Rotating Disk Electrode System Research Articles

Electrocatalysis of ferricyanide reduction mediated by electron transfer through the DNA duplex: Kinetic analysis by thin layer voltammetry

DNA-mediated electron transfer (ET) underlies a variety of bioelectronics applications, and, thus, simple approaches for its kinetic analysis are required. Here, electrocatalysis of a ferricyanide reduction catalyzed by methylene blue (MB) bound to either (dGdC)20 or (dAdT)25 duplexes tethered to gold via an alkanethiol linker was voltammetrically studied at stationary electrodes, and its kinetics was analyzed by two theoretical models. A thin layer voltammetry analysis, assuming that the reaction occurs within the l-nm thick layer formed by the DNA duplexes of the length l, yielded the electrocatalytic rate constant k1 of (2.1 ± 0.4)105 and (2.4 ± 0.5)106 M−1 s−1, for (dGdC)20 and (dAdT)25. The sequence-specific k1 values were consistent with structural differences of (dGdC)20 or (dAdT)25 at the negatively polarized interface and approached the k1 previously reported for the rotating disk electrode system (Angew. Chemie Int. Ed. 58 (2019) 3048). These results offer new tools for immediate kinetic analysis of electrocatalytic reactions involving long-range ET along the DNA duplexes, the tools that allow differentiating electrical properties of nucleic acids in the most convenient and simple way.

Synthesis of Surfactant-Free and Morphology-Controllable Vanadium Diselenide for Efficient Counter Electrodes in Dye-Sensitized Solar Cells.

In this study, a transition-metal selenide, vanadium diselenide (VSe2), with various morphologies was synthesized by employing a surfactant-free hydrothermal method under varied temperature conditions (190-220 °C). Although the physical properties of VSe2 have been studied before, only limited morphological change or application were explored. This study, for the first time, applied VSe2 as the electrocatalytic counter electrode (CE) in dye-sensitized solar cells (DSSCs) and showed an attractive cell efficiency. The mechanism of forming the tunable VSe2 morphologies is proposed. The evaluation of solar cell efficiency shows the correlation between morphology and electrocatalytic properties. It was further shown that VSe2-200 with the cauliflower-like morphology shows the highest cell performance of DSSC with an efficiency of 9.23 ± 0.07% under 1 sun irradiance, superior to that of the Pt-based DSSC (8.48 ± 0.08%). An electrochemical technique equipped with a rotating disk electrode system was introduced to confirm the high electrocatalytic performance with this particular morphology. The optimized VSe2 demonstrated good long-term stability with 78% retention after 500 cycles of the consecutive cyclic voltammetry, compared to 60% for the Pt CE. The control in morphology in vanadium diselenide synthesis and its usage in Pt-free CE DSSC have advanced the progress in electrochemistry.

The Influence of Catalyst Ink on the Urea Oxidation Reaction Activity Evaluated in a Three-Electrode System

Urea oxidation reaction (UOR) has been considered as a promising electrochemical reaction for hydrogen production since the theoretical reversible potential of urea electrolysis (0.084 V) is much lower than that of the water electrolysis (1.23 V)1. Urea is solid, non-toxic, non-flammable and stable compound, and hence easy to store and transport. In addition, urea is the largest constituent of urine, which is one of the most abundant wastes on earth. Among the extensively studied fuels in fuel cell systems, urea is the only non-flammable compound. In 2009, Botte et al. first developed the urea electrolysis technique to produce hydrogen2. Then in 2010, Irvine et al. reported a fuel cell system to generate electricity directly from urea3. With increasing interest in UOR in alkaline medium, a fast and reliable evaluation method for UOR catalysts is highly desirable. Currently, the validity of the test results is compromised due to uncertainties resulting from random selected ink composition, test protocols, operating parameters, etc. To understand and compare actual catalyst performance, it is necessary to minimize these uncertainties for further development of efficient UOR catalysts. Three-electrode system is the most commonly employed tools for evaluating UOR electrocatalysts due to its simplicity of the test setup and accuracy of the catalyst activity. The preparation and deposition technique of the catalyst ink as a thin-film catalyst layer (CL) on the glassy carbon electrode (GCE) have a significant effect on obtaining the intrinsic properties of applied materials. Although a few studies investigated the effect of catalyst ink on oxygen reduction reaction (ORR) or oxygen evolution reaction (OER) in a thin film rotating disk electrode system (TF-RDE), there are no report yet on the study related to ink composition optimization for anodic UOR in a three-electrode system4,5. In this study, we have investigated the role of solvent ratios (isopropyl alcohol and DI H2O) and ionomer on UOR catalyst activity in a three-electrode system. A commercial Ni-based catalyst is selected as our baseline catalyst, since Ni is found to be the most stable, economical and active catalyst for alkaline UOR. It is observed that the stability of the ink and particle size change with different solvent ratios, which leads to the variation of the catalyst film homogeneity on the GCE and consequently their electrochemical behavior. The role of ionomer is also studied through ex-situ measurements and in-situ performance evaluation including cyclic voltammetry, linear sweep voltammetry, chronoamperometry, and electrochemical impedance tests. Our results suggest that catalyst evaluation using a three-electrode system requires optimization of the catalyst ink to further understand the interfacial reaction mechanism. Detail experimental results will be shared at the conference.

