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Metal oxide semiconductor hetero- and homojunctions are commonly constructed to improve the performance of hydrogen sensors at room temperature. In this study, a simple two-step hydrothermal method was employed to prepare TiO2 films with homojunctions of rutile and anatase phases (denoted as TiO2-R/A). Then, the microstructure of anatase-phase TiO2 was altered by controlling the amount of hydrochloric acid to realize a more favorable porous structure for charge transport and a larger surface area for contact with H2. The sensor used a Pt interdigital electrode. At an optimal HCl dosage (25 mL), anatase-phase TiO2 uniformly covered rutile-phase TiO2 nanorods, resulting in a greater response to H2 at 2500 ppm compared with that of a rutile TiO2 nanorod sensor by a factor of 1153. The response time was 21 s, mainly because the homojunction formed by the TiO2 rutile and anatase phases increased the synergistic effect of the charge transfer and potential barrier between the two phases, resulting in the formation of more superoxide (O2−) free radicals on the surface. Furthermore, the porous structure increased the surface area for H2 adsorption. The TiO2-R/A-based sensor exhibited high selectivity, long-term stability, and a fast response. This study provides new insights into the design of commercially competitive hydrogen sensors. [ABSTRACT FROM AUTHOR]

In recent years, production of H 2 through photocatalytic water splitting has attracted considerable attention in the chemistry and material fields. In this work, TiO 2 based heterojunction photocatalyst, which is consisted of rutile nanorods and anatase nanoparticles, is systematically studied by controlling the HCl concentration in hydrothermal process. With the help of loaded Pt, an interesting two-peak feature (“M” shape) is observed in the HCl-dependent H 2 production efficiency. The peak values are 54.3 mmol h −1 g −1 and 74.4 mmol h −1 g −1 , corresponding to 83.9% and 12% anatase phase, respectively. A detailed analysis based on the microstructure and photoluminescence (PL) spectra indicate that the “M” shape feature is directly linked to the HCl-controlled interface area. Moreover, an unexpected zero interface area is revealed at an intermediate HCl concentration. In terms of homogeneous and heterogeneous nucleations, an interface growth mechanism is proposed to clarify its HCl-sensitive character. This work provides a route to enhance the photocatalytic activity in TiO 2 based photocatalyst via increasing the interface area. [ABSTRACT FROM AUTHOR]

Early detecting of the released gas during charging and discharging of lithium ion battery (LIB) is critical for safety monitoring of the equipment and devices which use LIB as power source. H 2 is one of the typical component of the released gas. The main challenges for detecting H 2 in LIB is the room temperature working, small size of the sensor and hypoxic environment. To address these problems, a room temperature working MEMS hydrogen sensor was developed with Pt-modified Nb-doped TiO 2 nanosheet as sensing material. The sensor has the advantages of a compact size (0.05 cm3), low power consumption (0.1 mW at room temperature), easy integration, and excellent sensing performance. The response achieved 12.3, and the response and recovery time are 31 s/270 s at room temperature to 1000 ppm H 2 (40 °C). The working mechanism of the sensor in the hypoxic environment, which is quite different from the traditional oxygen adsorption mechanism, is proposed according to the characterization of the MEMS sensors. [Display omitted] • The sensor with volume (0.05 cm3) and power consumption (0.1 mW at room temperature) have greatly the potential applications. • MEMS H 2 sensor shows high sensitivity to hydrogen at room temperature (S = 12.3–1000 ppm H 2). • Clarifies the mechanism of sensing mechanism in hypoxic environment. • The sensor shows excellent selectivity and long-term stability for 100 days. [ABSTRACT FROM AUTHOR]

Metal oxide semiconductor heterojunctions and homojunctions are considered to have better performance than single phase material for room temperature hydrogen gas sensing. In this work, TiO 2 facet homojunction (TiO 2 -FH) thin films were prepared by a two-step hydrothermal method. The TiO 2 -FH thin films were decorated with Pt nanoparticles using a green photodeposition method and then evaluated for H 2 sensing. Non-noble metal Al was used as finger electrodes instead of noble metal Pt. Compared with the TiO 2 -FH sensor, the H 2 detection limits of the platinum loaded TiO 2 -FH@Pt sensors are remarkably decreased from 8000 ppm to 1 ppm at room temperature. The optimized sensor achieves an excellent sensing performance of S = 1.21 and fast response / recovery times of about 42 s / 30 s when exposed to 1 ppm H 2 concentration. The synergy between the Schottky barrier at the Pt/TiO 2 interface and the barrier between the (110) and (001) facets of TiO 2 is the key to the improvement of the sensing performance. Replacement of noble metal Pt with Al and C electrodes greatly help to clarify the mechanism of the junctions in the thin film sensors, especially the function of the Pt/TiO 2 junction and the (110)/(001) TiO 2 junction. The simple and green fabrication method and cheap Al interdigitated electrodes are advantageous for practical applications. • Noble metal electrodes of gas sensors were substituted by non-noble metal Al and C. • Trace Pt decorated TiO 2 homojunction was designed for hydrogen sensing. • The sensors maintain the wide detection range and high response. • The Schottky barrier at Pt/TiO 2 interface is the main factor for the sensing performance. • The function of the barrier between the (110) and (001) facets of TiO 2 is clarified. [ABSTRACT FROM AUTHOR]

