Current-potential Curves Research Articles

Theoretical treatment of diffusion and kinetics of osmium redox polymer mediated glucose oxidase enzyme electrodes: Analytical expression of current density for varying potential

We present for the first time a mathematical model of osmium redox polymer mediated glucose oxidase enzyme electrodes. This model is based on a system of three coupled nonlinear reaction-diffusion equations under steady-state conditions for biochemical reactions occurring in the biofuel cells that describes the oxidized mediator, oxygen and substrate (Glucose) concentration within the biofuel cell. Simple analytical expressions for the concentration of oxidized mediator, oxygen and substrate and the corresponding current-potential response have been derived for all the values of reaction diffusion parameters using the new homotopy perturbation method (NHPM).The current-potential response in osmium redox polymer mediated glucose oxidase enzyme electrodes is discussed. The analytical results for the concentrations are also compared with numerical results and a satisfactory agreement is noted. The influence of diffusion coefficient of mediator, thickens of the film, turnover rate of Gluocose Oxidase and Michaelis-Menten constant on current-potential curve is also analyzed.

Measurement and Analysis of Exchange Current Density for U/U3+ Reaction in LiCl-KCl Eutectic Salt via Various Electrochemical Techniques

Electrochemical impedance spectroscopy (EIS), linear polarization (LP), Tafel and cyclic voltammetry (CV) were performed to investigate the exchange current density (i0) of U/U3+ reaction in LiCl-KCl eutectic salt under different UCl3 concentrations (0.5wt%–4wt%) and temperature conditions (723K–798K). The EIS spectra were measured by applying minimum overpotential from equilibrium potential and fitted to the proposed equivalent circuit. From the EIS experiments, the calculated values of i0 were varied from 0.0054Acm−2 to 0.102Acm−2. For the LP and Tafel methods, i0 values were determined from the linear fitting at small and large overpotential ranges of the current-potential curves. The measurement for i0 via CV was done analogously to the LP method. All i0 values have the linear trend with the change of concentration and temperature; however, these values measured by LP, Tafel, and CV methods are greatly influenced by the change in electrode surface area. Overall, i0 agreed within 33% relative error range with the EIS method being the most consistent and accurate in comparison to reported literature values. Dimensionless analysis was done on the EIS data sets providing insightful correlations for prediction of i0 under various experimental conditions.

Metallurgically prepared NiCu alloys as cathode materials for hydrogen evolution reaction

NiCu bimetallic alloys with Cu content of 5, 10, 20, 30 and 50 wt% are prepared by powder metallurgy method, which consisted of powder mixing, pressing and sintering processes. The X-ray diffraction (XRD) measurement confirms that all the five NiCu alloys possess the f.c.c. structure. The hydrogen evolution reaction (HER) activity of the prepared NiCu alloy electrodes was studied in 6 M KOH solution by cathodic current-potential curves and electrochemical impedance spectroscopy (EIS) techniques. It was found that the electrocatalytic activity for the HER depended on the composition of NiCu alloys, where Ni10Cu alloy exhibited considerably higher HER activity than Ni plate and other NiCu alloys, indicative of its chemical composition related intrinsic activity.

Growth-Inhibited Nucleation Enhancement: from High Density Nanoparticle Deposits to Nanometer Thin Continuous Films

