Polypyrrole Percolation Network Gas Sensors: Improved Reproducibility through Conductance Monitoring during Polymer Growth

Abstract

Conducting-polymer-based electrical percolation networks are promising materials for use in high-sensitivity chemiresistive devices. An ongoing challenge is to create percolation networks that have consistent properties, so that devices based on these materials do not have to be individually calibrated. Here, an in situ conductance technique is used during the electrochemical growth of polypyrrole (PPy) percolation networks. The drain current ( i d ) across the interdigitated electrodes (IDEs) is a measure of the conductance of the PPy network during electrochemical polymerization. The i d curve is used to determine the percolation region. To improve the reproducibility of PPy percolation networks, an in situ conductance monitoring method based on the value of i d is used. A set of optimal ammonia gas percolation sensors was created using this method with an average sensitivity of Δ R / R 0 × 100% ppm –1 = 11.3 ± 1.2% ppm –1 and an average limit of detection of 15.0 ± 3.6 ppb.

Chemiresistive Polymer Percolation Network Gas Sensor Created with a Nanosphere Template

“…Therefore, the LOD first decreases and then increases since it is determined by a competitive relationship between sensitivity and baseline noise, which is in agreement with our previous work for PPy percolation networks without the nanosphere templates. [ 15a,21 ] Especially for the sensor S N‐P3 , its high level of noise results in a very high LOD around 1 ppm, which is consistent with the result in Figure 8d. Among these sensors based on nanostructured PPy networks, S N‐P1 is regarded as the optimal sensor with a sensitivity of 2.59 ± 0.20% ppm −1 and a LOD of 71 ± 6 ppb.…”

“…As far as we know, only a few sensors exhibit high sensitivities above 2% ppm −1 with detection ranges under 10 ppm ( Figure ). [ 13c,i,15a,21,30 ] This indicates that S N‐P1 prepared with the nanosphere template shows a desirable sensitivity of 2.59 ± 0.20% ppm −1 at low concentrations. Moreover, its LOD of 71 ± 6 ppb demonstrates the ability to detect ammonia under 100 ppb, which is competitive with other PPy‐based chemiresistors.…”

“…This is in agreement with our previous work. [ 15a,21 ] It should be noted that the resistance change during the first exposure to 4 ppm ammonia is greater than those for subsequent exposures. This feature suggests that the interaction of nanostructured PPy networks with ammonia is not fully reversible on the time scale of these experiments.…”

“…The linear plot in black shows the conductance ranging from the insulating region to the percolation region and then the thin‐film region and is consistent with previously reported trends. [ 15a,21 ] The same data plotted as a semi‐logarithmic plot in blue is used to determine the boundaries between insulating, percolation, and thin film regions. Initially, PPy nucleates and grows between PS nanospheres on the Pt IDE fingers.…”

“…Sensing Experiments: Sensing experiments were carried out in a custom-made sensing chamber at room temperature under atmospheric pressure. [21] Ammonia gas (10 ppm, nitrogen fill) and nitrogen gas (for further dilution of the ammonia) were purchased from BOC gases UK. The flow rate from each gas cylinder was controlled by a mass flow controller (Alicat) and the concentration of ammonia gas was determined by the relative flow rates of the two mass flow controllers.…”