Amorphous Vanadium Oxides with Dual ion Storage Mechanism for High-Performance Aqueous Zinc ion Batteries.

Owing to the extremely limited structural deformation caused by the introduction of guest ions that their rigid structure can sustain, crystalline materials typically fail owing to structural collapse when utilized as electrode materials. Amorphous materials, conversely, are more resistant to volume expansion during dynamic ion transport and can introduce a lot of defects as active sites. Here, The amorphous polyaniline-coated/intercalated V2O5·nH2O (PVOH) nanowires are prepared by in situ chemical oxidation combined with self-assembly strategy, which exhibited impressive electrochemical properties because of its short-range ordered crystal structure, oxygen vacancy/defect-rich, improved electronic channels, and ionic channels. Through in situ techniques, the energy storage mechanism of its Zn2+/H+ co-storage is investigated and elucidated. Additionally, this work provides new insights and perspectives for the investigation and application of amorphous cathodes for aqueous zinc ion batteries.

One-Step Pyrolysis Construction of Bimetallic Atom-Cluster Sites for Boosting Bifunctional Catalytic Activity in Zn-Air Batteries.

Due to their unique advantages, single atoms and clusters of transition metals are expected to achieve a breakthrough in catalytic activity, but large-scale production of active materials remains a challenge. In this work, a simple solvent-free one-step annealing method is developed and applied to construct diatomic and cluster active sites in activated carbon by utilizing the strong anchoring ability of phenanthroline to metal ions, which can be scaled for mass productions. Benefiting from the synergy between the different metals, the obtained sub-nano-bimetallic atom-cluster catalysts (FeNiAC -NC) exhibit high oxygen reduction reactions (ORR) activity (E1/2 = 0.936 V vs. RHE) and a small ORR/oxygen evolution reaction (OER) potential gap of only 0.594 V. An in-house pouch Zn-air battery is assembled using an FeNiAC -NC catalyst, which demonstrates a stability of 1000 h, outperforming previous reports. The existence of clusters and their effects on catalytic activity is analyzed by density functional theory calculations to reveal the chemistry of nano-bimetallic atom-cluster catalysts.

In Situ Fast Construction of Ni3S4/FeS Catalysts on 3D Foam Structure Achieving Stable Large-Current-Density Water Oxidation.

By increasing the content of Ni3+, the catalytic activity of nickel-based catalysts for the oxygen evolution reaction (OER), which is still problematic with current synthesis routes, can be increased. Herein, a Ni3+-rich of Ni3S4/FeS on FeNi Foam (Ni3S4/FeS@FNF) via anodic electrodeposition to direct obtain high valence metal ions for OER catalyst is presented. XPS showed that the introduction of Fe not only further increased the Ni3+ concentration in Ni3S4/FeS to 95.02%, but also inhibited the dissolution of NiOOH by up to seven times. Furthermore, the OER kinetics is enhanced by the combination of the inner Ni3S4/FeS heterostructures and the electrochemically induced surface layers of oxides/hydroxides. Ni3S4/FeS@FNF shows the most excellent OER activity with a low Tafel slope of 11.2 mV dec-1 and overpotentials of 196 and 445 mV at current densities of 10 and 1400 mA cm-2, respectively. Furthermore, the Ni3S4/FeS@FNF catalyst can be operated stably at 1500 mA cm-2 for 200 h without significant performance degradation. In conclusion, this work has significantly increased the high activity Ni3+ content in nickel-based OER electrocatalysts through an anodic electrodeposition strategy. The preparation process is time-saving and mature, which is expected to be applied in large-scale industrialization.

Identification of Catalytic Active Sites for Durable Proton Exchange Membrane Fuel Cell: Catalytic Degradation and Poisoning Perspectives.