Transient Response of Chemical-Electrochemical (CE) Processes in Rotating Disk Electrode (RDE) Systems: Diffusion and Electrohydrodynamic Impedances

We present a transient treatment of chemical-electrochemical (CE) processes in rotating disk electrode systems as an extension to a steady-state analysis already initiated by our group (results have been submitted to the Journal of the Electrochemical Society). Our numerical procedure can investigate systems with different diffusion coefficients over a wide range of homogenous reaction rate constants and was used to investigate both diffusion and electrohydrodynamic impedance responses. Two sets of rate constants (termed “slow kinetics” and “fast kinetics”) were used to assess the impact of the chemical step on both impedances behavior. For diffusion impedances, slow kinetic systems displayed two impedance loops, one associated with the homogenous reaction and the other to the convective diffusion. As the value of the electroactive species rate constant grew relative to its chemical counterpart, the homogenous reaction loop started to dominate the overall impedance. For systems with fast kinetics, only the loop corresponding to the convective diffusion was visible (for frequencies up to 100 Hz) and the overall impedance decreased rapidly with an increase on the reaction rate of the electroactive species. Results for electrohydrodynamic impedance corroborated the previous findings: two time constants could be observed for slow kinetic systems, but only one in the case of fast kinetics. These findings show that impedance techniques can be of great help on establishing reaction mechanisms for complex systems, since they are sensitive to the presence of non-electrochemical activities as long as they interfere with the concentration profile of the electroactive species.

Highly active and stable ferrocene functionalized graphene encapsulated carbon felt array - A novel rotating disc electrode for electro-Fenton oxidation of pharmaceutical compounds

In this study, ferrocene functionalized electrochemically reduced graphene oxide (Fc-ErGO) was used as electro-Fenton catalyst in rotating disc electrode system for the continuous generation of reactive oxygen species without external aeration. The nature of Fc-ErGO was evaluated using X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy analysis. Degradation of ciprofloxacin and carbamazepine were carried out to evaluate the performance of reactor. Enhanced removal rate was achieved at a wider range of pH as compared to the unmodified and ErGO modified graphite felt electrode systems. An increase in rotational speed of the disc electrodes resulted in enhanced removal rate due to improved mass transfer activity. At neutral condition, the removal rate was found to be 0.199 min−1 and 0.082 min−1 for ciprofloxacin and carbamazepine, respectively. Quantification of reactive oxygen species was also done. The Fc-ErGO modified cathode showed 644 μM, 264 μM, and 163 μM of •OH radicals at pH 3.0, 7.0 and 9.0 respectively; it confirms that ferrocene efficiently catalyses the conversion of H2O2 to •OH radicals and facilitates the degradation of contaminants. Stable catalytic activity was achieved even upto 10 cycles of repeatable experimental runs. A highly efficient, cleaner electro-Fenton system without external aeration and chemical addition was successfully demonstrated.

