# A 3D Porous MXene/PNIPAAm Hydrogel Composite with Advanced Degradation Stability and Control of Electronic Properties in Air

## TL;DR

This paper introduces a new MXene and hydrogel composite with improved stability and tunable electronic properties for gas sensing.

## Contribution

The composite shows enhanced degradation resistance and controllable electronic states through a porous 3D structure.

## Key findings

- The composite exhibits a 3D spatial arrangement of MXene, avoiding stacked-sheet structures.
- The composite shows significantly improved stability against oxidation over three months.
- The material demonstrates tunable electronic states and potential for VOC sensing.

## Abstract

This study reports the fundamental investigation of a composite material consisting of MXene (Ti3C2Tx) and a stimulus‐responsive hydrogel (Poly(N‐isopropylacrylamide)–PNIPAAm). Thereby, the fabrication and comparison of pure MXene and composite samples featuring either a compact or a highly porous 3D microstructure, reveal unique properties with respect to: i) controllable 3D spatial arrangement of MXene instead of the prevalent stacked‐sheet structure, ii) reduction of oxidation‐induced degradation of MXene and substantially enhanced stability over the course of three months for the composite, and iii) tunable electronic states in response to gas interactions. Material characterization is conducted by scanning electron microscopy and rheology to assess the microstructural and mechanical properties, and in a chemiresistive measurement setup for the determination of electrical properties and the evaluation of the composite's potential for VOC sensing in a gaseous environment with the test analyte acetone. These investigations reveal material effects and properties that address some of the key MXene‐related challenges. Additionally, the interplay between the MXene and the hydrogel enables unprecedented opportunities for enhancing the sensing potential of stimulus‐responsive hydrogels, specifically in gaseous environments.

This paper reports a fundamental study of the mutual benefits of the components in an MXene/PNIPAAm hydrogel composite with regard to enhanced degradation stability and tailorable electronic properties. The presented work focuses on the investigation of the fundamental material properties and ways for their modification. Furthermore, a chemiresistive sensing mechanism is explored for a future application of volatile organic compound detection.