Fluorine-Lodged High-Valent High-Entropy Layered Double Hydroxide for Efficient, Long-Lasting Zinc-Air Batteries.

Efficient and stable bifunctional oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) catalysts are urgently needed to unlock the full potential of zinc-air batteries (ZABs). High-valence oxides (HVOs) and high entropy oxides (HEOs) are suitable candidates for their optimal electronic structures and stability but suffer from demanding synthesis. Here, a low-cost fluorine-lodged high-valent high-entropy layered double hydroxide (HV-HE-LDH) (FeCoNi2F4(OH)4) is conveniently prepared through multi-ions co-precipitation, where F- are firmly embedded into the individual hydroxide layers. Spectroscopic detections and theoretical simulations reveal high valent metal cations are obtained in FeCoNi2F4(OH)4, which enlarge the energy band overlap between metal 3d and O 2p, enhancing the electronic conductivity and charge transfer, thus affording high intrinsic OER catalytic activity. More importantly, the strengthened metal-oxygen (M-O) bonds and stable octahedral geometry (M-O(F)6) in FeCoNi2F4(OH)4 prevent structural reorganization, rendering long-term catalytic stability. Furthermore, an efficient three-phase reaction interface with fast oxygen transportation was constructed, significantly improving the ORR activity. ZABs assembled with FeCoNi2F4(OH)4@HCC (hydrophobic carbon cloth) cathodes deliver a top performance with high round-trip energy efficiency (61.3 % at 10 mA cm-2) and long-term stability (efficiency remains at 58.8 % after 1050 charge-discharge cycles).

Identifying Fe as OER Active Sites and Ultralow-Cost Bifunctional Electrocatalysts for Overall Water Splitting.

Electrocatalysts based on Fe and other transition metals are regarded as most promising candidates for accelerating the oxygen evolution reaction (OER), whereas whether Fe is the catalytic active site for OER is still under debate. Here, unary Fe- and binary FeNi- based catalysts, FeOOH and FeNi(OH)x , are produced by self-reconstruction. The former is a dual-phased FeOOH, possessing abundant oxygen vacancies (VO ) and mixed-valence states, delivering the highest OER performance among all the unary iron oxides- and hydroxides- based powder catalysts reported to date, supporting Fe can be catalytically active for OER. As to binary catalyst, FeNi(OH)x is fabricated featuring 1) an equal molar content of Fe and Ni and 2) rich VO , both of which are found essential to enable abundant stabilized reactive centers (FeOOHNi) for high OER performance. Fe is found to be oxidized to 3.5+ during the *OOH process, thus, Fe is identified to be the active site in this new layered double hydroxide (LDH) structure with Fe:Ni = 1:1. Furthermore, the maximized catalytic centers enable FeNi(OH)x @NF (nickel foam) as low-cost bifunctional electrodes for overall water-splitting, delivering excellent performance comparable to commercial electrodes based on precious metals, which overcomes a major obstacle to the commercialization of bifunctional electrodes: prohibitive cost.

Lamellarly Stacking Porous N, P Co-Doped Mo2 C/C Nanosheets as High Performance Anode for Lithium-Ion Batteries.

Layered stacking and highly porous N, P co-doped Mo2 C/C nanosheets are prepared from a stable Mo-enhanced hydrogel. The hydrogel is formed through the ultrafast cross-linking of phosphomolybdic acid and chitosan. During the reduction of the composite hydrogel framework under inert gas protection, highly porous N and P co-doped carbon nanosheets are produced with the in situ formation of ultrafine Mo2 C nanoparticles highly distributed throughout the nanosheets which are entangled via a hierarchical lamellar infrastructure. This unique architecture of the N, P co-doped Mo2 C/C nanosheets tremendously promote the electrochemical activity and operate stability with high specific capacity and extremely stable cycling. In particular, this versatile synthetic strategy can also be extended to other polyoxometalate (such as phosphotungstic acid) to provide greater opportunities for the controlled fabrication of novel hierarchical nanostructures for next-generation high performance energy storage applications.

The Electrocatalytic Role of Oxygen Vacancy in Nitrate Reduction Reactions.

