Development of Mo-Modified Pseudoboehmite Supported Ni Catalysts for Efficient Hydrogen Production from Formic Acid.

Formic acid (FA), as a safe and renewable liquid hydrogen storage material, has attracted extensive attention. In this paper, a series of Mo-modified pseudoboehmite supported Ni catalysts were developed and evaluated for efficient hydrogen production from formic acid. Pseudoboehmite (PB) as a catalyst carrier was used for the first time. Ni/PB and NiMo/PB possessed a mesostructure, and the pore size distribution was mainly concentrated between 2 and 20 nm. The oxygen vacancies caused by Mo enhanced Ni anchoring, thus inhibiting Ni sintering. Compared with Ni10/PB (7.62 nm), Ni10Mo1/PB had smaller Ni particles (5.08 nm). The Ni-O-Al solid solutions formed through the interaction of Ni with the PB improved the catalytic performance. Ni10Mo1/PB gave the highest conversion of 92.8% with a H2 selectivity of 98% at 300 °C, and the catalyst activity hardly decreased during the 50 h stability test. In short, Ni10Mo1/PB was a promising catalyst for hydrogen production from formic acid because of the oxygen vacancy anchoring effect as well as the formation of Ni-O-Al solid solutions which could effectively suppress the Ni sintering.

Enhanced photocatalytic hydrogen evolution and ammonia sensitivity of double-heterojunction g-C3N4/TiO2/CuO.

The performance of semiconductor photocatalysts has been limited by rapid electron-hole recombination. One strategy to overcome this problem is to construct a heterojunction structure to improve the survival rate of electrons. In this context, a novel g-C3N4/TiO2/CuO double-heterojunction photocatalyst was developed and characterized. Its photocatalytic activity for hydrogen production from water-methanol photocatalytic reforming was explored. Methanol is always used to eliminate semiconductor holes. The g-C3N4/TiO2/CuO double-heterojunction photocatalyst with a narrow bandgap of ∼1.38 eV presented excellent photocatalytic activity for hydrogen evolution (97.48 µmol (g h)-1) under visible light irradiation. Compared with g-C3N4/TiO2 and CuO/TiO2, the photocatalytic activity of g-C3N4/TiO2/CuO for hydrogen production was increased approximately 7.6 times and 1.8 times, respectively. Below 240 °C, the sensitivity of g-C3N4/TiO2/CuO to ammonia was approximately 90% and 46% higher than that of g-C3N4/TiO2 and CuO/TiO2, respectively. The enhancement of the photocatalytic activity and gas sensing properties of the g-C3N4/TiO2/CuO composite resulted from the close interface contact established by the double heterostructure. The trajectory of electrons in the double heterojunction conformed to the S-scheme. UV-vis, PL, and transient photocurrent characterization showed that the double heterostructure effectively inhibited the recombination of e-/h+ pairs and enhanced the migration of photogenerated electrons.

Catalytic Steam Reforming of Bio-Oil-Derived Acetic Acid over CeO2-ZnO Supported Ni Nanoparticle Catalysts.

The steam reforming of bio-oil-derived acetic acid over the developed Ni/CeO2-ZnO nanoparticle catalysts for hydrogen production was studied. The correlations of CeO2 to ZnO mass ratio (CZMR) and nickel loading with the properties and performances of Ni/CeO2-ZnO catalysts were explored. The H2, CO, and potential H2 yields followed a Gaussian normal distribution with increasing the CZMR. An exponential function equation was established to correlate the H2, CO, and potential H2 yields with Ni loading. As the CZMR increased from 0 to 1/3, the H2 yield increased from 57.8 to 69.4%, with a growth rate of 20.1%. Further, on increasing the CZMR from 1/3 to 3, the H2 yield decreased by 37.6%. The CO yield showed a similar trend for the H2 yield on increasing the CZMR, which first increased to a peak value, then started to decrease rapidly and finally stabilized. The yield of H2 increased significantly from 20.6 to 73.5%, with the increase of nickel loading from 0 to 15%. Further, on increasing the nickel loading from 15 to 25%, the H2 yield increased by only 5.8%. With the CZMR of 1/3 and the nickel loading of 15%, the selectivities of H2 and CO were as high as 91.6 and 42.3%, respectively.

