Rotating Disk Electrode System Research Articles

Effect of Micro- and Mesopore Size on Electronic Structure and Oxygen Reduction Kinetics of Platinum

Introduction Oxygen reduction reaction is an indispensable electrochemical reaction to utilize hydrogen or renewable energy in the form of electrochemical devices, i.e., fuel cells or metal-air batteries. However, the reaction overpotential, or activation and concentration overpotentials, must be reduced to raise its expected role in energy conversion. While porous electrodes contribute to decreasing the activation overpotential owing to their high surface area, the effect of pore structure on the reaction kinetics has not been clarified. It is expected that the electronic structures of electrocatalysts change when the pore size is in the range of a few nanometers. In our recent report, we fabricated platinum model electrodes with a uniform pore size of 1.8 nm and controlled electrode thicknesses.1 The intrinsic ORR kinetics was obtained by using a thin model electrode, and the extract activation overpotential was smaller than that of a planar platinum electrode. Herein, to further elucidate the relationship between the pore structure and the ORR kinetics, we present the effect of pore sizes using the platinum model electrodes with controlled pore sizes of 1.3 nm, 1.8 nm, and 3.0 nm (inset in Figure). Our study indicates that the d-band center is shifted downward with decreasing pore size and that ORR kinetics follows a volcano relationship with a maximum at a pore size of 1.8 nm. Experimental Platinum model electrodes were fabricated with the electrodeposition of platinum salt dissolved in a liquid crystalline phase of surfactant.2 The pore diameter was controlled by varying the chain length of the surfactants. The electrode thickness was assumed to be short (~50 nm) enough to mitigate the ORR concentration overpotential.1 Transmission electron microscopy (TEM) was employed to observe the pore structure. The electronic structures of the electrodes were characterized with angle-resolved X-ray photoelectron spectroscopy (ARXPS). The photoelectron takeoff angle was changed to distinguish the local electronic structure of the pore wall from that of the outer surface. Electrochemical measurements were carried out by cyclic voltammetry in N2/O2-saturated 0.1 mol dm–3 KOH solutions with a rotating disk electrode system. Results and discussion The model electrodes exhibited characteristic redox peaks of platinum polycrystalline facets in N2-saturated solution. ORR activities were evaluated in the Tafel plot (Figure), where current densities were normalized by electrochemical surface area and corrected for mass transport. It was found that the activation overpotential was the lowest at a pore size of 1.8 nm. Furthermore, the obtained Tafel slope (ca. –60 mV dec–1) was almost the same, suggesting that the rate-determining step is the same and the concentration activation overpotential is small among the electrodes.1 In ARXPS, the binding energy of the Pt 4f7/2 spectrum exhibited a high energy shift with a decrease in the pore size. The result suggests that the d-band center of platinum is shifted downward with decreasing pore size,3 and that the enhanced ORR kinetics at a pore size of 1.8 nm is attributed to the appropriate adsorption energy of the electrode to oxygen-containing species.4 We will also report the results collected in acidic solutions.

Rotating Disk Electrode Study of Sm(III)/Sm(II) in LiCl-KCl Eutectic Molten Salt

Understanding the redox reactions of fission products in molten salts is crucial for developing pyroprocessing techniques for used nuclear fuel. A rotating disk electrode is useful for investigating the electrochemical reactions with controlled mass transfer conditions, but its application has been limited in high-temperature corrosive molten salts. This study employs a tungsten (W) rotating disk electrode (RDE) to measure the electrochemical and kinetic properties of the Sm(III)/Sm(II) redox reaction in a LiCl-KCl eutectic molten salt. The properties of the Sm(III)/Sm(II) redox reaction, including diffusion coefficients, exchange current densities, charge transfer coefficients, activation energies, and Tafel slopes, were determined over a temperature range of 723–803 K using limiting currents in linear sweep voltammetry at various rotating speeds and mass transfer-corrected Tafel plots. The kinetic parameters obtained using the rotating disk electrode system can be useful for optimizing the design of pyroprocessing techniques.