Ammonia, with high energy density and easy transportation, holds significant potential to become an integral part of future energy systems. Among tremendous strategies, electrocatalytic ammonia production is no doubt an efficient and eco-friendly method. One particularly intriguing class of electrocatalysts for reducing nitrate to ammonia is transition metal oxides, which have been heavily researched. However, how these catalysts' oxygen vacancy (VO) affects their performance remains elusive. To address this, taking titania (the most important catalyst) as an example, we carried out experimental investigations and simulations. Contrary to the prevailing belief that the concentrated VO would increase the catalytic efficiency of nitrate reduction, it was found that a relatively low level of VO is favorable for maximizing catalytic efficiency. At low cathodic voltages, titania with minimal VO delivered both the highest reduction efficiency and the best selectivity among the different titania samples in this paper. In addition to outlining the merits of lower electron transfer resistance and accelerated reaction dynamics, we also put forth a previously unmentioned factor, the adsorption of hydrogen or the creation of an ordered hydrogen bond network, which put up a hydrogen-rich atmosphere for following nitrate reduction. Further simulation study revealed that within the hydrogen-rich atmosphere isolated VO serves as the ideal active center to enable the lowest energy barriers for the reduction of nitrate into ammonia. These findings offer fresh insights into the working mechanism of oxide-based electrocatalysts for ammonia production.

Coupling High Hardness and Zn Affinity in Amorphous-Crystalline Diamond for Stable Zn Metal Anodes.

The highly reversible plating/stripping of Zn is plagued by dendrite growth and side reactions on metallic Zn anodes, retarding the commercial application of aqueous Zn-ion batteries. Herein, a distinctive nano dual-phase diamond (NDPD) comprised of an amorphous-crystalline heterostructure is developed to regulate Zn deposition and mechanically block dendrite growth. The rich amorphous-crystalline heterointerfaces in the NDPD endow modified Zn anodes with enhanced Zn affinity and result in homogeneous nucleation. In addition, the unparalleled hardness of the NDPD effectively overcomes the high growth stress of dendrites and mechanically impedes their proliferation. Moreover, the hydrophobic surfaces of the NDPD facilitate the desolvation of hydrate Zn2+ and prevent water-mediated side reactions. Consequently, the Zn@NDPD presents an ultrastable lifespan exceeding 3200 h at 5 mA cm-2 and 1 mAh cm-2. The practical application potential of Zn@NDPD is further demonstrated in full cells. This work exhibits the great significance of a chemical-mechanical synergistic anode modification strategy in constructing high-performance aqueous Zn-ion batteries.

Diamond with Sp2-Sp3 composite phase for thermometry at Millikelvin temperatures.

Temperature is one of the seven fundamental physical quantities. The ability to measure temperatures approaching absolute zero has driven numerous advances in low-temperature physics and quantum physics. Currently, millikelvin temperatures and below are measured through the characterization of a certain thermal state of the system as there is no traditional thermometer capable of measuring temperatures at such low levels. In this study, we develop a kind of diamond with sp2-sp3 composite phase to tackle this problem. The synthesized composite phase diamond (CPD) exhibits a negative temperature coefficient, providing an excellent fit across a broad temperature range, and reaching a temperature measurement limit of 1 mK. Additionally, the CPD demonstrates low magnetic field sensitivity and excellent thermal stability, and can be fabricated into probes down to 1 micron in diameter, making it a promising candidate for the manufacture of next-generation cryogenic temperature sensors. This development is significant for the low-temperature physics researches, and can help facilitate the transition of quantum computing, quantum simulation, and other related technologies from research to practical applications.

Ultrafast construction of partially hydrogen-bonded metal-hyaluronan networks with multiple biotissue-related features.

This paper reports a versatile and dynamic hydrogel system based on ultrafast coordination between partially hydrogen-bonded (PHB) biopolymer hyaluronic acid and a series of transition metal ions at appropriate pH values. It was found that the procedure for the hydrogel synthesis was extremely facile, requiring a simple mixing of the components within 2 s. The hydrogels exhibited high water content, up to 96 %. Even so, the hydrogels can be stretched >50 times and rapidly self-heal from damage within only 10 s without using any healing agents or heating. Furthermore, this dynamic hydrogel network underwent reversible sol-gel transitions as response to multiple disparate stimuli, including pH, temperature, ions, redox, and light. The photo-patterning ability of the hydrogel with a rapid gel-sol transition upon exposure to light was also demonstrated. We disclosed the principle and methodology to use PHB metal-biopolymer systems for constructing dynamic bio-related soft matters.

Encapsulating atomic molybdenum into hierarchical nitrogen-doped carbon nanoboxes for efficient oxygen reduction.

