High-precision printable self-powered NH3 sensor enabled by 0D/1D synergistic black-TiO2/MWCNT heterostructure: Mass-produced, health monitoring

Abstract

Wearable NH3 sensors play a critical role in both early warning of high-concentration NH3 exposure under extreme working conditions (>25 ppm) and in the early diagnosis of kidney diseases through exhaled breath analysis (>4.88 ppm). However, the integration of these sensors into textiles or electronic skin is often hindered by their reliance on rigid, external power sources. In this study, we developed a fully printed, high-precision, and low-cost self-powered flexible sensing patch (device area: 5 × 5 mm) by leveraging the multifunctional properties of black titanium dioxide (B-TiO2) nanoparticles and multi-walled carbon nanotubes (MWCNTs) via a direct ink dispensing printing technique. Guided by the concept of 0D/1D material synergy, the MWCNTs serve as a mechanically robust conductive scaffold, while the oxygen-deficient 0D B-TiO2 nanoparticles act as highly active sites for pseudocapacitive charge storage. The resulting asymmetric microsupercapacitors (MSCs) achieves a high areal capacitance of 16.3 mF/cm2. Furthermore, the B-TiO2 exhibits a narrowed bandgap (1.1 eV), and its interface between the disordered oxygen-deficient shell and the crystalline core (n-n+ junction), as well as the heterojunction with MWCNTs (n-p junction), significantly enhances charge transport and provides a highly responsive platform for room-temperature NH3 sensing (131.14 % response at 300 ppm, defined as ΔR/R0 ×100 %). The device demonstrates excellent performance stability and cyclic durability under realistic mechanical deformation such as skin and joint bending. This multifunctional heterostructure-based strategy offers scalability and cost-effectiveness for batch manufacturing of self-powered sensing systems, addressing key requirements for next-generation wearable healthcare technologies.