Investigating the Role of Mixed Oxides for Oxygen Evolution Reaction on Iridium Oxide Electrocatalysts

Ongoing concerns over anthropogenic emissions, fossil fuel sustainability, and related geopolitical aspects point to an increasing need for cost-effective renewable fuel sources. A promising solution is the generation of hydrogen via the catalytic splitting of water, which can be achieved with the aid of proton exchange membrane (PEM) electrolyzers. Notably, the anode material in current commercially available PEM electrolyzers is typically iridium oxide. Despite its effectiveness in facilitating the oxygen evolution reaction (OER), the use of iridium oxide poses challenges due to the scarcity and high cost associated with this precious metal. As the quest for sustainable energy intensifies, ongoing research explores innovative approaches, such as the incorporation of alternative materials and catalysts, to enhance efficiency while addressing the economic and environmental concerns associated with iridium oxide. Studies have shown that incorporating mixed oxides and switching the supports for iridium oxide catalysts help lower the iridium loading while enhancing the OER performance.1,2 In this study, we investigate a series of different sputtered, mixed iridium oxides (Ta, Ti, Ir). We use a rotating disk electrode system to benchmark the catalytic activity of different loadings of mixed oxides. To measure the intrinsic activity of each catalytic active site, we use a home-built operando UV-Vis system to quantify the populations of surface species as well as track the kinetics of different redox transitions during OER. We incorporate nanoscale secondary ion mass spectrometry to probe the migration of different mixed oxide species before and after electrochemical cycling and use kelvin probe force microscopy to estimate the conductivity through the different films. In this study, we show the importance of cooperative effects between neighboring iridium oxide species and the coordination of iridium that are responsible for enhanced OER performance. These results indicate that doping modulates coverage dependent interactions at the surface, which affects both the binding energetics and populations of rate limiting intermediates. We believe this study will serve as a steppingstone for future designs of more cost-efficient PEM electrolyzers.(1) Oh, Hyung-Suk, et al. "Electrochemical catalyst–support effects and their stabilizing role for IrO x nanoparticle catalysts during the oxygen evolution reaction." Journal of the American Chemical Society 138.38 (2016): 12552-12563.(2) Zheng, Ya-Rong, et al. "Monitoring oxygen production on mass-selected iridium–tantalum oxide electrocatalysts." Nature Energy 7.1 (2022): 55-64.

Enhanced Kinetics of Oxygen Reduction Reactions in Alkaline Solutions inside Mesoporous Electrodes

Oxygen reduction reactions (ORR) in alkaline solutions attract increasing attention for their use as the cathodic reaction in metal-air batteries and alkaline fuel cells. However, the commercialization of these systems is impeded by high activation and concentration overpotentials of ORR, which originate from the sluggish kinetics on the catalyst surface and oxygen transport in the electrolyte, respectively. Although the practical electrode enables a decrease of the overpotentials with the porous structure, the effect of inner pores has not been understood. Among various pore sizes, it is crucial to investigate an electrochemical behavior in mesopores with a size of a few nm since such confined structures possibly change the intrinsic catalytic kinetics.1 In this study, we evaluated the ORR activity in the mesopore using Pt model electrodes with arrays of cylindrical pores with uniform pore sizes (Fig. a). We investigated the activity dependence on the electrode thickness to separate activation and concentration overpotentials, and found that the activation overpotential inside the mesopore with a size of 1.8 nm is smaller than that measured with the planer electrode. Pt model electrodes were electrodeposited from platinum salt in a liquid crystalline phase of a surfactant.2 The liquid crystalline phase was obtained by mixing 29 wt% of H2O, 29 wt% of hexachloroplatinic acid, and 42 wt% of octaethylene glycol monododecyl ether. The three-electrode cell consisted of an Au disk (φ 4 mm) working electrode, a Pt wire counter electrode, and an Ag|AgCl|sat’d KClaq reference electrode. The deposition was conducted at –0.055 V and 25 °C, and the charge densities were adjusted to obtain the electrode thickness of ca. 45, 100, 380, and 900 nm. Transmission electron microscopy (TEM) was performed to observe the pore structure. Electrochemical surface area (ECSA) and ORR activities were evaluated by cyclic voltammetry in N2/O2-saturated 0.1 mol dm–3 KOH solutions with a rotating disk electrode system, consisting of the porous model or a polished planar Pt working electrode, a Pt wire counter electrode, and a Hg|HgO reference electrode. The scan rate and rotation speed were 20 mV s–1 and 2000 rpm, respectively. TEM image exhibits the honeycomb arrays of mesopores with a pore size of 1.8 nm and a pore distance of 4.9 nm (Fig. a). The model electrodes possessed polycrystalline facets, and ECSA was calculated from the hydrogen adsorption peak area in blank voltammetry (Fig. b). The ECSA matched closely with the geometrically calculated surface area, suggesting that the cylindrical pores are uniformly distributed on the electrodes with defined pore lengths (Fig. c). ORR activities were evaluated with the Tafel plots (Fig. d), with current densities corrected for ECSA and concentration overpotential outside the mesopores. Since the oxygen transport resistance or the concentration overpotential is higher in longer pores, the electrodes with longer pore lengths caused smaller ORR current densities. In contrast, the concentration overpotential was suppressed enough to extract the activation overpotential when the pore length was 45 nm and 100 nm, and these electrodes led to higher ORR current density than the planar electrode. The result indicates that the activation overpotential inside the mesopore with a size of 1.8 nm is smaller than that measured with the planer electrode. We will report the origin of the enhanced kinetics inside the mesopore from the viewpoint of the electronic structure change.

