An underused parameter in electrochemistry is temperature. Controlling or altering the temperature at the electrode can provide several experimental benefits. Changes in kinetics and equilibrium constants are readily observed. Temperature dependent potential shifts and wave shapes can allow unique identification of chemical species. Thermal effects can also renew catalytic surfaces and improve mass transport by increasing diffusion coefficients or inducing convective currents.

Temperature control is readily achieved using thermostated electrochemical cells, but this produces several practical problems that may require addressing.  These include destruction of thermally unstable compounds, loss of volatile components, and reference electrode potential shifts.  In addition, the large thermal mass of an electrochemical cell does not favor rapid temperature changes.  These drawback can be minimized or eliminated by directly heating the electrode in a non-isothermal mode. (1)  For example, using high-voltage AC to heat cylindrical electrodes of mini to macroscopic dimension. These, and other types of electrode heating, produce a heated zone in the solution immediately adjacent to the electrode surface.  This then permits considering using temperature as a parameter in electrochemical imaging (cf. SECM) because of the potentially rapid temperature rise and fall at microscopic electrodes.  However, now several disadvantages are produced in the non-isothermal mode. These include reduced control over the temperature achieved, increased complexity of the experiment, and lower temperature precision.

Our goal is to develop heated-tip microelectrodes compatible with SECM and other SPM imaging.  We have developed a novel inductive heating procedure that can be used with electrodes of 1-20 μm. A small induction coil is placed entirely inside the electrode housing allowing the electrode shank to be heated by galvanically isolated induction. This electrode is physically small and is readily incorporated into the SECM instrument with no instrument modifications.

In this presentation, we demonstrate the rapid heating and cooling produced by the inductive method and show, using effects on kinetics and equilibrium potentials, that the temperature at the tip of the ultramicroelectrode may be altered up to the boiling point of the solvent. We also use finite element modelling to model the heating process and to estimate the temperature at the tip based on the geometry of the induction coil, the electrode material, the electrode body and any active cooling, and the solvent. In addition, we are modeling the rate of temperature rise and return to ambient relative to a heating pulse. Finally, we model the possibility of indirect, transient heating the imaged substrate by the heat flow from the closely-spaced heated tip.

 (1) Gründler, P.; Flechsig, G.-U. Microchim Acta 2006, 154 (3-4), 175–189.