Operando spectroscopy of electrochemical energy conversion devices

A fuel cell for operando FTIR and x-ray absorption spectroscopy (XAS) was designed and constructed. The cell is based on the combination of operando cells previously developed in the Smotkin group. Special consideration was put into the design to enable both transmission XAS, fluorescence XAS, and diffuse reflectance FTIR spectroscopy. Operando x-ray fluorescence spectroscopy of the Pt cathode was accomplished at Argonne national labs.;The x-ray absorption near edge structure (XANES) region of the fluorescence XAS spectra was analyzed by subtractive normalization (Delta-XANES). Using this technique, the trends in the data became apparent: there were both time- and potential-dependence in the reduction of surface and sub-surface Pt-oxides. The time constant for the reduction of these oxides was greater than two hours at 530 mV, much longer than previously expected.;Theoretical Delta-XANES (Delta-XANES signatures) of oxygen adsorbates on Pt clusters were modeled using FEFF8 software. Two new models were developed to generate the Delta-XANES signatures: the isolated all-atoms Janin cluster, and the embedded all-atoms Janin cluster. The progressive development of these models provides insight concerning the relative charge depletion of surface and subsurface atoms, and the compensation of charge transfer by platinum-reservoir electron density.;Future directions of the operando spectroscopy cell include using electrochemical promotion of organic chemistry (EPOCH) to assist epoxide ring-opening reactions for pharmaceutical building blocks, and the study of fuel cell poisoning by common atmospheric pollutants.