Gas Diffusion Electrode for Oxygen Evolution Reaction Catalyst Testing

The oxygen evolution reaction (OER) is one of the major contributors of efficiency loss in water electrolysis and consequently, development of OER catalysts to improve the electrolyser efficiency is a major reasearch theme in the field. Though the current commercial PEMWE may operate at anode potential <1.60 V, futue PEMWE may operate at potential higher than this as the drive to operate PEMWE at high current density is inceasing. Inorder to achieve this, an active and stable catalyst is required that can operate at this regime. Also, the potential experienced by the anode during the startup/shutdown of an electrolyser are different to the steady state value.Conventional OER testing involves catalysts coated on a conductive substrate submerged in an electrolyte solution, in a three electrode cell. However, such techniques are generally limited to low current densities due to oxygen bubble formation and site blocking at high current density limiting the system to study the OER kinetics below realistic operating current density. Although Rotating Disk Electrode(RDE) is widely employed to mitigate this, the RDE system is still not effective enough to remove the bubbles1.A floating electrode system developed by Kucernak et al2 shows that combining direct access with a lower catalyst loading improves the O2 gas mass transport and a higher current density could be achieved for the ORR. This technique also used for OER by Arenz et al.3, for easier bubble removal. Combining these two above mentioned systems, we have developed a new GDE cell system which allows screening of OER catalyst at industrially relevant current densities. This cell allows to study the OER kinetics at very realistic voltage/current regime and the information obtained helps to develop more active/stable catalyst.The OER catalyst diagnostics test from our GDE cell was comparable to the standard three electrode cell with an additional advantage of extended potential window upto 1.80 V vs.RHE. Preliminary results obtained from our study shows a promising opportunity to study the OER at high current densities.Reference FathiTovini, A.Hartig-Weiß, H.A.Gasteigerand, H.A.El Sayed, Journal of The ElectrochemicalSociety, 2021, 168, 014512.M.Zalitis,D.KramerandA.R.Kucernak,Phys.Chem.Chem.Phys.,2013,15,4329-4340Schröder,V.A.Mints,A.Bornet,E.Berner,M.FathiTovini,J.Quinson,etal., JACS Au 2021,1(3),247-25

A novel electrocoagulation process with centrifugal electrodes for wastewater treatment: Electrochemical behavior of anode and kinetics of heavy metal removal

Anodic passivation is a key problem to impair the efficiency of in the electrocoagulation (EC) process. Process intensification of EC has attracted increasingly greater attention. In this work, a novel centrifugal electrode reactor was designed and applied in EC process to enhance the treatment of simulated heavy metal wastewater using aluminum anode. Results showed that the removal efficiency of heavy metals was significantly improved by the centrifugal electrodes, compared with the stationary electrodes. Electrochemical behavior of centrifugal electrodes was analyzed by an improved rotating disk electrode system. Anodic polarization behavior of aluminium showed a typical characteristic of dissolution in centrifugal electrodes, rather than passivation in static condition. Anode dissolution was controlled by the diffusion of Cl− ion that was enhanced by centrifugal electrodes. Thus, anode passivation was reduced. In addition, the kinetics analysis indicated that the removal of heavy metals in EC by centrifugal electrodes conformed to Variable-Order-Kinetic (VOK) model based on the Langmuir adsorption.

