Danzhen Zhang1,Ruocun (John) Wang1,Xuehang Wang2,Yury Gogotsi1
Drexel University1,Delft University of Technology2
Danzhen Zhang1,Ruocun (John) Wang1,Xuehang Wang2,Yury Gogotsi1
Drexel University1,Delft University of Technology2
Understanding energy storage mechanisms in electrochemical energy storage devices lays the foundations for improving their energy and power density. Herein, we introduce a simple and easily accessible <i>in situ </i>ultraviolet-visible (UV-Vis) spectroscopy method to distinguish battery-type, pseudocapacitive, and electrical double-layer charge storage processes. Ti<sub>3</sub>C<sub>2</sub>T<i><sub>x</sub></i> MXene in aqueous acidic and neutral electrolytes, and lithium titanium oxide (LTO) in an organic electrolyte will be used to demonstrate the technique. We found a correlation between the evolution of UV-Vis spectra and the charge storage mechanism. The electron transfer number for Ti<sub>3</sub>C<sub>2</sub>T<i><sub>x</sub></i> in an acidic electrolyte was calculated using quantitative analysis, which was close to previous measurements using X-ray absorption spectroscopy. Further, we tested the methodology to distinguish the non-Faradaic process in Ti<sub>3</sub>C<sub>2</sub>T<i><sub>x</sub></i> MXene in a water-in-salt electrolyte, despite well-defined peaks in cyclic voltammograms. <i>In situ</i> UV–Vis spectroscopy is a fast and cost-effective technique that effectively supplements electrochemical characterization to track changes in oxidation state and materials chemistry and determine the charge storage mechanism.