In our group, we have been working on the electrochemical nucleation and growth of high island density deposits of copper, indium, nickel, cobalt and iron deposits for more than a decade. From simple electrolyte solutions, all metal systems seem to saturate at an island density of few times 1011 islands per cm2 at most or about 20-30nm spacing per particle. From direct copper plating for damascene processes, we know that the island density can be augmented by the introduction of growth inhibiting species such as the chloride-polyether suppressor additive combo. In this case, the Cl-suppressor adsorbs on the copper island as soon as it is formed. As the current-potential curve for the Cl-suppressor covered copper is polarized more negative with respect to the non-suppressed copper, the overpotential is driven more negative during galvanostatic deposition allowing higher island density [1]. As such the island density can be driven higher than 1013 cm-2 (spacing of about 3nm per particle) on oxide-poor noble metals such as Pt and up to 1012 cm-2(spacing of about 10nm per particle) for oxide-prone surfaces like RuTa alloys [2]. Note that these values are extrapolated as islands can no longer be distinguished from films at this point (coalescence thickness of 5nm and 2nm for hemispherical particles, respectively). The adsorbed suppressor typically also introduces flattened particle shapes helping to bring the effective coalescence thickness even lower. On platinum and cleaned RuTa surfaces, closed copper films with thicknesses down to 2-3nm could be obtained. From our study, it became apparent that the surface condition and overpotential were the two drivers.Based on the know-how from copper, several typical growth inhibiting additives (e.g. saccharine, 2-butyne-1,4-diol, PEG) were tried to increase the Ni and Co nanoparticle density. However, with no avail, as the adsorption and inhibition was typically too slow. In copper deposition, the additives already form complexes with the cuprous intermediate formed during copper deposition. As such the adsorption is very fast, whereas for Ni and Co, the additives need to adsorb via a physisorption which happens too late to affect the nucleation stage. Recently we found that the Ni particle density is strongly affected by the boric acid concentration [3]. The formation of growth inhibiting hydroxides gives the desired effect for growth-inhibited nucleation. However, the local pH cannot rise to fast as otherwise precipitation from solution already occurs in the depletion layer. Therefore a small concentration of boric acid was still needed at 5mM NiCl2 concentration to allow nickel growth to proceed long enough. At the best trade-off conditions a density of 4x1011 cm-2 Ni nanoparticles on TiN was obtained. By tuning the NiCl2 concentration, the growth-inhibited nucleation process could be extended to higher Ni island densities resulting in nanometer thin nickel films [4]; similar to what was achieved for copper. In this paper, we will go in on the mechanism of growth-inhibited growth for the fabrication of high density particles or (sub)nanometer thin films of Cu and Ni. “The Effect of Polyether Suppressors on the Nucleation and Growth of Copper on RuTa Seeded Substrate for Direct Copper Plating” M. Nagar, A. Radisic, K. Strubbe, P.M. Vereecken Electrochim. Acta, 127, 315-326 (2014).“Systematic studies of electrochemical nucleation and growth of copper on Ru-based substrates for damascene process”, Magi Margalit Nagar, PhD thesis, Universiteit Gent. “Enhanced nucleation of Ni nanoparticles on TiN through H3BO3-mediated growth inhibition” Johannes Vanpaemel, Marleen H. van der Veen, Stefan De Gendt, Stefan and Philippe Vereecken, Electrochimica Acta 109, 411-418 (2013).“Electrochemical deposition of sub-nanometer Ni films on TiN” Johannes Vanpaemel, Masahito Sugiura ,Daniel Cuypers, Marleen H. van der Veen, Stefan De Gendt, Stefan and Philippe M. Vereecken, Langmuir, 30 (8), 2047–2053 (2014).

Analytical approach to the transient and steady-state Cyclic Voltammetry of non-reversible electrode processes. Defining the transition from macro to microelectrodes

An explicit analytical easily programmable expression for the current-potential curves of electrode processes of any degree of reversibility in Cyclic Voltammetry (CV), valid for small spherical electrodes, is presented. From this solution a complete analysis of the most relevant parameters of the CV curves in terms of the electrode size and the scan rate is made, and the different influences of the kinetics of the electrode process clearly determined. Moreover, the evolution of the main characteristics of the voltammograms in the transition from macro- to micro-electrodes is described. A global expression for the rate constant collecting the influence of the kinetics in the complete range of electrode size from macro to nanoelectrodes is defined. Simple particular expressions covering different kinetic and geometric limits are presented. Methods for extracting kinetic parameters of the response are proposed.