Identifying diffusion limiting current to unravel the intrinsic kinetics of electrode reactions affected by mass transfer at rotating disk electrode

Rotating disk electrode systems are widely used to study the kinetics of electrocatalytic reactions that may suffer from insufficient mass transfer of the reactants. Kinetic current density at certain overpotential calculated by the Koutecky-Levich equation is commonly used as the metrics to evaluate the activity of electrocatalysts. However, it is frequently found that the diffusion limiting current density is not correctly identified in the literatures. Instead of kinetic current density, the measured current density normalized by diffusion limiting current density (j/jL) has also been frequently under circumstance where its validity is not justified. By taking oxygen reduction reaction/hydrogen oxidation reaction/hydrogen evolution reaction as examples, we demonstrate that identifying the actual diffusion limiting current density for the same reaction under otherwise identical conditions from the experimental data is essential to accurately deduce kinetic current density. Our analysis reveals that j/jL is a rough activity metric which can only be used to qualitatively compare the activity trend under conditions that the mass transfer conditions and the roughness factor of the electrode are exactly the same. In addition, if one wants to use j/jL to compare the intrinsic activity, the concentration overpotential should be eliminated.

Additively Manufactured Rotating Disk Electrodes and Experimental Setup.

This manuscript details the first report of a complete additively manufactured rotating disk electrode setup, highlighting how high-performing equipment can be designed and produced rapidly using additive manufacturing without compromising on performance. The additively manufactured rotating disk electrode system was printed using a predominantly acrylonitrile butadiene styrene (ABS) based filament and used widely available, low-cost electronics, and simplified machined parts to create. The additively manufactured rotating disk electrode system costs less than 2% of a comparable commercial solution (£84.47 ($102.26) total). The rotating disk electrode is also additively manufactured using a carbon black/polylactic acid (CB/PLA) equivalent, developing a completely additively manufactured rotating disk electrode system. The electrochemical characterization of the additively manufactured rotating disk electrode setup was performed using hexaamineruthenium(III) chloride and compared favorably with a commercial glassy carbon electrode. Finally, this work shows how the additively manufactured rotating disk electrode experimental system and additive manufactured electrodes can be utilized for the electroanalytical determination of levodopa, a drug used in the treatment of Parkinson’s disease, producing a limit of detection of 0.23 ± 0.03 μM. This work represents a step-change in how additive manufacturing can be used in research, allowing the production of high-end equipment for hugely reduced costs, without compromising on performance. Utilizing additive manufacturing in this way could greatly enhance the research possibilities for less well-funded research groups.

A new angle to control concentration profiles at electroactive biofilm interfaces: Investigating a microfluidic perpendicular flow approach

To meet the growing interest in bioelectrochemical flow systems, we propose a new microfluidic-based approach to studying electroactive biofilms (EABs). Despite the near limitless range of available channel designs and reaction control sequences , one of the main drawbacks compared rotating disk electrode systems, is the typical non-uniformity in the concentration boundary layer above the EAB outer surface. This drawback undermines the claim that microfluidic electrochemical systems provide pristine operating conditions. We address this challenge through the use of simulations, backed by experiments, to investigate microfluidic design parameters (flow orientation, counter-electrode placement, and channel dimensions) that significantly enhance the boundary layer uniformity across the entire EAB surface. Simulations confirmed that the large asymmetries in the boundary layer thickness between the upstream and downstream edges in conventional tangential flow systems are strongly reduced by transitioning to a perpendicular flow orientation. Further optimizations in electrode placement and channel design nearly erased the remaining inhomogeneity in the boundary layer thicknesses.

