In Situ Confocal Raman Microscopy of Redox Polymer Films on Bulk Electrode Supports

Abstract

A spectroelectrochemical cell is described that enables confocal Raman microscopy studies of electrode-supported films. The confocal probe volume (∼1 μm3) was treated as a fixed-volume reservoir for the observation of potential-induced changes in chemical composition at microscopic locations within an ∼20 μm thickness layer of a redox polymer cast onto a 3 mm diameter carbon disk electrode. Using a Raman system with high collection efficiency and wavelength reproducibility, spectral subtraction achieved excellent rejection of background interferences, opening opportunities for measuring within micrometer-scale thickness redox films on widely available, low-cost, and conventional carbon disk electrodes. The cell performance and spectral difference technique are demonstrated in experiments that detect transformations of redox-active molecules exchanged into electrode-supported ionomer membranes. The in situ measurements were sensitive to changes in the film oxidation state and swelling/deswelling of the polymer framework in response to the uptake and discharge of charge-compensating electrolyte ions. The studies lay a foundation for confocal Raman microscopy as a quantitative in situ probe of processes within electrode-immobilized redox polymers under development for a range of applications, including electrosynthesis, energy conversion, and chemical sensing.

Resonance Raman spectra and excited state properties of methyl viologen and its radical cation from time‐dependent density functional theory

“…In recent years, the incorporation of MV 2+ into polymers to form viologen‐based redox polymers and hydrogels has greatly advanced platforms for bioelectrocatalysis, with the polymer able to serve as a catalyst support matrix and O 2 scavenger in addition to an electron transport mediator 10–14 . The MV •+ radical, intensely colored with a broad absorption between 500 and 700 nm and peak near 600 nm, 2,3 has inspired the design of electrochromic devices 15,16 and is attractive as a model for spectroscopic absorption and resonance Raman studies of photo‐induced charge transfer processes 3,4,17,18 and properties of redox polymer films 19–21 …”

“…[10][11][12][13][14] The MV •+ radical, intensely colored with a broad absorption between 500 and 700 nm and peak near 600 nm, 2,3 has inspired the design of electrochromic devices 15,16 and is attractive as a model for spectroscopic absorption and resonance Raman studies of photo-induced charge transfer processes 3,4,17,18 and properties of redox polymer films. [19][20][21] To support advances in viologen-based redox and photo-sensitive materials, the reported work assesses the performance of modern quantum chemical methods for predicting electronic absorption and Raman spectral properties, including resonance Raman spectra, of MV 2+ and its MV •+ radical cation. The ORCA program suite 22 is adopted.…”