Construction of single-atom catalysts (SACs) with maximally exposed active sites remains a challenging task mainly because of the lack of suitable host matrices. In this study, hierarchical N-doped carbon nanoboxes composed of ultrathin nanosheets with dispersed atomic Mo (denoted as hierarchical SA-Mo-C nanoboxes) were fabricated via a template-engaged multistep synthesis process. Comprehensive characterizations, including X-ray absorption fine structure analysis, reveal the formation of Mo-N4 atomic sites uniformly anchored on the hierarchical carbon nanoboxes. The prepared catalysts offer structural and morphological advantages, including ultrathin nanosheet units, unique hollow structures and abundant active Mo-N4 species, that result in excellent activity with a half-wave potential of 0.86 V vs. RHE and superb stability for the oxygen reduction reaction in 0.1 M KOH; thus, the catalysts are promising air-cathode catalysts for Zn-air batteries with a high peak power density of 157.6 mW cm-2.

Two-dimensional mineral hydrogel-derived single atoms-anchored heterostructures for ultrastable hydrogen evolution.

Hydrogen energy is critical for achieving carbon neutrality. Heterostructured materials with single metal-atom dispersion are desirable for hydrogen production. However, it remains a great challenge to achieve large-scale fabrication of single atom-anchored heterostructured catalysts with high stability, low cost, and convenience. Here, we report single iron (Fe) atom-dispersed heterostructured Mo-based nanosheets developed from a mineral hydrogel. These rationally designed nanosheets exhibit excellent hydrogen evolution reaction (HER) activity and reliability in alkaline condition, manifesting an overpotential of 38.5 mV at 10 mA cm-2, and superior stability without performance deterioration over 600 h at current density up to 200 mA cm-2, superior to most previously reported non-noble-metal electrocatalysts. The experimental and density functional theory results reveal that the O-coordinated single Fe atom-dispersed heterostructures greatly facilitated H2O adsorption and enabled effective adsorbed hydrogen (H*) adsorption/desorption. The green, scalable production of single-atom-dispersed heterostructured HER electrocatalysts reported here is of great significance in promoting their large-scale implementation.

Nanoscale Heterogeneities of Non-Noble Iron-Based Metallic Glasses toward Efficient Water Oxidation at Industrial-Level Current Densities.

Scaling up the production of cost-effective electrocatalysts for efficient water splitting at the industrial level is critically important to achieve carbon neutrality in our society. While noble-metal-based materials represent a high-performance benchmark with superb activities for hydrogen and oxygen evolution reactions, their high cost, poor scalability, and scarcity are major impediments to achieve widespread commercialization. Herein, a flexible freestanding Fe-based metallic glass (MG) with an atomic composition of Fe50Ni30P13C7 was prepared by a large-scale metallurgical technique that can be employed directly as a bifunctional electrode for water splitting. The surface hydroxylation process created unique structural and chemical heterogeneities in the presence of amorphous FeOOH and Ni2P as well as nanocrystalline Ni2P that offered various active sites to optimize each rate-determining step for water oxidation. The achieved overpotentials for the oxygen evolution reaction were 327 and 382 mV at high current densities of 100 and 500 mA cm-2 in alkaline media, respectively, and a cell voltage of 1.59 V was obtained when using the MG as both the anode and the cathode for overall water splitting at a current density of 10 mA cm-2. Theoretical calculations unveiled that amorphous FeOOH makes a significant contribution to water molecule adsorption and oxygen evolution processes, while the amorphous and nanocrystalline Ni2P stabilize the free energy of hydrogen protons (ΔGH*) in the hydrogen evolution process. This MG alloy design concept is expected to stimulate the discovery of many more high-performance catalytic materials that can be produced at an industrial scale with customized properties in the near future.

Facile Surfactant-, Reductant-, and Ag Salt-free Growth of Ag Nanoparticles with Controllable Size from 35 to 660 nm on Bulk Ag Materials.

Morphologically and dimensionally controlled growth of Ag nanocrystals has long been plagued by surfactants or capping agents that complicate downstream applications, unstable Ag salts that impaired the reproducibility, and multistep seed injection that is troublesome and time-consuming. Here, we report a one-pot electro-chemical method to fast (∼2 min) produce Ag nanoparticles from commercial bulk Ag materials in a nitric acid solution, eliminating any need for surfactants or capping agents. Their size can be easily manipulated in an unprecedentedly wide range from 35 to 660 nm. Furthermore, the Ag nanoparticles are directly grown on the Ag substrate, highly desirable for promising applications such as catalysis and plasmonics. The mechanistic studies reveal that the concentration of Ag+ in the diffusion layer nearby the surface, controlled by the magnitude and duration of voltage, is critical in governing the nanoparticle formation (<1.3 mM) and its dimensional adjustability.

