cu Research Articles

Underpotential deposition of Cu onto Au(111) in the presence of acetate

The underpotential deposition (UPD) of Cu on Au(111) in the presence of acetate is investigated by cyclic voltammetry, potential step experiments, and in-situ STM imaging. The specific adsorption of acetate stabilizes the UPD monolayer (ML) of Cu on Au(111). Three distinct deposition processes are identified by cyclic voltammetry. The first two deposition processes corresponding to Cu sub-monolayer coverages are reversible. Strong kinetic effects arise for higher Cu coverage during the deposition and dissolution, which gradually lower the reversibility of the electrocrystallization process. Dissolution of the full Cu monolayer is shifted positively by about 0.3 V. In addition, bulk deposition is kinetically hindered for an extended potential region. The acetate coverage on the complete Cu monolayer is estimated to be 0.2–0.3 ML. It is proposed that adsorbed acetate on the Cu UPD ML is related to the kinetic hindrance observed in the experiments. (Surface) alloying of Cu and Au is observed by cyclic voltammetry and in-situ STM.

Underpotential Deposition of 3D Transition Metals: Versatile Electrosynthesis of Single-Atom Catalysts on Oxidized Carbon Supports.

Use of single-atom catalysts (SACs) has become a popular strategy for tuning activity and selectivity toward specific pathways. However, conventional SAC synthesis methods require high temperatures and pressures, complicated procedures, and expensive equipment. Recently, underpotential deposition (UPD) has been investigated as a promising alternative, yielding high-loading SAC electrodes under ambient conditions and within minutes. Yet only few studies have employed UPD to synthesize SACs, and all have been limited to UPD of Cu. In this work, a flexible UPD approach for synthesis of mono- and bi-metallic Cu, Fe, Co, and Ni SACs directly on oxidized, commercially available carbon electrodes is reported. The UPD mechanism is investigated using in situ X-ray absorption spectroscopy and, finally, the catalytic performance of a UPD-synthesized Co SAC is assessed for electrochemical nitrate reduction to ammonia. The findings expand upon the usefulness and versatility of UPD for SAC synthesis, with hopes of enabling future research toward realization of fast, reliable, and fully electrified SAC synthesis processes.

Investigation of copper underpotential deposition on polycrystalline gold electrodes

A combination of cyclic voltammetry, electrochemical impedance spectroscopy, and chronoamperometry techniques has been used to study the underpotential deposition (UPD) of copper on polycrystalline gold (pc Au) electrodes. The experiments were conducted in an electrolyte composed of CuSO4 (5 mM) and H2SO4 (0.5 M). The results revealed that the concentration of copper (II) ions and the applied voltage exerted a synergistic effect on the position, shape, and range of spanning of the curves describing the redox potential and current density. The charge transfer resistance (Rct) corresponding to the UPD of Cu decreased monotonically with a decrease in the applied voltage, and the phase angle shifted toward high-frequency regions with a negative shift in the potential. The process of UPD of Cu on pc Au can be divided into three stages: Langmuir-type adsorption, growth of Cu monolayers on pc Au following the process of two-dimensional instantaneous nucleation, and the continuous two-dimensional nucleation of grains on the Cu layer. UPD on single crystal substrates and the single-layer and multi-layer structures associated with UPD have been extensively studied worldwide. However, the UPD of polycrystalline electrodes with various crystal faces, grain boundaries, and defects is complex, and the associated mechanism has rarely been studied. In recent years, the process of UPD has been widely used in various fields, such as fields associated with electrochemical sensing, fabrication of fuel cells, electrochemical CO2 reduction, and fabrication of solar cells.

