Operating characteristics and comparison of photopyroelectric and piezoelectric sensors for trace hydrogen gas detection. II. Piezoelectric quartz-crystal microbalance sensor

A 6-MHz piezoelectric quartz-crystal microbalance coated with palladium electrodes has been used under STP gas flow-through conditions to detect hydrogen adsorption at low concentrations (<5% in nitrogen) where anomalous behavior has been observed due to interferences from other ambient or impurity gases (mainly O2). A systematic study showed that a concentration of 0.4% hydrogen produced no frequency shift in the sensor due to counterbalancing effects from other gases. Thus sensor sensitivity limits were established at 0.5% hydrogen, which is ca.∼200 times lower than the photopyroelectric (P2E) sensor (part I). The hydrogen selectivity of the piezoelectric sensor was found to be inferior to that of the P2E device.