(Invited) Confocal Raman Microscopy in the Study of Membrane Materials for Energy Conversion

Abstract

Confocal Raman microscopy techniques are being adapted for quantitation, structural characterization and spatial profiling in the development of materials for electrochemical energy conversion. This presentation will discuss applications to fuel cell catalytic membranes and bipolar membranes and strategies for estimation of the limiting spatial resolution in depth profiling.1,2 In the study of catalytic membranes, experiments have focused on steps in the processing of electrodes containing biocatalyst. Confocal Raman microscope measurements confirm the presence of entrapped enzymes within dispersion cast membranes and enable charge compensating mobile ions and protein to be quantified. For the enzyme laccase, a common biofuel cell O2reduction catalyst, features associated with ligands coordinating the T1 copper center are present between 400 cm-1- 500 cm-1 and provide a possible route to interrogate mechanistic chemistry at the active site of laccase biocathodes under fuel cell reaction conditions. Using a similar experimental approach, the junction connecting the anion exchange and cation exchange phases of a bipolar membrane was spatially profiled. The transition region separating the phases was broader than the limiting axial spatial resolution of the instrument, consistent with known roughness and inhomogeneity at the boundary on the order of a few micrometers. Strong Raman scattering from perchlorate enabled its use as a probe for mobile ions in the anion-exchange phase. Self-modeling curve resolution applied to spectral datasets within a depth profile enhanced spatial resolution and confirmed perchlorate ions track the spatial distribution of the AEM phase. 1Cai, R.; Abdellaouia, S.; Kitt, J.P.; Harris, J.M.; Minteer, S.D.; Korzeniewski, C. “Confocal Raman Microscopy for the Determination of Protein and Quaternary Ammonium Ion Loadings in Biocatalytic Membranes for Electrochemical Energy Conversion and Storage” Anal. Chem.(2017) 89, 13290-13298. DOI: 10.1021/acs.analchem.7b03380. 2Korzeniewski, C.; Kitt, J.P.; Bukola, S.; Creager, S.E.; Minteer, S.D.; Harris, J.M. ”Single layer graphene for estimation of axial spatial resolution in confocal Raman microscopy depth profiling” Anal. Chem. (DOI:DOI: 10.1021/acs.analchem.8b04390).