Thin sputtered platinum films on porous membranes as working electrodes in gas sensors

In sensors with porous gas diffusion membranes, the major control of mass transport often occurs at the three phase boundary between the gas, the electrolyte and the electrocatalyst [1]. This interphase is poorly defined and difficult to control. An attempt has been made using sputter deposition to make a more reproducible and controlled working electrode-gas environment. The electrodes have been tested in commercial sensors for ppm levels of CO, H2S, SO2 and Cl-2. All sensors showed the unexpected result of two response maxima as a function of thickness of platinum deposited. The electrochemical area of the film also showed a similar two maxima relationship. Cross-sectional SEM has been used for the analysis of the pore size distribution and the sensor response time and electrode resistance have also been measured, also as a function of electrode thickness. A simple model is proposed to explain the observed relationship. From a practical viewpoint, there is evidence that sputter deposition does allow better control of electrode structure than more traditional methods of production. (C) 1998 Elsevier Science Ltd. All rights reserved.