Sustainable hydrogen-rich syngas from steam reforming of bio-based acetic acid over ZnO and CeO2-ZnO supported Ni-based catalysts.

Sustainable hydrogen-rich syngas from steam reforming (SR) of bio-based acetic acid over ZnO and CeO2-ZnO supported Ni-based catalysts was studied by means of a bench-scale fixed-bed unit combined with NDIR/TCD techniques. The effects of Ni/ZnO catalysts with different nickel loadings (5-15%), temperature (T = 500-900 °C), steam to carbon molar ratio (S/C = 1-5) and weight hourly space velocity (WHSV = 3-7 h-1) on SR of acetic acid were explored. In addition, the influence of CeO2 addition on the catalytic performance was assessed to investigate the improvement effect of Ce as a promoter on the catalytic activity. As the nickel loading increased from 5 to 15%, the H2 yield increased significantly from 31.0 to 51.0% with a growth rate of 64.5%, while the CO yield first decreased from 31.6 to 27.7% and then increased to 35.7%. Between 500 and 900 °C, the yields of H2 and CO first increased and then decreased, corresponding to the peak yields of 51.0% and 35.7% at 800 °C, respectively. S/C gave a similar trend of H2 yield to the T, while the CO yield continued to decrease with increasing S/C from 1 to 5. The H2 yield gradually decreased from 54.1 to 28.7% as the WHSV increased, while the peak value of CO yield was 35.7%, corresponding to WHSV = 5. The addition of 25 wt% CeO2 to the Ni/ZnO catalyst with a nickel loading of 15% improved the H2 yield from 51.0 to 74.0% when reforming acetic acid under the optimal operating conditions of T = 800 °C, S/C = 3 and WHSV = 5 h-1. The CO yield was reduced from 35.7 to 33.2%, and the corresponding H2/CO ratio increased from 2.9 to 4.5. The excellent catalyst stability was obtained in the SR of acetic acid using Ni/CeO2-ZnO catalyst. H2 yield was reduced from 76.0 to 73.5% with a decrease of 3.4%, while CO yield increased from 32.1 to 41.3% with a growth rate of 28.7% within 15-360 minutes.

Synthesis of ZnO Hierarchical Structures and Their Gas Sensing Properties.

Firecracker-like ZnO hierarchical structures (ZnO HS1) were synthesized by combining electrospinning with hydrothermal methods. Flower-like ZnO hierarchical structures (ZnO HS2) were prepared by a hydrothermal method using ultrasound-treated ZnO nanofibers (ZnO NFs) as raw material which has rarely been reported in previous papers. Scanning electron microscope (SEM) and transmission electron microscope's (TEM) images clearly indicated the existence of nanoparticles on the ZnO HS2 material. Both gas sensors exhibited high selectivity toward H2S gas over various other gases at 180 °C. The ZnO HS2 gas sensor exhibited higher H2S sensitivity response (50 ppm H2S, 42.298) at 180 °C than ZnO NFs (50 ppm H2S, 9.223) and ZnO HS1 (50 ppm H2S, 17.506) gas sensors. Besides, the ZnO HS2 sensor showed a shorter response time (14 s) compared with the ZnO NFs (25 s) and ZnO HS1 (19 s) gas sensors. The formation diagram of ZnO hierarchical structures and the gas sensing mechanism were evaluated. Apart from the synergistic effect of nanoparticles and nanoflowers, more point-point contacts between flower-like ZnO nanorods were advantageous for the excellent H2S sensing properties of ZnO HS2 material.

Boosting the Reversibility of Sodium Metal Anode via Heteroatom-Doped Hollow Carbon Fibers.

