An analytical solution is herein presented for the current at a channel-type electrode associated with a simple first-order ͑in the reactant͒ heterogeneous electron transfer process involving a solution phase species. Assuming a fixed cell geometry, electrolyte composition, and temperature, a series expansion of this solution revealed that in the limit of small values of k 3 / o , where k is the first-order kinetic rate constant and o is the fluid velocity in the center of the channel, the reciprocal of the measured current, 1/i = 1/i k + ␤/i lim , where i k and i lim are the kinetic and diffusion limited currents, respectively, and ␤ = 27/͓8⌫͑2/3͒⌫͑1/3͔͒ = 0.93036. This equation bears striking resemblance to that reported by Koutecky and Levich for a rotating disk electrode, except that ␤ in the latter case is unity. Rather surprisingly, and in agreement with recent findings ͓Electrochim. Acta, 52, 4124 ͑2007͔͒, a plot of 1/i vs k/ o 1/3 was found to be close to linear, with a slope reaching values slightly higher than ␤ as the magnitude of k/ o 1/3 increased.

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Methods are herein described for monitoring in situ changes in the electrical resistance of a single, spherical ͑S-͒Ni͑OH͒ 2 microparticle electrode as a function of its state of charge. The general approach involves application of 1-2 mV across, and measuring the current through the particle either at a fixed state of charge ͑static͒ or during a linear voltammetric scan ͑dynamic͒. The data obtained for activated S-Ni͑OH͒ 2 microparticles agreed well with values reported in the literature measured by other means, whereas oxidation of the material yielded as expected a sizable increase in conductivity. Other methods reported in the literature for in situ resistivity measurements of electrodes as a function of the applied potential are also discussed.Reliable measurements of the physicochemical properties or charge storage materials within actual operating battery electrodes should afford significant insight into the factors that control the overall performance of devices, including failure modes. Attention in our laboratory has focused on the development and implementation of techniques for monitoring in situ the properties of individual Zn, 1 spherical Ni oxide, 2 denoted as S-Ni͑OH͒ 2 , carbon, 3 and lithiated transition metal oxide 4 microparticle electrodes using optical and spectroscopic probes.Broadly speaking, the charge storage mechanism of a variety of electrode materials involves changes in the oxidation of metal sites and incorporation of ions into the lattice, most vividly illustrated by state-of-the-art secondary lithium ion batteries. Changes in the state of charge of such electrodes bring about modifications in their intrinsic electrical conductivity, as has been typically found from measurements involving chemically ͑or electrochemically͒ prepared materials ex situ. Ingenious tactics have been developed and implemented for determining in situ the resistance of electrodes as a function of their state of charge. In particular, Zotti et al. 5 employed two potentiostats for determining the resistance of a conducting polymer, by measuring the current through the film, i, upon applying a constant potential difference across the film, ⌬V, at various fixed values of the electrode potential, E, vs. that of a reference electrode. This specific method was very recently implemented by Harima et al. 6 to study the same type of materials. Particularly noteworthy, however, is the work of Uchida and coworkers, 7,8 who succeeded in measuring the conductance as a function of potential for a single mesocarbon microbead ͑MCMB͒ in electrolytes of relevance to Li + batteries. These authors used a bipotentiostat to fix, ⌬V, and measured i while scanning E. Because the conductivity of the materials examined by these authors was relatively high, contributions due to ͑mostly͒ pseudocapacitive processes could be safely neglected, i.e., the measured current is purely ohmic. This would not be the case for materials that display relatively high resistivity, such as Ni͑OH͒ 2 9 for which particles of ca. 30 m in diameter are fo...

A method is herein described for the micromanipulation and subsequent in situ, real-time optical and spectroscopic characterization of individual micrometer-size particles of electrochemically active materials under potential control. This novel approach relies on the use of a micropipette to capture, by suction, single particles, which are then attached to the surface of a glass-encased microelectrode placed inside an empty, shallow Petri dish, and held in position by a small glass rod in the form of truncated cone. This configuration allows for particles to be placed directly beneath the microscope objective enabling visual and spectroscopic monitoring during electrochemical measurements by simply filling the dish with sufficient electrolyte to completely cover the particle and make electrolytic contact with a reference and a counter electrode. Illustrations are provided for particles of spherical Ni hydroxide, S-Ni͑OH) 2 , in alkaline solutions, which following activation at fairly positive potentials, yielded an electrochemical response characteristic of Ni͑OH) 2 in more conventional electrode configurations. The much darker appearance of NiOOH compared to the virtually translucent character of virgin S-Ni͑OH) 2 allowed for the spatial and temporal evolution of charge flow within the microparticle to be monitored in real time during the first scan in the positive direction using computer-controlled video imaging.