A Novel Multinary Intermetallic as an Active Electrocatalyst for Hydrogen Evolution.

Electrochemical water splitting offers an attractive approach for hydrogen production. However, the lack of high-performance cost-effective electrocatalyst severely hinders its applications. Here, a multinary high-entropy intermetallic (HEI) that possesses an unusual periodically ordered structure containing multiple non-noble elements is reported, which can serve as a highly efficient electrocatalyst for hydrogen evolution. This HEI exhibits excellent activities in alkalinity with an overpotential of 88.2 mV at a current density of 10 mA cm-2 and a Tafel slope of 40.1 mV dec-1 , which are comparable to those of noble catalysts. Theoretical calculations reveal that the chemical complexity and surprising atomic configurations provide a strong synergistic function to alter the electronic structure. Furthermore, the unique L12 -type ordered structure enables a specific site-isolation effect to further stabilize the H2 O/H* adsorption/desorption, which dramatically optimizes the energy barrier of hydrogen evolution. Such an HEI strategy uncovers a new paradigm to develop novel electrocatalyst with superior reaction activities.

Large-scale synthesis of carbon dots/TiO2 nanocomposites for the photocatalytic color switching system.

In view of the easy control and contactless spatial nature of light, the photoreversible color switching system has attracted tremendous attention. Although some progress has been achieved in the past few years, the practical applications have been limited by the complicated preparation process, material toxicity and low reaction yield. Herein, we report a rapid, a one-pot large-scale synthesis approach for the preparation of carbon dots (CDs)/TiO2 nanocomposites via the thermal condensation at 160 °C, affording high photocatalytic color switching on/off performance. Under ambient conditions and with the introduction of some oxygen gas, MB rapidly changed from blue to colorless in one minute under UV-vis irradiation and recovered (again showed its original blue color) in twenty minutes. We anticipate that the designed low-cost and green carbon dots (CDs)/TiO2 nanocomposites have much potential in practical applications and represent a solid step toward color switching applications.

Construction of FeP Hollow Nanoparticles Densely Encapsulated in Carbon Nanosheet Frameworks for Efficient and Durable Electrocatalytic Hydrogen Production.

Developing noble-metal-free based electrocatalysts with high activity, good stability, and low cost is critical for large-scale hydrogen production via water splitting. In this work, hollow FeP nanoparticles densely encapsulated in carbon nanosheet frameworks (donated as hollow FeP/C nanosheets), in situ converted from Fe-glycolate precursor nanosheets through carbonization and subsequent phosphorization, are designed and synthesized as an advanced electrocatalyst for the hydrogen evolution reaction. FeP hollow nanoparticles are transformed from intermediate Fe3O4 nanoparticles through the nanoscale Kirkendall effect. The two-dimensional architecture, densely embedding FeP hollow nanoparticles, provides abundant accessible active sites and short electron and ion pathways. The in situ generated carbon nanosheet frameworks can not only offer a conductive network but also protect the active FeP from oxidation. As a result, hollow FeP/C nanosheets exhibit excellent electrocatalytic performance for the hydrogen evolution reaction in 0.5 m H2SO4 with a quite low overpotential of 51.1 mV at 10 mA cm-2, small Tafel slope of 41.7 mV dec-1, and remarkable long-term stability. The study highlights the in situ synthesis of two-dimensional metal phosphide/C nanocomposites with highly porous features for advanced energy storage and conversion.

Bottom-up synthesis of iron and nitrogen dual-doped porous carbon nanosheets for efficient oxygen reduction.

Iron and nitrogen co-doped porous carbon nanosheets (Fe,N-PCNs) with a small thickness, smooth surface and high specific surface area are fabricated by a facile bottom-up approach as highly efficient noble metal-free catalysts for the oxygen reduction reaction (ORR). The Fe,N-PCN catalyst exhibits a positive half-wave potential (E1/2) (0.87 V vs. RHE), a similar four-electron pathway in 0.1 M KOH medium, and an excellent long-term stability.

High selective detection of mercury (II) ions by thioether side groups on metal-organic frameworks.