Synthesis and Evaluation of Iridium Oxide Nanoparticle Catalysts Supported on Nitrogen-Doped Reduced Graphene Oxides

Recently, progress toward sustainable societies with renewable energies is a critical issue to overcome environmental and social problems, for example, global warming and depletion of fossil fuels. To utilize effectively renewable energies such as solar and wind energy, conversion of renewable energies to hydrogen via water electrolysis is one of the most attractive approaches for energy storage. However, for the practical application of water electrolysis systems, its activity, durability, and catalysts cost are insufficient due to high over-potential and low kinetics of electrode reactions, especially, oxygen evolution reaction (OER) at the anode [1,2] for polymer electrolyte water electrolyzer (PEWE). As anode catalysts, iridium oxide (IrO2) particles have been used because of its high activity and durability for OER. However, iridium is one of the platinum group metals and reducing loading amount of iridium is required to reduce catalyst cost. Recently, we have successfully synthesized novel catalysts, IrO2 nanoparticle catalysts supported on nanocarbon materials with improved specific surface area, surface area per weight, of anode catalysts for PEWE. In this study, we focus on modification of IrO2 catalysts by doping of hetero atom (N) on supporting materials and characterization its electronic state condition and catalytic activity for OER. Novel catalyst of IrO2 nanoparticles supported on nitrogen-doped reduced graphene oxide (N-rGO) was prepared by hydrothermal synthesis. Graphene oxide (GO) prepared by modified Hummers method [3] was mixed with urea and hydrothermally treated at 180 ˚C for 12 h to synthesize N-rGO. For the synthesis of IrO2 / N-rGO catalysts, mixture of H2IrCl6 complex and N-rGO dispersed in ethanol/water mixture solution was stirred at 80 ˚C for 6 h in a flask to attach iridium oxide colloid to N-rGO and heated at 150 ˚C for 4 h in a hydrothermal autoclave to form IrO2 nanoparticles. The IrO2 / N-rGO catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersed X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), and electrochemical methods. The OER activity of the IrO2/ N-rGO was examined in sulfuric acid solution using rotating disk electrode system. Figure 1 shows TEM image of synthesized IrO2 / N-rGO catalysts. The IrO2 nanoparticles with an average particle size of 1.2 nm are uniformly dispersed on surface of the N-rGO substrate. The loading amount of the IrO2 nanoparticles and doping weight of nitrogen atom of the IrO2 / N-rGO catalysts are approximately 9 and 7 wt%, respectively, which was estimated from EDX measurements. Figure 2 shows the results of XPS investigation on GO, N-rGO, and IrO2 / N-rGO. The XPS data reveal nitrogen doping on GO by hydrothermal synthesis of GO with urea. After the reaction between Ir complexes and N-rGO, Ir 4f peak appeared on the spectrum and intensity of O 1s was decreased due to reduction of GO during the hydrothermal reaction. Deconvolution analysis of the N 1s peak of N-rGO indicates doped nitrogen has three different types, pyridinic, pyrrolic, and graphitic type. The binding energy of the Ir 4f peak was shifted to a lower energy state. In addition, XRD pattern of the IrO2 / N-rGO catalyst suggests that the interlayer distance of graphene sheets decreased during hydrothermal reaction because of reduction of GO. The XRD data suppot the results of the XPS measurement.Figure 3 shows linear sweep voltammogram of the IrO2 / N-rGO catalyst obtained in 0.5 M H2SO4 solution. Electrochemical measurement reveals high activity of the IrO2 / N-rGO catalyst for OER, onset potential of the reaction is ca. 1.43 V and mass activity at 1.60 V is ca. 1000 A g-1. The overvoltage of the IrO2 / N-rGO catalysts is 70 mV lower than that of conventional IrO2 powder catalysts. High activity of the IrO2 / N-rGO catalyst indicates that the IrO2 / N-rGO catalyst is a promising candidate of anode material for PEWE. Acknowledgements This work was supported by JSPS KAKENHI Grant number 17K05969. Reference[1] M. Carmo, D. L. Fritz, J. Mergel, D. Stolten, Int. J. Hydrogen Energy 38 (2013) 4901.[2] E. Antolini, ACS Catal. 4 (2014) 1426.[3] W. S. Hummers, R. E. Offeman, J. Am. Chem. Soc. 80 (1958) 1339. Figure 1

Bioinspired Mo2c-Based Catalyst with the Optimized P and S Heteroatom Incorporation for Efficient Hydrogen Production in Alkaline Media

