Speaker
Description
Understanding ion storage and transport in nanoporous electrodes for water desalination requires sophisticated experimental methods that can resolve how and in which pore regime ion concentration changes occur during operation. This information can be provided by operando X-ray techniques. Here, we present a correlative synchrotron approach under realistic operating conditions. We obtain element specificity with pore-hierarchy sensitivity within an electrochemical cell during charging and discharging by combining position- and time-resolved X-ray fluorescence (XRF), X-ray transmission (XRT), and Small-Angle X-Ray Scattering (SAXS).
We report an operando SAXS, XRF, and XRT study of electrochemical cells with 50 mM RbBr and SrBr₂ aqueous electrolytes. Carbon electrodes with hexagonally organized mesopores and disordered micro- and macropores serve as a hierarchically porous model system. Separating distinctive diffraction peaks from the ordered mesopores and the diffuse scattering from macro- and mesopores allows quantifying variations in electron density across several pore regimes of the hierarchical electrodes with SAXS. While XRF maps Rb, Sr, and Br to offer ion-specific concentration information, XRT reports the average concentration change within the electrodes.
Together, these methods offer cross-validation and reduce uncertainty in the interpretation of each individual signal, creating a cohesive picture of the relationship between changes in total concentration, ion species, and pore-scale specific response. In this way, the correlative synchrotron radiation approach allows to uniquely determine local charge balancing mechanisms, and helps understanding dynamic effects related to ion transport and accessibility in hierarchical electrode materials.