High Purity Pd Nanofilm Deposition Via Cu Incorporation Control in Slrr Process

Department of Materials Science & Chemical Engineering, Hanyang University, Ansan 15588, Korea *byyoo@hanyang.ac.kr ABSTRACT The deposition of palladium has been considered in many industrial applications and in fundamental science because of the high catalytic activities. Careful control of smooth and continuous Pd film less than 1nm thickness is critical for achieving highly active catalysts. Furthermore, perspective of cost-effective view, minimum usage of Pd is essential for catalyst while showing maximum activity for catalyst due to its high cost.Electrochemical-atomic layer deposition (E-ALD), can achieve the growth of atomic level of metal film under room temperature and simple condition. E- ALD protocol proceeds using surface limited redox replacement (SLRR). SLRR involves 2 step. First, Au substrate is covered with Cu monolayer, the result of underpotential deposition of Cu (sacrificial element). Underpotential deposition (UPD) is the deposition occurs at more positive potential than equilibrium potential which the potential where deposition actually strats and UPD can limit Cu deposition by atomic layer. Second, Cu atomic layer is replaced by more noble metal (Pd) by galvanic displacement without applying potential. In one cell approach, the concentration ratio of sacrificial metal and noble metal and potential set is carefully set in order to deposit pure noble metal layer. Therefore, precise control of potential and metal concentration is important to execute successful SLRR which prevent Cu incorporation and Pd overpotential deposition upon Cu UPD formation.In this study, pure Pd nanofilm was formed on Au substrate using Cu sacrificial metal by SLRR protocol. Effort of minimizing Cu incorporation was conducted by controlling Pd ion concentration, potential , open circuit potential condition and adding additive. Pd film was characterized by XPS, AFM and open circuit potential was analyzed by potentiostat. By controlling Pd deposition condition, pure Pd film was successfully formed. KEYWORDS Palladium, one-cell, nanofilm, SLRR, Cu UPD

Operando X-Ray Absorption Spectroscopic Study on Electrochemical Oxygen Reduction Mechanism of Novel Platinum-Based Nanostructured Catalysts

Polymer electrolyte fuel cells (PEFCs) have been developed for electric device applications such as fuel cell vehicles (FCV). PEFC cathode catalyst requires an excess Pt due to the degradation of oxygen reduction reaction (ORR) activity. Many research efforts aim to design Pt-based nanomaterials with controllable composition and structure to increase their activity while reducing the amount of Pt, like core-shell structure. The core-shell structure is obtained by Adzic’s method (Cu-UPD)1, where the underpotential deposition (UPD) of Cu mediator on Pt and the displacement of Cu mediator by Pt are conducted. This method requires the highly precise potential control for the UPD of Cu by means of potentiostats. In contrast, our previous research demonstrated the spontaneous two-step method (Galvanic cell) to synthesize spherical Pd@Pt core-shell catalyst without a special control of electrochemical equipment and reducing/stabilizing agents2. In this study, this Galvanic cell method was applied for Pd@Pt core-shell nanowire catalysts. Compared with the conventional Cu-UPD method, this method can synthesize the catalysts on a larger scale and form more uniform monolayer Pt shells, resulting in a higher ORR activity.Ultrathin Pd nanowires were prepared using surfactants as templates3. Briefly, palladium nitrate, ODA, and DTAB were dissolved in toluene under strong magnetic stirring. The mixture was placed in an inert atmosphere and sonicated for 20 min. NaBH4 was added to the above solution as a reducing agent. One hour later, the organic phase was recovered using distilled water and chloroform as extractants. After centrifugation, Pd nanowires can be obtained. After mixing the catalyst with carbon, the Pd/C powder is dispersed in the N2-saturated 0.01M CuSO4 and 0.5 M H2SO4 solution, with continual stirring. Then, a Cu wire is immersed in the above mixture2. Near 5 hours later, Cu wire is extracted, and successively N2-saturated 10 mM K2PtCl4 solution is added to the suspension to obtain Pd-nanowire@Pt/C. Electrochemical tests were performed in 0.1 M HClO4, and the catalyst ORR activity was evaluated at 0.9 V. XAS measurements of Pt L-edge were also performed under the same conditions.In contrast to the previously reported method (Cu-UPD)4, our proposed method does not require electrochemical equipment, or reducers/stabilizers, and uniform Pt shells in Pd-nanowire@Pt/C can be obtained. As shown in Figure 1, Core-shell catalysts have a lower white line intensity than Pt/C, meaning that they are more difficult to oxidize. The ligand effect causes surface Pt compression, and after calculating, the first-shell Pt-Pt bond length in the Pd-NW@Pt Gal. catalyst is shorter than that of the nanoparticle, which means a stable structure and less oxygen species generation. So, the catalysts synthesized using the Galvanic Cells method can provide higher ORR activity (specific activities: 0.8 mA/cm2 and mass activities: 1.3 A/mgPt) compared to the Cu-UPD method. Acknowledgement This work was supported by the project (JPNP20003) and a NEDO FC-Platform project commissioned by the New Energy and Industrial Technology Development Organization (NEDO). References; [1] Zhang, J.; Mo, Y.; Vukmirovic M. B.; Klie R; Sasaki K.; Adzic R R.; J. Phys. Chem. B 2004 108 (30), 10955-10964.[2] Wang, X.; Orikasa, Y.; Inaba, M.; Uchimoto, Y.; et al. ACS Catal., 2020, 10, 430– 434.[3] Teng, X.; Han, W.; Ku, W.; Hucker, M.; et al. Angew. Chem., Int. Ed. 2008, 47, 2055– 2058.[4] Koenigsmann, C., Adzic, R. R.; et al. J. Am. Chem. Soc., 2011 , 133, 9783– 9795. Figure 1

