Ammonia Electrosynthesis with a Stable Metal-Free 2D Silicon Phosphide Catalyst.

Metal-free 2D phosphorus-based materials are emerging catalysts for ammonia (NH3 ) production through a sustainable electrochemical nitrogen reduction reaction route under ambient conditions. However, their efficiency and stability remain challenging due to the surface oxidization. Herein, a stable phosphorus-based electrocatalyst, silicon phosphide (SiP), is explored. Density functional theory calculations certify that the N2 activation can be realized on the zigzag Si sites with a dimeric end-on coordinated mode. Such sites also allow the subsequent protonation process via the alternating associative mechanism. As the proof-of-concept demonstration, both the crystalline and amorphous SiP nanosheets (denoted as C-SiP NSs and A-SiP NSs, respectively) are obtained through ultrasonic exfoliation processes, but only the crystalline one enables effective and stable electrocatalytic nitrogen reduction reaction, in terms of an NH3 yield rate of 16.12 µg h-1  mgcat. -1 and a Faradaic efficiency of 22.48% at -0.3 V versus reversible hydrogen electrode. The resistance to oxidization plays the decisive role in guaranteeing the NH3 electrosynthesis activity for C-SiP NSs. This surface stability endows C-SiP NSs with the capability to serve as appealing electrocatalysts for nitrogen reduction reactions and other promising applications.

Atomic-Level Modulation of the Interface Chemistry of Platinum-Nickel Oxide toward Enhanced Hydrogen Electrocatalysis Kinetics.

Precise manipulation of the interactions between different components represents the frontier of heterostructured electrocatalysts and is crucial to understanding the structure-function relationship. Current studies, however, are quite limited. Here, we report targeted modulation of the atomic-level interface chemistry of Pt/NiO heterostructure via an annealing treatment, which results in substantially enhanced hydrogen electrocatalysis kinetics in alkaline media. Specifically, the optimized Pt/NiO heterostructure delivers by far the highest specific exchange current density of 8.1 mA cmPt-2 for hydrogen oxidation reaction. X-ray spectroscopy results suggest Pt-Ni interfacial bonds are formed after annealing, inducing more significant electron transfer from NiO to Pt. Also, the regulated interface chemistry, as proven by theoretical calculations, optimizes the binding behaviors of hydrogen and hydroxyl species. These findings emphasize the importance of interface engineering at the atomic level and inspire further explorations of heterostructured electrocatalysts.

Bridging Interparticle Li+ Conduction in a Soft Ceramic Oxide Electrolyte.

Li+-conductive ceramic oxide electrolytes, such as garnet-structured Li7La3Zr2O12, have been considered as promising candidates for realizing the next-generation solid-state Li-metal batteries with high energy density. Practically, the ceramic pellets sintered at elevated temperatures are often provided with high stiffness yet low fracture toughness, making them too brittle for the manufacture of thin-film electrolytes and strain-involved operation of solid-state batteries. The ceramic powder, though provided with ductility, does not yield satisfactorily high Li+ conductivity due to poor ion conduction at the boundaries of ceramic particles. Here we show, with solid-state nuclear magnetic resonance, that a uniform conjugated polymer nanocoating formed on the surface of ceramic oxide particles builds pathways for Li+ conduction between adjacent particles in the unsintered ceramics. A tape-casted thin-film electrolyte (thickness: <10 µm), prepared from the polymer-coated ceramic particles, exhibits sufficient ionic conductivity, a high Li+ transference number, and a broad electrochemical window to enable stable cycling of symmetric Li/Li cells and all-solid-state rechargeable Li-metal cells.

Gel-Derived Amorphous Bismuth-Nickel Alloy Promotes Electrocatalytic Nitrogen Fixation via Optimizing Nitrogen Adsorption and Activation.

To achieve the electrochemical nitrogen reduction reaction (NRR) for efficient and sustainable NH3 production, catalysts should exhibit high selectivity and activity with optimal adsorption energy. Herein we developed a three-dimensional (3D) amorphous BiNi alloy toward a significantly enhanced NRR compared with its crystalline and metal counterparts. Ni alloying enables the chemisorption of nitrogen and the lower free-energy change for the *NNH formation, and the 3D alloy electrocatalyst exhibits high catalytic activity for NH3 production with a yield rate of 17.5 µg h-1 mgcat -1 and Faradaic efficiency of 13.8 %. The enhanced electron transfer and increased electrochemical surface area were revealed in the interconnected porous scaffold, affording it sufficiently efficient and stable activity for potential practical applications. This work offers new insights into optimizing the adsorption energy of reactants and intermediates combined with tuning the crystallinity of NRR electrocatalysts.

