Manipulation of Electronic States of Pt Sites via d-Band Center Tuning for Enhanced Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cells.

Expediting the torpid kinetics of the oxygen reduction reaction (ORR) at the cathode with minimal amounts of Pt under acidic conditions plays a significant role in the development of proton exchange membrane fuel cells (PEMFCs). Herein, a novel Pt-N-C system consisting of Pt single atoms and nanoparticles anchored onto the defective carbon nanofibers is proposed as a highly active ORR catalyst (denoted as Pt-N-C). Detailed characterizations together with theoretical simulations illustrate that the strong coupling effect between different Pt sites can enrich the electron density of Pt sites, modify the d-band electronic environments, and optimize the oxygen intermediate adsorption energies, ultimately leading to significantly enhanced ORR performance. Specifically, the as-designed Pt-N-C demonstrates exceptional ORR properties with a high half-wave potential of 0.84 V. Moreover, the mass activity of Pt-N-C reaches 193.8 mA gPt-1 at 0.9 V versus RHE, which is 8-fold greater than that of Pt/C, highlighting the enormously improved electrochemical properties. More impressively, when integrated into a membrane electrode assembly as cathode in an air-fed PEMFC, Pt-N-C achieved a higher maximum power density (655.1 mW cm-2) as compared to Pt/C-based batteries (376.25 mW cm-2), hinting at the practical application of Pt-N-C in PEMFCs.

Balancing the Binding of Intermediates Enhances Alkaline Hydrogen Oxidation on D-Band Center Modulated Pd Sites.

Exploring efficient alkaline hydrogen oxidation reaction (HOR) electrocatalysts is of great concern for constructing anion exchange membrane fuel cells (AEMFCs). Herein, d-band center modulated PdCo alloys with ultralow Pd content anchored onto the defective carbon support (abbreviated as PdCo/NC hereafter) are proposed as highly efficient HOR catalyst. The as-prepared catalyst exhibits exceptional HOR performance compared to the Pt/C catalyst, achieving thermodynamically spontaneous and kinetically preferential reactions. Specifically, the resultant PdCo/NC demonstrates a marked enhancement in alkaline HOR performance, with the highest mass and specific activities of 1919.6 mA mgPd-1 and 1.9 mA cm-2, 51.1 and 4.2 times higher than those of benchmark of Pt/C, along with an excellent stability in a chronoamperometry test. In the analysis of in situ Raman spectra, it was discovered that tetrahedrally coordinated H-bonded water molecules were formed during the HOR process. This indicates that the promotion of interfacial water molecule formation and enhancement of HOR activities in PdCo/NC are facilitated by defect engineering and the turning of d-band center in PdCo alloy. The essential knowledge obtained in this study could open up a new direction for modifying the electronic structure of cost-effective HOR catalysts through electronic structure engineering.

Built-In Positive Valence Space Shifting the Chemical Equilibrium Forward for Nitrate Reduction to Ammonia.

The electrochemical conversion of nitrate pollutants into value-added ammonia (NH3) is an appealing alternative synthetic route for sustainable NH3 production. However, the development of the electrocatalytic nitrate-to-ammonia reduction reaction (NO3RR) has been hampered by unruly reactants and products at the interface and the accompanied sluggish kinetic rate. In this work, a built-in positive valence space is successfully constructed over FeCu nanocrystals to rationally regulate interfacial component concentrations and positively shift the chemical equilibrium. With positive valence Cu optimizing the active surface, the space between the stern and shear layers becomes positive, which is able to continuously attract the negatively charged NO3- reactant and repulse the positively charged NH4+ product even under high current density, thus significantly boosting the NO3RR kinetics. The system with a built-in positive valence space affords an ampere-level NO3RR performance with the highest NH3 yield rate of 150.27 mg h-1 mg-1 at -1.3 V versus RHE with an outstanding NH3 current density of 189.53 mA cm-2, as well as a superior Faradaic efficiency (FE) of 97.26% at -1.2 V versus RHE. The strategy proposed here underscores the importance of interfacial concentration regulation and can find wider applicability in other electrochemical syntheses suffering from sluggish kinetics.

Leveling the Zn Anode by Crystallographic Orientation Manipulation.

