Formation of iridium(IV) oxide (IrOX) films by electroflocculation.

Films of iridium(IV) oxide nanoparticles (IrOX NPs) become deposited on electrodes from nanoparticle solutions when potentials sufficient to initiate water oxidation are applied. Evidence is given that the film-forming mechanism is nanoparticle precipitation. Following an induction period during which a significant amount of charge is passed, the NPs begin to deposit as islands. It appears that the proton release that accompanies nanoparticle oxidation triggers the nanoparticle electroflocculation and subsequent precipitation. Flocculation from nanoparticle solutions can also be induced by the addition of a chemical oxidant (Ce(IV)). The film formation is followed by cyclic voltammetry (CV), rotated ring disk voltammetry (RRDE), and electrochemical quartz crystal microbalance (eQCM) measurements, supplemented with AFM and SEM microscopies.