E6.4 - H2S detection utilizing percolation effects in copper oxide

Abstract

A new type of hydrogen sulfide (H2S) sensor based on a (chemical) phase transformation in copper oxide (CuO; p-type semiconductor) is presented. Layers of electrospun copper oxide fibers show dosimeter-type behavior if exposed to highly diluted H2S at operating temperature of 170 °C. The conductance of these layers remains nearly constant for a certain time period (latency time) after which the conductance increases over several orders of magnitude. The latency time shows a linear dependence on the reciprocal H2S concentration; consequently the layers are acting as dosimeter. The presented sensor shows a switching point at a dose of ca. 210 ppm*s. The effect is reversible; operating the fiber network at 350 °C in air leads to a recovery of the initial conductance; higher doses can therefore be detected by cyclic operation mode. As could be shown the observed behavior is due to the formation of copper sulfide clusters (CuS; degenerate p-type semiconductor) on the outer face of the CuO-fibers. As long as the CuS clusters are disjunct the conductance is not changed effectively. After reaching a critical CuS cluster concentration (percolation threshold) a percolation network is formed. The conductance increases as a function of time and follows a power law for several orders of magnitude, which is in accordance with theoretical model.