查看更多>>摘要：? 2022 Elsevier B.V.Transition metal-based nitrogen-doped carbon materials have been proved to be a promising low-cost electrocatalyst for oxygen reduction reaction (ORR), which is a critical step in systems such as fuel batteries and zinc-air batteries. In this paper, transition metal (cobalt) N-doped carbon nanomaterials derived from metal-organic framework (MOFs) were synthesized by calcination of ZIF-67 precursors at high temperature (Co@NCNTs). Nitrogen atoms were introduced into the carbon matrix by capturing volatile CNx from dicyandiamide, and porous carbon nanotube structures with N-doped and uniformly dispersed active sites were obtained. The effects of different carbonization temperatures and molar ratio of Co/2-MI on the catalytic activity of materials for ORR reaction were studied. It was found that the Co@NCNTs prepared at 700 ℃ with the ratio of cobalt metal to dimethylimidazole of 1: 8 shows excellent ORR activity in both acidic and alkaline electrolytes. In alkaline conditions, the half-wave potential E1/2 = 0.81 V, initial potential Eonset = 0.89 V, and limiting current density even reaching 7.4 mA cm?2. And in acidic electrolytes, E1/2 = 0.66 V, while the limiting current density is 6.4 mA cm?2, which is still better than that of Pt/C. Its excellent ORR performance is due to the synergistic effect of the porous carbon nanotube structure, N-doped carbon and Co-Nx active sites. Meanwhile, the optimum catalyst also shows better stability and methanol resistance than Pt/C in both acidic and alkaline electrolytes.
查看更多>>摘要：? 2022 Elsevier B.V.The electrocatalytic hydrogen evolution reaction (HER) is an alternative eco-friendly strategy to obtain sustainable hydrogen energy. However, the HER in alkaline medium exhibits sluggish kinetics because of the difficulty of hydrogen adsorption and hydrolysis. Herein, a hierarchical nanoporous Ni/NiO catalyst with self-supported structures is prepared through dealloying followed by partial electro-oxidation. The catalytic activity for HER in alkaline medium is significantly enhanced by very short time electro-oxidation. The Ni/NiO-3 s sample (subjectied to 3 s of electro-oxidation) exhibits the outstanding catalytic performance with an overpotential of 25 mV at the current density of 10 mA cm?2. The synergic effect of NiO and Ni improves the kinetics of Volmer and Heyrosky steps. The nanoporous structure provides more active sites and facilities for the transfer of substances and charges. The self-supporting structure ensures long-term stability. This work offers an effective strategy to design metal/metal oxide catalysts for efficient hydrogen evolution reactions.
查看更多>>摘要：? 2022 Elsevier B.V.Today's society pays increasing attention to the issues of sustainable energy development and environmental protection. Photocatalytic technology based on semiconductor materials is of great importance to meet these challenges. Metal halide perovskite (MHP) materials have been developed rapidly in the field of photovoltaics and light-emitting diodes. In recent years, such materials have also attracted increasing attention in the field of photocatalysis. In this review, we introduce in detail the recent progress of MHP materials in the fields of photocatalytic CO2 reduction, pollutant degradation, photocatalytic chemical reaction and photocatalytic hydrogen evolution. In addition, some solutions are proposed to solve the problems of poor stability and weak photocatalytic performance of MHP photocatalysts. We hope that this review can provide ideas for researchers to further promote the research in the field of MHP-based photocatalysis.