The Electrocatalytic Reduction of Aqueous Selenate As Mediated By Underpotential Deposition of Cu and Cd on Au Electrodes

In analogy with many other oxyanions, the electrochemical reduction of selenate, SeO4 2-(aq) in aqueous solutions on most electrode surfaces is typically characterized by slow kinetics. Typical reduction strategies employ excessive amounts of cationic reducing agents like Cu(I) and Fe(II) compounds [1, 2]. Recently, Cu UPD on Au(poly) was found not only to promote reduction of SeO4 2-(aq) in acidic electrolytes, but advantage was taken of the resulting Cu/Se stripping peaks to develop an exceedingly sensitive analytical method for SeO4 2-(aq) detection down to the nM range [3]. An example of some typical qSe vs. [Na2SeO4] calibration curves, where qSe represents the charge under the Se stripping peak, (see insert in Fig. 1), are shown in Fig. 1. The rates of SeO4 2-(aq) reduction as catalyzed by Cu UPD are very time dependent, indicative of a complex electrocatalytic mechanism. Insight into some aspects of this process has been gained from studies involving the low index faces of single crystal Au via hold/strip voltammetry coupled with Normal Incidence Differential Reflectance (NIDR) and in the case of Au(111), by Electrochemical Quartz Crystal Microgravimetry (EQCM) studies. It has been found that a minimum surface coverage of Cu UPD is required before any reduction of SeO4 2-(aq) occurs, and that reduction slows over time as the surface saturates with Se atoms. However, excessively high Cu UPD coverages were found to hinder SeO4 2-(aq) reduction on the Au(111) plane. Some simple kinetic models have been formulated to attempt to capture the observed behavior. Additionally, at fixed coverages of Cu UPD, rates of SeO4 2-(aq) reduction increase with decreasing applied potential. To this end, the possible electrocatalytic properties of other metals capable of undergoing UPD at potentials more negative than those of Cu were considered. The first candidate to be examined was Cd, a metal for which the work function in bulk form is much lower than that of Cu [4] and, thus, its UPD should occur at more negative potentials. In addition, Cd UPD on Au has shown electrocatalytic activity for the reduction of NO3 -(aq), yet another example of a difficult to reduce oxyanion, in aqueous electrolytes [5]. It was found that SeO4 2-(aq)reduction can indeed be catalyzed by Cd UPD on Au, as shown in Fig. 2. In contrast to Cu UPD catalyzed reduction, it was found that under certain conditions the reduction rates of SeO4 2-(aq) were time independent when mediated by Cd UPD, as shown in Fig 3.

Fabrication of underpotentially deposited Cu monolayer/electrochemically reduced graphene oxide layered nanocomposites for enhanced ethanol electro-oxidation

Cu monolayer/electrochemically reduced graphene oxide (ML/ERGO) layered nanocomposites are grown on Au substrates by sequential underpotential deposition of Cu(ML)s and electrochemical reduction of graphene oxide for the electrocatalytic oxidation of ethanol. Characterization of the Au-Cu(ML)/ERGO layered composites by scanning electron microscopy and scanning tunneling microscopy reveal that the smooth Cu(ML) on the Au surface is transformed into parallel aligned nanoparticles after modification by the ERGO layer. X-ray photoelectron spectroscopy and Raman spectroscopy results for the Au-Cu(ML)/ERGO composites show the successful electrochemical reduction of GO to ERGO and the presence of metallic Cu in the nanocomposite structure. Electrochemical measurements of the as-prepared Au-(Cu(ML)/ERGO)1 electrodes exhibit excellent electrocatalytic performance (15 mA cm−2), which was 5.7 and 1.6 times higher than those from the naked Au and Au-Cu(ML) electrodes, respectively, toward ethanol electro-oxidation in alkaline condition.

