A MECHANISM FOR SENSING REDUCING GASES WITH VANADIUM PENTOXIDE FILMS

Vanadium pentoxide is generally a non-stoichiometric material, which is known for its catalytic properties in oxidation reactions. As it is an electric conductor when oxygen vacancies are present, the purpose of 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 reducing gas such as hydrogen increases the conductance of the film in air, if a platinum catalyst is added. For the recovery process, the presence of oxygen is necessary, as demonstrated by the responses to hydrogen and oxygen in a nitrogen flow. Additionally, vanadium pentoxide powder loses weight when exposed to 5000 ppm hydrogen in air, and regains it when exposed to air alone. To explain the observed response, a model is proposed that involves a surface reaction of atmospheric reducing gas and atmospheric oxygen, and diffusion of lattice oxygen in response to changes at the surface.