pH Sensors Using 3d-Block Metal Oxide-Coated Stainless Steel Electrodes

- The coated SUS electrodes were prepared using the sol-gel dip-coating method.
- Most of the coated SUS electrodes showed high pH sensitivity.
- The pH sensitivity was affected by the outer films and the underlying materials.
- All of the SUS electrodes showed very short initial pH response time.
- Co3O4/SUS and CuO/SUS electrodes are candidates for novel pH sensors.

The 3d-block metal oxide-coated SUS304 electrodes (MOx/SUS, M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) were prepared using the sol-gel dip-coating method in order to develop novel pH sensors. MOx/SUS electrodes showed a pH sensitivity of 88-100%, a pH repeatability of 0.1-0.6 in pH units and an initial pH response time of approximately 1 sec. The pH sensitivities of the SUS (as-received) and SUS-500 (heated at 500 °C) were 91% and 94%, respectively. Therefore, it appeared that the pH sensitivity of the MOx/SUS electrode was affected by the underlying materials (SUS substrate and its oxide layer) as well as by the outer MOx films. All of the MOx/SUS electrodes showed much shorter initial pH response time than a commercial glass electrode (14 sec). In particular, Co3O4/SUS and CuO/SUS electrodes were considered candidates for disposable pH electrodes, pH microelectrodes and tube and needle-type pH electrodes for novel pH sensors as a result of their favorable pH sensitivity, pH repeatability and initial pH response time.