Molecular Engineering of Azobenzene-Based Anolytes Towards High-Capacity Aqueous Redox Flow Batteries.

Aqueous redox flow batteries (RFBs) are promising alternatives for large-scale energy storage. However, new organic redox-active molecules with good chemical stability and high solubility are still desired for high-performance aqueous RFBs due to their low crossover capability and high abundance. We report azobenzene-based molecules with hydrophilic groups as new active materials for aqueous RFBs by utilizing the reversible redox activity of azo groups. By rationally tailoring the molecular structure of azobenzene, the solubility is favorably improved from near zero to 2 M due to the highly charged asymmetric structure formed in alkaline environment. DFT simulations suggest that the concentrated solution stability can be enhanced by adding hydrotropic agent to form intermolecular hydrogen bonds. The demonstrated RFB exhibits long cycling stability with a capacity retention of 99.95 % per cycle over 500 cycles. It presents a viable chemical design route towards advanced aqueous RFBs.

In Situ Formation of Liquid Metals via Galvanic Replacement Reaction to Build Dendrite-Free Alkali-Metal-Ion Batteries.

Galvanic replacement reactions have been studied as a versatile route to synthesize nanostructured alloys. However, the galvanic replacement chemistry of alkali metals has rarely been explored. A protective interphase layer will be formed outside templates when the redox potential exceeds the potential windows of nonaqueous solutions, and the complex interfacial chemistry remains elusive. Here, we demonstrate the formation of room-temperature liquid metal alloys of Na and K via galvanic replacement reaction. The fundamentals of the reaction at such low potentials are investigated via a combined experimental and computational method, which uncovers the critical role of solid-electrolyte interphase in regulating the migration of Na ions and thus the alloying reaction kinetics. With in situ formed NaK liquid alloys as an anode, the dendritic growth of alkali metals can be eliminated thanks to the deformable and self-healing features of liquid metals. The proof-of-concept battery delivers reasonable electrochemical performance, confirming the generality of this in situ approach and design principle for next-generation dendrite-free batteries.

Multifunctional Active-Center-Transferable Platinum/Lithium Cobalt Oxide Heterostructured Electrocatalysts towards Superior Water Splitting.

Designing cost-effective and efficient electrocatalysts plays a pivotal role in advancing the development of electrochemical water splitting for hydrogen generation. Herein, multifunctional active-center-transferable heterostructured electrocatalysts, platinum/lithium cobalt oxide (Pt/LiCoO2 ) composites with Pt nanoparticles (Pt NPs) anchored on LiCoO2 nanosheets, are designed towards highly efficient water splitting. In this electrocatalyst system, the active center can be alternatively switched between Pt species and LiCoO2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Specifically, Pt species are the active centers and LiCoO2 acts as the co-catalyst for HER, whereas the active center transfers to LiCoO2 and Pt turns into the co-catalyst for OER. The unique architecture of Pt/LiCoO2 heterostructure provides abundant interfaces with favorable electronic structure and coordination environment towards optimal adsorption behavior of reaction intermediates. The 30 % Pt/LiCoO2 heterostructured electrocatalyst delivers low overpotentials of 61 and 285 mV to achieve 10 mA cm-2 for HER and OER in alkaline medium, respectively.

Enhanced Surface Interactions Enable Fast Li+ Conduction in Oxide/Polymer Composite Electrolyte.

Li+ -conducting oxides are considered better ceramic fillers than Li+ -insulating oxides for improving Li+ conductivity in composite polymer electrolytes owing to their ability to conduct Li+ through the ceramic oxide as well as across the oxide/polymer interface. Here we use two Li+ -insulating oxides (fluorite Gd0.1 Ce0.9 O1.95 and perovskite La0.8 Sr0.2 Ga0.8 Mg0.2 O2.55 ) with a high concentration of oxygen vacancies to demonstrate two oxide/poly(ethylene oxide) (PEO)-based polymer composite electrolytes, each with a Li+ conductivity above 10-4  S cm-1 at 30 °C. Li solid-state NMR results show an increase in Li+ ions (>10 %) occupying the more mobile A2 environment in the composite electrolytes. This increase in A2-site occupancy originates from the strong interaction between the O2- of Li-salt anion and the surface oxygen vacancies of each oxide and contributes to the more facile Li+ transport. All-solid-state Li-metal cells with these composite electrolytes demonstrate a small interfacial resistance with good cycling performance at 35 °C.

