Construction of MXene/Bi2WO6 Schottky Junction for Highly Efficient Piezocatalytic Hydrogen Evolution and Unraveling Mechanism.

For the first time, a series of MXene (Ti3C2Tx)/Bi2WO6 Schottky junction piezocatalysts were constructed, and the piezocatalytic hydrogen evolution activity was explored. Optimal Ti3C2Tx/Bi2WO6 exhibits the highest piezocatalytic hydrogen evolution rate of 764.4 µmol g-1 h-1, which is nearly 8 times higher than that of pure Ti3C2Tx and twice as high as that of Bi2WO6. This value also surpasses that of most recently reported typical piezocatalysts. Moreover, related experimental results and density functional theory calculations reveal that Ti3C2Tx/Bi2WO6 can provide unique channels for efficient electron transfer, enhance piezoelectric properties, optimize the adsorption Gibbs free energy of water, reduce activation energy for hydrogen atoms, endow robust separation capacity of charge carrier, and restrict the electron-hole recombination rate, thus significantly promoting the efficiency of hydrogen evolution reaction. Ultimately, we have unraveled an innovative piezocatalytic mechanism. This work broadens the scope of MXene materials in a sustainable energy piezocatalysis application.

Strongly Coupled Heterostructured CoP/MoO2 as an Advanced Electrocatalyst for Urea-Assisted Water Electrolysis.

Developing low-cost electrocatalysts with excellent activity and durability in urea-assisted water splitting is urgently needed in order to achieve sustainable hydrogen production. Herein, we in situ synthesized a robust coupled heterostructured electrocatalyst (CoP/MoO2) on a nickel foam (NF) substrate and explored its electrocatalytic performances in the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and urea oxidation reaction (UOR). The overpotential of CoP/MoO2/NF is found to be only 11 mV at 10 mA cm-2 during the HER process, which is significantly lower than that of commercial Pt/C. Meanwhile, the UOR catalytic performance of CoP/MoO2/NF indicates fast reaction kinetics, along with a considerable low driving potential (1.26 V) compared to that of the OER (1.51 V). In situ and ex situ techniques demonstrate that these excellent electrocatalytic properties are mainly ascribed to the effective synergistic coupled effect and strong electronic interactions between single-component CoP and MoO2, which can tune electronic states of Co and Mo, expose more active sites, enhance intrinsic catalytic activity, and accelerate charge transfer. Moreover, when used in electrochemical overall water splitting and urea-assisted water electrolysis, CoP/MoO2/NF can reach a current density of 10 mA cm-2 at only 1.46 and 1.32 V. This outperforms Pt/C||RuO2 and numerous nonprecious metal electrocatalysts and maintains a stable long-term electrolytic operation for 84 h. This work provides a promising pathway for the development of efficient catalysts during urea-assisted water electrolysis for hydrogen production.

Sulfur-Bridged Bonds Heightened Na-Storage Properties in MnS Nanocubes Encapsulated by S-Doped Carbon Matrix Synthesized via Solvent-Free Tactics for High-Performance Hybrid Sodium Ion Capacitors.

The exploitation of electrode materials with ability to balance capacity and kinetics between cathode and anode is a challenge for sodium-ion hybrid capacitors (SIHCs). Mn-based anode materials are limited by poor electrical conductivity, sluggish reaction kinetics, large volume variation, weak cycling stability, and inferior reversible capacity. Herein, MnS nanocubes encapsulated in S-doped porous carbon matrix (MSC) with strong sulfur-bridged bond interactions (CSMn) are successfully synthesized by solvent-free tactics. The CSMn bonds generated between MnS and carbon significantly inhibit the aggregation of nanostructural MnS cubes, restrict the volume expansion, and stabilize the nanostructure, which improves the Na+ storage reversibility and stability. Moreover, S-doped porous carbon enhances the electrical conductivity and electrons/ions diffusion rate, which boosts a fast kinetic reaction. As expected, MSC anode presents an outstanding reversible capacity of 600 mAh g-1 at 0.2 A g-1 and a long-term stable capacity of 357 mAh g-1 for 1000 cycles at a high current density of 10 A g-1 in sodium-ion batteries (SIBs). The as-assembled SIHCs deliver a high energy density of 109 W h kg-1 and a high power output of 98 W kg-1 , with 88% capacity retention at 2 A g-1 after 2000 cycles and practical applications (55 LEDs can be lighted for 10 min).