Recent progress in synthetic strategies, analysis techniques, and computational modeling assist researchers to develop more active catalysts including metallic clusters to single-atom active sites (SACs). Metal coordinated N-doped carbons (M-N-C) are the most auspicious, with a large number of atomic sites, markedly performing for a series of electrochemical reactions. This perspective sums up the latest innovative and computational comprehension, while giving credit to earlier/pioneering work in carbonaceous assembly materials towards robust electrocatalytic activity for proton exchange membrane fuel cells via inclusive performance assessment of the oxygen reduction reaction (ORR). M-Nx -Cy are exclusively defined active sites for ORR, so there is a unique possibility to intellectually design the relatively new catalysts with much improved activity, selectivity, and durability. Moreover, some SACs structures provide better performance in fuel cells testing with long-term durability. The efforts to understand the connection in SACs based M-Nx -Cy moieties and how these relate to catalytic ORR performance are also conveyed. Owing to comprehensive practical application in the field, this study has covered very encouraging aspects to the current durability status of M-N-C based catalysts for fuel cells followed by degradation mechanisms such as macro-, microdegradation, catalytic poisoning, and future challenges.

Design of an amperometric glucose oxidase biosensor with added protective and adhesion layers.

Enzymes have demonstrated great potential in the development of advanced electroanalysis devices due to their unique recognition and catalytic properties. However, unsatisfactory stability and limited electron communication of traditional enzyme sensors seriously hinder their large-scale application. In this work, a simple and effective method is proposed to improve the stability of enzyme sensors by using sodium hyaluronate (SH) as a protective film, MXene-Ti3C2/Glucose oxidase (GOD) as the reaction layer, and chitosan (CS) /reduced graphene oxide (rGO) as the adhesion layer. Results demonstrate that the repeatability of the designed sensor increased by 73.3% after improving the adhesion between the reaction layer and the current collector and that its response ability was greatly enhanced. Moreover, the long-term stability of the electrode surface with SH protective film proved to be superior than that without protective film, which suggests that this design can effectively improve the overall performance of the enzyme biosensor. This work proposed a multi-tier synergistic approach for improving the reliability of enzyme sensors. Graphical abstract Our proposed protective and adhesion layer can greatly improve the stability of enzyme sensor and realize the rapid detection of glucose in serum sample.

BC@DNA-Mn3(PO4)2 Nanozyme for Real-Time Detection of Superoxide from Living Cells.

Electrochemical in situ sensing of small signal molecules released from living cells has an increasing significance in early diagnosis, pathological analyses, and drug discovery. Here, a living cell-fixed sensing platform was built using the BC@DNA-Mn3(PO4)2 nanozyme, in which a highly biocompatible bacterial cellulose riveted with very tiny Mn3(PO4)2; it not only delivers high catalytic activity toward superoxide anions but possesses excellent biocompatibility for cell adsorption and growth. Additionally, the experimental results suggested that fixing the living cells on the surface of the sensing platform facilitates tiny Mn3(PO4)2 activity centers to capture and detect O2•- very quickly and simultaneously has great potential in miniaturization, cost reduction, and real-time monitoring.

A coaxial nanocable textured by a cerium oxide shell and carbon core for sensing nitric oxide.

A corn-like CeO2/C coaxial cable textured by a cerium oxide shell and a carbon core was designed to sense NO. The carbon core possesses high electrical conductivity, and the CeO2 surface delivers excellent electrocatalytic activity. The sensor, typically operated at 0.8 V (vs. Ag/AgCl), exhibits a detection limit of 1.7 nM, which is 4-times lower than that of CeO2 nanotubes based one (at S/N = 3). It also displays wide linear response (up to 83 µM), a sensitivity of 0.81 µA µM-1 cm-2, and fast response (2 s). These values are highly competitive to that of a CeO2 tube (0.92 µA µM-1 cm-2 and 2 s). The sensor was used to quantify NO that is released by Aspergillus flavus. Graphical abstractSchematic representation of corn-like CeO2/C which can more sensitively and effectively detect NO released from A. flavus than when using CeO2 nanotubes, benefitting from its unique coaxial cable structure.

FePO4 embedded in nanofibers consisting of amorphous carbon and reduced graphene oxide as an enzyme mimetic for monitoring superoxide anions released by living cells.