New insights into the effect of pH on the mechanism of ofloxacin electrochemical detection in aqueous solution.

Antibiotic contamination in water has become an increasingly serious problem that poses a potentially huge threat to human health. Ofloxacin (OFL) is a typical broad-spectrum quinolone antibiotic and is frequently detected in a wide variety of aquatic environments. Given its frequent contamination, the need for new electrochemical sensors to quickly and efficiently detect OFL in aquatic environments has attracted increasing attention. Solution pH is an important factor affecting the performance of electrochemical sensors. This work investigates OFL detection using graphene/glassy carbon electrodes (Gr/GCE) in phosphate-buffered saline across a range of pH (3-8). The molecular polarity analysis method was first used to reveal interactions between target contaminants and the electrode interface. The electrode properties and the polarity of OFL were studied using SEM, XPS, FT-IR spectrometry, zeta potentiometry and modelling calculation of molecular properties. Our results showed that OFL interacts with the surface of Gr/GCE via both hydrogen bonding and coulomb electrostatic forces. The electrical signal decreased more quickly in an alkaline than acidic environment, which was due to the differences between coulomb electrostatic and hydrogen bonding forces. These results also showed variations in the OFL peak current response under different pH conditions. Collectively, these findings provide a better foundation for the rapid identification of the optimal pH environment for the electrical analysis of contaminants like antibiotics in an aquatic environment.

Solvent-Dependent Intercalation and Molecular Configurations in Metallocene-Layered Crystal Superlattices.

Organic-inorganic superlattices are a class of artificial structures of significant scientific and technological importance. Forming these hybrid materials can be achieved via controlled intercalation of organic molecules into inorganic layered hosts, which is a complex course involving multiple physicochemical processes. In solution phase, it is further complicated by interaction of solvent molecules with the intercalant and/or host. Here we describe an intercalation system exhibiting strong solvent-dependent kinetics and phase evolution. In revisiting intercalation of ferrocene into layered VOPO4·2H2O material by taking into account the influence of solvent, we are able to unravel molecular configurations of ferrocene molecules. An exclusive orientation of ferrocene but different arrangements among the layers are concluded in two model solvents. Resolving this complicated structure is possible thanks to a combined experimental and theoretical approach. Our study provides new insights into understanding molecular configurations and controlling intercalation kinetics in creating organic-inorganic superlattices, which may offer unprecedented properties beyond conventional materials.

Biredox Eutectic Electrolytes Derived from Organic Redox-Active Molecules: High-Energy Storage Systems.

One promising candidate for high-energy storage systems is the nonaqueous redox flow battery (NARFB). However, their application is limited by low solubility of redox-active materials and poor performance at high current density. Reported here is a new strategy, a biredox eutectic, as the sole electrolyte for NARFB to achieve a significantly higher concentration of redox-active materials and enhance the cell performance. Without other auxiliary solvents, the biredox eutectic electrolyte is formed directly by the molecular interactions between two different redox-active molecules. Such a unique electrolyte possesses high concentration with low viscosity (3.5 m, for N-butylphthalimide and 1,1-dimethylferrocene system) and a relatively high working voltage of 1.8 V, enabling high capacity and energy density of NARFB. The resulting high-performance NARFB demonstrates that the biredox eutectic based strategy is potentially promising for low-cost and high-energy storage systems.

Dual Tuning of Ni-Co-A (A = P, Se, O) Nanosheets by Anion Substitution and Holey Engineering for Efficient Hydrogen Evolution.

Seeking earth-abundant electrocatalysts with high efficiency and durability has become the frontier of energy conversion research. Mixed-transition-metal (MTM)-based electrocatalysts, owing to the desirable electrical conductivity, synergistic effect of bimetal atoms, and structural stability, have recently emerged as new-generation hydrogen evolution reaction (HER) electrocatalysts. However, the correlation between anion species and their intrinsic electrocatalytic properties in MTM-based electrocatalysts is still not well understood. Here we present a novel approach to tuning the anion-dependent electrocatalytic characteristics in MTM-based catalyst for HER, using holey Ni/Co-based phosphides/selenides/oxides (Ni-Co-A, A = P, Se, O) as the model materials. The electrochemical results, combined with the electrical conductivity measurement and DFT calculation, reveal that P substitution could modulate the electron configuration, lower the hydrogen adsorption energy, and facilitate the desorption of hydrogen on the active sites in Ni-Co-A holey nanostructures, resulting in superior HER catalytic activity. Accordingly we fabricate the NCP holey nanosheet electrocatalyst for HER with an ultralow onset overpotential of nearly zero, an overpotential of 58 mV, and long-term durability, along with an applied potential of 1.56 V to boost overall water splitting at 10 mA cm-2, among the best electrocatalysts reported for non-noble-metal catalysts to date. This work not only presents a deeper understanding of the intrinsic HER electrocatalytic properties for MTM-based electrocatalyst with various anion species but also offers new insights to better design efficient and durable water-splitting electrocatalysts.

