Spectroelectrochemistry

Spectroelectrochemistry is a suite of techniques that merge electrochemical methods with spectroscopy to observe the species formed and consumed during redox processes in real time. By coupling controlled electrical potentials with optical or vibrational measurements, it reveals correlations between oxidation state, electronic structure, and chemical reactivity.

The most common form is UV‑visible spectroelectrochemistry, which tracks changes in absorbance as a function of potential or time. Other modalities include infrared and Raman spectroelectrochemistry, which monitor vibrational fingerprints, and electron paramagnetic resonance (EPR) spectroelectrochemistry for paramagnetic intermediates. Each modality provides complementary information.

Instrumentation typically combines an electrochemical cell with an in situ spectroscopic probe. A transparent or windowed electrode, such as an optically transparent thin-layer electrode or indium tin oxide, permits light to reach the sample while a working, reference, and counter electrode complete the circuit. Detectors may be UV–vis spectrometers, FTIR or Raman spectrographs, or EPR spectrometers.

Experiments involve applying a potential profile—step, pulse, or cyclic voltammetry—while recording spectra. Analysis links spectral features to oxidation states, determines the number of electrons transferred, and identifies transient intermediates. Time-resolved measurements can yield kinetic information about electron transfer and follow-up reactions.

Applications span inorganic and organometallic redox chemistry, catalysis, electrochromic materials, energy storage devices, and sensing. Spectroelectrochemistry helps assign redox-active species, study catalytic cycles, and optimize materials by correlating spectral changes with performance.

Advantages include in situ observation of species under electrochemical control and direct mechanistic insight. Limitations include spectral overlap, limited sensitivity for weak absorbers, and the need for optically accessible samples or electrode configurations, which can constrain cell design and experimental conditions.