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Among different materials that have been used for hydrogen sensing, one-dimensional (1D) nanostructures have shown promising results due to their enhanced specific surface area, nanoporosity and improved surface characteristics (in particular, uniformity and stability) facilitate high number of active sites. This paper aims to comprehensively review 1D nanostructure-based hydrogen sensors from three different aspects including: (1) Synthesis techniques: briefly overview the four primary synthesis techniques and how the critical processing parameters affect the morphology and sensing behavior, (2) Materials: properly distinguish the sensing mechanisms and properties of inorganic materials such as metal oxide semiconductors (MOS) combined/doped with organic carbon-based materials and polymers, and how the heterostructures can improve the sensing performance, and (3) Enhancement schemes such as additive functionalisation, material composition and light-assisted approaches to further elevate sensing characteristics. Future challenges are yet to be investigated in this area, which is discussed in this review to enlighten the way for future explorations. • 1D nanostructures demonstrate an enhancement in H 2 sensing performance. • Inorganic/organic based H 2 sensors show enhanced sensing characteristics. • Palladium acts as an electron acceptor to further modulate the depletion layer. • Adding bimetallic nanoparticles improve H 2 sensing due to their synergistic effects. [ABSTRACT FROM AUTHOR]

Making reliable gas sensors that function at low temperatures is important for safely detecting hydrogen gas. This work proposes sensitising reduced graphene oxide (rGO) nanosheet encapsulated TiO 2 nano-spheres (TiO 2 -NS) with highly sensitive Pd receptors (rGPT-NS). It demonstrates for the first time, hydrogen gas sensing of rGPT-NS under 490 nm visible light conditions at low operating temperatures (25–35 °C) using a low voltage bias (0.1 V). The method suppresses of the electron-hole recombination and creating interfacial nano-Schottky junctions (i.e., heterojunctions) to enhance sensing performances. As a result, chemiresistive based highly responsive, selective, stable, environmentally friendly, and energy-efficient rGPT-NS are synthesised via sol-gel and hydrothermal methods. The fabricated sensing material exhibits high responses of 100.23%, 100.28% and 100.36% with rapid response/recovery (19 s/62 s, 12 s/57 s and 11 s/53 s) towards 500 ppm hydrogen at 25 °C, 30 °C and 35 °C, respectively under 0.1 V and 490 nm visible light. In this work, we have developed a semiconductor gas sensor by sensitising reduced graphene oxide (rGO) nanosheet encapsulated TiO 2 nano-spheres (NS) with highly sensitive Pd receptors (rGPT NS) via sol-gel and hydrothermal methods. The developed sensor shows promising hydrogen sensing properties at low temperatures (25–35 °C) under 490 nm blue light (visible light) conditions and low voltage bias (0.1 V). [Display omitted] • Novel rGO nanosheet encapsulated Pd quantum-sized dots deposited TiO 2 nano-spheres (rGPT) for hydrogen sensing are developed. • The sensor operates at low temperatures (25–35 °C) under visible light conditions and low input voltage bias (0.1 V). • The sensor exhibits high response with fast response/recovery, selectivity and excellent repeatability. • The sensor can detect different hydrogen concentrations from 50 ppm to 2250 ppm in less than 30 s. [ABSTRACT FROM AUTHOR]