PNNL

Abstract

Spectroelectrochemistry (SEC) is a powerful technique that enables a variety of redox properties to be studied. This includes formal potential (Eo), thermodynamic values (?Gcell, ?H, ?S), diffusion coefficient (D), electron transfer stoichiometry (n), and others. SEC requires an optically transparent electrode (OTE), traditionally composed of metal or metal oxide films atop transparent substrates like glass, quartz, and/or metallic mesh. Robust electrode materials like boron-doped diamond (BDD) could help expand the environments in which SEC can be performed, but most designs are limited to thin films (~100-200 nm) on transparent substrates less resilient than free-standing BDD. This work presents a free-standing BDD grid electrode (G-BDD) for fundamental SEC measurements, using the well-characterized Fe(CN)63-/4- redox couple as proof-of-concept. With a combination of cyclic voltammetry (CV), thin-layer SEC, and chronoabsorptometry, several of the redox properties mentioned above were calculated and compared. For Eo’, n, and D, similar results were obtained when comparing the CV [Eo’ = +0.279 (? 0.002) V vs. Ag/AgCl; n = 0.97; D = 4.1 × 10-6 cm2*s-1] and SEC [Eo’ = +0.278 (? 0.001) V vs. Ag/AgCl; n = 0.91; D = 5.2 × 10-6 cm2*s-1] techniques. Both values align with what has been previously reported. To calculate D from the SEC data, modification to the classical equation used in chronoabsorptometry was required to accommodate the G-BDD electrode geometry. Overall, this work expands on the applicability of BDD as an electrode material and broadens the general applicability of SEC.