Investigation of a Free-Standing Boron-Doped Diamond Grid Electrode for Fundamental Spectroelectrochemistry

In fifteen words or less, explain the significance of this contribution (Novel Aspect).: Expands spectroelectrochemistry to robust BDD electrodes by modifying models for complex diffusion geometry

Abstract Text:

Spectroelectrochemistry (SEC) is a powerful technique that enables a variety of redox properties to be studied to characterize the electrochemical and optical properties of various electrodes. This includes diffusion coefficient (D) and heterogenous electron transfer rate constant (k). SEC measurements historically require an optically transparent electrode (OTE), traditionally composed of metal or metal oxide films atop transparent substrates (one-electroactive side) or the use of a metallic mesh (two-electroactive sides). Robust electrode materials like boron-doped diamond (BDD) could expand the environments in which SEC can be performed, but most designs are limited to thin films on transparent substrates which are less resilient than free-standing BDD. In this work, a grid was laser-cut into a free standing BDD electrode (G-BDD) for fundamental SEC measurements, such as chronoabsorptometry for the determination of D and k. The chronoabsorptometry equation relates the Beer-Lambert Law and the Anson equation which displays a relationship between absorbance and D. Previous literature by the Murray group and the Rusinek group have shown that the chronoabsorptometry equation needs to be modified to account for the electroactive dimensions of the electrode. An electrode with two electroactive sides develops two diffusion layers which the incident light beam must transverse and therefore the chronoabsorptometry equation be multiplied by a factor of two. To accurately determine the electrochemical properties of the G-BDD electrode a third dimension must be considered due to the development of diffusion layers on either side and inside the grid holes. Furthermore in 1981 Hawkridge and Blount reported on a spectroelectrochemical method for the determination of k that is independent of the surface area of the working electrode. The redox couple of ferricyanide(II) (Fe(CN)₆^4-/3-) was used to compare the redox properties obtained from cyclic voltammetry, chronoabsorptometry, and electrochemical impedance spectroscopy. The redox properties of the G-BDD were compared with electrodes with one- and two- electroactive dimensions using various equations. Future work entails varying the G-BDD electrode thickness and grid hole size to better predict the modifications of fundamental equations. Overall, this work expands on the applicability of BDD as an electrode material and broadens the general applicability of SEC.