FePO4 is biocompatible and can act as a kind of promising enzyme mimetic. Unfortunately, the electrical conductivity of FePO4 is poor. In order to enhance its conductivity, FePO4 was embedded into nanofibers consisting of amorphous carbon and reduced graphene oxide (rGO) by an electrospinning technique. As a sensing material for monitoring superoxide anion (O2•-) and typically operated at 0.5 V (vs. SCE), it displays high sensitivity (9.6 µA⋅µM-1⋅cm-2), a low detection limit (9.7 nM at S/N = 3), a wide linear response range (10 nM to 10 µM), and fast response (1.6 s). Due to its low detection limit and fast response, the sensor in our perception has a large potential for detecting superoxide anions released by HeLa cancer cells. Graphical abstract Schematic of the microstructure of FePO4/C and FePO4/rGO-C nanofibers, a photograph of cancer cells (HeLa), and the electrochemical response towards O2-• of the sensor.

Nanosized Metal Phosphides Embedded in Nitrogen-Doped Porous Carbon Nanofibers for Enhanced Hydrogen Evolution at All pH Values.

Transition-metal phosphides (TMPs) have emerged as promising catalyst candidates for the hydrogen evolution reaction (HER). Although numerous methods have been investigated to obtain TMPs, most rely on traditional synthetic methods that produce materials that are inherently deficient with respect to electrical conductivity. An electrospinning-based reduction approach is presented, which generates nickel phosphide nanoparticles in N-doped porous carbon nanofibers (Ni2 P@NPCNFs) in situ. Ni2 P nanoparticles are protected from irreversible fusion and aggregation in subsequent high-temperature pyrolysis. The resistivity of Ni2 P@NPCNFs (5.34â€…Ω cm) is greatly decreased by 104 times compared to Ni2 P (>104 â€…Ω cm) because N-doped carbon NFs are incorporated. As an electrocatalyst for HER, Ni2 P@NPCNFs reveal remarkable performance compared to other previously reported catalysts in acidic media. Additionally, it offers excellent catalytic ability and durability in both neutral and basic media. Encouraged by the excellent electrocatalytic performance of Ni2 P@NPCNFs, a series of pea-like Mx P@NPCNFs, including Fe2 P@NPCNFs, Co2 P@NPCNFs, and Cu3 P@NPCNFs, were synthesized by the same method. Detailed characterization suggests that the newly developed method could render combinations of ultrafine metal phosphides with porous carbon accessible; thereby, extending opportunities in electrocatalytic applications.

Analysis of cobalt phosphide (CoP) nanorods designed for non-enzyme glucose detection.

The nanorods of cobalt phosphide have been prepared and evaluated as an electrocatalyst for non-enzyme glucose detection. The nanorods were used to modify the surface of an electrode and detect glucose without the help of an enzyme for the first time. The crystal structure and composition of cobalt phosphide were identified by XRD and XPS, respectively, and the morphology of the as-prepared samples was observed by FESEM and TEM. The electrochemical measurement results indicate that the CoP-based sensor exhibits excellent catalytic activity and a far lower detection potential compared to bare GCE. Specifically, the electrocatalytic mechanism of CoP in the detection of glucose was proposed based on a series of physical characterization methods, electrochemical measurements, and theoretical calculations.

Carbon nanotubes implanted manganese-based MOFs for simultaneous detection of biomolecules in body fluids.

Metal-organic frameworks (MOFs) have recently attracted much interest in electrochemical fields due to their controlled porosity, large internal surface area, and countless structural topologies. However, the direct application of single component MOFs is limited since they also exhibit poor electronic conductivity, low mechanical stability, and inferior electrocatalytic ability. To overcome these problems, we implanted multi-walled carbon nanotubes (MWCNTs) into manganese-based metal-organic frameworks (Mn-BDC) using a one-step solvothermal method and found that the introduction of MWCNTs can initiate the splitting of bulky Mn-BDC into thin layers. This splitting is highly significant in that it enhances the electronic conductivity and electrocatalytic ability of Mn-BDC. The constructed Mn-BDC@MWCNT composites were utilized as an electrode modifying material in the fabrication of an electrochemical sensor and then were used successfully for the determination of biomolecules in human body fluid. The sensor displayed successful detection performance with wide linear detection ranges (0.1-1150, 0.01-500, and 0.02-1100 µM for AA, DA and UA, respectively) and low limits of detection (0.01, 0.002, and 0.005 µM for AA, DA and UA, respectively); thus, this preliminary study presents an electrochemical biosensor constructed with a novel electrode modifying material that exhibits superior potential for the practical detection of AA, DA and UA in urine samples.

