Fine-tuning of ceramic-based chemical sensors via novel microstructural modification: I: Low level CO sensing by tungsten oxide, WO 3

Abstract

High selectivity, enhanced sensitivity, short response time and long shelf-life are some of the key features sought in the solid-state ceramic-based chemical sensors. Since the sensing mechanism and catalytic activity are predominantly surface-dominated, benign surface features in terms of small grain size, large surface area, and open and connected porosity, are required to realize a successful material. In order to incorporate these morphological features, a technique based on rigorous thermodynamic consideration of the metal/metal oxide coexistence, is described. By modulating the oxygen partial pressure across the equilibrium metal/metal oxide (M/MO) proximity line, formation and growth of new oxide surface on an atomic/submolecular level under conditions of ‘oxygen deprivation’, with exotic morphological features has been achieved in potential sensor materials. This paper describes the methodology and discusses the results obtained in the case of tungsten oxide-based carbon monoxide sensors (in the range of 14–100 ppm CO) with enhanced sensing characteristics.