pH response behaviors and mechanisms of different tungsten/tungsten oxide electrodes for long-term monitoring

Tungsten/tungsten oxide electrodes were prepared by four kinds of methods and their pH response behaviors in lithium borate buffer solutions at 25 °C have been investigated by electrochemical measurements. It was found that tungsten/tungsten oxide electrode made by immersion in HNO3 solution was unsuited to the testing environment because it tended to exfoliate or dissolve during tests. All the other tungsten/tungsten oxide electrodes showed linear response to pH values and good stability during the long-term potential monitoring. The lower dissolution rate of tungsten/tungsten oxide electrode made by heat-treatment made it the best candidate for the long-term monitoring due to its compact oxide film formed on the surface. X-ray photoelectron spectroscopy and thermodynamic analysis have been done to evaluate pH response mechanisms of the corresponding electrodes.