Dendrite growth and corrosion of Zn metal anodes result in the limited reversibility of aqueous Zn metal batteries (ZMBs), hindering their prospects as large-scale energy storage devices. Inspired by the similarity of conventional electroplating industrial engineering and Zn deposition in ZMBs, we tend to utilize a low-cost leveling agent (LEA), 1,4-butynediol, to level the Zn deposition. Combining theoretical with in situ experimental characterizations, the preferential adsorption of LEA molecules on different lattice planes can contribute to crystallographic orientation manipulation of the (002) plane, causing good inhibition of dendrite growth. Additionally, the adsorption of LEA molecules on the Zn surface can also prevent undesirable corrosion. Endowed with these merits, symmetric cells and full cells with the LEA additive achieve improved stability and reversibility. This work provides new inspiration for introducing traditional electroplating additives into high-performance ZMBs and gives researchers a direction for choosing electrolyte additives, which also has potential to be applied to other metal anodes.

Achieving Rapid Ultralow-Temperature Ion Transfer via Constructing Lithium-Anion Nanometric Aggregates to Eliminate Li+-Dipole Interactions.

Sluggish desolvation in extremely cold environments caused by strong Li+-dipole interactions is a key inducement for the capacity decline of a battery. Although the Li+-dipole interaction is reduced by increasing the electrolyte concentration, its high viscosity inevitably limits ion transfer at low temperatures. Herein, Li+-dipole interactions were eliminated to accelerate the migration rate of ions in electrolytes and at the electrode interface via designing Li+-anion nanometric aggregates (LA-nAGGs) in low-concentration electrolytes. Li+ coordinated by TFSI- and FSI- anions instead of a donor solvent promotes the formation of an inorganic-rich interfacial layer and facilitates Li+ transfer. Consequently, the LA-nAGG-type electrolyte demonstrated a high ionic conductivity (0.6 mS cm-1) at -70 °C and a low activation energy of charge transfer (38.24 kJ mol-1), enabling Li||NiFe-Prussian blue derivative cells to deliver ∼83.1% of their room-temperature capacity at -60 °C. This work provides an advanced strategy for the development of low-temperature electrolytes.

Sustained-Compensated Interfacial Zincophilic Sites to Assist High-Capacity Aqueous Zn Metal Batteries.

Aqueous Zn metal batteries have attracted extensive attention due to their intrinsic advantages. However, zinc ions tend to deposit irregularly, seriously depleting the capacity and stability of the battery. The construction of zincophilic sites can effectively regulate the nucleation and growth of Zn, but there is a defect that these sites will be covered with gradual failure after long-term cycling. Here, in combination with the sustained-compensated strategy, interfacial zincophilic sites are continuously constructed, thus effectively avoiding the threat of dendrites and improving the electrochemical performance. Impressively, at 10 mA cm-2 and 5 mAh cm-2, the protected Zn metal exhibits excellent cycling stability over 2000 cycles in the Zn//Zn battery. Moreover, even the cathode mass loading is considerably high (35 mg cm-2), and the Zn//NVO full cell significantly outperforms with high areal capacity (up to 4 mAh cm-2). This novel strategy provides a direction for the development of high-capacity aqueous batteries.

Extending Ring-Chain Coupling Empirical Law to Lithium-Mediated Electrochemical Ammonia Synthesis.

With its efficient nitrogen fixation kinetics, electrochemical lithium-mediated nitrogen reduction reaction (LMNRR) holds promise for replacing Haber-Bosch process and realizing sustainable and green ammonia production. However, the general interface problem in lithium electrochemistry seriously impedes the further enhancement of LMNRR performance. Inspired by the development history of lithium battery electrolytes, here, we extend the ring-chain solvents coupling law to LMNRR system to rationally optimize the interface during the reaction process, achieving nearly a two-fold Faradaic efficiency up to 54.78±1.60 %. Systematic theoretical simulations and experimental analysis jointly decipher that the anion-rich Li+ solvation structure derived from ring tetrahydrofuran coupling with chain ether successfully suppresses the excessive passivation of electrolyte decomposition at the reaction interface, thus promoting the mass transfer of active species and enhancing the nitrogen fixation kinetics. This work offers a progressive insight into the electrolyte design of LMNRR system.

Principles and Design of Biphasic Self-Stratifying Batteries Toward Next-Generation Energy Storage.

Large-scale energy storage devices play pivotal roles in effectively harvesting and utilizing green renewable energies (such as solar and wind energy) with capricious nature. Biphasic self-stratifying batteries (BSBs) have emerged as a promising alternative for grid energy storage owing to their membraneless architecture and innovative battery design philosophy, which holds promise for enhancing the overall performance of the energy storage system and reducing operation and maintenance costs. This minireview aims to provide a timely review of such emerging energy storage technology, including its fundamental design principles, existing categories, and prototype architectures. The challenges and opportunities of this undergoing research topic will also be systematically highlighted and discussed to provide guidance for the subsequent R&D of superior BSBs while conducive to bridging the gap for their future practical application.

