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

A sequential chlorination and electrochemical reduction process is demonstrated to convert Na-doped iridium oxide nanoparticles into useful (IrCl6(aq)3-)-Cl-III 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 degree celsius for 18 h to form (IrCl6(aq)2-)-Cl-IV with pH of 0.3, so the latter could be readily reduced to (IrCl6(aq)3-)-Cl-III at a potentiostatic mode of 0.6 V (vs. SCE). The oxidation state and the nature of complexing ligands for the regenerated (IrCl63-)-Cl-III and IrIVCl62-, as well as commercially available (IrCl63-)-Cl-III are validated by X-ray Absorption Spectroscopy. UV-Vis profiles of regenerated (IrCl6(aq)2-)-Cl-IV are recorded and the absorbance at 487 nm signal is benchmarked against that of standard (IrCl6(aq)2-)-Cl-IV 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 (IrCl63-)-Cl-III 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/cm(2)-nm and impressive stability that are comparable to those of fresh Na-doped iridium oxide thin film derived from commercially available (IrCl63-)-Cl-III.