Exploring the Influence of the Nickel Oxide Species on the Kinetics of Hydrogen Electrode Reactions in Alkaline Media

The influence of the oxidation of Ni electrodes on the kinetics of the hydrogen oxidation (HOR) and evolution reactions (HER) has been explored by combining an experimental cyclic voltammetry study, microkinetic modeling and X-ray photoelectron spectroscopic analysis. Almost 10 times enhancement of the activity of Ni in the HOR/HER has been observed after its oxidation under the contact with air at ambient conditions and assigned to the presence of NiO species on the surface of metallic Ni. The experimental cyclic voltammetry curves have been analyzed with the help of kinetic model in order to shed light on the mechanism of the HOR/HER for two types of Ni electrodes and its dependence on the presence of NiO on the surface of the electrode. The main features of the experimental current-potential curves can be reproduced with a kinetic model assuming that the free energy of the adsorbed hydrogen intermediate is increased and that the kinetics of the Volmer step is enhanced in the presence of nickel oxide species. The kinetic model provides evidence for the switching from the Heyrovsky–Volmer mechanism on metallic Ni to Tafel–Volmer mechanism on the activated electrode, where surface oxide species co-exist with metal Ni sites.

(Invited) Tri-Copper-Incorporated Carbon Catalyst for Oxygen Reduction Reaction

Platinum metal group (PMG) catalysts are used for oxygen reduction reaction (ORR) at cathodes in state-of-the-art polymer electrolyte fuel cells (PEFCs). Since the PMG catalysts contain expensive rare metals, they should be replaced with rare-metal-free catalysts for widespread PEFCs. Recently, electrocatalysts synthesized from carbon and transition metal complexes have been studied [1,2]. It is known that ORR catalysts with multi-nuclear-active sites have high ORR activity [3]. It is also known that natural ORR catalysts such as laccases have a multinuclear copper complex as an active center and show high ORR activity [4], suggesting that laccase-inspired artificial ORR catalysts prepared from carbon and a multi-nuclear copper complex would show high ORR activity. In the present work, we incorporated a trinuclear copper complex ([Cu3(trz)3(μ3-OH)]Cl2·6H2O) [5] into graphene nanosheets to synthesize laccase-inspired electrocatalysts for ORR, where grapheme nanosheets worked as an electrical conductive material and the trinuclear copper complex with a triangle core imitated the active center of laccases. The trinuclear copper complex was prepared from copper chloride and 1,2,4-triazole according to the literature [5]. This copper complex and graphene oxide (GO) were mixed and then reduced in two methods. The first method is heat treatment at high temperature for a short time. The second method is electrochemical reduction on a glassy carbon (GC) electrode (-1.1 V vs. Ag|AgCl, 300 s). We carried out powdery X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES) to characterize the catalysts. X-ray absorption fine structure (XAFS) spectroscopy was also carried out to estimate the molecular structure. For electrochemical measurements of the catalysts, the powdery catalyst was suspended in an ethanol-Nafion mixture to make ink containing the catalyst. The catalyst ink was put on a GC electrode and dried under the air at room temperature. Linear Sweep Voltammetry (LSV) was carried out under a saturated O2atmosphere using a rotary disk electrode to obtain current-potential curves. Britton-Robinson buffered solutions were used as electrolyte solutions. The heat or electrochemical reduction improved ORR activity. The catalyst obtained after the heat treatment showed higher ORR activity than that obtained after the electrochemical reduction. This result indicated that the two reduction methods might give different structures of ORR active sites. XPS spectra of the catalyst before and after the heat treatment were recorded to obtain information on structural changes. A peak originating from C-O was observed before the heat treatment. It disappeared after the heat treatment. This result indicated that GO was reduced to rGO by the heat treatment. The Cu2p spectra showed that CuII was also reduced to CuI. A new peak was observed in N1s spectra after the heat treatment. This peak might be attributed to new configuration that triazole rings were incorporated into graphene nanoshheets. References. [1] K. Kamiya, K. Hashimoto, S. Nakanishi, Chem. Commun., 2012, 48, 10213–10215. [2] T. Taniguchi, et al., Part. Part. Syst. Charact., 2013, 30, 1063-1070. [3] M. Thorum, J. Yadav, A. Gewirth, Angew. Chem. Int. Ed., 2009, 48, 165–167. [4] N. Mano, V. Soukharev, A. Heller, J. Phys. Chem. B, 2006, 110, 11180–11187. [5] T. Yamada, G. Maruta, S. Takeda, Chem. Commun., 2011, 47, 653–655

