Effect of Ga-modified layer on flexible hydrogen sensor using ZnO nanorods decorated by Pd catalysts

Vertically well-aligned zinc oxide (ZnO) nanorods were grown on a low cost, flexible polyimide substrate using an aqueous solution method under various gallium (Ga)-modified ZnO seed layer conditions. This paper reports fabrication and characterization of flexible hydrogen sensors using a modified ZnO template followed by ZnO nanorods (NRs) incorporated with palladium (Pd) catalyst for hydrogen detection at room temperature. We further explored the effect of a modified seed layer on hydrogen gas sensing at various bending states. Experimental results indicate the diameter of ZnO NRs can be controlled on flexible substrates by using a modified seed layer with moderate crystallinity and improved optical properties. All fabricated sensors have high performance with good mechanical flexibility to a curvature angle of 90° at various seed layer conditions. 3%-Ga modified seed layer showed the highest response factor of ∼91% with good repeatability and stability, which were achieved for 1000 ppm hydrogen at room temperature; the sensor limit of detection (LOD) was 0.2 ppm. For a future hydrogen-based economy, this work can provide the possibility of a versatile route to fabricate flexible hydrogen sensors with controllable sensing area and optimized sensing properties using a simple method.