Spectroelectrochemistry: A Powerful Tool for Studying Fundamental Properties and Emerging Applications of Solid-State Materials Including Metal–Organic Frameworks

Deanna M D'Alessandro,Pavel M Usov

doi:10.1071/ch20301

Abstract

Spectroelectrochemistry (SEC) encompasses a broad suite of electroanalytical techniques where electrochemistry is coupled with various spectroscopic methods. This powerful and versatile array of methods is characterised as in situ, where a fundamental property is measured in real time as the redox state is varied through an applied voltage. SEC has a long and rich history and has proved highly valuable for discerning mechanistic aspects of redox reactions that underpin the function of biological, chemical, and physical systems in the solid and solution states, as well as in thin films and even in single molecules. This perspective article highlights the state of the art in solid-state SEC (ultraviolet–visible–near-infrared, infrared, Raman, photoluminescence, electron paramagnetic resonance, and X-ray absorption spectroscopy) relevant to interrogating solid state materials, particularly those in the burgeoning field of metal–organic frameworks (MOFs). Emphasis is on developments in the field over the past 10 years and prospects for application of SEC techniques to probing fundamental aspects of MOFs and MOF-derived materials, along with their emerging applications in next-generation technologies for energy storage and transformation. Along with informing the already expert practitioner of SEC, this article provides some guidance for researchers interested in entering the field.

Highlights

Electroanalytical methods such as voltammetry techniques have been the primary tool for interrogation of redox-active compounds with a well-established theoretical framework to interpret the data; the nature of the electrogenerated species can be difficult to elucidate from electrochemical techniques alone
Richter proposed the application of a ‘pouch’ SEC cell for solid-state NMR, which was employed to quantitatively monitor an evolved reaction product (CO2) from the electrocatalytic oxidation of ethanol.[136]
An important future prospect is the monitoring, in real time, of material evolution itself, providing a comprehensive picture of structural effects coupled with the substrate redox processes and changes in the reactant and product composition

Summary

Introduction

Electroanalytical methods such as voltammetry techniques have been the primary tool for interrogation of redox-active compounds with a well-established theoretical framework to interpret the data; the nature of the electrogenerated species can be difficult to elucidate from electrochemical techniques alone. A highlighted case here is the report of the NH2-MIL-125(Ti) [Ti8O8(OH)4(2OC-NH2-C6H3-CO2)6] MOF, which has attracted significant attention owing to its relevance in the field of photocatalysis for solar fuel production.[68] On reduction, soluble clusters of Ti8O8(O2C2(CH3)3) generated a new band in the NIR region that was attributed to Ti3þ/Ti4þ mixed valency (Fig. 3) This result provided strong evidence for the ligand-tometal-charge transfer (LMCT) character of the NH2-MIL125(Ti) photoexcited state, enabling important mechanistic insights into the function of the photocatalyst. This compartment was connected to two side-arms used to harbour

Objective lens Light source Polariser

Summary and Outlook