In Situ Construction of MnO2-Co3O4 Nanosheet Heterojunctions on Co@NCNT Surfaces for Oxygen Evolution.

Electrocatalytic water splitting is still circuitous and controversial because of the lack of highly active electrocatalysts to decrease the overpotential. Herein, we report a feasible method for constructing heterojunctions of MnO2-Co3O4 nanosheets on Co@NCNT support surfaces (MnO2-Co3O4/Co@NCNT) by spontaneous redox reactions. Experimental results indicate that Co embedded in Co@NCNT can be used as the carbon support and anchoring sites for heterojunctions, thus exposing a large number of active sites, adjusting the surface electronic structure, changing the OER rate-determining step of the catalyst, and reducing the reaction energy barrier. Besides, the in situ formation of MnO2-Co3O4 nanosheets on Co@NCNT inhibits the loss and aggregation of the catalyst, leading to robust structural stability. Therefore, the synergistic effects of these factors provide multi-functional active sites to enhance the intrinsic activity and achieve maximum catalytic performances. To deliver a current density of 10 mA cm-2, the catalyst of MnO2-Co3O4/Co@NCNT achieves an overpotential (η) of 303 mV in 1.0 M KOH media for OER. This simple redox strategy can be easily extended to prepare other ultrathin transition-metal oxide heterojunctions, which could be applied not only for water splitting but also for other energy conversion and storage technologies.

Construction of an Advanced NiFe-LDH/MoS2-Ni3S2/NF Heterostructure Catalyst toward Efficient Electrocatalytic Overall Water Splitting.

Developing high-efficiency, low-cost, and earth-abundant electrocatalysts toward the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) is highly desirable for boosting the energy efficiency of water splitting. Herein, we adopted an interfacial engineering strategy to enhance the overall water splitting (OWS) activity via constructing a bifunctional OER/HER electrocatalyst combining MoS2-Ni3S2 with NiFe layered double hydroxide (NiFe-LDH) on a nickel foam substrate. The NiFe-LDH/MoS2-Ni3S2/NF electrocatalyst delivers superior OER/HER activity and stability, such as low overpotentials (220 and 79 mV for OER and HER at current densities of 50 and 10 mA cm-2, respectively) and a low Tafel slope. This excellent electrocatalytic performance mainly benefits from the electronic structure modulation and synergistic effects between NiFe-LDH and MoS2-Ni3S2, which provides a high electrochemical activity area, more active sites, and strong electron interaction. Furthermore, the assembly of NiFe-LDH/MoS2-Ni3S2/NF into a two-electrode system only requires an ultra-low cell voltage of 1.50 V at a current density of 10 mA cm-2 and exhibits outstanding stability with a decay of current density of only 2.11% @50 mA cm-2 after 50 h, which is far superior to numerous other reported transition metal NiFe-LDH and MoS2-Ni3S2-based as well as RuO2||Pt-C electrocatalysts. This research highlights the rational design of heterostructures to efficiently advance electrocatalysis for water splitting applications.

Boosting the Photocatalytic Activity and Resistance of Photostability of ZnS Nanoparticles.

Defects play a vital role in improving photocatalytic performance. However, the specific influence mechanism of sulfur defects (DSS) on sulfide photocatalytic performance and stability is still unclear. In this work, an ingenious solvent-free self-overflow strategy is designed to introduce DSS into ZnS nanoparticles and explore the specific promotion mechanism of photocatalytic performance and photostability. The results indicate that the introduced DSS in ZnS nanoparticles can simultaneously boost the photocatalytic hydrogen production (PHE) performance and photostability of ZnS: the PHE rate of the defective ZnS can increase up to 21350.23 µmol·h-1·g-1, which is roughly 4.7 times higher than that of pristine ZnS. Both experiments and theoretical calculationsshow that the enhanced photocatalytic performance could be attributed to the change of energy band position after introducing DSS. Specifically, the introduction of DSS can raise the conduction band (CB) position of ZnS to enhance the reducing ability of photogenerated electrons. Besides, the valence band (VB) position can also be raised to boost the light absorption ability of ZnS and restrain the photocorrosion by weakening the oxidation capacity of the photogenerated holes. The ingenious strategy and interesting mechanism in this job provide a simple artful tactic to fabricate other defective sulfide photocatalysts and open up a particular path to promote the photostability of the photocatalysts.

