Time-resolved XAS studies reveal sequential oxidative–reductive formation of Na-doped iridium oxide films with enhanced bio-stimulating performance†
Abstract
We synthesize a Na-doped iridium oxide thin film via a sequential oxidative–reductive reaction in which the Ir3+ precursor undergoes a ligand exchange and oxidation process by sodium hypochlorite and oxygen to form Ir>4+, followed by an immediate reduction step to produce Na-doped iridium oxide. Detailed reaction steps occurring in the wet chemical bath are validated by time-resolved X-ray absorption spectroscopy. Analysis using X-ray photoelectron spectroscopy indicates the composition to be Na0.44IrO1.55(OH)1.55(H2O)0.73. In addition, the Na-doped iridium oxide reveals an amorphous structure with a smooth surface morphology. In electrochemical characterization, the Na-doped iridium oxide exhibits a significantly larger normalized charge storage capacity of 0.32 mC cm−2 nm−1 over that of sputtered iridium oxide (0.08 mC cm−2 nm−1). In a cell viability test, the Na-doped iridium oxide shows a negligible bio-toxicity. In short, the Na-doped iridium oxide demonstrates promising potential as a bio-stimulating electrode for implantable bio-electronics.
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