H-2 selective gas sensor based on SnO2

A highly selective H-2 gas sensor was developed based on a 'hot wire type' gas sensor commercially available. Tin oxide semiconductor was sintered in a bead (0.5 mm in diameter) covering over a platinum wire (0.02 mm in diame ter) coil. The gas sensor was operated by a bridge electric circuit. A dens e layer of approximate to 0.1 mm in depth near the surface of the porous be ad, was formed by chemical vapor deposition of hexamethyldisiloxane (HMDS). The dense layer functioned as a 'molecular sieve', thereby the diffusion o f gases with large molecular diameters, except for H-2, was effectively con trolled, resulting in a prominent selectivity for H-2. On the other hand, d iffusion control of O-2 caused a strong H-2 reduction of the tin oxide in t he inner layer covered with the dense layer, resulting in decay in sensor o utput and irreversible reduction of the hydrogen sensitivity (deactivation of tin oxide). As a countermeasure against the damage, addition effect of c erium oxide from 0.5 to 5.0 at% was investigated. The H-2 selective gas sen sor thus obtained, had a significantly minor humidity dependence and a prom inent long term stability. (C) 1998 Elsevier Science S.A. All rights reserv ed.