Cu2(ZnSn)(S)4 Electrodeposition from a Single Bath By Both DC and Pulsing Current with Atomic Ratio Optimization

Cu2(ZnSn)(Se)4 (CTZSS) has an significant advantages over CIGS as thin film solar cell due to its optimum band gap. Producing thin film layers by electroplating techniques is chiefly attractive due to low production cost and high throughput 1-3. Several publication reports CTZS electrodeposition; however, the electrodeposition method still has an important challenge such as a annealing process due to partial pressure variation4. We introduce in this work an advance lower electrolyte concentration which suitable to single bath electroplating similar to prvious work with CIGS5. The electrolyte is significantly more dilute in comparison to common electrolytes designated in the literature1-4. We use pulsing technique with current pulsing technique to improve the deposit adhesion and quality. Theelectrolyte composition is: 0.0042 M CuSO4, 0.0031 M ZnSO4, 0.0051 M SnCl2, 0.0062 M Na2S2O3, and 0.19 mM Na2S2O3. PHydrion is used as a buffer (pH=2), and 0.61 M LiCl is used as supporting electrolyte.Electroplating experiments was carried out at a rotating disk electrode system which provides a better controlled electroplating condition. Rotating disk function is to have better control to experiment parameters and to compare Dc current efficiency with pulsing current. electrochemical behavior study and the deposit equality investigation are provided in Fig. 1. The effects of pulsing time and current density on the CTZS alloy atomic composition, deposit quality, and its adhesion to the back contact are discussed. The post annealing treatment was performed under sulfur element atmosphere with no necessity for metals addition at this phase. The electroplating parameters was optimized according. The final composition was investigated using Energy-dispersive X-ray spectroscopy technique (EDS) Fig. 2. XRD technique used to analyze CTZS crystallography and thickness. Acknowledgements Case Western Reserve University for using their instruments References [1] M. Cao, L. Li, B. L. Zhang, J. Huang, L. J. Wang, Y. Shen, Y. Sun, J. C. Jiang, G. J. Hu, Sol. Energy Mater. Sol.Cells, 93, 583 (2009). [2] Y. Lin, S. Ikeda, W. Septina, Y. Kawasaki, T. Harada, M. Matsumura, Sol. Energy Mater. Sol. Cells, 120, 218 (2014).[3] H. Guan, H. Shen, C. Gao, X. He, , J. Mater. Sci.:Mater. Electron., 24, 1490 (2013).[4] S. Abermann, , Solar Energy, 94, 37 (2013).[5] Saeed, M.; González Peña, O.I, Nanomaterials 2021, 11, Figure 1

Electrode Kinetic Study of Cu Electrodeposition with Supercritical CO2 by High Pressure Rotating Disk Electrode Method

The electrochemical reaction mechanism on the electrode surface for the activation of Cu electrodeposition in a sulfate-based Cu plating solution containing poly ethylene glycol (PEG) and supercritical CO2 (Sc-CO2) was studied by hydrodynamic voltammetry experiments and electrochemical impedance spectroscopy performed using a rotating disk electrode system specially designed for high pressure environment. The experimental results demonstrated that the mixed Sc-CO2 had a significant inhibitory effect on Cu electrodeposition. In addition, a kinetics model was attempted to be constructed for the Sc-CO2 mixed system based on the conventional model for the system with suppressor. As a result, the same mechanism as in the conventional model can be used to explain the Sc-CO2 mixed system, Sc-CO2 micelles in the solution were suggested to adsorb on the electrode surface in the same manner as the PEG molecules, which affected the reaction mechanism and was expected to inhibit the reduction reaction of Cu ions. Furthermore, the mixed Sc-CO2 was presumed to reduce the transition coefficient by suppressing the reduction reaction of Cu2+ ions to the Cu+ complex by adsorption on the electrode surface.

