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.