(Invited) Development and Application of Core-Shell Cathode Catalysts in PEM Fuel Cell

Platinum group metals (PGM) catalysts are presently the most promising catalysts for the oxygen reduction reaction (ORR). However, the total PGM content in the PEM fuel cell should be reduced. To meet longer term passenger vehicle automotive targets, catalyst with at least 4 times higher mass activity over the currently available commercial Pt/C is required. One promising approach to meet this goal is the development of Pt monolayer core-shell catalysts through electro under-potential deposition of Cu onto a core (Pd, PdAu, etc.), followed by galvanic replacement of the Cu by Pt salt [1]. It is widely accepted that Pt monolayer catalysts exhibit at least 4-8 times higher mass activity vs. Pt/C, while also demonstrating excellent durability during accelerated stress testing on rotating disk electrodes (RDE) [2]. However, the scale-up synthesis of the platinum monolayer core-shell catalysts and the retention of favorable catalytic performance in the membrane electrode assemblies (MEA) are still quite challenging [3]. In this work, we will present the results of Pd@Pt/C core-shell catalysts successfully scaled up (in-house) from a conventional synthetic approach (micro gram level) to a large 3-electrodes reactor (gram level). It is demonstrated that this scale up is successful, with the gram level batch showing comparable activity to the small scale batch, based on RDE testing. In addition, preliminary in-situ MEA tests of commercial core-shell catalysts will be presented, demonstrating the performance and durability of these monolayer core-shell catalysts under fuel cell operating conditions. [1] R. R. Adzic. Electrocatalysis, 2012, 3 (3-4):163-169. [2] J. Hu, L. Wu, K. A. Kuttiyiel, K. R. Goodman, C. Zhang, Y. Zhu, M. B. Vukmirovic, M. G. White, K. Sasaki, R. R. Adzic, J. Am. Chem. Soc. 2016, 138: 9294-9300. [3] L. L. Zhang, S. Zhu, Q. Zhang, D. Su, J. Yue, Z. Du, M. Shao. ACS Catal. 2016, 6: 3428 −3432.

Tuning the branches and composition of PtCu nanodendrites through underpotential deposition of Cu towards advanced electrocatalytic activity

PtCu nanodendrites with tunable sizes, branches, and composition are rapidly and cost-effectively prepared for efficient oxygen reduction and methanol oxidation.

Underpotential deposition of Cu on Au(111) from neutral chloride containing electrolyte.

The structure of a chloride terminated copper monolayer electrodeposited onto Au(111) from a CuSO4/KCl electrolyte was investigated ex situ by three complementary experimental techniques (scanning tunneling microscopy (STM), photoelectron spectroscopy (PES), X-ray standing wave (XSW) excitation) and density functional theory (DFT) calculations. STM at atomic resolution reveals a stable, highly ordered layer which exhibits a Moiré structure and is described by a (5 × 5) unit cell. The XSW/PES data yield a well-defined position of the Cu layer and the value of 2.16 Å above the topmost Au layer suggests that the atoms are adsorbed in threefold hollow sites. The chloride exhibits some distribution around a distance of 3.77 Å in agreement with the observed Moiré pattern due to a higher order commensurate lattice. This structure, a high order commensurate Cl overlayer on top of a commensurate (1 × 1) Cu layer with Cu at threefold hollow sites, is corroborated by the DFT calculations.

Calorimetric measurement of adsorption and adhesion energies of Cu on Pt(111)

The adsorption energies of submonolayer amounts of one metal on the surface of another metal have been measured for decades by temperature programmed desorption. However, that method fails for metals that alloy. We report here the first measurement of the adsorption energy for any such metal-on-metal combination that forms a bulk alloy. The adsorption and interfacial energetics of vapor deposited Cu onto Pt(111) at 300K has been studied using single crystal adsorption calorimetry (SCAC) and X-ray photoelectron spectroscopy (XPS). The Cu grows as 2D pseudomorphic islands in the first layer and its heat of adsorption decreased linearly from 358 to 339kJ/mol. This is attributed to increasing lattice strain with island size, associated with the small lattice mismatch (8%). It adsorbs ~2kJ/mol more weakly in the 2nd layer than above 3ML, where it reaches the bulk heat of sublimation of Cu(solid), 337kJ/mol. The adhesion energy of multilayer Cu onto Pt(111) is 3.76J/m2. The extra stability of the first Cu monolayer compared to bulk Cu measured here is ~12kJ/mol, compared to a difference of ~83kJ/mol for underpotential deposition of Cu on a Pt(111) electrode, with the difference attributed to stronger bonding of Cu to the solvent and double layer compared to Pt.

