Electrochemical Redox Couples: A Combined XAS and Modulation excitation study

Authors: Armando Ibraliu (The University of Mancheste; Diamond Light Source; ISIS Facility) , Xiaolei Fan (The University of Manchester) , Luke Keenan (Diamond Light Source) , Daniel Bowron (ISIS Facility) , Sofia Diaz-Moreno (Diamond Light Source) , Chris Hardacre (The University of Manchester)
Co-authored by industrial partner: No

Type: Conference Paper
Conference: XAFS2021
Peer Reviewed: No

State: Published (Approved)
Published: July 2021

Abstract: The use of X-ray absorption spectroscopy (XAS) to follow liquid phase catalysed reactions is widely used. However, in catalysis, small quantities of active species are usually present, complicating the differentiation of spectator and active species. In these cases, the use of Modulation Excitation (ME) techniques can be used to achieve a better signal-to-noise ratio by cycle averaging. ME coupled with phase-sensitive detection can significantly improve the sensitivity of the spectroscopic technique by filtering out contributions of spectator species that are unaltered by the external stimulation. This has been used in combined XAS/DRIFTS studies of gas phase reactions, successfully identifying surface intermediates present in small concentration. [1] In this study, ME assisted by phase-sensitive detection analysis has been applied to the study of liquid-phase reactions using XAS. This methodology has been successfully applied to the study of the electrochemical oxidation of Na4FeII(CN)6. The experiment was undertaken in a newly three-electrode designed electrochemical cell at the I20-EDE beamline at Diamond Light Source. 30, 50, and 75 mM aqueous solutions of the iron complex in 1 M NaF/NaCl electrolytes were investigated. Cyclic voltammograms were measured during potential cycling with potential limits ± 1.5 V, at 200 and 300 mV/s scan rates, for 100 cycles. This perturbed the system reversibly allowing the cycle averaging of the XAS data. This study shows that ME assisted by phase-sensitive detection analysis can be successfully applied to XAS for the study of liquid-phase reactions. Signal-to-noise ratios were improved significantly through cycle averaging, and additional information were extracted from the phase-resolved FT-EXAFS spectra demonstrating the enhanced sensitivity.

Subject Areas: Chemistry

Instruments: I20-EDE-Energy Dispersive EXAFS (EDE)

Added On: 09/08/2021 13:24

Discipline Tags:

Physical Chemistry Catalysis Chemistry

Technical Tags:

Spectroscopy X-ray Absorption Spectroscopy (XAS)