Optimizing Intermediate Adsorption over PdM (M=Fe, Co, Ni, Cu) Bimetallene for Boosted Nitrate Electroreduction to Ammonia.

Electrochemical reduction of nitrate to ammonia (NO3RR) is a promising and eco-friendly strategy for ammonia production. However, the sluggish kinetics of the eight-electron transfer process and poor mechanistic understanding strongly impedes its application. To unveil the internal laws, herein, a library of Pd-based bimetallene with various transition metal dopants (PdM (M=Fe, Co, Ni, Cu)) are screened to learn their structure-activity relationship towards NO3RR. The ultra-thin structure of metallene greatly facilitates the exposure of active sites, and the transition metals dopants break the electronic balance and upshift its d-band center, thus optimizing intermediates adsorption. The anisotropic electronic characteristics of these transition metals make the NO3RR activity in the order of PdCu>PdCo≈PdFe>PdNi>Pd, and a record-high NH3 yield rate of 295 mg h-1 mgcat -1 along with Faradaic efficiency of 90.9 % is achieved in neutral electrolyte on PdCu bimetallene. Detailed studies further reveal that the moderate N-species (*NO3 and *NO2) adsorption ability, enhanced *NO activation, and reduced HER activity facilitate the NH3 production. We believe our results will give a systematic guidance to the future design of NO3RR catalysts.

Facilitating Reconstruction of the Heterointerface Electronic Structure by the Enriched Oxygen Vacancy for the Oxygen Evolution Reaction.

Exploring high-performance non-precious metal-based electrocatalysts for the sluggish oxygen evolution reaction (OER) process is fundamentally significant for the development of multifarious renewable energy conversion and storage systems. Oxygen vacancy (Vo) engineering is an effective leverage to boost the intrinsic activity of OER, but the underlying catalytic mechanism remains anfractuous. Herein, we realize the construction of oxygen vacancy-enriched porous NiO/ln2O3 nanofibers (designated as Vo-NiO/ln2O3@NFs hereafter) via a facile fabrication strategy for efficient oxygen evolution electrocatalysis. Theoretical calculations and experimental results uncover that, compared with the no-plasma engraving component, the presence of abundant oxygen vacancies in the Vo-NiO/ln2O3@NFs is conducive to modulating the electronic configuration of the catalyst, altering the adsorption of intermediates to reduce the OER overpotential and promote O* formation, upshifting the d band center of metal centers near the Fermi level (Ef), and also increasing the electrical conductivity and enhancing the OER reaction kinetics simultaneously. In situ Raman spectra proclaim that the oxygen vacancy can render the NiO/ln2O3 more easily reconstructible on the surface during the OER course. Therefore, the as-obtained Vo-NiO/ln2O3@NFs demonstrated distinguished OER activity, with an overpotential of only 230 mV at 10 mA cm-2 and excellent stability in alkaline medium, surmounting the majority of the previously reported representative non-noble metal-based candidates. The fundamental insights gained from this work can pave a new path for the electronic structure modulation of efficient, inexpensive OER catalysts via Vo engineering.

Surpassing the Redox Potential Limit of Organic Cathode Materials via Extended p-π Conjugation of Dioxin.

The key to enabling high energy density of organic energy-storage systems is the development of high-voltage organic cathodes; however, the redox voltage (<4.0 V vs Li/Li+) of state-of-the-art organic electrode materials (OEMs) remains unsatisfactory. Herein, we propose a novel dibromotetraoxapentacene (DBTOP) redox center to surpass the redox potential limit of OEMs, achieving ultrahigh discharge plateaus of approximately 4.4 V (vs Li+/Li). As theoretically analyzed, electron delocalization between dioxin active centers and benzene rings as well as electron-withdrawing bromine atoms endows the molecule with a low occupied molecular orbital level by diluting the electron density of dioxin in the whole p-π conjugated skeleton, and the strong π-π interactions among the DBTOP molecules provide a faster electrochemical kinetic pathway. This tetraoxapentacene redox center makes the working voltage of OEMS closer to the high-voltage inorganic electrodes, and its chemical and structural tunability may stimulate the further development of high-voltage organic cathodes.

New Type of Dynamically "Solid-Liquid" Interconvertible Electrolyte for High-Rate Zn Metal Battery.