查看更多>>摘要：? 2022 Elsevier B.V.Niobium pentoxide (Nb2O5) anodes have attracted much attention as a candidate for the next generation lithium-ion batteries (LIBs) due to the unique physical and chemical properties. However, some critical issues, like low electronic conductivity, inefficient ionic diffusion, must be addressed before practical applications. In this work, we employed a facile NaBH4 engaged chemical reduction method to modify Nb2O5 anodes. Microstructure and surface chemistry analysis indicated that the Nb2O5 materials have micro/nanoscale three-dimensionally interconnected morphology, and contain three different phases (T-, M-, and H-Nb2O5). More importantly, oxygen vacancies are introduced by the NaBH4 reduction treatment, and the oxygen vacancy amount can be modulated by changing the NaBH4 concentration. As anodes for LIBs, the optimized sample exhibited a reversible capacity of 252.2 mAh·g?1 after 100 cycles at a current density of 1 C, and a reversible capacity of 139.4 mAh·g?1 at a large current density of 10 C. The electrochemical performance enhancement can be attributed to the combination of multiscale structural design, i.e., oxygen vacancy, nanoscale phase interface, and micro/nanoscale three-dimension assembly. We expect the present synergistic strategy can be employed to manipulate the key structures in different functional materials for broader applications.
查看更多>>摘要：? 2022 Elsevier B.V.MAX phase materials, the precursors of MXenes (2D transition metal carbides, carbon nitrides, and nitrides), have become increasingly popular in electrochemical applications. In this study, we have successfully prepared Ti2SnC with high lithium capacity via the in-situ formation of SnO2. Results show that there are TiC nanowhiskers and SnO2 inside the Ti2SnC MAX calcined at 800 ℃, and the initial specific capacity could reach 377 and 371 mAh·g?1 at high current densities of 400 mA·g?1 and 1.0 A·g?1, respectively. These values are higher than those of most MAX phase materials reported in previous studies, such as Ti3SiC2 and Nb2SnC, but the stability and rate performance are inferior, which is a direction for the future. This paper provides a new pathway for the application of MAX phases in electrochemistry, which has more in-depth application prospects.
查看更多>>摘要：? 2022 Elsevier B.V.An innovative self-powered ultraviolet photodetector based on ZnO/CuBO2 core-shell nanorod arrays was fabricated using cost-efficient and scalable preparation technologies, including a chemical hydrothermal method and an impregnation technique. The ZnO/CuBO2 core-shell heterostructure exhibits significant diode behavior with a rectification ratio approaching 7016 at± 1 V because of the type-II band alignment formed at the heterojunction interface, acquiring a maximum responsivity of 165 mA /W1 with an external quantum efficiency of 55.3% (370 nm, 65 mW cm?2) and specific detectivity (4.13 ×1012 cm Hz1/2 W?1) under zero bias. Simultaneously, by applying an external bias to adjust the photovoltaic and pyroelectric effects and delving into the operating mechanisms, the photodetector based on the ZnO/CuBO2 heterostructure achieves enhanced performance. The decay time has been shortened, and the responsivity has reached up to 38.82 A W?1 (apparent quantum efficiency ~ 13,010%) at ? 2.5 V. Moreover, the effects of the power density on the photocurrent response and temperature induced by the photovoltaic-pyroelectric effect are discussed. This study reveals the potential of CuBO2 (one of the Cu-delafossite families) as a hole transport layer in optoelectronic devices, broadens the application prospects of core-shell nanorod arrays based on the photovoltaic-pyroelectric effect, and provides a direction for modulating the performance of such devices.
查看更多>>摘要：? 2022 Elsevier B.V.Lithium vanadyl phosphate (LiVOPO4) is a derivative of vanadyl phosphate (VOPO4) with different polymorphs that can be obtained based on employed synthesis approach. LiVOPO4 has recently gained attention due to multielectron electrochemical properties that result from varying vanadium redox activities as electrodes for lithium-ion batteries. In this work, we obtained single crystalline tetragonal layered LiVOPO4 (LVOP) by Li intercalation into solvothermal synthesized polycrystalline tetragonal layered VOPO4.2H2O (VOP) by a microwave-assisted hydrothermal method. We found that intercalation of Li+ into layered VOP resulted in a decrease in the interlayer spacing from 0.726 nm to 0.449 nm as well as a reduction of the vanadium oxidation state (+5 to +4), which resulted in a decrease of the band gap. Electrochemical properties of LVOP were evaluated as both a cathode and an anode in a half-cell lithium-ion battery system. The electrode used as a cathode, demonstrated a high capacity of 265 mAhg?1 at 0.1 C as well as 77 mAhg?1 at a high rate of 2 C. When used as an anode, the material exhibits an initial capacity of 865 mAhg?1 at 0.1 C. The electrode demonstrated good rate capability by maintaining a high capacity of 220 mAhg?1 at a high rate of 10 C. We also demonstrated for the first time that VOP can be utilized as a working electrode in an aqueous-based three-electrode supercapacitor and shows good capacitance properties.
