Surface renewable nano-iridium oxide polymeric composite pH electrodes

A simple but effective preparation method of a surface renewable nano-iridium oxide polymeric composite electrode showing highly improved pH response characteristics was developed. Nano-iridium oxide was incorporated in polymethylmethacrylate (PMMA) matrix as an electrical conductor and active sensing material for hydrogen ion. It was prepared by the hydrolysis of (NH4)2IrCl6 and were then simply dispersed in acetone containing PMMA. The suspension of the nano-iridium oxide and PMMA was precipitated rapidly into water and then pressure-molded to disk-type nano-iridium oxide composite electrode material. The electrode showed excellent linear response between pH 3 and 11 with a slope of −59.6 mV/pH (R = 0.9999) and fast response time of τ90 < 2 s. Steady response with an average slope of −58.9 ± 0.3 mV/pH and Eo′ intercept of 653.4 ± 2.9 mV vs. 3 M Ag/AgCl reference electrode was observed for a month without appreciable deactivation. Less porous and hydrophobic surface of the polymeric composite electrode minimized equilibration time resulting in the fast response. The electrode can be stored in deionized water or in air after uses. The lifetime of the electrode was extended greatly because the surface can be renewed reproducibly by simple polishing whenever contaminated or deactivated.