The practical application of aqueous high-rate Zn metal battery (ZMB) is limited due to accelerated dendrite formation at high current densities. It is urgent to find an electrolyte, which could not only be mechanically stiff to clamp down dendrites but also not sacrifice ionic conductivity and interfacial compatibility. Herein, a new type of dynamically "solid-liquid" interconvertible electrolyte based on non-Newtonian fluid (NNFE) is proposed. Liquidity characteristic of NNFE is favorable for electrochemical kinetics and interfacial compatibility. Furthermore, in an area with high current rate NNFE would respond and mechanically stiffen to dissuade localized increase in Zn dendrite growth. Even at a current density of 50 mA cm-2, NNFE enables reversible and stable operation of a Zn symmetrical cell over 20 000 cycles. For Zn//Na5V12O32 (NVO) full cell, the NNFE also realizes lengthy cycling for 5000 periods at 5 A g-1. This research opens up new inspirations to high-rate Zn metal even other metal batteries.

Vibration-driven Reduction of CO2 to Acetate with 100 % Selectivity by SnS Nanobelt Piezocatalysts.

Converting CO2 into high-value C2 chemicals such as acetate with high selectivity and efficiency is a critical issue in renewable energy storage. Herein, for the first time we present a vibration-driven piezocatalysis with tin(II) monosulfide (SnS) nanobelts for conversion of CO2 to acetate with 100 % selectivity, and the highest production rate (2.21 mM h-1 ) compared with reported catalysts. Mechanism analysis reveal that the polarized charges triggered by periodic mechanical vibration promote the adsorption and activation of CO2 . The electron transfer can be facilitated due to built-in electric field, decreased band gap and work function of SnS under stress. Remarkably, reduced distance between active sites leads to charge enrichment on Sn sites, promoting the C-C coupling, reducing the energy barriers of the rate determining step. It puts forward a bran-new strategy for converting CO2 into high-value C2 products with efficient, low-cost and environment-friendly piezocatalysis utilizing mechanical energy.

Eliminating Concentration Polarization with Cationic Covalent Organic Polymer to Promote Effective Overpotential of Nitrogen Fixation.

Electrocatalytic nitrogen reduction reaction offers a sustainable alternative to the conventional Haber-Bosch process. However, it is currently restricted by low effective overpotential due to the concentration polarization, which arises from accumulated products, ammonium, at the reaction interface. Here, a novel covalent organic polymer with ordered periodic cationic sites is proposed to tackle this challenge. The whole network exhibits strong positive charge and effectively repels the positively charged ammonium, enabling an ultra-low interfacial product concentration, and successfully driving the reaction equilibrium to the forward direction. With the given potential unchanged, the suppressed overpotential can be much liberated, ultimately leading to a continuous high-level reaction rate. As expected, when this tailored microenvironment is coupled with a transition metal-based catalyst, a 24-fold improvement is generated in the Faradaic efficiency (73.74 %) as compared with the bare one. The proposed strategy underscores the importance of optimizing dynamic processes as a means of improving overall performance in electrochemical syntheses.

Propagation of Spin Waves in a 2D Vortex Network.

Efficient propagation of spin waves in a magnetically coupled vortex is crucial to the development of future magnonic devices. Thus far, only a double vortex can serve as spin-wave emitter or oscillator; the propagation of spin waves in the higher-order vortex is still lacking. Here, we experimentally realize a higher-order vortex (2D vortex network) by a designed nanostructure, containing four cross-type chiral substructures. We employ this vortex network as a waveguide to propagate short-wavelength spin waves (∼100 nm) and demonstrate the possibility of guiding spin waves from one vortex to the network. It is observed that the spin waves can propagate into the network through the nanochannels formed by the Bloch-Néel-type domain walls, with a propagation decay length of several micrometers. This technique paves the way for the development of low-energy, reprogrammable, and miniaturized magnonic devices.

Healable Lithium Alloy Anode with Ultrahigh Capacity.

Effective recycling of spent Li metal anodes is an urgent need for energy/resource conservation and environmental protection, making Li metal batteries more affordable and sustainable. For the first time, we explore a unique sustainable healable lithium alloy anode inspired by the intrinsic healing ability of liquid metal. This lithium alloy anode can transform back to the liquid state through Li-completed extraction, and then the structure degradation generated during operation could be healed. Therefore, an ultralong cycle life of more than 1300 times can be successfully realized under harsh conditions of 5 mA h cm-2 capacitance by a process of two healing behaviors. This design improves the sustainable utilization of Li metal to a great extent, bringing about unexpected effects in the field of lithium-based anodes even at an unprecedentedly high discharge current density (up to 25 mA cm-2) and capacity (up to 50 mA h cm-2).

Identification of iron ore brands by multi-component analysis and chemometric tools.

