High anti-interference ability induced by the SP/SiO_x/ImIL composite film on IrO_x pH electrodes

High concentrations of redox substances in the solution may cause severe electrode potential drift, resulting in the inaccuracy of in situ measurements. Sulfide anion, a highly reductive substance, is the killer of all metal oxide electrodes because of its small size and strong surface activity. We first proposed to use SPEEK (SP) with silica-stabilized imidazole-type ionic liquid (ImIL) to fabricate a composite film (SP/SiO_x/ImIL) to achieve a high anti-interference ability for metal electrodes. The composite film was especially designed to address the interference caused by sulfide anions and other small-sized anions (i.e., I^-, F^- and ascorbic acid). The reduced proton conductivity was restored by introducing ImIL into SPEEK matrix. Open circuit potential tests showed that the potential of the SP/SiO_x/ImIL modified IrO_x electrode fluctuated within 0.3 mV in 30 min continuous test at a concentration of 10^-3 M Na₂S, exhibiting good stability in moderately high sulfide solution. It also exhibited fast response and good reversibility. In addition, no potential drift was measured under other anions interferences. XPS survey verified that the Ir⁴⁺/Ir³⁺ ratio of the IrO_x electrode did not change before and after application in sulfide-containing solution, indicating that the SP/SiO_x/ImIL composite film has good anion isolation capacity.