Transport and chemistry at electroactive interfaces studied using line-imaging Raman spectroscopy

Line-imaging Raman spectroscopy provides a contiguous series of Raman spectra along a line in space. The resulting image provides a one-dimensional spatial profile containing information about the bonding and chemical environment being sampled. The instrument configuration described here has a spatial resolution of about 5 μm and a spectral resolution of approximately 10 cm−1. Two examples highlight the use of in situ line-imaging Raman spectroscopy in electrochemical engineering. In the first example, the cation transport and redox characteristics of a thin (≈36 nm) nickel hexacyanoferrate film are probed. The oxidation state of iron centers within the nickel hexacyanoferrate thin film is shown to be readily modulated between ferric and ferrous states in the freshly prepared film. However, repeated cycling results in an irreversible loss of capacity as the iron centers no longer are able to efficiently switch into the ferric state. In the second example, we demonstrate the simultaneous imaging of a thin film of semiconducting copper (I) thiocyanate and the electrolyte chemistry from which the film was deposited. We show that copper thiocyanate electrodeposits have the β crystal form and the deposition involves a CuSCN+ precursor that forms via homogeneous solution phase chemistry upon addition of copper sulfate to a potassium thiocyanate containing electrolyte.