High-Performance Ru 2 P Anodic Catalyst for Alkaline Polymer Electrolyte Fuel Cells

High-Performance Ru ₂ P Anodic Catalyst for Alkaline Polymer Electrolyte Fuel Cells

Insights into the design of homogeneous electrocatalytic flow sensor via a rotating disc electrode system

Homogeneous electrocatalytic reaction has been extensively applied in electrochemical flow sensors especially for the detection of non-electroactive species. Herein, homogeneous electrocatalytic reaction is studied on a rotating disc electrode (RDE) system to mimic the forced convection in flow sensors in both experiments and theory. The experimental RDE voltammogram reveals a pre plateau feature under the rotation frequency of 25 rpm and the corresponding theoretical current–potential curves generated by 2D axisymmetric electrochemical analysis model is in good consistency with the experimental voltammetric responses. Based on the same model, mediator and substrate concentration distributions and the diffusion layer thicknesses are discussed in detail. Moreover, the interference of direct electrochemical oxidation of the substrate is investigated via the homogeneous electrocatalytic reaction between 1,1′-ferrocenedicarboxylic acid and L-cysteine and the corresponding second-order rate constant (372 (mol m−3)−1 s−1) is shown by the modified model. Also, the influence of substrate diffusion coefficients in homogeneous electrocatalytic reaction is analyzed and the obtained transition point indicates the specific critical second-order rate constant for both ferroceneacetic acid (106.02 (mol m−3)−1 s−1) and 1,1′-ferrocenedicarboxylic acid (105.36 (mol m−3)−1 s−1) as the mediator. At last, the design principle of homogeneous electrocatalytic flow sensor is summarized.

Pt nanoparticles supported on nitrogen-doped porous carbon as efficient oxygen reduction catalysts synthesized via a simple alcohol reduction method

Pt nanoparticles supported on nitrogen-doped porous carbon (NPC) were investigated as both a highly active catalyst for the oxygen reduction reaction (ORR) and a suitable porous support structure. Pt/NPC catalysts with loadings of 8.8–35.4 wt.% were prepared via a simple alcohol reduction method and exhibited homogeneously dispersed Pt nanoparticles with a small mean size ranging from 1.90 to 2.99 nm. X-ray photoelectron spectroscopy measurement suggested the presence of strong interactions between the Pt nanoparticles and NPC support. 27.4% Pt/NPC demonstrated high catalytic activity for the ORR in a rotating disk electrode system and was also effectively applied to a gas diffusion electrode (GDE). A GDE fabricated using the Pt/NPC with a fine pore network exhibited excellent performance, especially at high current densities. Specific activity of Pt/NPC and Pt/carbon black catalysts for the ORR correlated with the peak potential of adsorbed OH reduction on Pt, which was dependent on the particle size and support.Graphic abstract

Investigation of electrodeposition kinetics of In, Sb, and Zn for advanced designing of InSb and ZnSb thin films

In this work, the kinetics of indium, antimony, and zinc electrodepositions were investigated by using a gold rotating disc electrode (RDE). The performed studies shed light on the influence of electrodeposition parameters (i.e., working electrode potential and hydrodynamic conditions) on the chemical composition of In-Sb and Zn-Sb films. Stoichiometric InSb and ZnSb are one of the most promising thermoelectric materials, therefore a strictly controlled chemical composition of deposits is required. During electrochemical studies, as a primary electrolyte, a citrate bath with the addition of metal ion precursors, i.e., 0.06 M InCl 3 and/or 0.045 M SbCl 3 and/or 0.045 M ZnCl 2 , was applied. Based on the linear voltammetry measurements in the RDE system, the Koutecký-Levich analyses were performed. The diffusion coefficients ( D ) determined at 293 K for indium, antimony, and zinc ions equal to 1.45 × 10 −6 , 3.76 × 10 −6 , and 5.94 × 10 −6 cm 2 s −1 , respectively. The activation energy ( E A ) for the diffusion of metal ions was determined using D values calculated at different temperatures. E A of indium, antimony, and zinc ions equals to 25.1, 9.2, and 10.6 kJ mol −1 , respectively. The number of transferred electrons ( n ) and rate constant for heterogeneous reactions ( k ) occurring in the studied electrolytes at different potentials were also determined. • Electrodeposition of In, Sb, and Zn is under diffusion and kinetics control. • Diffusion coefficient of ion increase in line: In-citrate<Sb-citrate<Zn-citrate. • Adsorption of citrate ions on the RDE surface slows down electroreduction of In. • Indium-citrate ions have the highest E A of diffusion among studied species.

