Understanding Electrochemical Interface Using Atom-By-Atom Metal Substitution of Redox Species

Abstract

Molecular-level understanding of electrochemical processes at nanostructured electrode-electrolyte interfaces (EEI) is key to the development of clean and sustainable electrochemical technologies in energy generation and storage as well as water and chemical separation and purification. Herein, we introduced a novel in situ electrochemical cell coupled with ion soft landing to study the precisely defined operating EEI. Ion soft landing is a mass spectrometry based deposition technique which enables to land uniform layers of redox-active ions onto electrode surfaces with precise control over the charge state, composition, and kinetic energy. In this work, we used ion soft landing to study (i) the multi-electron redox activity of Keggin polyoxometalate anions (POMs) to design high-performance EEIs for energy storage (ii) examined how “atom-by-atom” metal substitution affects the redox activity of well-defined mixed addenda POM anions, PMoxW12-xO40 3- (x = 0,1,2,3,6,9,12) at ionic liquid based in situ electrochemical cell. We made a striking observation in in situ experiment and well-supported by theoretical calculation, which is that substantial increase in the first reduction potential obtained by substitution of only few tungsten by molybdenum atoms in the PW12O40 3- anions. More specifically, PMo3W9O40 3- showed the highest redox activity compared to all other mixed-addenda POM anions, which making it as a “super active redox anion” for this class of redox species. This presentation will also focus how these fundamental understanding on the activity of mixed addenda POMs was translated well into achieving device-level supercapacitor performance with superior capacity and capacity retention.