The development of efficient and low-cost catalysts for water splitting is a fundamental challenge for electrochemical hydrogen production. For commercialization of water electrolyzer, highly efficient catalyst for hydrogen evolution reaction (HER) under basic condition is required. Low-cost molybdenum-based catalysts have attracted much attention, but they have not proven to be sufficiently active or stable in alkaline media. Inspired by biomolecular systems, we now present our successful use of polydopamines, a component of adhesive proteins secreted by marine mussels, to synthesize a new, enhanced molybdenum-based catalyst. Moreover, through combinatorial controlling P and S heteroatom elements, further enhanced electrochemical performance was realized. Firstly, to study the effect of P incorporation, we synthesized Mo2C:P using a hydrothermal process. Dopamine (2 mg) was used as a monomer and mixed in tris-(hydroxy-methyl) aminomethane solution (10 mM, pH 8.5). Mo precursors in ammonium heptamolybate (3 mM) and the P precursors in ammonium phosphate (0 to 100 mM) were introduced into the dopamine solution. In order to carbonize the solution, it was dried and then thermally treated in a nitrogen-rich tube furnace at 800 ℃. The electrocatalytic activity of the catalyst was measured using cyclic voltammetry with a rotating disk electrode system in a three-electrode cell at 1M KOH. The 50mM of P sample showed optimal HER catalytic activity, showing the overpotential of 133 mV to attain a current density of 10 mA/cm2. Further improvement could be achieved via S incorporation into the optimized Mo2C:P catalyst. To find optimal concentration of S element, S precursors in sodium sulfide (0 to 50 mM) were introduced into the dopamine solution with Mo and P precursors and the solution was dried and carbonized at 800 ℃. From the current-potential plot, the overpotential was further decreased (113 mV). From XRD, TEM and XPS analysis, we also identified that the incorporation of S and P changed the crystallinity and electronic structure on the surface, possibly resulting in the improved electrochemical performance. In conclusion, we have designed a new bio-mimetic Mo2C:S:P catalyst with enhanced HER properties. The significant catalytic enhancement achieved in this study emphasizes the potential to be explored in strategies applying bioinspired materials as HER catalysts.

Optimisation of the electrodeposition process of Ni-W/ZrO2 nanocomposites

Ni-W/ZrO2 nanocomposite coatings were synthesised by electrochemical deposition from an aqueous sulphate-citrate electroplating solution containing zirconia nanoparticles in suspension. The electrodeposition process was carried out under a galvanostatic regime and controlled hydrodynamic conditions (in a rotating disc electrode system). The main aim of the study was to optimise the process parameters for the electrodeposition of Ni–W coatings modified by ZrO2 particles. Based on the results of previously conducted research, the set of experiments (eight series) was designed. The relationship between chemical composition, microstructure, and mechanical, wear and corrosion properties of Ni-W/ZrO2 nanocomposites, along with the electrodeposition parameters such as content of ZrO2 powder suspended in the galvanic bath, cathodic current density, hydrodynamic conditions and, ultrasonic field frequency were studied. Within the range of the experiments, the preferred combination of process parameters was determined to be zirconia nanoparticle content in the plating bath of about 5 g/L, ultrasonic (35 kHz) DC electrodeposition with current density of 11 A/dm2, applied cathode rotating rate of 600 rpm, yielding hardness, wear and corrosion rates of about 8 GPa and 1.4·10−6 mm3/Nm and 6 μA/cm2, respectively.

Numerical Analysis of the Steady-State Behavior of CE Processes in Rotating Disk Electrode Systems

This paper presents a numerical analysis of the chemical-electrochemical (CE) mechanism of a rotating disk electrode at steady-state. Two sets of kinetic constants (denominated “fast kinetics” and “slow kinetics”) were used to evaluate how they alter the original concentration profiles and the current response. Comparing the results obtained with those in the literature allows concluding that the range of validity of the reaction layer hypothesis, although able to accurately predict the current density in some cases, is intrinsically limited, because it will always fail for sufficiently high rotation speeds. Hence, a system with “fast kinetics” is merely one in which the hypothesis is applicable for all the rotation speeds that were studied. It was also observed that the range of validity of the reaction layer hypothesis is independent of the equilibrium constant of the chemical process and is determined solely by the absolute values of the kinetic constants.