Nanostring-cluster hierarchical structured Bi2O3: synthesis, evolution and application in biosensing.

In the present study, a simple strategy was developed to fabricate a new Bi2O3 nanostring-cluster hierarchical structure. Precursor microrods composed of Bi(C2O4)OH were initially grown under hydrothermal conditions. After calcination in air, Bi(C2O4)OH microrods were carved into unique string-cluster structures by the gas produced during the decomposition process. To explain the formation mechanism, the effects of pyrolysis temperature and time on the morphology of the as-prepared samples were investigated and are discussed in detail. It was discovered that the nanostring-cluster-structured Bi2O3 consists of thin nanoplatelet arrays, which is advantageous for glucose enzyme immobilization and for designing biosensors. The resulting Bi2O3 structure showed an excellent capability in the modification of electrode surfaces in biosensors by enhancing the sensitivity, with good specificity and response time. Such qualities of a biosensor are ideal characteristics for glucose sensing performance and allow for further explorations of its application in other fields.

pH-controllable synthesis of unique nanostructured tungsten oxide aerogel and its sensitive glucose biosensor.

This work presents a controllable synthesis of nanowire-networked tungsten oxide aerogels, which was performed by varying the pH in a polyethyleneimine (PEI)-assisted hydrothermal process. An enzyme-tungsten oxide aerogel co-modified electrode shows high activity and selectivity toward glucose oxidation, thus holding great promise for applications in bioelectronics.

ZnO Additive Boosts Charging Speed and Cycling Stability of Electrolytic Zn-Mn Batteries.

Electrolytic aqueous zinc-manganese (Zn-Mn) batteries have the advantage of high discharge voltage and high capacity due to two-electron reactions. However, the pitfall of electrolytic Zn-Mn batteries is the sluggish deposition reaction kinetics of manganese oxide during the charge process and short cycle life. We show that, incorporating ZnO electrolyte additive can form a neutral and highly viscous gel-like electrolyte and render a new form of electrolytic Zn-Mn batteries with significantly improved charging capabilities. Specifically, the ZnO gel-like electrolyte activates the zinc sulfate hydroxide hydrate assisted Mn2+ deposition reaction and induces phase and structure change of the deposited manganese oxide (Zn2Mn3O8·H2O nanorods array), resulting in a significant enhancement of the charge capability and discharge efficiency. The charge capacity increases to 2.5 mAh cm-2 after 1 h constant-voltage charging at 2.0 V vs. Zn/Zn2+, and the capacity can retain for up to 2000 cycles with negligible attenuation. This research lays the foundation for the advancement of electrolytic Zn-Mn batteries with enhanced charging capability.

A green and facile route for constructing flower-shaped TiO2 nanocrystals assembled on graphene oxide sheets for enhanced photocatalytic activity.

We have demonstrated an environmentally friendly in situ assembly method for the preparation of novel three-dimensional TiO2/graphene oxide (TiO2/GO) nanostructures with favorable flower-shaped architectures. Very little information on such a morphology of TiO2/GO nanostructures is available in the literature. The as-synthesized sample was characterized by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, N2 adsorption-desorption measurements and Raman spectroscopy. Also the TiO2/GO composites exhibited enhanced photocatalytic properties.

A salt-baking 'recipe' of commercial nickel-molybdenum alloy foam for oxygen evolution catalysis in water splitting.

Ni-based metal foam holds promise as an electrochemical water-splitting catalyst, due to its low cost, acceptable catalytic activity and superior stability. However, its catalytic activity must be improved before it can be used as an energy-saving catalyst. Here, a traditional Chinese recipe, salt-baking, was employed to surface engineering of nickel-molybdenum alloy (NiMo) foam. During salt-baking, a thin layer of FeOOH nano-flowers was assembled on the NiMo foam surface then the resultant NiMo-Fe catalytic material was evaluated for its ability to support oxygen evolution reaction (OER) activity. The NiMo-Fe foam catalyst generated an electric current density of 100 mA cm-2 that required an overpotential of only 280 mV, thus demonstrating that its performance far exceeded that of the benchmark catalyst RuO2 (375 mV). When employed as both the anode and cathode for use in alkaline water electrolysis, the NiMo-Fe foam generated a current density (j) output that was 3.5 times greater than that of NiMo. Thus, our proposed salt-baking method is a promising simple and environmentally friendly approach for surface engineering of metal foam for designing catalysts.

