The reaction of superoxide with carbon dioxide is studied using voltammetry and potential step chronoamperometry at polycrystalline gold disk microelectrodes in a DMSO electrolyte. In agreement with prior work, it is found that a reaction occurs between the superoxide anion radical and carbon dioxide, effectively precluding their simultaneous detection at low levels of carbon dioxide. The reaction rate is found to be first-order with respect to both carbon dioxide and superoxide, consistent with an ECE or DISP1 type process. A rate constant is determined for this reaction based upon two independent methods: fast scan cyclic voltammetric measurements and steady-state voltammetric signals. These methods yield a consistent rate constant of 3.7 ( 1.6 × 10 5 M -1 s -1 . Potential step chronoamperometric measurements reveal that oxygen adsorbs onto a gold electrode surface, to form a monolayer both in the presence and absence of carbon dioxide. A rate constant for the reduction of surface-bound oxygen to superoxide is reported.
A numerical method is used to characterize the steady-state voltammetry at microdisk electrodes of a new electrocatalytic reaction. This reaction, which occurs for the oxidation of N,N-dimethylphenylenediamine (DMPD, A) in the presence of H2S (X) is believed to proceed via the following route: A − 2e- ⇄ B, B + X → BX (k 2), B−X − 2e- ⇄ [BX]2+. Due to the presence of a reagent restricted homogeneous kinetic step, the reaction is labeled EC2XE. The numerical method for simulating this reaction scheme is based on the finite-difference formulation of coupled mass transport and kinetic equations in oblate spherical coordinates. The method is illustrated for not only the EC2XE but also the EC‘ reaction and is applicable to the simulation of steady-state limiting currents at microdisk electrodes. Iterative solutions are calculated using a Gauss−Newton scheme to overcome nonlinear homogeneous kinetic terms. The spatial convergence of the simulation for both reactions is investigated by considering the form of the concentration function describing the species. Via the comparison of working surfaces generated from simulated results, measuring the steady-state limiting current is shown to be insensitive to the resolution of EC‘, ECE, and EC2XE reactions. Experimental steady-state limiting current data is reported for the DMPD/H2S system at microelectrodes of 7.3, 19.5, and 25.0 μm diameter to verify the theory behind the EC2XE reaction. These results are shown to closely fit experimental data using a working surface interpolation method. Specifically, this method correctly predicts the variation of the steady-state limiting current with the concentration of H2S for a 19.5 μm diameter microelectrode to a relative standard deviation of 1.9%. Similar analysis for the 7.3 and 25.0 μm electrodes results in a mean value of 1.4 × 107 mol-1 cm3 s-1 for the rate constant k 2 in the DMPD/H2S system.
A numerical method is illustrated for the modeling of an important electrocatalytic reaction at the rotating disk electrode (RDE). This reaction, labeled EC2XE, occurs via the following route: A − 2e- ⇌ B, B + X → B−X (k 2), B−X − 2e- ⇌ [B−X]2+. The numerical method is based on a finite difference formulation of coupled mass transport and kinetic equations and makes use of a Hale coordinate transformation. Iterative solutions are performed using a Gauss−Newton scheme to solve the nonlinear differential equations. Numerical solutions are calculated to generate working surfaces in the effective number of electrons transferred, N eff. Cyclic voltammetry is reported in hydrostatic conditions with a 4-acetamidophenol (paracetamol)/cysteine system, which is shown to proceed via the EC2XE reaction pathway. The resulting data is modeled using the commercial package DIGISIM, and a result of k 2 = 1.25 ± 0.25 × 107 mol-1 cm3 s-1 is obtained. RDE studies of the same system using steady-state linear sweep hydrodynamic voltammetry is next performed to collect limiting current data at rotation speeds of 2, 4, 8, 16, and 25 Hz. Working surface interpolation of the resulting data results in a mean value of 1.6 ± 0.35 × 107 mol-1 cm3 s-1 for the rate constant k 2.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.