Tracking surface evolution using ligand-assisted dissolution of cobalt oxyhydroxide.

The use of surface-specific reactions to probe reactive surface area is a promising direction in materials research. The work presented herein examines how the kinetics of dissolution can be used to quantify particle growth as well as the evolution of site-specific reactive surface area. The dissolution of heterogenite (ß-CoOOH) by IDA results in two geometric isomers of Co(IDA)(2)(-): the s-fac and u-fac isomers. The heterogenite particles studied here can generally be described as cylindrical plates, and the relative amount of s-fac isomer produced is found to increase as the height of the plates increases. The quantity of each isomer produced is shown to correlate with the relative number of two different types of surface sites, designated as edge and corner sites, while basal sites are seemingly unreactive. It is hypothesized that u-fac isomer results from the more accessible Co centers at the corner sites, while the s-fac isomer results from the less accessible edge sites. An empirical relationship is developed between the fraction of s-fac isomer produced and the height of the ß-CoOOH particles, and this relationship is used to quantify particle growth by analysis of kinetic data. Finally, this new information is used to modify a previously proposed pH-dependent growth model, resulting in a significant improvement in the fit and physical relevance of the model.