Overall Water Splitting By Series-Connected La5Ti2(Cu,Ag)S5O7 Photocathode and BaTaO2 N Photoanode Utilizing Visible Light up to 650nm

Introduction. A p/n photoelectrochemical (PEC) system composed of series-connected photocathode and photoanode is highly desirable for solar-energy conversion to storable and conveyable hydrogen via overall water splitting. To achieve a solar-to-hydrogen conversion efficiency (STH) as high as or higher than 10%, it is needed to use photocatalytic materials permitting visible light absorption up to >650 nm. We have recently reported that a p/n PEC system composed of a La5Ti2(Cu,Ag)S5O7 (LTCA) photocathode[1] and a BaTaO2N (BTON) photoanode[2], both of which have photoactivity under irradiation up to 650 nm, is capable of spontaneous overall water splitting under visible light irradiation without external bias voltage[3]. The STH of the p/n PEC system of LTCA and BTON was approximately 0.1 % in the initial stage[3]. In the p/n PEC system of LTCA-BTON, the photocurrent and the working-potential (E work) are determined by the intersection of the current-potential curves of the respective LTCA photocathode and the BTON photoanode used. Therefore, an increment of the photocurrent and a high stability in aqueous electrolyte solutions at E work are important. Intriguingly, both the water reduction reaction on LTCA photocathodes and the water oxidation reaction on BTON photoanodes are strongly affected by ionic species existing in the electrolyte solution. We will demonstrate in this paper the effect of coexistent ions in aqueous solutions and surface modification of the LTCA and BTON photoelectrodes upon the performance of the p/n PEC systems in the overall water splitting reaction. Experimental. LTCA photocathodes and BTON photoanodes were prepared using powder materials through the particle transfer method[4]. For LTCA photocathodes, Pt catalyst promoting hydrogen evolution reaction was deposited by potentiostatic photodeposition under irradiation of simulated sunlight (AM1.5G) [3]. For BTON photoanodes, CoPi catalysts for oxygen evolution reaction was deposited on the surface by electrodeposition[2]. The PEC measurement was carried out using an Ag/AgCl/sat’d KCl reference electrode and a coiled Pt wire counter electrode in an Ar gas atmosphere at room temperature. To examine the effect of coexistent ions in aqueous solution, M2SO4, MClO4, and M2HPO4 (M = Li, Na, K) were used as supporting electrolytes. The pH of aqueous solutions was adjusted to 11–13 by an aqueous MOH (M = Li, Na, K) solution. A p/n PEC system was prepared by connecting a LTCA photocathode and a BTON photoanode fabricated individually. The p/n PEC system was irradiated with visible light from a 300 W Xe lamp through a cut-off filter (l > 420 nm). The amounts of evolved H2 and O2 were quantified with a gas chromatograph. Results and Discussion. The photocurrents of LTCA photocathodes at 0.7 VRHE, typical E work for p/n PEC systems of LTCA-BTON, increased in the order of Li+ > Na+ > K+ and ClO4 - > SO4 2- >> PO4 3- when coexistent cations and anions were changed, respectively. The photocurrents of BTON photoanodes at 0.7 VRHE increased in the order of K+ > Na+ > Li+ and PO4 3- > (ClO4 - ~ SO4 2-) for variation of cationic and anionic species, respectively. It is likely that the dependence of the photocurrent of the respective photoelectrodes on the coexistent ions is attributable in part to the specific adsorption of ions. For the p/n PEC systems of LTCA-BTON, LiClO4 was employed as a supporting electrolyte because the LTCA photocathode in the presence of Li+ and ClO4 - generated the high photocathodic current. A p/n PEC system composed of a LTCA photocathode and a BTON photoanode in 0.1 M LiClO4 + LiOH (pH = 12) was active in overall water splitting without external voltage. Hydrogen and oxygen were generated at the stoichiometric ratio of 2:1 over 20 h. In this presentation, the effect of surface modification for respective photoelectrodes on the performance of the p/n PEC system will be discussed in detail. References. [1] J. Liu et al., Energy Environ. Sci., 7, 2239-2242 (2014). [2] K. Ueda et al., J. Am. Chem. Soc., 137, 2227-2230 (2015). [3] T. Hisatomi et al., Energy Environ. Sci., 8, 3354-3362, (2015). [4] T. Minegishi et al., Chem. Sci., 4, 1120-1124 (2013).

