关键词: 纳米电极, 稳态电流, 有限元模拟, 尺寸和形貌

Steady-state cyclic voltammetry has several advantages that make it extremely useful for characterization of ultramicroelectrodes, such as rapid electrode performance assessment and size determination. However, due to the nanoscale size effect, the slight variations in geometry of the nanoelectrodes can lead to significant perturbations in its performance. In this study, electrochemical experiments and finite-element simulations using COMSOL Multiphysics software were conducted to characterize the steady-state current dependence on electrode radii, geometries and recesses. To study the above characterics, the Pt nanodisk electrodes with different sizes were fabricated using a laser-assisted wire pulling method on a P-2000 laser puller. Sluggish current responses were obtained for electrodes with a radius smaller than 80 nm in a 5 mmol/L ferrocene (Fc) CH₃CN electrolyte solution containing 0.2 mol/L Tetra-n-butylammonium hexafluorophosphate (TBAPF₆). The experimental results agree very well with the simulations. It was discovered that the sluggish responses are due to the kinetically limited electron transfer resulting from the slow reaction rate relative to diffusion. Moreover, a minimum, constant steady state current value was measured once the RG value (i.e., the ratio of overall electrode radius to active electrode radius) was greater than 3. However, the current increased obviously with the RG value decreased below this value due to the enhanced mass transport. In addition, the steady-state voltammetric responses of recessed nanoelectrodes were investigated. It was found that the steady-state current decreased rapidly as the recess depth increased and a classical sigmoidal shape current response was obtained recovering from a sluggish current response. The unique current responses resulted from the restriction of the diffusion of redox molecules in a deep channel to the electrode. To verify the correlation of recess depth to current response, a model was built based on two-dimensional axial symmetry and the obtained simulation results were consistent well with the experimental data. Our findings offer an understanding on the relationship between the nanoelectrode geometry and steady-state cyclic voltammetry, which can provide insight into their electrochemical behaviors.

Key words: nanoelectrode, steady-state cyclic voltammetry, finite-element simulations, size and geometry