EXPRESS: Automating Absorbance Spectroelectrochemistry using Normal Pulse Voltammetry

Absorbance spectroelectrochemistry is a powerful in situ technique utilized to investigate redox changes and charge carrier properties in electronic materials, such as mixed ionic-electronic conducting polymers. In this method, the absorption spectrum of the material is obtained as a function of applied potential, and the results are used to understand its electrochemical behavior. The standard approach uses chronoamperometry, in which a constant potential is applied, and an absorption spectrum is measured at electrochemical equilibrium for a series of potentials selected across the electrochemical window of the sample. However, this method is limited by slow, labor-intensive data acquisition and lack of time-resolved absorbance information. Herein, we describe an automated absorbance spectroelectrochemical method that couples a high-speed, broadband optical absorbance instrument with normal pulse voltammetry to capture full absorbance spectroelectrochemistry spectra in a single measurement. The instrument measures absorption spectra over a 400 - 2500 nm window at a maximum spectral acquisition rate of 200 Hz (5 ms response time). We demonstrated the capability of this spectroscopy technique to automatically obtain a full set of potential-dependent absorbance spectra and absorbance transients by applying it to study the electrochemical charging behavior of a polythiophene electrode, which was time-resolved at 1 spectrum/s.