Effect of Silver Modification on Glycerol Oxidation Reaction Activity of Palladium Electrode in Alkaline Medium

Introduction Biodiesel fuel (BDF) attracts attention as a carbon-neutral fuel as well as bioethanol. As the production of BDF increases, the production of the glycerol byproduct is also increasing. It is important to develop new uses for glycerol to cope with the mass production of BDF. The use of glycerol as a fuel for direct alcohol fuel cells is promising, because anodic oxidation of glycerol produced by bioprocesses occurs in carbon-neutral cycles and direct glycerol fuel cells are expected to produce electricity with a low environmental load and to be energy efficient. It is well-known that Pd is cheaper than Pt and Au, and Pd-based alloy electrodes are highly active for the oxidation of alcohols in alkaline media. We also have reported the PdAg alloys-loaded carbon exhibited higher glycerol oxidation reaction (GOR) activity and tolerance to poisoning species than Pd.1 The mechanism for GOR, however, is not so clear. In this study we prepared an Ag atomic layer-modified Pd model electrode, and investigated the potential dependence of GOR products by in situ infrared reflectance-absorption spectroscopy (IRAS). In addition, we discussed the GOR mechanism based on these data. Experimental The Ag atomic layer-loaded Pd (Ag/Pd) electrode was prepared by underpotential deposition of Cu (Cu-upd) on a Pt polycrystalline substrate and the following galvanic replacement with Ag. The coverage of Ag (θ Ag) on the Pd substrate was evaluated to be 0.5 from the charges for Cu-upd before and after the Ag modification. 1 M KOH and (1 M KOH + 0.5 M glycerol) solution were used for electrochemical measurements. In situ infrared reflection-absorption spectroscopy (IRAS) was used to qualitatively analyze the products of GOR on the Pd and Ag/Pd electrodes in alkaline solution. All electrochemical measurements were performed at room temperature. Results and Discussion The cyclic voltammograms of the Pd and Ag/Pd electrodes in a (1 M KOH + 0.5 M glycerol) solution is shown in Fig. 1. The Ag/Pd electrode had higher oxidation current and more negative onset potential of the oxidation current than the Pd electrode, clearly indicating that the GOR activity was enhanced by the modification of the Ag atomic layer. In addition, the peak potential of the oxidation current for the Ag/Pd electrode was more positive than that for the Pd electrode, suggesting that the former was superior in tolerance to poisoning species to the latter. IRAS spectra for the Pt electrode exhibited that the absorption peak at 1335 cm-1 assigned to the formation of dihydroxyacetone was mainly increased at lower potentials, but the absorption peak at 1310 cm-1 assigned to the formation of glycerate was increased at higher potentials. This suggests that the secondary OH group in a glycerol molecule is preferentially oxidized at smaller overpotentials, and the primary OH group is greatly oxidized at larger overpotentials. For the Ag/Pd electrode, the oxidation of the primary OH group occurred even at smaller overpotentials, and hydroxypyruvate was also formed at larger overpotentials. Acknowledgement This work was partially supported by JSPS KAKENHI Grant Number 15H04162. Reference 1 B. T. X. Lam, M. Chiku, E. Higuchi, H. Inoue, J. Power Sources, 297, 149 (2015). Figure 1

Glycerol Oxidation Reaction Mechanism on Ag-Modified Pt Electrode in Alkaline Medium

