THIN SPUTTERED PLATINUM FILMS ON POROUS MEMBRANES AS WORKING ELECTRODES IN GAS SENSORS

In sensors with porous gas diffusion membranes, the major control of m ass transport often occurs at the three phase boundary between the gas , the electrolyte and the electrocatalyst [1]. This interphase is poor ly defined and difficult to control. An attempt has been made using sp utter deposition to make a more reproducible and controlled working el ectrode-gas environment. The electrodes have been tested in commercial sensors for ppm levels of CO, H2S, SO2 and Cl-2. All sensors showed t he unexpected result of two response maxima as a function of thickness of platinum deposited. The electrochemical area of the film also show ed a similar two maxima relationship. Cross-sectional SEM has been use d for the analysis of the pore size distribution and the sensor respon se time and electrode resistance have also been measured, also as a fu nction of electrode thickness. A simple model is proposed to explain t he observed relationship. From a practical viewpoint, there is evidenc e that sputter deposition does allow better control of electrode struc ture than more traditional methods of production. (C) 1998 Elsevier Sc ience Ltd. All rights reserved.