Bridging Fundamental Electrochemistry with Applied Fuel Cell Testing: A Novel and Economical Rotating Disk Electrode Tip for Electrochemical Assessment of Catalyst-Coated Membranes

A novel rotating disk electrode (RDE) tip capable of characterizing catalyst coated substrates and compatible with commercial RDE systems is presented. The RDE tip, which uses a top-oriented Ti-based current collector, is demonstrated with Pt foil and commercial catalyst coated membranes (CCM). The specific activity of the platinum foil for oxygen reduction reaction is about 1.55mAkineticcmPt−2 in 0.1M HClO4 at room temperature (20°C), which is in agreement with the measurements reported for polycrystalline Pt. The Ti-based current collector leads to a very small (≈ 5.6%) loss in the electrochemical surface area (ECSA). Hydrodynamic calculations and oxygen reduction measurements confirm that even at the fastest rotation speeds used in this type of measurement (i.e., 1600rpm), the laminar flow regime (Re≈56) is maintained, allowing one to apply classical RDE analysis. Repeatable and high quality cyclic voltammograms (CVs), oxygen reduction curves, and mass and specific activities for commercial CCMs were obtained in 0.1M HClO4 at room temperature (20°C). The activities determined from these experiments are in agreement with those of the H2/O2 fuel cell measurements under equivalent operating conditions. Degradation of the CCM’s catalyst during a 30,000 potential cycling accelerated degradation test (ADT) is performed using a 0.4mgPtcm−2 commercial CCM and shows an ECSA loss of ≈ 0.0010m2gPt−1 cycle−1 and a mass activity loss of ≈ 1.8×10−6AmgPt−1 cycle−1. Details of the design, implementation, and results of this economical and novel approach for characterization of CCMs are presented and discussed.

Determination of heavy metal toxicity by using a micro-droplet hydrodynamic voltammetry for microalgal bioassay based on alkaline phosphatase

We developed an electrochemical microalgal bioassay for the determination of heavy metal toxicity in water on the basis of the alkaline phosphatase (ALP) enzyme inhibition of Chlamydomonas reinhardtii. Five heavy metals were chosen as toxicants: Hg, Cd, Pb, Zn, and Cu. The induced ALP activity of C. reinhardtii was inhibited using the phosphate starvation method, and the results were evaluated by measuring the electrochemical oxidation of p-aminophenol (PAP) following the enzymatic conversion of p-aminophenyl phosphate (PAPP) as a substrate. The rapid determination of enzymatic activity was achieved using hydrodynamic voltammetry in a 50 μL micro-droplet with a rotating disk electrode (RDE). Enzymatic activity over a PAPP substrate is affected by heavy metal ions, and this phenomenon decreases the chronoamperometric current signal. The concentrations of Hg, Cd, Pb, Zn, and Cu in which the ALP activity was half that of the control (EC50) were found to be 0.017, 0.021, 0.27, 1.30, and 1.36 μM, respectively. The RDE system was demonstrated to be capable of detecting enzymatic activity by using a small amount of regent, a reaction time of only 60 s, and a detection limit of 5.4 × 10−7 U.

Corrosion of Carbon Steel in CO2-Saturated Brines Investigated by Rotating Disk Electrode and Scanning Vibrating Electrode Technique

CO2 makes carbon steels susceptible to corrosion and failure during oil and natural gas exploration, production, transmission, and processing as well as in CO2 capture and sequestration systems. CO2 corrosion of carbon steel grade X65 was investigated in deaerated 3.5 wt% NaCl solutions from pH 4 to 7 at 30 oC in a rotating disk electrode system. The effects of CO2, pH, and mass transport were studied using in situ electrochemical methods. The CR increased by ~20 times by CO2 through facilitating anodic and cathodic reactions. The CR decreased at higher pH mostly due to suppressed cathodic reactions. Higher rotation rate slightly increased CR without changing the reaction mechanism. The cathodic reaction was limited by slow hydration of CO2. The scanning vibrating electrode technique showed a growing pit after corroded in the N2 deaerated solution, and the corrosion products covered surface served as the cathode in the CO2 saturated solution.

Determination of Heavy Metals in Sea Salt Using Anodic Stripping Voltammetry

Salt, as food, is the most essential element for human survival due to its significant physiological functions. Here, we report the simultaneous detection of Pb and Cd in sea salt by square wave anodic stripping voltammetry (SWASV). Stripping voltammetric measurements were conducted using a manufactured rotating disk electrode system (MRDES). The detection limit was 3.6±0.18 μgL−1 for Pb and 3.9±0.37 μgL−1 Cd in NaCl solution. When the pH increased from 5.5 to 8.5, the peak currents of Pb and Cd decreased. At a pH of 8.3, the ratio of the current drop compared with that at a pH of 5.5 was 0.6 for Pb and 0.73 for Cd. The concentrations corrected by the current drop are in agreement with the concentrations obtained with ICP (inductively coupled plasma). This system demonstrates the reliable detection of heavy metals in aqueous media and, at a high Na+ concentration, the successful application for the determination of Pb and Cd in sea salts.