Ce-regulating defect and morphology engineering for efficiently enhancing the piezocatalytic performances of BiOBr.

Cerium-doped bismuth oxybromide (1%, 5% and 10% Ce-BiOBr) piezocatalysts were synthesized. The piezocatalytic activity was efficiently regulated by defect and morphology engineering. Among them, the 5% Ce-BiOBr exhibits the highest piezocatalytic hydrogen production property with an evolution rate of 1147.6 µmol g-1 h-1, nearly twice that of the original BiOBr. Additionally, the MO dye degradation efficiency of 5% Ce-BiOBr reaches 91.9% within 60 min, with a higher reaction kinetic constant (0.0376 min-1) that was 6.1 times larger than that of pure BiOBr. These outstanding performances of 5% Ce-BiOBr surpass those of most other piezocatalytic material systems.

Rational design of CdS/BiOCl S-scheme heterojunction for effective boosting piezocatalytic H2 evolution and pollutants degradation performances.

Piezocatalysis as an emerging technology is broadly applied in hydrogen evolution and organic pollutants degradation aspects. However, the dissatisfactory piezocatalytic activity is a severe bottleneck for its practical applications. In this work, CdS/BiOCl S-scheme heterojunction piezocatalysts were constructed and explored the performances of piezocatalytic hydrogen (H2) evolution and organic pollutants degradation (methylene orange, rhodamine B and tetracycline hydrochloride) under strain by ultrasonic vibration. Interestingly, CdS/BiOCl presents a volcano-type relationship between catalytic activity and CdS contents, namely firstly increases and then decreases with the increase of CdS content. Optimal 20 % CdS/BiOCl endows superior piezocatalytic H2 generation rate of 1048.2 µmol g-1h-1 in methanol solution, which is 2.3 and 3.4 times higher than that of pure BiOCl and CdS, respectively. This value is also much higher than the recently reported Bi-based and most of other typical piezocatalysts. Meanwhile, 5 % CdS/BiOCl delivers the highest reaction kinetics rate constant and degradation rate toward various pollutants compared with other catalysts, which also exceeds that of the previously numerous results. Improved catalytic capacity of CdS/BiOCl is mainly ascribed to the construction of S-scheme heterojunction for enhancing the redox capacity as well as inducing more effective charge carriers separation and transfer. Moreover, S-scheme charge transfer mechanism is demonstrated via electron paramagnetic resonance and Quasi-In-situ X-ray photoelectron spectroscopy measurements. Eventually, a novel piezocatalytic mechanism of CdS/BiOCl S-scheme heterojunction has been proposed. This research develops a novel pathway for designing highly efficient piezocatalysts and provides a deeper understanding in construction of Bi-based S-scheme heterojunction catalysts for energy conservation and wastewater disposal applications.

Construction of oxygen vacancies and heterostructure in VO2-x/NC with enhanced reversible capacity, accelerated redox kinetics, and stable cycling life for sodium ion storage.

Developing anode materials with high reversible capacity, fast redox kinetics, and stable cycling life for Na+ storage remains a great challenge. Herein, the VO2 nanobelts with oxygen vacancies supported on nitrogen-doped carbon nanosheets (VO2-x/NC) were developed. Benefitting from the enhanced electrical conductivity, the accelerated kinetics, the increased active sites as well as the constructed 2D heterostructure, the VO2-x/NC delivered extraordinary Na+ storage performance in half/full battery. Theoretical calculations (DFT) demonstrated that oxygen vacancies could regulate the adsorption ability for Na+, enhance electronic conductivity, as well as achieve rapid and reversible Na+ adsorption/desorption. The VO2-x/NC exhibited high Na+ storage capacity of 270 mAh g-1 at 0.2 A g-1, and impressive cyclic stability with 258 mAh g-1 after 1800 cycles at 10 A g-1. The assembled sodium-ion hybrid capacitors (SIHCs) could achieve maximum energy density/power output of 122 Wh kg-1/9985 W kg-1, ultralong cycling life with 88.4% capacity retention after 25,000 cycles at 2 A g-1, and practical applications (55 LEDs could be actuated for 10 min), promising to be utilized in a practicable Na+ storage.