Abstract A unique double core-shell structure of Si@PANI@TiO 2 nanocomposite is synthesized by a simple in-situ growth method. The two shells of polyaniline (PANI) and TiO 2 , hand in hand, play a key role to improve the electrochemical performance: First, the flexible properties of polyaniline (PANI) effectively accommodate the volume change of Si during the cycling. Second, the good mechanical feature of TiO 2 can maintain the structural integrity and attenuate the volume expansion of Si cores. Finally, both of polyaniline and the lithiated TiO 2 enhance the conductivity of Si, which promotes the electrons transport. Resulting in the Si@PANI@TiO 2 double core-shell nanocomposite exhibits remarkable synergy in large, reversible lithium storage, delivering a reversible capacity as high as 1027 mAh g−1 after 500 cycles and a superior rate capacity of 640 mAh g−1, at a current of 500 and 4000 mA g−1, respectively. This excellent cycling and high-rate capability can be ascribed to the unique and well-designed double core-shell structure with the synergistic effect between polyaniline (PANI) and TiO 2. Graphical abstract Image 1 Highlights • Double core-shell of Si@PANI@TiO 2 was prepared by a simple in-situ growth method. • PANI and TiO 2 shell played the important role for buffering the volume expansion of SiO 2. • TiO 2 shell maintain the integrity of the material structure. • PANI and the Lithiated TiO 2 improved the conductivity of Si. • Excellent cycling stability and superior rate capacity were demonstrated. [ABSTRACT FROM AUTHOR]

Constructing a heterojunction is an effective way to improve the gas sensing properties of metal oxide semiconductors. In this work, a hydrogen sensor containing hierarchical and porous NiO/TiO 2 heterojunction bilayer structure was designed. The top layer is formed by the NiO nanowalls grown along the [220] direction with exposed (111) facets, and the bottom layer is formed by the [002] oriented TiO 2 nanorod arrays. The exposed high energy crystal surfaces of NiO and TiO 2 , together with the adapted surface depletion region, induced by the formation of the heterojunction, enable the hydrogen sensor to have both a wide detection range and a much higher response to hydrogen than single layer materials. With the optimized size of the pores existing between the walls, the hydrogen sensor shows excellent prevention to interference from CO. Both the gas diffusion regulated by the porous structure and the surface interaction between H 2 /CO and O 2 - controlled by the heterojunction barrier contribute to the distinctive detection of H 2 and CO at room temperature (25 ℃ ± 2 ℃). • A (111)NiO/(002)TiO 2 hierarchical heterojunction was designed for hydrogen sensing. • The sensor has wide detection range and high response than single layer materials. • The hydrogen sensor shows excellent performance to prevent interference from CO. • The hierarchical diffusion and the interface adsorption reaction are the key factors. [ABSTRACT FROM AUTHOR]

Development of advanced hydrogen sensors with high sensitivity, fast response speed, and long term stability is essential for safe utilization of hydrogen energy. In this work, a gas sensor with TiO 2 hierarchical trunk/branch structure as the sensing material is prepared by hydrothermal and immersion method. The experimental results show that facet homojunctions are formed by the facet contacts at the trunk/branch interfaces. The optimized sensor works at room temperature with an excellent sensing performance of S = 31.6% when exposed to 1 ppm H 2 concentration and a fast response and recovery time of about 10 s. The sensor also shows long-term stability, high sensing gas selectivity and high humidity resistance. It is found that the facet homojunction in the hierarchical structure of TiO 2 results in a significantly increased density of the charged oxygen ions absorbed on the surface and an enhanced effective barrier height, which are responsible for the much promoted sensing performance. This work provides a new way for designing gas sensors with highly commercial competitiveness. • TiO 2 hierarchical trunk/branch structure are fabricated. • Facet homojunctions are formed at the trunk/branch interfaces. • The hydrogen sensing performance is comprehensively enhanced. [ABSTRACT FROM AUTHOR]