Optimum design for the sensing electrode mixtures of PbSnF4-based oxygen sensors for fast response at ambient temperature

The amperometric oxygen sensors of the type, Ag\Ag6I4WO4\PbSnF4\ sensing el ectrode (a mixture of iron(II) phthalocyanine (FePc), PbSnF4 and a whisker material) have been fabricated and effects of the incorporated whiskers on response properties have been examined to design the optimum sensing electr ode mixture. The selected whiskers were several 9Al(2)O(3) . 2B(2)O(3) and TiO2 whiskers different in length and conductivity (with or without conduct ive SnO2 coating film). Fast response comparable to that of galvanic-cell-t ype sensors was realized with the sensing electrode mixture designed on the basis of the following two points: (1) the sensing electrode should be a t ernary mixture of whiskers, FePc and PbSnF4 with a volume ratio of 1:7:2; ( 2) the whiskers should have a length around 20 mu m, an aspect ratio of abo ut 20 and a good electronic conductivity. The mean response time, 25 s, was to date the shortest of those of known solid-state electrochemical sensors at room temperature. The incorporation also greatly improved other respons e properties such as transient behavior, drifts and hysteresis. The roles o f the incorporated conductive whiskers are to form the conductive whisker n etworks in the sensing electrode mixture and to make the reduction sites of oxygen molecules electrochemically uniform by localizing the sites along t he networks. (C) 1999 Elsevier Science B.V. All rights reserved.