查看更多>>摘要：? 2022 Elsevier B.V.Hydrogen production through chemical processes has received considerable attention. Replacing precious-metal-based catalysts in NaBH4 hydrolysis entails challenges such as the low durability and efficiency of non-precious metals. Here, carbon nanofiber (CNF)-supported NiCo2O4 and CoB were synthesized to form a burr-shaped rod-like catalyst (CNF-NiCo2O4-CoB). The morphology and microstructure of the catalyst were characterized through scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, X-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller adsorption analysis. Then, NaBH4 hydrolysis was catalyzed using CNF-NiCo2O4-CoB. At 303 K, the hydrogen production rate and activation energy of the hydrolysis reaction were 5225 mL min?1 g?1 and 38.32 kJ mol?1, respectively. The maximum hydrogen production rate achieved using this composite catalyst was significantly higher than that of a pure CoB catalyst. The composite catalyst also exhibited high durability, maintaining 82.5% of its initial catalytic activity even after nine hydrolysis cycles. The magnetic nature of the catalyst improved its recyclability. This work provides a new method for synthesizing composite-structured catalysts, exhibiting considerable potential in the hydrolysis of NaBH4.
查看更多>>摘要：? 2022 Elsevier B.V.Aging is a traditional strengthening method used for heat-treatable Al alloys. Cyclic strengthening has recently received widespread attention as a novel method for alloy strengthening. This study applied cyclic deformation to introduce dislocations and promote cluster formation in an Al-Mg-Cu alloy. Cyclically-strengthened (CS) samples have higher strength and ductility than peak-aged samples. The aging behaviors of the CS samples and the effect of pre-aging (artificial aging prior to cyclic deformation) on cyclic strengthening were also studied. Recovery and precipitation promotion were found during the aging of the CS samples regardless of pre-aging for 20 min. The pre-aged CS samples show higher strength than the CS samples without pre-aging. Interestingly, after subsequent aging, the mechanical properties of the CS samples with and without 20 min of pre-aging became the same. In summary, aging and cyclic deformation methods were combined to maximize the effects of precipitation strengthening and work-hardening. The strength limit obtained by individual aging or cyclic deformation methods was successfully overcome. This study provides new insights into alloy strengthening.
查看更多>>摘要：? 2022 Elsevier B.V.Non-precious metal nitrogen-carbon composites (M-N-C) derived from ZIFs are an excellent non-precious metal catalyst for use in energy conversion and storage devices such as fuel cells and metal-air batteries. Herein ZIF-67 precursor with good dispersion, perfect crystal structure and size of below 270 nm was synthesized by consuming low amount of 2-methylimidazole ligand using a mixture of ethanol (EA) and methanol (MT) as the reaction medium. Compared with the traditional method of reducing the size of ZIF-67 by increasing the amount of ligands in methanol, this method avoids the waste of raw materials and saves the cost. The Co-N-C-MT/EA catalysts derived from ZIF-67 exhibits good ORR activity in alkaline media (0.1 M KOH) with a half-wave potential of 0.81 V vs RHE. After 5000 cycles, the initial potential and half-wave potential basically remain no change, showing excellent long-term stability. And remarkable methanol resistance is also displayed comparing with commercial Pt/C. The present experimental result shows that the improved synthesis method of ZIF-67 precursors has far-reaching implications for the field of catalyst research.
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