In Situ Visualization of Lithium Ion Intercalation into MoS2 Single Crystals using Differential Optical Microscopy with Atomic Layer Resolution.

Atomic-level visualization of the intercalation of layered materials, such as metal chalcogenides, is of paramount importance in the development of high-performance batteries. In situ images of the dynamic intercalation of Li ions into MoS2 single-crystal electrodes were acquired for the first time, under potential control, with the use of a technique combining laser confocal microscopy with differential interference microscopy. Intercalation proceeded via a distinct phase separation of lithiated and delithiated regions. The process started at the atomic steps of the first layer beneath the selvedge and progressed in a layer-by-layer fashion. The intercalated regions consisted of Li-ion channels into which the newly inserted Li ions were pushed atom-by-atom. Interlayer diffusion of Li ions was not observed. Deintercalation was also clearly imaged and was found to transpire in a layer-by-layer mode. The intercalation and deintercalation processes were chemically reversible and can be repeated many times within a few atomic layers. Extensive intercalation of Li ions disrupted the atomically flat surface of MoS2 because of the formation of small lithiated domains that peeled off from the surface of the crystal. The current-potential curves of the intercalation and deintercalation processes were independent of the scan rate, thereby suggesting that the rate-determining step was not governed by Butler-Volmer kinetics.

Characteristics of a sintered porous Ni–Cu alloy cathode for hydrogen production in a potassium hydroxide solution

A porous Ni–Cu alloy with a most probable pore size of 2.4 μm and an open porosity over 31.5% was synthesized by step sintering pressed compacts consisted of mixed Ni and Cu powders in a vacuum furnace. The electrocatalytic activity and stability of the fabricated porous Ni–Cu alloy as cathode for the HER (hydrogen evolution reaction) in 6.0 mol/L potassium hydroxide solution were investigated by cathodic current–potential curves, CV (cyclic voltammetry) and EIS (electrochemical impedance spectroscopy) techniques. Results show that the onset potential of the porous Ni–Cu for HER greatly shifts to the positive direction compared with the dense Ni and dense Ni–Cu alloy. The electrochemical activation energy is determined to be 26.7 kJ mol−1 for the porous Ni–Cu alloy, against 44.1 kJ mol−1 and 32.6 kJ mol−1 for the dense Ni and dense Ni–Cu alloy, respectively. The increased activity of the porous Ni–Cu alloy for HER is related to the micro-porous structure as well as synergistic interaction of Ni and Cu. Besides, the fabricated porous Ni–Cu alloy displays good corrosion resistance in potassium hydroxide solution during the immersion test, which makes it possible for long-time running as cathode in the process of hydrogen evolution reaction.

Bridging surface states and current–potential response over hematite-based photoelectrochemical water oxidation

The relation between surface states and the photoresponse on a hematite photoanode unraveled in electrochemical way indicates that the distribution of surface states determines the current–potential curves.

