Gas Sensing and Electrochemical Properties of CNT/WS₂ Core–shell Nanostructures

Abstract

Tungsten disulfide (WS 2 ) layers with different thicknesses were deposited on carbon nanotubes (CNTs) by atomic layer deposition (ALD) to obtain CNT/WS 2 core−shell heteronanostructures. WS 2 conformally grows like small platelet-flakes on the CNTs initially at low ALD cycles, while, with increasing the number of ALD cycles, WS 2 platelets further grow to form a continuous film. The electrical and electrochemical properties of the synthesized CNT/WS 2 hierarchical heterostructures were evaluated for sensing and electrocatalysis applications. First, a CNT/WS 2 conductometric sensor was developed for gas-sensing monitoring of nitrogen dioxide (NO 2 ). CNT/WS 2 heteronanostructures were also tested as effective electrochemical probes for detecting riboflavin (vitamin B6) and as electrocatalysts for CO 2 reduction. The results of gas sensing and electrochemical tests were discussed and correlated to the morphology and surface coverage of WS 2 shell on CNT core. CNT/WS 2 with 200−300 ALD cycles demonstrated the best performances because of the optimal catalytic WS 2 properties and the formation of CNT/WS 2 junctions, allowing the sensitive and selective detection of NO 2 gas and riboflavin with a limit of detection (LOD) of 70 ppb and 0.4 μM, respectively, and formate production in the electrocatalytic reduction of CO 2 .