Corrosion of Carbon Steel in CO2-Saturated Brines Investigated By Rotating Disk Electrode and Scanning Vibrating Electrode Technique

CO2 corrosion has been extensively studied because dissolved CO2 makes carbon steels susceptible to corrosion and failure during oil and natural gas exploration, production, transmission, and processing as well as in CO2 sequestration and capture systems. A rotating disk electrode (RDE) system and the scanning vibrating electrode technique (SVET) were used to study CO2 corrosion, including localized corrosion that often occurs when dissolved CO2 is present, especially at higher pH. The carbon steel, which meets the American Petroleum Institute 5L grade X65 standard, was investigated in 3.5%wt NaCl solutions from pH 4 to 8 at 30 oC. The effects of CO2, pH, and mass transport were studied. In situ electrochemical measurements were carried out in the RDE system at different rotating rates to measure the corrosion rates and determine the corrosion mechanism, including linear polarization resistance, electrochemical impedance spectroscopy, electrochemical frequency modulation, cyclic voltammetry, and Tafel analysis. Surface analysis using scanning electron microscopy and X-ray photoelectron spectroscopy was performed on the corroded samples. SVET was used to characterize the localized corrosion on the steel surfaces at different conditions.

Microwave-assisted synthesis and prototype oxygen reduction electrocatalyst application of N-doped carbon-coated Fe3O4 nanorods

Fe3O4 nanorods coated with nitrogen-doped mesoporous carbon (ND-Fe3O4@mC) shells of defined thicknesses have been prepared via a new microwave-assisted approach. Microstructural characterization of these ND-Fe3O4@mC structures was performed using x-ray diffraction, x-ray photoelectron spectroscopy, transmission electron microscopy, and scanning electron microscopy. Following identification, the electrochemical performance of the catalysts was evaluated using linear sweep voltammetry with a rotating disc electrode system. The present investigation reveals enhanced oxygen reduction reaction catalytic activity and the carbon layer thickness influences oxygen diffusion to the active Fe3O4 nanorod core.

Highly porous nitrogen-doped carbon nanoparticles synthesized via simple thermal treatment and their electrocatalytic activity for oxygen reduction reaction

This paper presents a materials study with the aim of obtaining nitrogen-doped porous carbon nanoparticles (NPCNs) with a fine pore network that provides efficient access for mass transport as well as abundant electrocatalytic active sites for oxygen reduction reactions (ORR). Carbon black (CB) after pretreatment by either heat or nitric acid was used as a carbon source. NPCNs were prepared using the pretreated CB impregnated with cyanamide via a simple thermal treatment. The pretreatment and the synthesis temperature have significant effects on the amount of nitrogen species present and pore structures of the NPCNs. Thermal treatment incorporates nitrogen into the carbon network but also increases the volume of pores larger than 2 nm in diameter and surface area. Heating of nitric acid-pretreated CB impregnated with cyanamide at 1000 °C gives NPCNs contained an optimal combination between the concentration of quaternary N and surface area. The NPCNs exhibited high activity for ORR in a rotating disk electrode system and were also effectively applied to a gas diffusion electrode. The specific current density normalized to the surface area depends on the quaternary N concentration, suggesting that quaternary N creates the active sites for ORR.

