David O. Wipf

Chemical Imaging of Surfaces with the Scanning Electrochemical Microscope

Scanning electrochemical microscopy is a scanning probe technique that is based on faradaic current changes as a small electrode is moved across the surface of a sample. The images obtained depend on the sample topography and surface reactivity. The response of the scanning electrochemical microscope is sensitive to the presence of conducting and electroactive species, which makes it useful for imaging heterogeneous surfaces. The principles and instrumentation used to obtain images and surface reaction-kinetic information are discussed, and examples of applications to the study of electrodes, minerals, and biological samples are given.

Scanning Electrochemical Microscopy VII . Effect of Heterogeneous Electron‐Transfer Rate at the Substrate on the Tip Feedback Current

The dependence of the SECM feedback current on finite heterogeneous electron-transfer kinetics at the substrate electrode was examined by experimental studies of the reduction of Fe(III) in 1M H 2 SO 4 at a Pt tip over a biased glassy-carbon substrate

Microdisk electrodes: Part II. Fast-scan cyclic voltammetry with very small electrodes

Abstract Cyclic voltammetry has been investigated at inlaid disk electrodes with nominal radii of 0.3, 1.0, and 5.0 μm. The electrode capacitance is found to be much larger than expected for the two smaller radii electrodes. This effect is attributed to the capacitance between the inner conductor and the electrolyte solution. The excess capacitive current is minimized by the use of a conductive shield around the electrode which is connected to ground potential. Criteria are investigated for the degree of filtering of steady-state voltammograms to minimize noise while avoiding distortion of the experimental data. Experimental voltammograms for the oxidation of ferrocene in acetonitrile solutions are found to be in good agreement with existing theories for scan rates in which linear and convergent diffusion occur. The factors which limit the use of very small electrodes are discussed in terms of signal-to-noise, ohmic drop, and linear diffusion.

Application of rapid scan cyclic voltammetry to a study of the oxidation and dimerization of N,N-dimethylaniline in acetonitrile

Abstract Rapid scan cyclic voltammetry was used to investigate the mechanism of the anodic oxidation and dimerization of N, N-dimethylaniline (DMA) in acetonitrile solution. The reduction wave for the DMA.+ radical cation was observed at scan rates above 500 V s−1. Electrogenerated DMA.+ radical cations underwent a second-order radical cation-radical cation coupling with deprotonation to form N,N,N′,N′-tetramethylbenzidine; no evidence of polymerization was detected. The experimental results best fit an EC2EE reaction mechanism determined by fitting the data with working curves obtained by digital simulation. A rate constant of 6.3 × 105 M−1 s−1 was found for the coupling reaction. The clean reaction process suggests that the oxidation of DMA can serve as a model for the EC2EE reaction mechanism in kinetic studies.