Aluminum Doped Zinc Oxide and Silver Nanowire Composite Based Printed CO$_{2}$ Gas Sensor

Carbon dioxide (CO<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula>) is a significant greenhouse gas and an essential indicator of effective air circulation in enclosed spaces, requiring precise and continuous monitoring. Traditional chemiresistive CO<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> sensors have high operating temperatures that require external heating elements limiting their applicability in low-power portable electronics. This work demonstrates a miniaturized printed CO<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> gas sensor, based on aluminium-doped zinc oxide (AZO) and silver nanowire (Ag NW) nanocomposite ink, which operates efficiently at room temperature. The AZO-Ag NW nanocomposite ink is optimized for direct ink writing (DIW) to obtain a uniform printed pattern. The composite ink helps overcome the inherent high resistance of AZO nanostructures by taking advantage of Ag NW's high conductivity and surface reactivity. The sensor shows a quick response time of 19 s and a recovery time of 36 s for 400 ppm CO<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula>. The sensor exhibits a response (R) of 32.5% with a limit of detection (LOD) of 24.04 ppm, while operating at a low bias of 1 V. The integration of DIW, cost-effective ink formulation, and scalable fabrication is a significant advancement for real-time CO<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> monitoring at low power.