%A Nikoloz Nioradze
%T NANOGAP-ENABLED STUDY OF ELECTRODE REACTIONS BY SCANNING ELECTROCHEMICAL MICROSCOPY
%X NANOGAP-ENABLED STUDY OF ELECTRODE REACTIONS BY SCANNING ELECTROCHEMICAL MICROSCOPY
Nikoloz Nioradze, PhD
University of Pittsburgh, 2014

The nanogap quasi-steady-state voltammetry, developed in my work, presents the way to monitor and study rapid electron transfer reactions on macroscopic substrates of scanning electrochemical microscopy (SECM). It combines the cyclic voltammetry and SECM and monitors substrate reaction as a tip current. The resulting plot of iT versus ES features the retraceable sigmoidal shape of a quasi-steady state voltammogram although a transient peak-shape voltammogram is obtained simultaneously at the macroscopic substrate. This simplifies measurement and analysis of a quasi-steady-state voltammogram and gives information about thermodynamic as well as kinetic parameters of the reaction taking place at the interface. No charging current at the amperometric tip, high and adjustable mass transport under the tip and high spatial resolution are all advantages of quasi-steady-state voltammetry. I also introduced generalized theory for nanoscale iT-ES voltammetry of substrate reactions with arbitrary reversibility and mechanism under comprehensive experimental conditions including any substrate potential and both SECM modes (feedback and substrate generation tip collection, SG/TC). I nanofabricated submicrometer size highly reliable Pt SECM  tips and found the way of protection of these tiny electrodes from the damage caused either by electrostatic discharge or electrochemical etching. Subsequent application of quasi-steady-state voltammetry and reliable nanofabricated SECM probes enabled sensitive detection of adsorption of organic impurities from air and ultrapure water to the HOPG surface as evidenced by redox reaction of ferrocenylmethyl)trimethyl ammonium (FcTMA+). Study revealed that hydrophobic contaminant layer slows down the access of hydrophilic aqueous redox species to the underlying HOPG surface, thereby yielding a lower standard rate constant, k0. Moreover, this barrier effects stronger to a more charged form (FcTMA2+)  of a redox couple so that the electron-transfer reaction of the more hydrophilic form is slower to yield a lower k0 value.

%D 2015
%K Voltammetry, graphite, electrostatic discharge, approach curve, feedback mode.
%I University of Pittsburgh
%L pittir23890