Introduction Recently, biodiesel fuel (BDF) attracts attention due to the progress of global warming. Glycerol as a byproduct is produced with BDF, and practically used for pharmaceuticals, cosmetics, food additives and so on. With the mass production of BDF, new applications of the glycerol byproduct need to be found. The application of glycerol as anode for direct alcohol fuel cells (DAFCs) can be an important solution because it has low toxicity and high specific energy (5.0 kWh kg-1). However, glycerol has two C-C bonds and three OH groups, so the mechanism for glycerol oxidation reaction (GOR) is complex,1 and the rate for GOR is so slow that the complete oxidation to CO2 is very difficult. Palladium is known to be one of active materials for GOR. We have found the alloy nanoparticles of Pd with Ag or Au improved the GOR activity and tolerance to the poisoning species on Pd nanoparticle in alkaline medium due to the electronic and bi-functional effects.2 Meanwhile, the Pt electrode had higher GOR activity than the Pd electrode in terms of the onset potential of GOR current, and Ag would improve the GOR activity of Pt. In this study, the effect of the modification with Ag on the GOR activity of a Pt substrate was evaluated by cyclic voltammetry (CV). Moreover, the mechanism for GOR on the Ag-modified Pt (Ag/Pt) electrode was discussed based on in situ infrared reflection absorption spectra at different potentials. Experimental The Ag/Pt electrode was prepared by underpotential deposition of Cu (Cu-upd) on a Pt substrate and the following galvanic replacement with Ag. The coverage of Ag (θ Ag) on the Pt substrate were calculated from the charge for H desorption before and after the Ag modification. The Ag/Pt electrodes with θ Ag = 0.8 and 0.5 were used in this study, which are denoted as Ag(0.8)/Pt and Ag(0.5)/Pt, respectively. The electrolytes were 1 M KOH or (1 M KOH + 0.5 M glycerol) solutions. Pt plate (1 cm × 1 cm) and a Hg/HgO electrode were used as counter and reference electrodes, respectively. In situ infrared reflection-absorption spectroscopy (IRAS) was used to qualitatively analyze the products of GOR on the Pt, Ag(0.8)/Pt and Ag(0.5)/Pt electrodes in alkaline solution. All electrochemical measurements were performed at room temperature. Results and Discussion The GOR activity for the Pt, Ag(0.8)/Pt and Ag(0.5)/Pt electrodes in alkaline medium was evaluated by CV (Fig. 1). Both Ag(0.8)/Pt and Ag(0.5)/Pt electrodes had twice higher current density and about 150 mV lower onset potential than the Pt substrate. This means that the enhancement of the GOR activity is caused by the modification of Ag atomic layers. Moreover, as θ Ag increased, a GOR wave was separated into two. The durability for GOR was evaluated by potentiostatic electrolysis for 60 min at -0.1 V and -0.3 V (vs. Hg/HgO). At -0.1 V, the durability for GOR was decreased in the order of Ag(0.5)/Pt > Pt > Ag(0.8)/Pt. On the other hand, at -0.3 V, the Ag(0.5)/Pt electrode still showed the best tolerance to the poisoning species, but the durability for GOR of Ag(0.5)/Pt was poorer than that of Pt. These results indicated that the modification of Ag on Pt improved the GOR activity and durability. IRAS gives us the information on the GOR mechanism. In the case of the Pt electrode, the mainly absorption band are observed at 1310 cm-1, 1335 cm-1, 1350 cm-1, 1385 cm-1 and 1575 cm-1 which can be attributed to glyceraldehyde or glycerate, dihydroxyacetone, hydroxypyruvate, symmetric and symmetric O-C-O stretching of carboxylate, respectively. At higher potentials, the absorption band at 1310 cm-1 was obviously observed. On the other hand, in the case of both Ag(0.8)/Pt and Ag(0.5)/Pt electrodes, the absorption band at 1335 cm-1 due to dihydroxyacetone was more obviously observed at -0.4 to -0.2 V, whereas at -0.2 to 0.1 V, the absorption band at 1310 and 1350 cm-1 was strengthen. This results indicate that the oxidation of primary and secondary OH groups depends on potential, and the secondary OH (-0.4 to -0.2 V) and the primary OH ( -0.1 V) are preferentially oxidized on the Ag modified Pt electrodes. Acknowledgement This work was partially supported by JSPS KAKENHI Grant Number 15H04162. References 1) M. Simoes et al., Appl. Catal. B: Environ., 93, 354 (2010).2) B. T. X. Lam et al., J. Power Sources, 297, 149 (2015). Figure 1

Electrocatalytic Activity for Oxygen Reduction Reaction of Au Core/Pt Shell Nanoparticle-Loaded Carbon Black Catalyst with Different Core Sizes