Defect Engineering Metal-Free Polymeric Carbon Nitride Electrocatalyst for Effective Nitrogen Fixation under Ambient Conditions.

Electrocatalytic nitrogen reduction reaction (NRR) under ambient conditions provides an intriguing picture for the conversion of N2 into NH3 . However, electrocatalytic NRR mainly relies on metal-based catalysts, and it remains a grand challenge in enabling effective N2 activation on metal-free catalysts. Here we report a defect engineering strategy to realize effective NRR performance (NH3 yield: 8.09 µg h-1 mg-1cat. , Faradaic efficiency: 11.59 %) on metal-free polymeric carbon nitride (PCN) catalyst. Illustrated by density functional theory calculations, dinitrogen molecule can be chemisorbed on as-engineered nitrogen vacancies of PCN through constructing a dinuclear end-on bound structure for spatial electron transfer. Furthermore, the N-N bond length of adsorbed N2 increases dramatically, which corresponds to "strong activation" system to reduce N2 into NH3 . This work also highlights the significance of defect engineering for improving electrocatalysts with weak N2 adsorption and activation ability.

Polyanthraquinone as a Reliable Organic Electrode for Stable and Fast Lithium Storage.

In spite of recent progress, there is still a lack of reliable organic electrodes for Li storage with high comprehensive performance, especially in terms of long-term cycling stability. Herein, we report an ideal polymer electrode based on anthraquinone, namely, polyanthraquinone (PAQ), or specifically, poly(1,4-anthraquinone) (P14AQ) and poly(1,5-anthraquinone) (P15AQ). As a lithium-storage cathode, P14AQ showed exceptional performance, including reversible capacity almost equal to the theoretical value (260 mA h g(-1); >257 mA h g(-1) for AQ), a very small voltage gap between the charge and discharge curves (2.18-2.14=0.04 V), stable cycling performance (99.4% capacity retention after 1000 cycles), and fast-discharge/charge ability (release of 69% of the low-rate capacity or 64% of the energy in just 2 min). Exploration of the structure-performance relationship between P14AQ and related materials also provided us with deeper understanding for the design of organic electrodes.

An ultrastable anode for long-life room-temperature sodium-ion batteries.

Sodium-ion batteries are important alternative energy storage devices that have recently come again into focus for the development of large-scale energy storage devices because sodium is an abundant and low-cost material. However, the development of electrode materials with long-term stability has remained a great challenge. A novel negative-electrode material, a P2-type layered oxide with the chemical composition Na(2/3)Co(1/3)Ti(2/3)O2, exhibits outstanding cycle stability (ca. 84.84 % capacity retention for 3000 cycles, very small decrease in the volume (0.046 %) after 500 cycles), good rate capability (ca. 41 % capacity retention at a discharge/charge rate of 10 C), and a usable reversible capacity of about 90 mAh g(-1) with a safe average storage voltage of approximately 0.7 V in the sodium half-cell. This P2-type layered oxide is a promising anode material for sodium-ion batteries with a long cycle life and should greatly promote the development of room-temperature sodium-ion batteries.

Recent Developments of Cathode Materials for Thermal Batteries.

Big progress has been made in batteries based on an intercalation mechanism in the last 20 years, but limited capacity in batteries hinders their further increase in energy density. The demand for more energy intensity makes research communities turn to conversion-type batteries. Thermal batteries are a special kind of conversion-type battery, which are thermally activated primary batteries composed mainly of cathode, anode, separator (electrolyte), and heating mass. Such kinds of battery employ an internal pyrotechnic source to make the battery stack reach its operating temperature. Thermal batteries have a long history of research and usage in military fields because of their high specific capacity, high specific energy, high thermal stability, long shelf life, and fast activation. These experiences and knowledge are of vital importance for the development of conversion-type batteries. This review provides a comprehensive account of recent studies on cathode materials. The paper covers the preparation, characterization of various cathode materials, and the performance test of thermal batteries. These advances have significant implications for the development of high-performance, low-cost, and mass production conversion-type batteries in the near future.

