Elevating the Photocatalytic Performance of BiOCl by Promoting Light Utilization: From Co doping to the Microreactor.

Owing to its unique layered structure, BiOCl demonstrates high photocatalytic activity. However, its wide bandgap hinders the absorption of visible light. Doping modification is an effective method to expand the light absorption edge of photocatalysts by creating a doping energy level within the bandgap. Herein, Co as a variable valence element was used to dope the BiOCl nanosheets through a simple hydrothermal approach. As a result, the absorption edge of Co-BiOCl extends to the visible light region, and the photocatalytic performance was enhanced by 3.02 times. To overcome the shortcoming of photons being consumed easily in the bulk reactor, a planar microreactor was introduced to reduce the attenuation of light and accelerate the mass transfer. By comparison to the bulk reactor, a maximum of 15.3-fold additional activity promotion emerged. This work combines doping modification and reactor improvement to realize highly efficient photocatalysis in practical application.

Tuning the number of redox groups in the cathode toward high rate and long lifespan zinc-ion batteries.

We synthesized a small molecule, DBPTO, and used it as a cathode material in aqueous zinc-ion batteries. DBPTO presented a high reversible capacity of 382 mA h g-1 at 0.05 A g-1 and a long lifespan of over 60 000 cycles. In the same π-conjugated skeleton, DBPTO (containing four CO and two CN groups) shows a narrower energy gap than TAPQ (containing CO and four CN groups), which leads to the superior rate and cycling performance of DBPTO. The mechanism of charge storage of DBPTO also revealed that H+ and Zn2+ coordinated with the CO and CN sites by ex situ structural characterization and DFT calculations. Our results provide new insights into the design of organic cathodes with a high rate capability and long lifespan. Further efforts will focus on a deeper understanding of the charge storage mechanism.

Solid-solution MAX phase TiVAlC assisted with impurity for enhancing hydrogen storage performance of magnesium hydride.

Although MXene catalysts etched from precursor MAX have greatly improved the hydrogen storage performance of magnesium hydride (MgH2), the use of dangerous and polluting etchers (such as hydrofluoric acid) and the direct removal of potentially catalytically active A-layer substances (such as Al) present certain limitations. Here, solid-solution MAX phase TiVAlC catalyst without etching treatment has been directly introduced into MgH2 system to improve the hydrogen storage performance. The optimal MgH2-10 wt% TiVAlC can release about 6.00 wt% hydrogen at 300 °C within 378 s and absorb about 4.82 wt% hydrogen at 175 °C within 900 s. After 50 isothermal hydrogen ab/desorption cycles, the excellent cyclic stability and capacity retention (6.4 wt%, 99.6%) can be found for MgH2-10 wt% TiVAlC. The superb catalytic activity of TiVAlC catalyst can be explained by abundant electron transfer at external interfaces with MgH2/Mg, which can be further enhanced by impurity phase Ti3AlC2 due to strong H affinity brought from abundant electron transfer at internal interfaces (Ti3AlC2/TiVAlC). The influence of impurity phase which is common in MAX phase on the overall activity of catalysts has been firstly studied here, providing a unique method for designing composite catalyst to improve hydrogen storage performance of MgH2.

Vacancy-Mediated Hydrogen Spillover Improving Hydrogen Storage Properties and Air Stability of Metal Hydrides.

Hydrogen storage in metal hydrides is a promising solution for sustainable and clean energy carriers. Although Mg-based metal hydrides are considered as potential hydrogen storage media, severe surface passivation has limited their industrial application. In this study, a simple, cheap, and efficient method is proposed to produce highly reactive and air-stable bulk Mg-Ni-based hydrides by rapid treatment with water for 3 min. The nickel-decorated Mg(OH)2 nanosheets formed in situ during hydrolysis can provide a pathway for hydrogen desorption via vacancy-mediated hydrogen spillover, as revealed by density functional theory calculations, thereby significantly decreasing the peak dehydrogenation temperature by 108.2 °C. Moreover, water-activated hydrides can be stored under ambient conditions without surface decay and activity loss, exhibiting excellent air stability, which can be attributed to the chemical stability of the surface layer. The results provide alternative insights into the design of highly active, air-stable metal hydrides with low cost and promote the industrial application of hydrogen energy.

Effect of Few-Layer Ti3C2Tx Supported Nano-Ni via Self-Assembly Reduction on Hydrogen Storage Performance of MgH2.

For the first time, few-layer Ti3C2Tx (FL-Ti3C2Tx) supporting highly dispersed nano-Ni particles with an interconnected and interlaced structure was elaborated through a self-assembly reduction process. FL-Ti3C2Tx not only acts as a supporting material but also self-assembles with Ni2+ ions through the electrostatic interaction, assisting in the reduction of nano-Ni. After ball milling with MgH2, Ni30/FL-Ti3C2Tx (few-layer Ti3C2Tx supported 30 wt % nano-Ni via self-assembly reduction) shows superior catalytic activity for MgH2. For example, MgH2-5 wt % Ni30/FL-Ti3C2Tx can release approximately 5.83 wt % hydrogen within 1800 s at 250 °C and absorb 5 wt % hydrogen within 1700 s at 100 °C. The combined effects of finely dispersed nano-Ni in situ-grown on FL-Ti3C2Tx, large specific area of FL-Ti3C2Tx, multiple-valence Ti (Ti4+, Ti3+, Ti2+, and Ti0) derived from FL-Ti3C2Tx, and the electronic interaction between Ni and FL-Ti3C2Tx can explain the superb hydrogen storage performance. Our results will attract more attention to the elaboration of the metal/FL-Ti3C2Tx composite via self-assembly reduction and provide a guideline to design high-efficiency composite catalysts with MXene in hydrogen storage fields.

Catalytic effect of sandwich-like Ti3C2/TiO2(A)-C on hydrogen storage performance of MgH2.

A sandwich-like Ti3C2/TiO2(A)-C prepared through a facile gas-solid method was doped into MgH2 by ball milling. Ti3C2/TiO2(A)-C shows a far superior catalytic effect on the hydrogen storage of MgH2 than individual Ti3C2 or TiO2(A)-C, assigning as a synergistic catalysis between Ti3C2 and TiO2(A)-C. For example, the peak dehydrogenation temperature of MgH2-5 wt% Ti3C2/TiO2(A)-C is reduced to 308 °C, much lower than that of MgH2-5 wt% Ti3C2 (340 °C) or MgH2-5 wt% TiO2(A)-C (356 °C). After dehydrogenation, the dehydrogenated MgH2-5 wt% Ti3C2/TiO2(A)-C can uptake approximately 4 wt% of hydrogen within 800 s at 125 °C, while for the dehydrogenated MgH2-5 wt% Ti3C2 and MgH2-5 wt% TiO2(A)-C, only 3 wt% and 2.65 wt% hydrogen content can be obtained, respectively. Besides this, MgH2-5 wt% Ti3C2/TiO2(A)-C exhibits the lowest apparent activation energies (42.32 kJ mol-1 H2 for the hydrogen absorption and 77.69 kJ mol-1 H2 for the hydrogen desorption), which can explain the excellent hydrogen ab/desorption kinetic properties. The synergetic effects between the special layered structure and multiple valence titanium compounds (Ti4+, Ti3+, Ti2+, Ti0) verified by the x-ray photoelectron spectroscopy results are responsible for the catalytic mechanism on the hydrogen storage of MgH2. This study also supplies innovative insights into designing high efficiency MXene derivative catalysts in hydrogen storage.