Activation of the Oxygen Reduction Reaction at an Interface-Regulated Pt/Nb-SnO2 Catalyst

The sluggish oxygen reduction reaction (ORR) kinetics on carbon-supported Pt catalysts has impeded the large-scale commercialization of polymer electrolyte fuel cells (PEFCs). More active ORR electrocatalysts are highly desired to improve PEFC performance with low Pt cathode loading. The adoption of alternative support material such as doped SnO2 represents a promising way forward for improving the activity of Pt-based catalysts while maintaining high durability.1 However, the correlation between the microstructure of the Pt/doped SnO2 and ORR activity remains ambiguous. In the present work, we, for the first time, show that the ORR kinetics of Pt can be boosted by the PtSn alloy formed at the interface between the loaded Pt nanoparticles and the Nb-SnO2 support.The Nb-SnO2 support was synthesized by the flame oxide-synthesis method. The Pt nanoparticles were loaded on the Nb-SnO2 by the colloidal method. The Pt loading amount in the Pt/Nb-SnO2 catalyst was determined by plasma-mass spectroscopy (ICP-MS). The microstructure of the Pt/Nb-SnO2 was characterized by scanning transmission electron microscopy with energy dispersive X-ray spectroscopy (STEM-EDX). A commercial catalyst c-Pt/C (TEC10E30E, TKK) was used for comparison. The electrochemical measurements were carried out by use of the rotating disk electrode (RDE) technique from 20 to 80 oC. The experimental procedure was the same as that described earlier.1 All of the electrode potentials in this paper are given versus the reversible hydrogen electrode (RHE).The Pt loading of Pt/Nb-SnO2 was measured to be 16.3 wt.%. The catalyst was uniformly dispersed on the support with an average Pt particle size of 2.7 ± 0.5 nm. EDX line scan analysis shows that Sn diffused into the Pt particle to form a PtSn alloy near the interface between Pt and Nb-SnO2, as illustrated in Fig. 1a. As shown in Fig. 1b, the Pt/Nb-SnO2 achieved 1.54 times higher specific activity and 1.47 times higher mass activity than c-Pt/C. Fig. 1c shows Arrhenius plots of the apparent rate constant k app for the ORR. Good linear relationships between the logarithm of k app and 1/T are observed for both electrodes. The k app values for c-Pt/C and Pt/Nb-SnO2 at 80 °C were, respectively, about 12 and 7 times higher than those at 20 °C. Thus, elevating the operating temperature significantly enhanced the ORR kinetics, which makes it possible to reduce Pt loadings in PEFCs. The apparent activation energy E a of c-Pt/C was calculated to be 36 kJ mol-1, which is well consistent with the result of Yano et al.2 Impressively, Pt/Nb-SnO2 exhibited a lower E a, 27 kJ mol-1, which is responsible for the high k app. The enhanced ORR kinetics is ascribed to the modified adsorption of oxygen species on the Pt surface by the PtSn alloys at the support-Pt interface, as revealed by DFT calculations. Acknowledgement This work was supported by funds for the JSPS KAKENHI Grant Number 20H02839 from the Japan Ministry of Education, Culture, Sports, Science and Technology. We are also grateful to Prof. Minoru Inaba and Prof. Hideo Daimon from Doshisha University for kindly providing the instruction of the RDE system (controlling temperature).

Quantifying intrinsic kinetics of electrochemical reaction controlled by mass transfer of multiple species under rotating disk electrode configuration

Precise measurements and accurate analysis of reaction processes are the prerequisite for correctly understanding the key factors that control kinetics of electrode reaction. Rotating disk electrode systems are widely used to study the kinetics of reactions that may suffer from insufficient mass transfer. The commonly used Koutecky-Levich equation is only applicable for reactions affected by the mass transfer of single reactant. In this work, we propose a general method for estimating the intrinsic kinetics of reactions hampered by the mass transfer of more than one reactant. Its application is demonstrated by the kinetic study of oxygen reduction reaction (ORR) at Pt (111) in un-buffered solutions with medium pH, where the mass transfer of both O2 and H+ are slow. Our analysis reveals that the kinetic rate constant at activation overpotential around 300 mV (~0.9 V vs RHE) increases for ca. three orders of magnitude with the increase of solution pH from 1 to 3. Possible origins for such pH effect are discussed.