Water induced ultrathin Mo2C nanosheets with high-density grain boundaries for enhanced hydrogen evolution.

Grain boundary controlling is an effective approach for manipulating the electronic structure of electrocatalysts to improve their hydrogen evolution reaction performance. However, probing the direct effect of grain boundaries as highly active catalytic hot spots is very challenging. Herein, we demonstrate a general water-assisted carbothermal reaction strategy for the construction of ultrathin Mo2C nanosheets with high-density grain boundaries supported on N-doped graphene. The polycrystalline Mo2C nanosheets are connected with N-doped graphene through Mo-C bonds, which affords an ultra-high density of active sites, giving excellent hydrogen evolution activity and superior electrocatalytic stability. Theoretical calculations reveal that the dz2 orbital energy level of Mo atoms is controlled by the MoC3 pyramid configuration, which plays a vital role in governing the hydrogen evolution activity. The dz2 orbital energy level of metal atoms exhibits an intrinsic relationship with the catalyst activity and is regarded as a descriptor for predicting the hydrogen evolution activity.

General Design Methodology for Organic Eutectic Electrolytes toward High-Energy-Density Redox Flow Batteries.

By virtue of strong molecular interactions, eutectic electrolytes provide highly concentrated redox-active materials without other auxiliary solvents, hence achieving high volumetric capacities and energy density for redox flow batteries (RFBs). However, it is critical to unveil the underlying mechanism in this system, which will be undoubtedly beneficial for their future research on high-energy storage systems. Herein, a general formation mechanism of organic eutectic electrolytes (OEEs) is developed, and it is found that molecules with specific functional groups such as carbonyl (CO), nitroxyl radical (NO•), and methoxy (OCH3 ) groups can coordinate with alkali metal fluorinated sulfonylimide salts (especially for bis(trifluoromethanesulfonyl)imide, TFSI), thereby forming OEEs. Molecular designs further demonstrate that the redox-inactive methoxy group functionalized ferrocene derivative maintains the liquid OEE at both reduced and oxidized states. Over threefold increase in solubility is obtained (2.8 m for ferrocene derivative OEE) and high actual discharge energy density of 188 Wh L-1 (75% of the theoretical value) is achieved in the Li hybrid cell. The established mechanism presents new ways of designing desirable electrolytes through molecular interactions for the development of high-energy-density organic RFBs.

Gutzwiller density functional studies of FeAs-based superconductors: structure optimization and evidence for a three-dimensional Fermi surface.

The electronic structures of FeAs compounds are sensitive to FeAs bonding, which is described unsuccessfully by the local density approximation (LDA). Treating the multiorbital fluctuations from ab inito LDA+Gutzwiller method, we can now predict the correct FeAs bond length and bonding strength, which will explain the observed "soft phonon." The bands are narrowed by a factor of 2 from their LDA widths. The d{3z{2}-r{2}} orbital is pushed up to cross the Fermi level, forming a three-dimensional Fermi surface, which reduces the anisotropy. The interorbital Hund's coupling J rather than U plays a crucial role in obtaining these results.

Low-Temperature Multielement Fusible Alloy-Based Molten Sodium Batteries for Grid-Scale Energy Storage.

The sustainable future of modern society relies on the development of advanced energy systems. Alkali metals, such as Li, Na, and K, are promising to construct high-energy-density batteries to complement the fast-growing implementation of renewable sources. The stripping/deposition of alkali metals is compromised by serious dendrite growth, which can be intrinsically eliminated by using molten alkali metal anodes. Up to now, most of the conventional molten alkali metal-based batteries need to be operated at high temperatures. To decrease the operating temperature, we extended the battery chemistry to multielement alloys, which provide more flexibility for wide selection and rational screening of cost-effective and fusible metallic electrodes. On the basis of an integrated experimental and theoretical study, the depressed melting point and enhanced interfacial compatibility are elucidated. The proof-of-concept molten sodium battery enabled by the Bi-Pb-Sn fusible alloy not only circumvents the use of costly Ga and In elements but also delivers attractive performance at 100 °C, holding great promise for grid-scale energy storage.