Application Of Ultramicroelectrodes Research Articles

(General Student Poster Award Winner - 1st Place) Nitrogen-Doped and Phosphorus-Doped Carbon Fiber Ultramicroelectrodes As Electrochemical Sensors for Detection of Hydrogen Peroxide

Ultramicroelectrodes (UMEs) are generally defined as electrodes with sizes ≤25 µm. UMEs can be prepared by several methods including by sealing a conductive filament like thin metal wire or a single carbon fiber in a glass capillary. The small size of UMEs makes them useful as probes for measuring electroactive species in confined spaces (for example, inside living cells, etc.), and also enables very effective mass transport, resulting in rapid achievement of steady-state response and facilitating measurement of fast electrochemical reactions. Application of UMEs often requires modification of the electrode surface to improve the selectivity and the sensitivity towards the target analyte. Surface modification methods are time-consuming and may require expensive equipment. Previous research in our group demonstrated that a simple soft nitriding method could be employed to introduce surface nitrogen on carbon fiber (CF). The technique improved electrochemical response of CF-UMEs towards hydrogen peroxide (a reactive oxygen species that has been related to various malignancies and disorders) and, in separate experiments, also enabled deposition of electroactive metal nanoparticles on the UME surface. Since the presence of phosphorus heteroatoms on carbon electrodes has been shown to impart similar benefits, here we investigate a simple phosphorus doping strategy to make P-doped CF-UMEs. We compare their properties towards the electrocatalytic reduction of H2O2 to both N-doped CF-UMEs and unmodified CF-UMEs.

The application of ultramicroelectrode in homogeneous catalytic reaction—V. Electrochemical behaviour of macro-micro-macro triple and micro-micro twin electrodes and the quasi-first-order homogeneous catalytic reaction (EC′) at generation/collection electrode

A new type of macro-micro-macro triple electrode has been fabricated, the steady-state currents of solution redox species have been observed at an ultramicroband electrode by linear potential scan voltammetry, and generation/collection experiments have also been performed at macro-micro-macro triple and micro-micro twin electrodes. The electrochemical behaviour of a single reversible couple with a homogeneous catalytic reaction has been studied at each of the above two kinds of electrodes. We firstly obtained the kinetic equation based on a decrease of the collection current to determine the kinetic constant of the quasi-first-order homogeneous catalytic reaction, as (1 − i cc/ i c) i G  nF AD 1 2 0 C 0[(1 + m) kC z ] 1 2 and we gave the experimental method to determine the kinetic constant. This method can be used with versatility to study homogeneous chemical reactions over a wide range of kinetic constants, which overcomes the disadvantage that an ultramicroelectrode is only suitable for fast catalytic reactions. Two systems, K 4Fe(CN) 6-ascorbic acid and benzoquinone ( Q) − O 2 were chosen to check the equation and to determine their kinetic constants.

Application of ultramicroelectrodes in studies of homogeneous catalytic reactions—part III. The condition for quasi-first and second order homogeneous catalytic reactions at ultramicrodisk electrodes in the steady state

The conditions for quasi-first and second order homogeneous catalytic reactions and their variation with each other at an ultramicrodisk electrode in the steady state are discussed in this paper. The order of reaction can be controlled by changing the dimension of the ultramicroelectrode: the second order reaction can be changed to quasi-first by decreasing the dimension of the ultramicroelectrode. An example of this is given. The main factor effect on the reaction order is the dimension of the ultramicroelectrode. The K 4Fe(CN) 6-aminopyrine system is selected to confirm the theory, the experiments showing that the system is a second order reaction at a 432 μm microelectrode, and a quasi-first order reaction at a 19 μm ultramicroelectrode. The kinetic constant of the system can be determined by applying the previous theory of homogeneous catalytic reaction.

Application of ultramicroelectrodes in studies of homogeneous catalytic reactions—part II. A theory of quasi-first and second-order homogeneous catalytic reactions

The analytical expressions of quasi-first and second order homogeneous catalytic reactions with different diffusion coefficients at ultramicrodisk electrodes under steady state conditions are obtained by using the reaction layer concept. The method of treatment is simple and its physical meaning is clear. The relationship between the diffusion layer, reaction layer, the electrode dimension and the kinetic rate constant at an ultramicroelectrode is discussed and the factor effect on the reaction order is described. The order of a catalytic reaction at an ultramicroelectrode under steady state conditions is related not only to C * z / C * o but also to the kinetic rate constant and the dimension of the ultramicroelectrode; thus the order of reaction can be controlled by the dimension of the ultramicroelectrode. The steady state voltammetry of the ultramicroelectrode is one of the most simple methods available to study the kinetics of fast catalytic reactions.

ChemInform Abstract: Anodic Stripping Voltammetry at Ultramicroelectrodes for Metal Speciation Studies in Aqueous Solutions of Low Ionic Strength.

AbstractThe application of ultramicroelectrodes is shown to be very promising for the study of metal speciation in water samples of low ionic strength.