Influence of thickness of sub-micron Cu2O-doped RuO2 electrode on sensing performance of planar electrochemical pH sensors

Influence of thickness of sensing electrodes (SEs) based on screen-printed sub-micron Cu2O-doped RuO2 films on characteristics of the planar pH sensors has been investigated. It was determined that as thickness of Cu2O-doped RuO2-SE increased from similar to 2.0 mu m to similar to 5.0 mu m, variations in the sensor's pH sensitivity were negligible. However, the sensor's response time improved from similar to 80-120 s for SE with thickness of 2.0 mu m to similar to 25 s for SE with thickness of 5.0 mu m. The enhancement of dynamic characteristics is potentially related to the establishment of the improved-structured "thick" SE, as more advanced crystallisation is achieved as thickness increased. Moreover, morphology of the "thick" SE revealed both the presence of "inner" active surfaces within SE and the developed open porosity of SE.