Optically Reconfigurable Complementary Logic Gates Enabled by Bipolar Photoresponse in Gallium Selenide Memtransistor.

To avoid the complexity of the circuit for in-memory computing, simultaneous execution of multiple logic gates (OR, AND, NOR, and NAND) and memory behavior are demonstrated in a single device of oxygen plasma-treated gallium selenide (GaSe) memtransistor. Resistive switching behavior with RON /ROFF ratio in the range of 104 to 106 is obtained depending on the channel length (150 to 1600 nm). Oxygen plasma treatment on GaSe film created shallow and deep-level defect states, which exhibit carriers trapping/de-trapping, that lead to negative and positive photoconductance at positive and negative gate voltages, respectively. This distinguishing feature of gate-dependent transition of negative to positive photoconductance encourages the execution of four logic gates in the single memory device, which is elusive in conventional memtransistor. Additionally, it is feasible to reversibly switch between two logic gates by just adjusting the gate voltages, e.g., NAND/NOR and AND/NAND. All logic gates presented high stability. Additionally, memtransistor array (1×8) is fabricated and programmed into binary bits representing ASCII (American Standard Code for Information Interchange) code for the uppercase letter "N". This facile device configuration can provide the functionality of both logic and memory devices for emerging neuromorphic computing.

Doping-engineered bifunctional oxygen electrocatalyst with Se/Fe-doped Co3O4/N-doped carbon nanosheets as highly efficient rechargeable zinc-air batteries.

Highly efficient oxygen reduction and oxygen evolution reactions have the critical role in the practical application of zinc-air batteries. Herein, doping engineering strategy has been adopted by construction of Se/Fe-doped in Co3O4/N-doped carbon nanosheets (denoted as Se/Fe-Co3O4/N-CNs) catalyst for boosting oxygen electrocatalytic activity. The achieved Se/Fe-Co3O4/N-CNs catalyst presents high-performances electrocatalytic characteristics, which exhibits a small overpotential gap (0.79 V), excellent oxygen evolution reaction activity with a small overpotential of 361 mV and a low Tafel slope of 57.3 mV dec-1 at 10 mA cm-2 as well as excellent oxygen reduction reaction activity with a large half-wave potential of 0.8 V, also surpassing the majority of reported Co3O4-based electrocatalysts. The outstanding catalytic performances are benefiting from the contributions between Se/Fe doping engineering and N-doped carbon nanosheets optimizing the electronic structure of Co species, endowing more active sites, enhancing the intrinsic catalytic activity and accelerating charge transfer rate for oxygen electrocatalytic process. Particularly, the as-fabricated zinc-air batteries with Se/Fe-Co3O4/N-CNs as air cathode presents a high open circuit potential of 1.41 V, a prominent highly efficient peak power density of 141.3 mW cm-2, a high specific capacity of 765.6 mAh g-1 and energy density 861.3 Wh kg-1 at current density of 10 mA cm-2 as well as an excellent cycling stability, which are exceeding the commercial Pt/C-RuO2 based zinc-air batteries. This work lays a foundation for design and development of high-performance bifunctional cobalt-based electrocatalysts for rechargeable metal-air batteries application.

Insight into the effect of OH modification on the piezo-photocatalytic hydrogen production activity of SrTiO3.

Surface modification by hydrophilic functional group have a tremendous influence on the catalytic activity of photocatalyst, however, there are few reports on improving piezoelectric catalytic performance through surface functionalization. Herein, OH-modified SrTiO3 was successfully obtained via a novel low-temperature solid-state precursor method and employed as a catalyst for photocatalytic, piezocatalytic and piezo-photocatalytic hydrogen production. Thanks to the super hydrophilic that is facilitating the contact of catalyst and water molecular and the more oxygen vacancies that can promote electron-hole separation, the photocatalytic, piezocatalytic and piezo-photocatalytic hydrogen generation of OH-modified SrTiO3 (OH-STO) is about two times higher than pristine SrTiO3 (STO). It is worth mentioning that the optimal piezo-photocatalytic hydrogen evolution rate of OH-STO (701.2 µmol h-1 g-1) is 5.3 times higher than the photocatalytic hydrogen evolution process of STO. This study presents a low-energy approach to the rational design of functional group modification nanomaterials that possess excellent piezo-photocatalytic performance.

