Speaker
Description
Layered double hydroxides (LDH), with the typical formula [M1-x2+Mx3+(OH)2]x+[Ax/n]n-.mH2O, also known as anionic clays, are hydrotalcite-type positively charged lamellar material, in which a part of the divalent M2+ cations is substituted by trivalent M3+ cations. The electroneutrality of the material is ensured by the presence of anion located in the interlayer domain. The composition of the LDH can be easily tuned by varying the nature of the divalent and/or trivalent cations within the layers and/or by changing the interlamellar counter-anions, thus allowing modulation of their physicochemical properties. This versality makes the LDH promising materials for a wide range of applications, particularly in electrochemistry [1].
The present work [2] focuses on the use of Co3Mn-based LDH for the development of electrochemical sensors for the detection of H2O2. The electrochemical activity of the Co3Mn LDH was monitored by quick-EXAFS at the Co and Mn K-edges on the ROCK beamline at the SOLEIL synchrotron [3]. The LDH was deposited on a carbon paper, used as working electrode, and placed in contact with 0.1 M NaOH in a dedicated cell designed for XAS measurements. The electrochemical treatment consisted of cyclic voltammetry (CV) between 0 and 0.6V. Between the first and the last CV at 0.66 mV s-1, modulation excitation XAS (MEXAS) measurements were performed by acquiring 20 CV cycles at 10 mV s-1. The obtained datasets were first analysed via multivariate curve resolution with alternating least squares (MCR-ALS). The results revealed that Mn(III) is irreversibly transformed to Mn(IV) during the 1st cycle, while the Co(II) oxidised in two distinct species, Co(III)1-εCo(III)ε and Co(III), which proportions perfectly matched the CV curves. The findings were further supported by applying phase sensitive detection (PSD) on the MEXAS [4] data obtained from the 20 intermediate CV cycles. While only noise was observed in the phase-resolved spectra at Mn K-edge, meaning that Mn species do not evolve during CVs, the phase-resolved spectra obtained at the Co K-edge can be superimposed to the scaled difference of the two Co species extracted from MCR-ALS.
This work highlights the excellent complementarity of MCR-ALS and MEXAS-PSD analyses in unravelling small changes occurring during electrochemical treatments of materials.
[1] Mousty C., & Farhat H. (2023). Electroanalysis, 35.
[2] Farhat H., et al (2024). J. Phys. Chem. C, 128, 21023-21037.
[3] Briois V., et al (2016). J. Phys.: Conf. Ser., 712, 012149.
[4] Urakawa A., et al (2023). in Springer Handbook of Advanced Catalyst Characterization