Hydrogen Permeation as a Tool for Quantitative Characterization of Oxygen Reduction Kinetics at Buried Metal-Coating Interfaces

The electrochemical stability of the buried metal-organic coating interface of painted metal is crucially governed by how effectively the oxygen reduction reaction at the interface is inhibited. As this interface is not directly accessible for study by conventional electrochemical techniques, a new non-destructive method has been developed wherein hydrogen permeation is used to quantitatively measure the oxygen reduction kinetics underneath the coatings. Presented here are results obtained with an adaptation of the Devanathan-Stachurski cell where the oxygen reduction reaction kinetics on the coated exit is probed by monitoring the dynamic electrochemical equilibrium potential established as a result of oxygen reduction and hydrogen oxidation reactions. From the hydrogen uptake on the entry side thus a full current-potential relationship curve (I (U)) can be constructed. First tested on non-coated Palladium, the results show very good concurrence of the oxygen reduction currents from the permeation experiments and that from standard cyclic-voltammetry (CV) measurements in buffered and non-buffered acidic electrolyte and under alkaline condition. Initial results obtained on coated samples are also presented.

Enhancement of electrochemical activity of Raney-type NiZn coatings by modifying with PtRu binary deposits: Application for alkaline water electrolysis

This study presents electrochemical preparation and characterization of PtRu-modified Cu/Ni/NiZn electrodes (Cu/Ni/NiZn–PtRu) as cathode materials for alkaline water electrolysis. The electrodes were characterized using energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. Their electrochemical activities as cathode materials for alkaline water electrolysis were evaluated with the help of current–potential curves. The results showed that the PtRu-modified layers have porous structures with relatively low Pt and Ru chemical compositions. The modification of the alkaline leached Cu/Ni/NiZn surface by Pt and/or Ru enhances the electrochemical activity of the electrode. Their catalytic activity depends on the molar ratios of Pt and Ru; the PtRu binary deposit with the percentage weight ratio of approximately 56:44 exhibits the highest hydrogen evolution activity among the studied electrodes. The enhanced hydrogen evolution activity of the PtRu-modified electrodes was related to the porous surface and/or a possible synergistic effect between the metals.

Cyclic Voltammetry of Electrocatalytic Films: Fast Catalysis Regimes

AbstractUnderstanding how electrocatalytic films function is of considerable current interest in view of modern energy and analytical challenges. Application of cyclic voltammetry to the analysis of these systems is a worthy alternative to steady‐state techniques in terms of simplicity and rapidity of the current–potential curve recording and the larger extent by which the rate of substrate diffusion may be varied through the rate of potential scanning. The interplay between catalytic reaction, diffusive permeation of the substrate, and diffusion‐like transport of charge is analyzed for fast catalytic reactions as a function of two dimensionless parameters. Procedures for determining the kinetic constants that govern the responses and, particularly, the rate of the catalytic reaction, ensue, based upon on the variations observed when changing scan rate, substrate concentration, and film thickness. These analyses also provide a basis for rational benchmarking of catalysts.

Corrosion behaviour of WC-10% AISI 304 cemented carbides

The corrosion behavior of tungsten carbide hard metal composites with AISI 304L stainless steel as binder matrix and a WC–Co composite with similar grain size and binder content was investigated using electrochemical techniques (open circuit potential monitoring, current-potential curves, electrochemical impedance spectroscopy, scanning vibrating electrode technique) and scanning electron microscopy.

Influence of Marine Aerobic Biofilms on Corrosion of 316L Stainless Steel

The influence of marine aerobic biofilms on the corrosion of 316L stainless steel (SS) in aerated and deaerated seawater was studied by electrochemical impedance spectroscopy (EIS), potentiodynamic polarisation curves, current-potential curves and scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS). EIS and SEM-EDS results showed that the aerobic biofilms inhibited 316L SS corrosion within the test duration. Comparison of results under aerated and deaerated conditions revealed that O2 enhanced the inhibition efficiency of the aerobic biofilms. This result indicated that living cells were necessary for the aerobic biofilms to inhibit the corrosion of 316L SS. Polarization curves indicated that the biofilms mainly inhibited anode action. Current-potential curves under deaerated conditions showed that electron transfer processes occurred between microorganisms and electrodes. Moreover, 316L SS as an electron acceptor was protected from corrosion.

