Scanning Electrochemical Microscopy with Forced Convection Introduced by High-Precision Stirring

In the present report the well-known advantages of hydrodynamic mass transport in electrochemical systems are used in combination with scanning electrochemical microscopy (SECM). The hydrodynamic SECM system integrates a high-precision stirring device into the experimental setup. The well-defined stirring of the SECM electrolyte results in steady state diffusion layer characteristics in the vicinity of large substrate electrodes operated in chronoamperometric measuring mode. For a range of rotation frequencies of a rotating cylinder the thickness and the stability of the diffusion layer was studied by hydrodynamic SECM in the substrate generation/tip collection (SG/TC) as well as in the competition mode using ferrocene methanol as redox mediator. Different UME probe dimensions ranging from Pt diameters of 20 μm down to 0.6 μm were used. The smallest probe with d_Pt = 0.6 μm was found most suitable for these studies due to the almost convection-independent amperometric response associated with subμm electrodes. Additionally, preliminary studies of hydrodynamic SECM imaging of a 2 mm Pt disk electrode surface in the SG/TC mode based on in situ produced hydrogen as a mediator are presented. Comparative images measured in the conventional positive feedback mode in quiescent solution show that hydrodynamic SECM offers attractive complementary information.