Au core/Pt shell nanoparticle-loaded carbon black catalysts were prepared by forming a Pt monolayer on newly prepared Au nanoparticles and their electrocatalytic activities for the oxygen reduction reaction (ORR) were evaluated by the rotating disk electrode method. The Au nanoparticles were prepared by bubbling CO as a reducing agent in KAuCl4 aqueous solutions containing glutathione (GSH) as a stabilizer, and GSH on the resultant Au nanoparticles was removed by electrochemical oxidation. Underpotential deposition of Cu on the electrochemically treated Au nanoparticles (AuG-ET) and subsequent galvanic displacement of Cu with Pt led to the production of Au core/Pt shell nanoparticle-loaded carbon black (AuG-ET@Pt). In the X-ray photoelectron spectra, the S0 peak of AuG-ET completely disappeared, while the Au0 peaks returned to their intrinsic positions. From transmission electron microscopy images, particle size of Au on AuG-ET was 2.5±0.5nm. These results indicate that GSH was completely removed from the Au surface without increasing the size. The Pt coverage of AuG-ET@Pt was 0.95. The electrocatalytic activity per unit mass of Pt (MAPt) at 0.9V vs RHE for the AuG-ET@Pt was 1.3 and 6.6 times higher than that for our previous Au@Pt of 2.8±0.5nm in size and commercial Pt/carbon black, respectively. Reducing the size of the Au nanoparticles can increase MAPt. After durability test, the particle size and standard deviation of AuG-ET@Pt were 3.9±0.9nm, which were larger than the initial values (3.0±0.5nm), leading to the decrease in specific surface area of Pt.

Invited: Applications of DFT Calculations to Platinum Surface Electrochemistry

The current status of electronic structure calculations on electrocatalysis will be discussed in this presentation. After a quick review of atomistic modellings of electrified solid / liquid interfaces, a method combining density functional theory and a continuum electrolyte theory will be presented. It will be shown that this theory can give thermodynamic properties of electrochemical reactions, such as electro-oxidation, specific anion adsorptions, underpotential deposition of Cu and oxygen reduction reaction, on closed packed single crystal platinum surfaces within practically useful accuracies. When the method is applied to structures other than the closed packed surfaces, such as stepped platinum surfaces, difficulties arise in modellings and accuracies. Some prescriptions to overcome those problems also will be discussed.[1] R. Jinnouchi and A. B. Anderson, Phys. Rev. B, 77, 245417 (2008).[2] R. Jinnouchi and A. B. Anderson, J. Phys. Chem. C, 112, 8747 (2008).[3] R. Jinnouchi, E. Toyoda, T. Hatanaka and Y. Morimoto, J. Phys. Chem. C, 114, 17557 (2010).[4] R. Jinnouchi, T. Hatanaka, Y. Morimoto and M. Osawa, Phys. Chem. Chem. Phys., 14, 3208 (2012).[5] R. Jinnouchi, T. Hatanaka, Y. Morimoto and M. Osawa, Electrochim. Acta, 101, 254 (2013).[6] K. Kodama, A. Shinohara, N. Hasegawa, K. Shinozaki, R. Jinnouchi, T. Suzuki, T. Hatanaka and Y. Morimoto, ECS Trans., 58, 363 (2013).[7] R. Jinnouchi, K. Kodama, T. Hatanaka and Y. Morimoto, Phys. Chem. Chem. Phys., 13, 21070 (2011).[8] E. Toyoda, R. Jinnouchi, T. Ohsuna, T. Hatanaka, T. Aizawa, S. Otani, Y. Kido and Y. Morimoto, Angew. Chem. Int. Ed., 52, 4137 (2013).[9] R. Jinnouchi, K. Kodama and Y. Morimoto, J. Electroanal. Chem.,716, 31 (2013).

ToF-secondary ion mass-spectrometric study of copper deposition and stripping on directly heated screen-printed gold electrodes

We report about a new kind of directly heated gold electrode. All electrodes including a directly heated gold loop electrode, a Ag pseudo reference, and a carbon counter electrode have been screen-printed on a ceramic alumina substrate. Thermal behaviour was studied by potentiometry using either an external or the integrated reference electrode. Stripping voltammetric copper signals were greatly improved at elevated deposition temperature. Secondary ion mass spectrometric studies (ToF-SIMS) revealed that different negative ionic species of copper complexes can be found on the gold electrode surface as a result of ion bombardment during SIMS analysis like Cu−, CuCl− and CuCl2 −. SIMS surface imaging using a fine focussed ion beam over the surface allowed us to obtain ion images (chemical maps) of the analyzed sample. SIMS depth profile analysis of the gold loop electrode was performed after copper deposition at room temperature (23 °C) and at 60 °C. CuCl2 − ion was used for the depth profile studies as it has shown the highest intensity among other observed species. Surface spectroscopic analysis, surface imaging and depth profile analysis have shown that the amount of deposited copper species on the gold loop electrode was increased upon increasing electrode temperature during the deposition step. Therefore, the presence of chloride in the solution will hinder underpotential deposition of Cu(0) and lead to badly defined and resolved stripping peaks.