Electrostatically directed assembly of two-dimensional ultrathin Co2Ni-MOF/Ti3C2Tx nanosheets for electrocatalytic oxygen evolution.

Hydrogen production from water electrolysis is severely restricted by the poor reaction kinetics of oxygen evolution reaction (OER). In this work, a series of two-dimensional (2D) composites MOF/Ti3C2Tx (the MXene phase) were fabricated by electrostatically directed assembly and used as catalysts for OER. The obtained composite materials exhibit enhanced electrocatalytic properties, thanks to the ultrathin 2D/2D heterostructure with abundant active sites in Co2Ni-MOF and the high electronic conductivity of Ti3C2Tx. Among all the catalysts, Co2Ni-MOF@MX-1 achieved the best oxygen evolution performance with the lowest Tafel slope (51.7 mV dec-1) and the lowest overpotential (265 mV on carbon paper) at the current density of 10 mA cm-2. These results demonstrated that the synthesis of 2D composite materials by electrostatically directed assembly could be a feasible and promising method for the preparation of 2D heterostructure catalysts.

Environment-friendly biomimetic synthesis of TiO2 nanomaterials for photocatalytic application.

We have demonstrated an environment-friendly biomimetic synthesis method for the preparation of TiO(2) nanomaterials with different crystal phases and morphologies. This is the first time that it has been found that the crystal phase of TiO(2) can be controlled just by using different biotemplates, and cannot be changed by calcination up to 750 °C. In our experiment, anatase TiO(2) was obtained by using yeast and albumen templates, while rutile TiO(2) was formed by using dandelion pollen as the template.

Why does the capacity of vanadium selenide based aqueous zinc ion batteries continue to increase during long cycles?

At present, rechargeable aqueous zinc ion batteries (RZIBs) have become a rising star and highly sought after in the field of new energy. While vanadium-based RZIBs often exhibit an anomaly of increased long-cycle capacity, which has not been explored in depth. Nevertheless, it is critical to understand this phenomenon to develop high-performance RZIBs. Therefore, this study investigated the growth mechanism of VSe2-based RZIBs using VSe2/MXene as the cathode material via in-situ and ex-situ characterization techniques and electrochemical measurements. Experimental results indicated that with the interaction/extraction of Zn2+/H+ in the host material during cycling, an obvious oxidation reaction occurs at high voltage, and the formed vanadium oxide further reacts with Zn2+ from the electrolyte. As a result, Zn0.25V2O5·H2O is continuously produced and accumulated, contributing to the increasing capacity of the prepared RZIBs.

Reunderstanding the Reaction Mechanism of Aqueous Zn-Mn Batteries with Sulfate Electrolytes: Role of the Zinc Sulfate Hydroxide.

Rechargeable aqueous Zn-Mn batteries have garnered extensive attention for next-generation high-safety energy storage. However, the charge-storage chemistry of Zn-Mn batteries remains controversial. Prevailing mechanisms include conversion reaction and cation (de)intercalation in mild acid or neutral electrolytes, and a MnO2 /Mn2+ dissolution-deposition reaction in strong acidic electrolytes. Herein, a Zn4 SO4 ·(OH)6 ·xH2 O (ZSH)-assisted deposition-dissolution model is proposed to elucidate the reaction mechanism and capacity origin in Zn-Mn batteries based on mild acidic sulfate electrolytes. In this new model, the reversible capacity originates from a reversible conversion reaction between ZSH and Znx MnO(OH)2 nanosheets in which the MnO2 initiates the formation of ZSH but contributes negligibly to the apparent capacity. The role of ZSH in this new model is confirmed by a series of operando characterizations and by constructing Zn batteries using other cathode materials (including ZSH, ZnO, MgO, and CaO). This research may refresh the understanding of the most promising Zn-Mn batteries and guide the design of high-capacity aqueous Zn batteries.