Development of low-cost metal oxide pH electrodes based on the polymeric precursor method

In this work, the polymeric precursor method was used to prepare low-cost solid-state sensors for pH determination based on iridium oxide as the main pH sensitive material. The iridium content was reduced with addition of TiO₂, forming the binary system IrO_x–TiO₂, whose electroanalytical properties were evaluated in comparison with a commercial glass pH electrode. The minimum iridium content which gave suitable results was 30 mol%, and the electrode presented Nernstian and fast response in the pH range from 1 to 13, with no hysteresis effect observed. Besides, the electrode showed high selectivity in the presence of alkali ions as Li⁺, Na⁺ or K⁺. The amount of iridium in the prepared electrodes was very small (<0.1 mg), supporting the efficiency of this method on the simple preparation of functional low-cost pH electrodes.