Simple Preparation of Au Nanoparticles and Their Application to Au Core/Pt Shell Catalysts for Oxygen Reduction Reaction

Au nanoparticle-loaded carbon black (Au/CB) was prepared simply by bubbling CO as a reducing agent in a KAuCl4 aqueous solution containing polyvinyl alcohol as a stabilizer and then mixing Ketjen black as carbon black. X-ray diffraction spectra and transmission electron micrographs exhibited that the Au nanoparticles loaded on CB had the mean size of 3.3 nm which was scarcely increased even by the heat-treatment at 400 °C. For the Au/CB heat-treated at 400 °C (Au/CB-HT400), the modification of the Au nanoparticles with a Pt monolayer shell was performed by underpotential deposition of Cu and the following galvanic displacement with Pt. Cyclic voltammograms of Au–Pt1/CB-HT400 and Au–Pt2/CB-HT400 electrodes, which mean a Pt monolayer shell was deposited once and twice on Au/CB-HT400, indicated that 73 % and 97 % of the Au core nanoparticle surface were covered with the Pt shell, respectively. Koutecky–Levich plots made from hydrodynamic voltammograms of the Au–Ptx/CB-HT400 (x = 1, 2) electrodes exhibited that oxygen reduction reaction at both electrodes proceeded in four-electron mechanism like commercial Pt/CB. The mass activity at 0.9 V vs. RHE for Au–Pt1/CB-HT400 and Au–Pt2/CB-HT400 was ca. 5.1 and 4.4 times as high as that for the commercial Pt/CB, respectively. Moreover, in durability tests in which the square-wave potential cycling between 0.6 and 1.0 V vs. RHE was repeated 104 times, both catalysts were equivalent or superior to the commercial Pt/CB.

Underpotential Deposition of Cu on Au(111) in Acid Sulfate Solution

not Available.

Au-supported Pt–Au mixed atomic monolayer electrocatalyst with ultrahigh specific activity for oxidation of formic acid in acidic solution

Au-supported Pt-Au mixed atomic monolayer electrocatalyst was prepared by underpotential deposition of Cu on Au and then redox replacement with noble metal atoms, which shows an ultrahigh Pt-mass (or Pt-area) normalized specific electrocatalytic activity of 102 mA μg(Pt)(-1) (124 mA cm(Pt)(-2)) for oxidation of formic acid in acidic aqueous solution.

Exploring the First Steps in Core–Shell Electrocatalyst Preparation: In Situ Characterization of the Underpotential Deposition of Cu on Supported Au Nanoparticles

The underpotential deposition (upd) of a Cu shell on a non-Pt nanoparticle core followed by galvanic displacement of the Cu template shell to form core–shell electrocatalyst materials is one means by which the Pt-based mass activity targets required for commercialization of PEM fuel cells may be reached. In situ EXAFS measurements were conducted at both the Au L3 and the Cu K absorption edges during deposition of Cu onto a carbon-supported Au electrocatalyst to study the initial stages of formation of such a core–shell electrocatalyst. The Au L3 EXAFS data obtained in 0.5 mol dm–3 H2SO4 show that the shape of the Au core is potential dependent, from a flattened to a round spherical shape as the Cu upd potential is approached. Following the addition of 2 mmol dm–3 Cu, the structure was also measured as a function of the applied potential. At +0.2 V vs Hg/Hg2SO4, the Cu2+ species was found to be a hydrated octahedron. As the potential was made more negative, single-crystal studies predict an ordered bilayer of sulfate anions and partially discharged Cu ions, followed by a complete/uniform layer of Cu atoms. In contrast, the model obtained by fitting the Au L3 and Cu K EXAFS data corresponds first to partially discharged Cu ions deposited at the defect sites in the outer shell of the Au nanoparticles at −0.42 V, followed by the growth of clusters of Cu atoms at −0.51 V. The absence of a uniform/complete Cu shell, even at the most negative potentials investigated, has implications for the structure, and the activity and/or stability, of the core–shell catalyst that would be subsequently formed following galvanic displacement of the Cu shell.