Operating characteristics and comparison of photopyroelectric and piezoelectric sensors for trace hydrogen gas detection. I. Development of a new photopyroelectric sensor

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Abstract
A new type of solid‐state sensor for the detection of minute concentrations of hydrogen gas has been developed. The sensor was made of thin, commercially available polyvinylidene fluoride (PVDF) pyroelectric film, sputter coated with Pd. An infrared laser beam served to produce alternating temperature gradients on the Pd‐PVDF and on reference Al‐Ni‐PVDF films, which, in turn, generated ac voltages due to the photopyroelectric (P2E) effect. Exposure to hydrogen gas was shown to produce an increased differential signal between the Pd and reference electrodes; this was tentatively attributed to the adsorption and dissociation of hydrogen molecules on the Pd surface, which caused a shift on the Pd‐PVDF pyroelectric coefficient, due to interactions at the Pd‐PVDF interface. The differential signal was found to be proportional to the square root of the hydrogen partial pressure at very low concentrations (200 Pa) the paper is limited only to a phenomenological description. The thickness of the palladium layer has been found to play an important role with respect to the signal response. Presently, hydrogen concentrations as small as 40 ppm, in a flowing H2+N2 mixture, have been detected. The influence of gas flow rate has also been studied. Other characteristics such as the response times, the reversibility, and the durability of the Pd‐PVDF‐P2E hydrogen detector will also be presented.

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