Effect of Added Graphitized Carbon Black on Both Performance and Durability of Pt/Nb-SnO2 Cathodes for PEFCs

The development of cathode catalysts that have both high activity for the oxygen reduction reaction (ORR) and high durability is an important subject for the application of PEFCs in fuel cell vehicles. At present, Pt nanoparticle catalysts supported on carbon black (Pt/CB) are typically being used in PEFC cathodes. While CB supports are essential for the high performance of PEFCs because of their large surface area, high electrical conductivity and well-developed pore structure, they corrode seriously during startup and shutdown of the fuel cell. Graphitized carbon black (GCB), which has a high degree of graphitization, has been used to mitigate such corrosion. According to our previous studies, the high stability of a Pt catalyst supported on GCB (Pt/GCB) was confirmed by use of simulated startup/shutdown evaluation.1 Electrochemical catalysts for PEFCs are required to have both electrically conductive paths and gas diffusion paths in order to form effective catalyst layers (CL). Therefore well-developed pore structures are needed in addition to high conductivity. We have developed Pt catalysts supported on doped SnO2 (Pt/Sb-SnO2, Nb-SnO2, and Ta-SnO2) with fused aggregate structures, which are similar to that of CB, constructed by the fusion of nearest-neighbor particles to form a branched structure.2,3 The Pt/doped SnO2 catalyst provides high electronic conductivity due to the low grain boundary resistance and also has a large micropore volume. Due to the effect of the doped SnO2 with fused aggregate structure, the high performance of these cathodes, which was superior to that of Pt/CB, was confirmed by use of single cell measurements.4,5 In this research,6 we report a detailed investigation of a single cell using Pt/Nb-SnO2 with the fused aggregate structure under actual operating conditions. For instance, we confirmed that the steady-state current-potential (I–E) curves of membrane-electrode assemblies (MEAs) were strongly dependent on the humidity condition of the supplied gases. We also investigated the effects of the addition of GCB into the Pt/Nb-SnO2cathode for the improvement of the cell performance. In Fig.1, the single cell performances using Pt/Nb-SnO2 with/without GCB as function of relative humidity were compared with that of a cell using Pt/GCB at 80◦C and hydrogen/air under 1 atm. The Pt-mass specific power of the Pt/Nb-SnO2 cathode under low humidity conditions was superior to that of the Pt/GCB cathode, because the hydrophilic SnO2 support helped to increase the proton conductivity of the ionomer, which led to high Pt effectiveness. The addition of GCB to the Pt/Nb-SnO2 cathode improved the cell performance under high humidity, and the Pt-mass specific power value reached more than 10 kW gPt −1. The improved performance was attributed to the formation of gas diffusion paths due to the addition of hydrophobic GCB. Fig. 2 shows that the Pt/Nb-SnO2 cathodes, with/without GCB, had greater durability than that of the Pt/GCB cathode after 60,000 cycles of potential sweep cycle evaluation (1.0-1.5 V, 0.5 V s-1). Fig. 3 shows transmission electron microscopic (TEM) images of the Pt/Nb-SnO2 CL and Pt/GCB CL both before and after durability evaluation. The Pt nanoparticle size on the Pt/Nb-SnO2 surface increased to 4.9 ± 0.8 nm (after 60000 cycles) from 3.0 ± 0.6 nm (initial state) in diameter during durability evaluation, becoming spherical in shape (Fig. 3(a) and 3(b)). In contrast, it can be observed that the Pt particles on GCB formed elongated clusters, most likely due to the aggregation of spheres, after 60000 cycles in Fig. 3(d). Moreover, we confirmed that the Pt (111) lattice planes were parallel to those of SnO2 (110), and that the Pt nanoparticles were well oriented on the Nb-SnO2 surface in the initial state, as shown in Fig. 4. We consider that such interaction between the Pt nanoparticles and the Nb-SnO2 support could also have suppressed the migration of the Pt nanoparticles during the durability evaluation. We conclude that the Pt/Nb-SnO2 cathodes, both with and without GCB, exhibited outstanding durability during the startup / shutdown potential sweep evaluation in PEFCs.6 Acknowledgement This research was supported by funds for the “Research on Nanotechnology for High Performance Fuel Cells” (HiPer-FC) project from the New Energy and Industrial Technology Development Organization (NEDO) of Japan, and the JSPS KAKENHI grant Number B24350093. References M. Uchida et al., Physical Chemistry Chemical Physics, 15, 11236 (2012). K. Kakinuma et al., Electrochimica Acta, 56, 2881 (2011). Y. Senoo et al., RSC Advances, 4, 32180 (2014). K. Kakinuma et al., Electrochimica Acta, 110, 316 (2013). Y. Senoo et al., Electrochemistry Communications, 51, 37 (2015). Y. Chino et al., Journal of the Electrochemical Society, 162, F736 (2015). Figure 1

