Reuse of sodium–doped iridium oxide nanoparticles as a bio–stimulating electrode by a chemical and electrochemical recovery process

Abstract

A sequential chlorination and electrochemical reduction process is demonstrated to convert Na–doped iridium oxide nanoparticles into useful IrIIICl63−(aq) serving as the precursor for the fabrication of bio–stimulating electrode. The Na–doped iridium oxide nanoparticles are treated in 35 wt% hydrochloric acid at 70 °C for 18 h to form IrIVCl62−(aq) with pH of 0.3, so the latter could be readily reduced to IrIIICl63−(aq) at a potentiostatic mode of 0.6 V (vs. SCE). The oxidation state and the nature of complexing ligands for the regenerated IrIIICl63− and IrIVCl62−, as well as commercially available IrIIICl63− are validated by X–ray Absorption Spectroscopy. UV–Vis profiles of regenerated IrIVCl62−(aq) are recorded and the absorbance at 487 nm signal is benchmarked against that of standard IrIVCl62−(aq) to obtain the effective regeneration ratio of 68.6%. X–ray diffraction patterns of Na–doped iridium oxide nanoparticles before and after the annealing treatment indicate the amorphous structure facilitates the chlorination step. The regenerated IrIIICl63− is reused to synthesize Na–doped iridium oxide thin film serving as a bio–stimulating electrode for implantable bio–electronics. The regenerated Na–doped iridium oxide thin film reveals a charge-storage capacity of 0.32 mC/cm2-nm and impressive stability that are comparable to those of fresh Na–doped iridium oxide thin film derived from commercially available IrIIICl63−.