Modification of Metal Oxide Semiconductor Gas Sensors Using Conducting Polymer Materials

Conducting polymers have shown great potential in detecting gases at room temperature. This has caused the rapid development of these materials for gas sensing because their conductivity can be altered when exposed to oxidant or reductant molecules at room temperature. Nevertheless, due to their relatively high attraction to volatile organic and water molecules and low conductivity, they show low sensitivity, selectivity, and thermal instability that impede their practical applications as sensors. Moreover, semiconducting inorganic (metal oxide) sensors show distinct advantages in sensing gases, including high sensitivity, rapid response to low-concentration analytes, versatile exterior or surface chemistry, and high-surface area. However, their high-temperature operation has limited their sensing applications while performing excellently at room temperature. Combining these two sensitive materials brings synergistic effects. The hybrid increases sensitivity, selectivity, long-term stability, and low-temperature operation, which has concerned extensive interest in their use as sensors. This review summarizes the use of semiconducting metal oxides, conducting polymers, and the recent advancement in metal oxide-conducting polymer composites for their gas-sensing applications. Moreover, in this review, the advantages and limitations of these sensor materials are presented, and why the composites give an excellent synergistic effect by increasing sensing performance have been highlighted.