Effect of Gd-Doping on Structural, Optical, and Magnetic Properties of NiFe2O4 As-prepared Thin Films via Facile Sol-Gel Approach.

In the present research work, gadolinium-doped nickel ferrite (NiFe2-x Gd x O4, x = 0-0.1) thin films have been synthesized by a facile sol-gel approach. The structural, optical, and magnetic performances of Gd-doping on nickel ferrite films have been investigated. The X-ray diffraction pattern indicated a cubic spinel ferrite structure and that the lattice parameter increased, while the crystalline size decreased with increasing the Gd concentration. Scanning electron microscopy analysis indicated that Gd-doped thin films were dense and smooth. The optical band gap value of the as-prepared thin films increased with increasing the Gd concentration. It showed that Gd-doping endowed nickel ferrite thin films with much better saturation magnetization (278.53 emu/cc) and remnant magnetization (67.83 emu/cc) at an appropriate 0.05 Gd-doping concentration. In addition, our results also revealed that the saturation magnetization remarkably increased, then sharply decreased with increasing of Gd doping content, which is attributed to effects of Gd-doping, exchange interaction, and redistribution of cations. Moreover, X-ray photoelectron spectroscopy analysis exhibited the effect of Gd-doping substitution on exchange interaction and redistribution of cations at the octahedral site and tetrahedral site.

Effective promoting piezocatalytic property of zinc oxide for degradation of organic pollutants and insight into piezocatalytic mechanism.

The piezoelectric zinc oxides with different morphology (ZnO nanoparticles and nanorods, hereafter abbreviated as ZnO NPs and NRs) are successfully synthesized using facile, green and harmless solid-state chemistry method at room temperature. The piezocatalytic activity of zinc oxide towards methylene blue (MB) of organic pollutants degradation has been explored under ultrasonic vibration. The ZnO NRs exhibit effectively enhanced piezocatalytic performance towards degradation dye compared with the ZnO NPs. In particular, the piezocatalytic decolorization ratio of MB solution is up to ~38% in ZnO NRs under 120 min, ~ 99% under 5.5 h and show good recycling utilization characteristics, indicating great potential for dye wastewater decolorization treatment. The main oxidizing hydroxyl radical (OH) and superoxide radicals (O2-) of the piezocatalytic reactions are confirmed and the production of piezocatalytic degradation process induced polarization electric charges. Moreover, we investigate the relationship between morphology and piezoelectric potential based on the finite element method for ZnO NPs and NRs, which further clarify the enhanced piezocatalytic activity and insight into piezocatalytic mechanism. This work offers a novel strategy towards wastewater decontamination applications and further understanding the relationship between piezocatalysis, morphology, and piezocatalytic mechanism in piezoelectric materials.

Annealing atmosphere effect on the resistive switching and magnetic properties of spinel Co3O4 thin films prepared by a sol-gel technique.

Spinel Co3O4 thin films were synthesized using a sol-gel technique to study the annealing atmosphere effect on resistive switching (RS) and magnetic modulation properties. Compared with oxygen and air annealed Pt/Co3O4/Pt stacks, the nitrogen annealed Pt/Co3O4/Pt stack shows optimal switching parameters such as a lower forming voltage, uniform distribution of switching voltages, excellent cycle-to-cycle endurance (>800 cycles), and good data retention. Improvement in switching parameters is ascribed to the formation of confined conducting filaments (CFs) which are composed of oxygen vacancies. From the analysis of current-voltage characteristics and their temperature dependence, the carrier transport mechanism in the high-field region of the high resistance state was dominated by Schottky emission. Besides, temperature dependent resistance and magnetization variations revealed that the physical mechanism of RS can be explained based on the formation and rupture of oxygen vacancy based CFs. In addition, multilevel saturation magnetization under different resistance states is attributed to the variation of oxygen vacancy concentration accompanied with the changes in the valence state of cations. Results suggested that using a nitrogen annealing atmosphere to anneal the thin films is a feasible approach to improve RS parameters and enhance the magnetic properties of Co3O4 thin film, which shows promising applications to design multifunctional electro-magnetic coupling nonvolatile memory devices.