Production of synthesis gas (H2 and CO) by high-temperature Co-electrolysis of H2O and CO2

The present work is focused on production of H2 and H2/CO-rich mixtures by electrolysis and co-electrolysis in Solid Oxide Electrolysis Cell (SOEC)-based stacks. The stack consists of 6 anode supported cells. Measurements are performed on a proprietary test bench designed to test stacks in the power range of 20–200 W. The performance of the stack is initially investigated in SOFC-mode, performing current-potential polarization curves in the range 650 °C–750 °C. After that the stack was tested under the reverse mode (SOEC, Co-electrolysis measurements are performed at 750 °C using a gas mixture containing different CO2/(H2+H2O) ratios. In order to investigate the influence of the operating parameters and fuel composition on the relative amounts of H2, CO and CO2 produced in the stack, a gas chromatography is used to analyze the composition of downstream gases after H2O condensation. As expected, the amount of H2 in the mixture increases with the increase of current density. The conversion of CO2 to CO increases linearly with the current density but it is quite insensitive to CO2 concentration in the cathode atmosphere. The concentration of CO2 affects the overall electrochemical performances of the stack by allowing to operate at higher current density but, however, a large part of CO2 seems to remain unreacted.

Polypyridyl ruthenium complexes containing anchoring nitrile groups as TiO2 sensitizers for application in solar cells

Ruthenium polypyridyl complexes of general formula [Ru(bpy)3−x(Mebpy-CN)x]2+ (x=1,2 and 3, bpy=2,2′-bipyridine, Mebpy-CN=4-methyl-2,2′-bipyridine-4′-carbonitrile) can be used as visible dyes in novel solar cells formed with a porous TiO2 film (1cm2), Pt counter-electrode and iodine/iodide as the redox mediator electrolyte dissolved in a polymeric matrix. These complexes can be anchored over the surface of nanocrystalline TiO2 through nitrile groups, as evidenced by Raman spectra of the adsorbed species. Irradiated by a solar simulator (67mWcm−2), the cells assembled with the Ru complexes with x=2 and 3 as TiO2 sensitizers exhibit almost identical current–potential curves, with short-circuit photocurrents of 1.25mAcm−2, fill factors of 0.5 and overall efficiencies around 0.44%. The Ru complex with x=1 and a similar Re complex did not perform as well as sensitizers. These data were consistent with results obtained from quantum efficiency curves and impedance spectra. We conclude that complexes with nitrile groups as anchoring entities are promising candidates for designing efficient DSCCs.

Influence of zinc (II) ion concentration on Ni–Zn–P coatings deposited onto aluminum and their corrosion behavior

Abstract Various Ni–Zn–P alloy coatings were deposited onto aluminum substrates using electroless plating from a sulphate bath containing varying amounts of zinc (II) ions. Different techniques, such as scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction, were employed to characterize the morphology, composition and structural properties of the resulting films. The effect of varying Zn content on the corrosion properties of the coatings was tested in 3 wt.% NaCl media, by means of current–potential curves, potential transients and electrochemical impedance spectroscopy measurements. It was found that increasing ZnSO4 concentration from 5 to 25 g l−1 in the plating bath, increases the Zn content in the film from 9.90 wt.% to 12.7 wt.%, reduces the film thickness, modifies the surface morphology and significantly reduces the corrosion rate.