Design of a scanning tunneling microscope for electrochemical applications

A design for a scanning tunneling microscope that is well suited for electrochemical investigations is presented. The construction of the microscope ensures that only the tunneling tip and the sample participate in electrochemical reactions. The design also allows rapid replacement of the tip or sample, and enables facile introduction of auxiliary electrodes for use in electrochemical experiments. The microscope utilizes stepper motor driven approach mechanics in order to achieve fully remote operation and to allow reproducible coarse control of tip/sample spacings for electrochemical experiments. Highly ordered pyrolytic graphite images at atomic resolution in air and aqueous solutions can be obtained with this microscope

Nitrogen evolution as anodic reaction in molten LiF–CaF2

The electrochemical behaviour of nitride ions has been studied in fluoride melts (eutectic LiF-CaF2) by cyclic voltammetry and square wave voltammetry. The purpose of this work is to propose an alternative way for anodic reaction in molten fluorides processes. Thermodynamical analysis can be used for the evaluation of the anodic material regarding to its oxidation potential and reactivity with nitrogen. Then electrochemical investigations confirm the oxidation of nitride ions into nitrogen in a one-step process exchanging 3 electrons, and let propose several materials usable for nitrogen evolving

New aspects of operando Raman spectroscopy applied to electrochemical CO2 reduction on Cu foams

The mechanism of electrochemical CO2 reduction (CO2RR) on copper surfaces is still insufficiently understood. Operando Raman spectroscopy is ideally suited to elucidate the role of adsorbed reaction intermediates and products. For a Cu foam material which has been previously characterized regarding electrochemical properties and product spectrum, 129 operando spectra are reported, covering the spectral range from 250 to 3300 cm−1. (1) The dendritic foam structure facilitates surface-enhanced Raman spectroscopy (SERS) and thus electrochemical operando spectroscopy, without any further surface manipulations. (2) Both Raman enhancement and SERS background depend strongly on the electric potential and the “history” of preceding potential sequences. (3) To restore the plausible intensity dependencies of Raman bands, normalization to the SERS background intensity is proposed. (4) Two distinct types of *CO adsorption modes are resolved. (5) Hysteresis in the potential-dependent *CO desorption supports previous electrochemical analyses; saturating *CO adsorption may limit CO formation rates. (6) HCO3− likely deprotonates upon adsorption so that exclusively adsorbed carbonate is detectable, but with strong dependence on the preceding potential sequences. (7) A variety of species and adsorption modes of reaction products containing C—H bonds were detected and compared to reference solutions of likely reaction products, but further investigations are required for assignment to specific molecular species. (8) The Raman bands of adsorbed reaction products depend weakly or strongly on the preceding potential sequences. In future investigations, suitably designed potential protocols could provide valuable insights into the potential-dependent kinetics of product formation, adsorption, and desorption

Electrochemical performance investigations on the hydrogen depolarized CO2 concentrator

An extensive investigation of anode and cathode polarization in complete cells and half cells was conducted to determine the factors affecting HDC electrode polarization and the nature of this polarization. Matrix-electrolyte-electrode interactions and cell electrolyte composition were also investigated. The electrodes were found to have normal performance capabilities. The HDC anode polarization characteristics were correlated with a theoretical kinetic analysis; and, except for some quantitative details, a rather complete understanding of the causes for HDC electrode polarization was formulated. One of the important finding resulting from the kinetic analysis was that platinum appears to catalyze the decomposition of carbonic acid to carbon dioxide and water. It was concluded that the abnormal voltage performance of the One Man ARS HDC cells was caused by insufficient cell electrolyte volume under normal operating conditions due to deficiencies in the reservoir to cell interfacing

DNA-Mediated Electrochemistry

The base pair stack of DNA has been demonstrated as a medium for long-range charge transport chemistry both in solution and at DNA-modified surfaces. This chemistry is exquisitely sensitive to structural perturbations in the base pair stack as occur with lesions, single base mismatches, and protein binding. We have exploited this sensitivity for the development of reliable electrochemical assays based on DNA charge transport at self-assembled DNA monolayers. Here, we discuss the characteristic features, applications, and advantages of DNA-mediated electrochemistry

A new view of electrochemistry at highly oriented pyrolytic graphite

Major new insights on electrochemical processes at graphite electrodes are reported, following extensive investigations of two of the most studied redox couples, Fe(CN)64–/3– and Ru(NH3)63+/2+. Experiments have been carried out on five different grades of highly oriented pyrolytic graphite (HOPG) that vary in step-edge height and surface coverage. Significantly, the same electrochemical characteristic is observed on all surfaces, independent of surface quality: initial cyclic voltammetry (CV) is close to reversible on freshly cleaved surfaces (>400 measurements for Fe(CN)64–/3– and >100 for Ru(NH3)63+/2+), in marked contrast to previous studies that have found very slow electron transfer (ET) kinetics, with an interpretation that ET only occurs at step edges. Significantly, high spatial resolution electrochemical imaging with scanning electrochemical cell microscopy, on the highest quality mechanically cleaved HOPG, demonstrates definitively that the pristine basal surface supports fast ET, and that ET is not confined to step edges. However, the history of the HOPG surface strongly influences the electrochemical behavior. Thus, Fe(CN)64–/3– shows markedly diminished ET kinetics with either extended exposure of the HOPG surface to the ambient environment or repeated CV measurements. In situ atomic force microscopy (AFM) reveals that the deterioration in apparent ET kinetics is coupled with the deposition of material on the HOPG electrode, while conducting-AFM highlights that, after cleaving, the local surface conductivity of HOPG deteriorates significantly with time. These observations and new insights are not only important for graphite, but have significant implications for electrochemistry at related carbon materials such as graphene and carbon nanotubes

Electrochemically Deposited Cadmium Electrode for Sealed Ni-cd Cells

An investigation into the work on electrochemical cadmium deposition processes is describred. A beaker impregnation system is constructed to investigate the practical limits of loading and the effect of various process parameters. Reasonably high loadings of cadmium are obtained and the process appears amenable to tight control and the production of uniform consistent electrodes. A pilot impregnation facility is built to further investigate electrodeposition processes. Both the inert anode and consummable anode processes are investigated. Results of this evaluation and an analysis of associated problems are presented