Sodium (Na) metal anodes stand out with their remarkable capacity and natural abundance. However, the dendritic Na growth, infinite dimensional changes, and low Coulombic efficiency (CE) present key bottlenecks plaguing practical applications. Here, heteroatom-doped (nitrogen, sulfur) hollow carbon fibers (D-HCF) are rationally synthesized as a nucleation-assisting host to enable a highly reversible Na metal. The "sodiophilic" functional groups introduced by the heteroatom-doping and large surface area (≈1052 m2 g-1 ) synchronously contribute to a homogenous plating morphology with dissipated local current density. High "sodiophilicity" of the D-HCF is confirmed by first-principle calculations and experimental results, where strong adsorption energy of -3.52 eV with low Na+ nucleation overpotential of 3.2 mV at 0.2 mA cm-2 is realized. As such, highly reversible plating/stripping is achieved at 1.0 mA cm-2 with average CE approximating 99.52% over 600 cycles. The as-assembled Na@D-HCF symmetric cells exhibit a prolonged lifetime for 1000 h. A full-cell paired with Na3 V2 (PO4 )3 cathode further demonstrates stable electrochemical behavior for 200 cycles at 1 C along with excellent rate performance (102 mAh g-1 at 5 C). The results clearly show the effectiveness of the D-HCF in manipulating Na+ deposition and thus the significance of nucleation control in realizing dendrite-free metal anodes.

Tactile-Sensing Based on Flexible PVDF Nanofibers via Electrospinning: A Review.

The flexible tactile sensor has attracted widespread attention because of its great flexibility, high sensitivity, and large workable range. It can be integrated into clothing, electronic skin, or mounted on to human skin. Various nanostructured materials and nanocomposites with high flexibility and electrical performance have been widely utilized as functional materials in flexible tactile sensors. Polymer nanomaterials, representing the most promising materials, especially polyvinylidene fluoride (PVDF), PVDF co-polymer and their nanocomposites with ultra-sensitivity, high deformability, outstanding chemical resistance, high thermal stability and low permittivity, can meet the flexibility requirements for dynamic tactile sensing in wearable electronics. Electrospinning has been recognized as an excellent straightforward and versatile technique for preparing nanofiber materials. This review will present a brief overview of the recent advances in PVDF nanofibers by electrospinning for flexible tactile sensor applications. PVDF, PVDF co-polymers and their nanocomposites have been successfully formed as ultrafine nanofibers, even as randomly oriented PVDF nanofibers by electrospinning. These nanofibers used as the functional layers in flexible tactile sensors have been reviewed briefly in this paper. The ß-phase content, which is the strongest polar moment contributing to piezoelectric properties among all the crystalline phases of PVDF, can be improved by adjusting the technical parameters in electrospun PVDF process. The piezoelectric properties and the sensibility for the pressure sensor are improved greatly when the PVDF fibers become more oriented. The tactile performance of PVDF composite nanofibers can be further promoted by doping with nanofillers and nanoclay. Electrospun P(VDF-TrFE) nanofiber mats used for the 3D pressure sensor achieved excellent sensitivity, even at 0.1 Pa. The most significant enhancement is that the aligned electrospun core-shell P(VDF-TrFE) nanofibers exhibited almost 40 times higher sensitivity than that of pressure sensor based on thin-film PVDF.

Aligned hierarchical Ag/ZnO nano-heterostructure arrays via electrohydrodynamic nanowire template for enhanced gas-sensing properties.

Gas sensing performance can be improved significantly by the increase in both the effective gas exposure area and the surface reactivitiy of ZnO nanorods. Here, we propose aligned hierarchical Ag/ZnO nano-heterostructure arrays (h-Ag/ZnO-NAs) via electrohydrodynamic nanowire template, together with a subsequent hydrothermal synthesis and photoreduction reaction. The h-Ag/ZnO-NAs scatter at top for higher specific surface areas with the air, simultaneously contact at root for the electrical conduction. Besides, the ZnO nanorods are uniformly coated with dispersed Ag nanoparticles, resulting in a tremendous enhancement of the surface reactivity. Compared with pure ZnO, such h-Ag/ZnO-NAs exhibit lower electrical resistance and faster responses. Moreover, they demonstrate enhanced NO2 gas sensing properties. Self-assembly via electrohydrodynamic nanowire template paves a new way for the preparation of high performance gas sensors.

A patterned ZnO nanorod array/gas sensor fabricated by mechanoelectrospinning-assisted selective growth.

Micropatterned ZnO nanorod arrays were fabricated by the mechanoelectrospinning-assisted direct-writing process and the hydrothermal growth process, and utilized as gas sensors that exhibited excellent Ohmic behavior and sensitivity response to oxidizing gas NO2 at low concentrations (1-100 ppm).