Modification of H2-sensitive breakdown voltages of SnO2 varistors with noble metals

Abstract

Effects of noble metals on the H2-sensitive nonlinear I–V characteristics of SnO2 varistors have been investigated. All the SnO2 varistors exhibited nonlinear I–V characteristics in air at 300–600°C. The breakdown voltage shifted to a lower electric field upon exposure to 1.0% H2 at elevated temperatures, thus exhibiting H2 sensitivity. It was found that SnO2 varistors loaded with a noble metal such as Au, Pt, and Pd exhibited a higher breakdown voltage than a pure SnO2 varistor in air. The increase in the breakdown voltage in air arose mainly from the electronic interaction based on the difference between the electron affinity of SnO2 and the work function of the metal loaded. Effects of noble metals on the H2 sensitivity were strongly dependent on the kind of noble metals. Addition of Au resulted in an increase in sensitivity owing to ‘chemical sensitization’, but Pt and Pd caused a decrease in sensitivity due to ‘configurational effect’ associated with their high catalytic activities. Among the varistors tested, SnO2 loaded with 0.1 wt% Au exhibited the largest H2-sensitive breakdown voltage shift at 300°C.