A MECHANISM FOR SENSING REDUCING GASES WITH VANADIUM PENTOXIDE FILMS

Vanadium pentoxide is generally a non-stoichiometric material, which i s known for its catalytic properties in oxidation reactions. As it is an electric conductor when oxygen vacancies are present, the purpose o f this investigation is to determine the influence that reducing gases have on the conductance of vanadium pentoxide films. These films are prepared from crushed powder and by evaporation. It is found that a re ducing gas such as hydrogen increases the conductance of the film in a ir, if a platinum catalyst is added. For the recovery process, the pre sence of oxygen is necessary, as demonstrated by the responses to hydr ogen and oxygen in a nitrogen flow. Additionally, vanadium pentoxide p owder loses weight when exposed to 5000 ppm hydrogen in air, and regai ns it when exposed to air alone. To explain the observed response, a m odel is proposed that involves a surface reaction of atmospheric reduc ing gas and atmospheric oxygen, and diffusion of lattice oxygen in res ponse to changes at the surface.