Performance and Durability of Pt-Ti Catalyst for Oxygen Electroreduction

Fuel cells are expected to be a key next-generation energy source used for vehicles and homes, offering high energy conversion efficiency and minimal pollutant emissions. The high efficiency arises from the fact that fuel cells convert chemical energy directly into electrical energy without the Carnot limitation of thermal engines. However, due to the extreme operating environment, Pt was almost exclusively the only practical catalyst for molecular oxygen electroreduction in PEM fuel cells. Recently, considerable efforts have been made to investigate synergy effects of platinum alloyed with base metals to improve the sluggish kinetics of oxygen reduction reaction of Pt catalyst. The more active Pt-alloy catalysts, in return, may arise the durability issue under the extreme environment of PEM fuel cell operation. In this presentation, results of a more active yet durable PtTi alloy catalyst will be discussed for oxygen reduction reaction in acidic media, including (i) combinatorial high-throughput discovery of PtTi alloy composition; (ii) synthesis and characterization of nano-scale PtTi particles with controllable size, phase, and individual particle composition; and (iii) electrochemical STM and ICP characterization of coarsening and corrosion of PtTi alloy catalyst in comparison with Pt and PtCo catalysts. A novel combinatorial high-throughput electrocatalyst discovery workflow and associated tools were developed [1-4], where thin films of alloys can be made through a Multi-sources Physical Vapor Deposition system [5], and the resulted materials can be electrochemically screened by a Multi-channel Rotating Disk Electrode system [6]. PtTi binary system has been screened using this methodology for activity-stability-composition relationship and the best alloy composition was identified. In addition to the discovery of alloy compositions, engineering the PtTi alloy particles in nanoscale has been a challenge. Several synthesis technologies were studied and developed to achieve capabilities of controlling particle size and particle microcomposition [7]. The results show that by careful engineering the particle size and microcomposition in nanoscale, it is able to achieve the superior electrocatalytic activity predicted by the combinatorial high-throughput discovery. Electrochemical STM technique, in combination with electrochemical potentiostating, potential cycling, and ICP analysis, was used to monitor the coarsening and base metal corrosion under dynamic fuel cell operation conditions and compared with phenomena observed from Pt and PtCo catalysts [8-10]. The results show that PtTi not only is more active than Pt and much stable than PtCo, but also can mitigate the catalyst coarsening. Reference [1] T. He and E. Kreidler, Phys. Chem. Chem. Phys. 10, 3731 (2008). “Combinatorial screening of PtTiMe ternary alloys for oxygen electroreduction”. [2] E. Kreidler and T. He, in Catalysts for Oxygen Electroreduction – Recent Developments and New Directions (Ed. T. He, Transworld Research Network) Chapter 4, p.63 (2009). “Oxygen reduction on Pt alloys: high throughput combinatorial screening of Pt binary alloys”. [3] T. He, E. Kreidler, L. Xiong and E. Ding, J. Power Sources 165, 87 (2007). “Combinatorial screening and nano-synthesis of platinum binary alloys for oxygen electroreduction”. [4] T. He, E. Kreidler, L. Xiong, J. Luo and C.J. Zhong, J. Electrochem. Soc. 153, A1637 (2006). “Alloy electrocatalysts: combinatorial discovery and nano-synthesis”. [5] T. He, E.R. Kreidler and T. Nomura, US 8,944,002 (2015). “High throughput physical vapor deposition system for material combinatorial studies”. [6] T. He, US 7,077,946 (2006). “High throughput multi-channel rotating disk or ring-disk electrode assembly and method”. [7] E. Ding, K.L. More and T. He, J. Power Sources 175, 794 (2008). "Preparation and characterization of carbon-supported PtTi alloy electrocatalysts". [8] L. Tang, B. Han, K. Persson, C. Friesen, T. He, K. Sieradzki and G. Ceder, J. Am. Chem. Soc. 132, 596 (2010). “Electrochemical stability of nanometer-scale Pt particles in acidic environments”. [9] Q. Xu, E. Kreidler, D.O. Wipf and T. He, J. Electrochem. Soc. 155, B228 (2008). "An in-situ electrochemical STM study of potential-induced coarsening and corrosion of platinum nano crystals". [10] Q. Xu, T. He and D. Wipf, Langmuir 32, 9098 (2007). "An in-situ electrochemical STM study of the coarsening of platinum islands at double-layer potentials".

Near-Wall Hindered Diffusion in Convective Systems: Transport Limitations in Colloidal and Nanoparticulate Systems

Redox flow cells have a significant potential as efficient, scalable energy storage, and use of nanomaterials is likely to increase the energy density even further. Efficient cell design requires understanding of mass transport effects, and for colloidal systems the theoretical assumptions commonly used for molecular species require re-evaluation. In the present work the effect of near-wall hindered diffusion is investigated in the convective–diffusive system of a colloidal suspension of nanoparticles. The rotating disk electrode system is used as a model due to the wide applicability of the technique for battery testing. A major influence of near-wall hindered diffusion is observed in the resulting concentration profiles of the nanoparticles (aqueous concentration as a function of distance) and the current responses in the case of the colloidal suspensions, and the finding is likely to have a significant impact on the understanding of physical processes underlying the practical cell design and modeling.

