Spectroscopic Studies of Nanoparticulate Thin Films of a Cobalt-Based Oxygen Evolution Catalyst

Nanoparticle (NP) cobalt–phosphate (Co-P_i) water oxidation catalysts are prepared as thin films by anodic electrodeposition from solutions of Co²⁺ dissolved in proton-accepting electrolytes. Compositional and structural insight into the nature of the catalyst film is provided from advanced spectroscopy. Infrared spectra demonstrate that counteranions incorporate into the Co-P_i thin films and that the phosphate ion, among various anion electrolytes, exhibits the highest binding affinity to the cobalt centers. Atomic force microscopy images show a highly porous morphology of the thin film that is composed of Co-P_i NPs. Whereas conventional X-ray powder diffraction technique shows catalyst films to be amorphous, synchrotron-based X-ray grazing incidence diffraction reveals well-defined diffraction patterns that are indicative of long-range ordering within the film. Azimuthal scans imply that as-prepared films possess a highly preferred orientation and texture on the electrode surface.