Identification of iron ore brand is one of the most important precautions against fraud in the international iron ore trade. However, the identification of iron ore brand can be sophisticated, due to fact that the role played by multi-component in iron ore brand identification was unclear. This study aims to establish an objective approach to identify iron ore brands based on their multi-component content. A total of 1469 batches of iron ore samples, covering 16 commonly consumed iron ore brands from 3 countries, were analyzed for multi-component content. It was investigated that 10 primary, minor, and trace chemical components varied significantly in contents according to different iron ore brands. This prospective relationship between the multi-component contents and the iron ore brand was then used to place 16 brands into 12 groups and 8 brands of them were correctly identified by a flowchart. Furthermore, chemometric tools such as linear discriminant analysis (LDA), k-nearest neighbor (k-NN), and support vector machine (SVM) were applied to construct models to simultaneously discriminate 16 iron ore brands. Both the training and test results proved that LDA performed best in this circumstance. In the LDA method, MgO, Fe, SiO2, and P are the feature components contributing the most to the identification of 16 brands of iron ore. Based on the findings, the multi-components are distinct variables to establish an internationally recognized model of iron ore brand identification.

Magnetic-Photoacoustic Dual-Mode Probe for the Visualization of H2S in Colorectal Cancer.

Techniques for the qualitative and quantitative detection of H2S in vivo have attracted considerable attention due to the key role of H2S in various physiological and pathological processes. However, in vivo detection strategies for H2S are mainly based on fluorescence imaging, which is limited by its poor tissue penetration. Moreover, the limitations of single-mode probes are amplified in complex physiological environments. Herein, a core-shell Fe3O4@Cu2O nanoparticle was constructed as a magnetic-photoacoustic dual-mode probe for H2S detection in vitro and in vivo based on the in situ response of Cu2O to endogenous H2S in colon tumors. This probe is expected to greatly improve the accuracy of H2S detection in vivo because it employs two detection methods with complementary advantages. The new probe was experimentally applied to the in vivo and in vitro visualization of H2S in mice with colorectal cancer, validating the in situ reaction-activated dual-detection method. This work establishes a simple and efficient dual-mode imaging method based on a novel trigger mechanism. The findings provide a new strategy for colon cancer detection based on the in situ reactions at tumor sites.

Mechanically Robust Gel Polymer Electrolyte for an Ultrastable Sodium Metal Battery.

Sodium dendrite growth is responsible for short circuiting and fire hazard of metal batteries, which limits the potential application of sodium metal anode. Sodium dendrite can be effectively suppressed by applying mechanically robust electrolyte in battery systems. Herein, a composite gel polymer electrolyte (GPE) is designed and fabricated, mainly consisting of graphene oxide (GO) and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP). With the addition of an appropriate amount of GO content, the compressive Young's modulus of 2 wt% GO+PVDF-HFP (2-GPH) composite GPE is greatly enhanced by a factor of 10, reaching 2.5 GPa, which is crucial in the suppression of sodium dendrite growth. As a result, uniform sodium deposition and ultralong reversible sodium plating/stripping (over 400 h) at high current density (5 mA cm-2 ) are achieved. Furthermore, as evidenced by molecular dynamics simulation, the GO content facilitates the sodium ion transportation, giving a high ionic conductivity of 2.3 × 10-3 S cm-1 . When coupled with Na3 V2 (PO4 )3 cathode in a full sodium metal battery, a high initial capacity of 107 mA h g-1 at 1 C (1 C = 117 mA g-1 ) is recorded, with an excellent capacity retention rate of 93.5% and high coulombic efficiency of 99.8% after 1100 cycles.

Strongly trapping soluble lithium polysulfides using polar cysteamine groups for highly stable lithium sulfur batteries.

Sulfur has become one of the most promising positive electrode materials for lithium sulfur batteries due to its high theoretical capacity and high energy density (2500 Wh kg-1). The use of common nonpolar carbon/sulfur composites has proved to be a good way to improve the performance, but they still cannot efficiently trap highly polar lithium polysulfides due to the weak interactions between nonpolar carbon and polar polysulfides. Herein, we report a new strategy of using polar cysteamine groups to trap polar polysulfides, leading to greatly enhanced capacity of ∼920 mAh g-1 at 1 C with a high Coulombic efficiency of ∼99.1%, and a long cycle life of over 600 cycles with a capacity retention higher than 80%. Importantly, in situ UV/Vis spectroscopy was employed to identify intermediates during cycling, which demonstrates the constructed unique polar cysteamine functionalized carbon nanotubes (CNTs) can greatly reduce the production of polysulfides and suppress the shuttle effect. The broken-bond model of linear polysulfane during cycling was further demonstrated by density functional theory calculations. The present strategy of using polar cysteamine-functionalized CNTs to trap soluble intermediates is promising and has significant potential for the development of highly efficient lithium sulfur batteries.