Perovskite-Based Oxide Catalysts to Improve the Oxygen Evolution and Reduction Activity

Unitized regenerative fuel cells (URFCs), which include water electrolysis and fuel cells, have received many attentions due to the production of hydrogen gas and electricity in one electrochemical device. Water electrolysis is one of the most pollution-free and renewable ways to produce hydrogen. However, the slow kinetics of oxygen evolution reactions (OERs) in the URFC anode are limited by high polarization resistance for oxidation of water. Likewise, oxygen reduction reactions (ORRs) for the fuel cell cathode also show slow rates due to the multi-step electrochemical reactions demands of 4-electrons in reactions, limiting the overall reaction rate of the fuel cells. Up to date, the noble metal-based catalysts, such as carbon-supported iridium, ruthenium, platinum and alloys, have still used as OER and ORR catalysts. The use of precious metal-based materials is not suitable for the commercialization of the electrochemical cells. In order to replace these noble metal catalysts, studies of perovskite-based oxide catalysts for URFCs have carried out intensively these days. In particular, various dopants in the perovskite materials may help to improve the electrochemical properties significantly. Herein, the perovskite-based catalysts are synthesized by the glycine-nitrate combustion method with various A site material (Nd, Sm and Gd) in ABO3 structure. Then, the ashes are calcined at 900 oC for 4h in electric furnace at a heating rate of 5 oC min-1. The physicochemical properties of the final products are characterized by several analytic tools such as X-ray diffraction, scanning electron microscope, transmission electron microscope and BET. For electrochemical analysis, a rotating disk electrode system is used with an Hg/HgO and a Pt wire and a 0.1 M KOH solution for reference, counter and electrolyte, respectively. The pre-conditioning of catalysts is carried out by cyclic voltammetry (CV) at a scan rate of 100 mV s-1 for 50 cycles with nitrogen-purged electrolyte. The OER (1.2 V ~ 1.7 V) and ORR (0.05 V ~ 1.2 V) activities are measured by linear sweep voltammetry (LSV) at a scan rate of 5 mV s-1 and for the performance and long-term stability. A. Grimaud, K.J. May, C.E. Carlton, Y.-L. Lee, M. Risch, W.T. Hong, J. Zhou and Y. Shao-Horn, Nat. Comm., 4, 2439 (2013).Y. Liang, Y. Li, H. Wang, J. Zhou, J. Wang, T. Regier, H. Dai, Nature Materials, 10, 780 (2011).J. Kim, X. Yin, K.-C. Tsao, S. Fang and H. Yang, J. Am. Chem. Soc., 136, 14646 (2014).J.-I. Jung, H.Y. Jeong, M.G. Kim, G. Nam, J. Park and J. Cho, Adv. Mater., 27, 266 (2015).J. Suntivich, K.J. May, H.A. Gasteiger, J.B. Goodenough, Y. Shao-Horn, Science, 334, 1383 (2011).J. Suntivich, H. A. Gasteiger, N. Yabuuchi, Y. Shao-Horn, Nature Chemistry , 3, 546 (2011).T. Reier, M. Oezaslan, P.Strasser, ACS Catal., 2, 1765 (2012).I. C. Man, H. Y. Su, F. C. Vallejo, H. A. Hansen, J. I. Martínez, N. G. Inoglu, J. Kitchin, T. F. Jaramillo, J. K. Nørskov, J. Rossmeisl, ChemCatChem, 3, 1159 (2011)

Electrochemical characteristic of based on carbon mixed with organic metal complex (Co(mqph)) in alkaline media Li–air battery

The electrochemical performance of RGO-Co(mqph) electrocatalyst for Li–air batteries with hybrid electrolyte was investigated. The RGO-Co(mqph) showed high onset potential (−0.09 V vs. Ag/AgCl) under oxygen condition in the rotating disk electrode system for oxygen reduction reaction, which was higher than that of RGO (−0.17 V vs. Ag/AgCl). Furthermore, the ORR mechanism of RGO-Co(mqph) showed 3.52 electron pathway. On the other hand, the RGO only exhibited the electron transfer number of 2.22 for ORR. Moreover, the electrochemical performance of Li–air batteries with hybrid electrolyte showed that the RGO-Co(mqph) provided good discharge performance and cycle performance. It was thus considered that the Co(mqph) strongly affected ORR activity for cathode electrode. This was ascribed to synergic effect due to combination between RGO and Co(mqph).