Numerical Analysis of CE Processes in RDE Systems: Diffusion and Electro-hydrodynamic Impedances

This paper presents a numerical analysis of the effect of different parameters (rotation speed, equilibrium constant and Schmidt numbers) on the diffusion (ZD) and electro-hydrodynamic (ZEHD) impedances of chemical-electrochemical (CE) systems in a rotating disk electrode (RDE) configuration. For this purpose, we used a finite difference algorithm to discretize and solve the governing equations. Our results show that the separation between convection-diffusion and reaction impedance loops depends on the ratio between diffusion layer thickness () and reaction layer thickness (). Also, we have demonstrated that the characteristic frequency of the reaction impedance loop is a function of As for ZEHD data, we found that, for slow kinetics, the plots do not overlap for different rotation speeds. Further, the upper limit of the negative phase is different for both, slow and fast kinetics, from the usual 180° value found for single charge transfer systems. The increment of the equilibrium constant, obtained via increasing the reaction rate constant of the electroactive species, caused the magnitude ZD to decrease and that of ZEHD to increase. Lastly, we found that changing ScA mainly affects the concentration gradient at the surface while the effect of ScB will depend on the kinetic regime.

Computational Modeling of Copper Deposition in through Silicon Via Structures

Copper electrodeposition is critical to integrated circuit manufacturing, ranging in scale from nanometer features in damascene plating to micrometer scale through-silicon via structures and even millimeter scale printed circuit board fabrication. Essential to this technology is electrodeposition of void-free copper in high aspect ratio cavities, which is achieved through various additives that enable bottom-up filling. In through-silicon-via structures, void-free filling can be realized with micro-to-milli molar concentrations of polyether suppressor and chloride additives. A variety of analytical measurements have shown chloride adsorption on copper is a necessary precursor to formation of a polyether blocking layer to suppress deposition. In this study, experimental measurements and computational models are presented exploring the dynamics of polyether and chloride adsorption during copper deposition. Microelectrode measurements eliminate solution iR effects, while demonstrating comparable results to rotating disk electrode systems at equivalent transport conditions. A two-additive co-adsorption model for polyether and chloride is presented, comparing simulations to experimental feature filling at conditions when chloride transport is limiting formation of the inhibiting ad-layer (< 80 μmol/L). Suppression breakdown is related to the local polyether coverage, which is in turn limited by the chloride coverage on the depositing interface. A passive-active transition of copper deposition is associated with limited flux of chloride in the feature. At higher chloride concentrations (≥ 80 μmol/L), sidewall breakdown during deposition occurs nearer to the bottom of the via, followed by a shift to bottom-up growth.

Effects of Crystallographic Structures of Metal-Phthalocyanine on Electrocatalytic Properties of Oxygen Reduction in Acidic Condition

Effects of the crystallographic structures of metal-phthalocyanines (metal: Co, Ni, Cu, Zn) between α and β phases on electrochemical oxygen reduction catalytic activities were investigated in acidic condition. As the distances of centered-metal in the structures of α and β phases are 3.8 A and 4.8 A, respectively, they were closed to the size of an oxygen molecule (3.6 A). The phases of metal-phthalocyanines were conducted by an interface deposition method. The obtained catalyst powders were characterized by means of X-ray diffraction and X-ray photoelectron spectra analyses. Electrochemical oxygen reduction performances were mainly measured by using a gas diffusion type carbon electrode loaded with a metal-phthalocyanine. It was confirmed that the catalytic activities of cobalt- and copper-centered phthalocyanines were enhanced by the conversion from β to α phases. The effects of the distance between the metals in the crystallographic structures of metal-phthalocyanines should be explained by the adsorbed oxygen states that depend on the distance between the metals. The α phase has the distance which allows to form the bridge configuration of oxygen molecule which requires two adsorption sites and that eventually produces H2O by the direct 4-electron pathway. Analysis with the rotating disk electrode system showed that the α-phased metal-phthalocyanines enhance the 4-electron reduction pathway.