Mercury ions can significantly affect the organism and environment even at a very low concentration. Thus, great efforts have been devoted to developing high sensitive electrochemical sensors, especially the one that not only detect the mercury ions but also effective sensitive to thymine-Hg2+-thymine in aqueous solution. Metal-organic-frameworks (MOFs) possess hollow nature and are easy for grafting functional groups, however, there is still no attempts for working as electrochemical sensors in detecting mercury ions. Herein, we report a novel type sensor of Zr(IV)-based MOFs with specifically attached thioether side groups allowing mercury ions to be easily adsorbed and detected. The Zr(IV)-involved MOFs show strong binding to mercury ions compared with the bare MOFs, as confirmed by both experiment measurements and theoretical calculations. The as-prepared senor is sensitive ranging from 0.01 nM to 3 µM with detection limitation of 7.3 fM, which is better than most of T-Hg2+-T- and enzyme-based sensors reported so far. The high sensitivity could be due to the straightforward adsorption pathway and the biomolecule exclusion nature of the Zr(IV)-involved MOFs sensor. We anticipate that our findings could pave the way for MOFs-based sensor exploration towards its commercial applications.

Synergistic Effects of C/α-MoC and Ag for Efficient Oxygen Reduction Reaction.

It remains challenging to prepare highly active and stable catalysts from earth-abundant elements for the oxygen reduction reaction (ORR). Herein we report a facile method to synthesize cost-effective heterogeneous C/α-MoC/Ag electrocatalysts. Rotating disc electrode (RDE) experiments revealed that the obtained C/α-MoC/Ag exhibited much superior catalytic performance for ORR than that of C/Ag, C/α-MoC, or even the conventional Pt/C. First-principles calculations indicated that the enhanced activity could be attributed to the efficient synergistic effects between Ag and α-MoC/C by which the energy barrier for O2 dissociation has been substantially reduced. Furthermore, Li-air and Al-air cells were assembled to demonstrate the unprecedented electrochemical performance of C/α-MoC/Ag nanocomposites surpassing the Pt/C. Thus experimental results and theoretical calculations together showed that the heterogeneous C/α-MoC/Ag nanocomposites are a promising alternative to platinum for applications in industrial metal-air batteries.

Biopolymer-chitosan based supramolecular hydrogels as solid state electrolytes for electrochemical energy storage.

A biopolymer-chitosan based Supramolecular Hydrogel type solid state Electrolyte (SHE) is prepared via a simple and fast cross-linking between chitosan and Li+/Ag+. The obtained SHE itself shows high thermal stability and excellent flexible and mouldable properties. When integrated in an asymmetric supercapacitor with MnO2 as the positive electrode and active carbon as the negative electrode, it can survive more than 10 000 cycles with the areal capacity of 10 mF cm-2 at the 1.8 mA cm-2 current density.

Supramolecular hydrogel directed self-assembly of C- and N-doped hollow CuO as high-performance anode materials for Li-ion batteries.

A novel hollow-structured CuO derived from chitosan-coated Cu/Cu2O composite hollow spheres was mass produced via a supramolecular hydrogel templating method and homogeneously co-doped with C and N. Evaluation of the as-produced co-doped CuO hollow spheres as anode materials for Li ion batteries showed that they had superior electrochemical properties.

Low-Cost and Novel Si-Based Gel for Li-Ion Batteries.

Si-based nanostructure composites have been intensively investigated as anode materials for next-generation lithium-ion batteries because of their ultra-high-energy storage capacity. However, it is still a great challenge to fabricate a perfect structure satisfying all the requirements of good electrical conductivity, robust matrix for buffering large volume expansion, and intact linkage of Si particles upon long-term cycling. Here, we report a novel design of Si-based multicomponent three-dimensional (3D) networks in which the Si core is capped with phytic acid shell layers through a facile high-energy ball-milling method. By mixing the functional Si with graphene oxide and functionalized carbon nanotube, we successfully obtained a homogeneous and conductive rigid silicon-based gel through complexation. Interestingly, this Si-based gel with a fancy 3D cross-linking structure could be writable and printable. In particular, this Si-based gel composite delivers a moderate specific capacity of 2711 mA h g-1 at a current density of 420 mA g-1 and retained a competitive discharge capacity of more than 800.00 mA h g-1 at the current density of 420 mA g-1 after 700 cycles. We provide a new method to fabricate durable Si-based anode material for next-generation high-performance lithium-ion batteries.