In situ spectroscopic studies of energy storage and electrocatalytic materials

Techniques have been developed and implemented for the capture and manipulation of electroactive particles of mum dimensions and their subsequent characterization by electrochemical and in situ Raman microscopy to gain insight into the factors that control the capacity and cycle-life of battery materials. The materials selected for these studies included lithiated transition metal oxides and graphitic carbons as Li+-intercalation cathodes and anodes, respectively, and Zn particles. Experiments were performed as a function of the state and rates of charge and discharge in electrolytes of relevance to technical applications, yielding quantitative correlations between the recorded spectra and the extent of charge of the materials. These findings open exciting new prospects for monitoring in real time and with spatial resolution the flow of charge within actual electrochemical energy storage devices. In other studies, the nitrosyl adduct of hemin adsorbed on roughened silver electrodes, a model electrocatalyst/support system with relevance to environmental remediation, was characterized by in situ surface enhanced Raman spectroscopy. Although no evidence was found for the presence of bands directly attributable to NO or Fe-NO, other strong spectral markers for NO binding to the Fe site in hemin could be clearly identified. Also examined in this study were aspects of the electrochemistry and vibrational properties of tetrahedral amorphous carbon incorporating nitrogen films (taC:N) prepared by techniques developed at Case. In particular, strong Raman signals were observed for taC:N films grown on roughened Ag surfaces. Insight into metal electrodeposition on taC:N was obtained from studies involving Pb 2+ in aqueous media, which displayed properties very similar to those found for electrodeposition of boron doped diamond electrodes.