Investigation of gas-sensitivity of sensor structures to hydrogen in a wide range of temperature, concentration and humidity of gas medium

Response to H-2 of seven sensor structures of SnO2 with various catalytic additives, made by thick-film technology,was investigated in a dry gas medium at a concentration of 200 ppm H-2 in a temperature range of 100-600 degrees C. Concentration dependence of six sensors (pure SnO2 and doped with five catalytic additives: 3% Pd, 3% La2O3, 1% Pt + 3% Pd, 1% Sb-2 O-5 + 3% La2O3 and 3% Pd with a support layer from Al2O3) was investigated in a range of 1-19,700 ppm H-2 of different relative humidity (RH) in a range of 0-100% RH at two operating temperatures. The resistance and response of the sensors weakly depended on the humidity of the gas medium at RH >= 0 or 10%. Arithmetic mean values of response and resistance in the range of 0(10)-100% RH were approximated by linear functions of log(S-ma- 1) = B + n log C and log R-ma = A+ k log C, respectively. Based on the comparative analysis of experimental data (response to H-2, reproducibility of indications, influence of humidity on the resistance and response, response threshold and a resistance drift in pure air), the best for H-2 detection were the two sensor structures of pure SnO2 and SnO2 + 3% La2O3, working at temperatures 500 degrees C and 450 degrees C, respectively. Formulas for resistance and response of these sensors were presented, which allowed estimation of H-2 concentration in air based on the measured parameters. Reproducibility of indications in the range of 1-19,700 ppm H-2 was within 4-10%. The response threshold was 0.08 +/- 0.006 ppm H-2 in the mentioned range of humidity at the response equal to 1.1. The interpretation was given for the mechanism of interaction of H-2 with the catalytic surface of semiconductive sensors. The present sensors can be recommended as the primary transducer of H-2 concentration in air for the gas control devices. (c) 2008 Elsevier B.V. Ail rights reserved.