H₂S Dosimetry by CuO: Towards Stable Sensors by Unravelling the Underlying Solid‐State Chemistry

Abstract

The precise detection of the toxic gas H2S requires reliable sensitivity and specificity of sensors even at minute concentrations of as low as 10 ppm, the value corresponding to typical exposure limits. CuO can be used for H2S dosimetry, based on the formation of conductive CuS and the concomitant significant increase in conductance. In theory, at elevated temperature the reaction is reversed and CuO is formed, ideally enabling repeated and long‐term use of one sensor. Yet, the performance of CuO tends to drop upon cycling. Utilizing defined CuO nanorods we thoroughly elucidated the associated detrimental chemical changes directly on the sensors, by Raman and electron microscopy analysis of each step during sensing (CuO→CuS) and regeneration (CuS→CuO) cycles. We find the decrease in the sensing performance is mainly caused by the irreversible formation of CuSO4 during regeneration. The findings allowed us to develop strategies to reduce CuSO4 formation and thus to substantially maintain the sensing stability even for repeated cycles. We achieved CuO‐based dosimeters possessing a response time of a few minutes only, even for 10 ppm H2S, and prolonged life‐time.

A Strategy to Enhance Humidity Robustness of p‐Type CuO Sensors for Breath Acetone Quantification

“…This sensor detects also CH 4 and H 2 S (Figure S7, Supporting Information, normalized response of 0.1 and 0.14 at 1 ppm, respectively) but features much smaller signals compared to acetone (i.e., 90% and 86%, respectively). Note that despite the good selectivity, CuO sensors are known to deteriorate upon prolonged exposure to H 2 S (i.e., forming CuS [40] ), so this sensor may not be suitable for use in halitosis, where H 2 S can reach up to 0.5 ppm. [41] To challenge the sensor even more, and as human breath is a complex mixture of various analytes, its performance was evaluated in gas mixtures.…”