The invention of the battery can be attributed to Alessandro Volta (1745-1827) of Como, Italy, who in 1800 described an assembly consisting of plates of two different metals, such as Zn and Cu, placed alternately in a stack-like fashion separated by paper soaked in aqueous solution, such as brine or vinegar.

Methods are herein described for the assembly and electrochemical characterization of Zn͉MnO 2 and nickel͉metal-hydride ͑Ni͉MH͒ alkaline batteries incorporating single microparticles of the active materials. As evidenced by the data collected, the voltage-time profiles for constant current operation for both types of devices were found to be similar to those of commercially available batteries involving the same chemistries. These results open new prospects for the development of aqueous primary and secondary micropower sources for application in a variety of technical areas.The development of new methodologies for the assembly of reliable microbatteries is key to the further development of microsensors and other microdevices with applications in such diverse areas as biomedical engineering and homeland security. Efforts in our laboratories have recently focused on the search for novel techniques for the micromanipulation of single-particle electrodes of micrometer dimensions, and their subsequent characterization using electrochemical and in situ optical techniques. Indeed, particular success was achieved using microaspirators, spears, are other tactics to establish mechanical/electrical contact between individual microparticles and a current collector allowing in situ optical and Raman data of microparticle electrodes to be acquired as a function of the applied potential. 1-4 More recently, some of the same strategies were successfully employed to assemble and study the self-discharge characteristics of a Li-ion battery incorporating a single mesocarbon microbead and a single LiCoO 2 microparticle only a few tens of micrometers in diameter. 5 The present contribution illustrates the versatility of such methods for the assembly and characterization of Zn͉MnO 2 and nickel͉metal-hydride ͑Ni͉MH͒ batteries, which rank, respectively, among the most common commercial primary and secondary aqueous systems in use today. Voltage vs time curves recorded under galvanostatic conditions for both types of systems were found to be in agreement with corresponding data made available by commercial manufacturers 6 affording strong evidence for the operational reliability of the microbatteries examined. ExperimentalChemicals and electrochemical instrumentation.-Spherical Ni oxide, S-Ni͑OH͒ 2 , particles of micrometer dimensions were obtained from Tanaka Chemicals and also from Ovonic Battery Company. Hydrogen storage alloy ͑standard mishmetal denoted as Mm͒ particles were obtained from Ovonic Battery Company; MnO 2 ͑EMD͒ and Zn particles were provided by Eveready Battery Company. Experiments were performed in 9 M solutions prepared by dissolving solid KOH pellets ͑Aldrich, 99.99% semiconductor grade͒ in ultrapure water ͑Barnstead͒. Electrical contact to the microparticles was made with Au microdisk electrodes prepared by first melting the end of a glass tube around the end of a Au wire ͑0.1 mm diam, Alfa Aesar, Premion, 99.998% purity͒ forming a small sphere, which was then polished to expose a circular cross section of the wire. ...

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Testing of inhibitors for CO 2 -corrosion at elevated temperatures is often performed so as to delay or avoid formation of a protective iron carbonate layer. Inhibitor performance in the presence of FeCO 3 (partly or fully covering the steel surface), however, also deserves attention. This is relevant for parts of pipelines where rapid iron carbonate formation is expected, or when formation water breakthrough requires switching from pH stabilization to inhibition. From a methodological viewpoint such studies may indicate whether experiments in the presence of FeCO 3 layers should be included in routine inhibitor performance testing. Investigating and comparing the behavior of corrosion inhibitors in the presence of iron carbonate layers of varying degrees of protectiveness was the objective of a series of experiments within the framework of a Joint Industry Project focusing on high temperature inhibition, carried out in our laboratories.This contribution presents the results obtained with an imidazoline type generic inhibitor in high salinity brines with pH above 6, with 0.5 and 1 bar CO 2 partial pressure. Inhibitor performance was studied by means of electrochemical measurements in glass cells at 80°C as well as in a pressurized jet impingement apparatus at 100°C and 120°C. Timing of the inhibitor injection was based on the development of the iron carbonate layer.The inhibitor effectively reduced the corrosion rate when protective FeCO 3 formation was not yet complete. Measurements of the Fe 2ϩ concentration also revealed that the inhibiting effect hindered the increase of the supersaturation required for effective FeCO 3 precipitation, slowing down or completely halting the film formation process. In contrast, once a fully protective iron carbonate layer has developed, no additional corrosion rate reduction can be observed upon inhibitor addition.The results provide insight into how the inhibitor effect manifests itself when applied at various stages of iron carbonate formation on a steel surface. The experiments performed under enhanced convection illustrate the important role mass transport plays in the formation of iron carbonate layers and on inhibition. Both aspects are important for an improved understanding of inhibition of CO 2 -corrosion in oil and gas pipelines.