Revealing the Effect of the Microstructure on Potassium Storage Behavior in a Two-Dimensional Mesoporous Carbon Anode.

Hard carbon is considered as the most promising anode material for potassium-ion energy storage devices. Substantial progress has been made in exploring advanced hard carbons to solve the issues of sluggish kinetics and large volume changes caused by the large radius of K+. However, the relationship between their complicated microstructures and the K+ charge storage behavior is still not fully explored. Herein, a series of two-dimensional mesoporous carbon microcoins (2D-MCMs) with tunable microstructures in heteroatom content and graphitization degree are synthesized by a facile hard-template method and follow a temperature-controllable annealing process. It is found that high heteroatom content makes for surface-driven K+ storage behavior, which increases the capacity-contribution ratio from a high potential region, while a high graphitization degree makes for K+ intercalation behavior, which increases the capacity-contribution ratio from a low potential region. Electrochemical results from a three-electrode Swagelok cell demonstrate that a 2D-MCM anode with more capacity contribution from a low working region allows the porous carbon cathode to be operated in a much wider electrochemical window, thus storing more charge. As a result, potassium-ion capacitors based on the optimized 2D-MCM anode deliver a high energy density of 113 Wh kg-1 and an exhilarating power density of 51,000 W kg-1.

Robust All-Solid-State Lithium Metal Batteries Enabled by a Composite Lithium Anode with Improved Bulk Li Diffusion Kinetics Properties.

All-solid-state batteries (ASSBs) with a Li metal anode are expected to be one of the most promising energy storage systems to achieve high energy density. However, the interfacial instability between the Li metal anode and solid-state electrolyte (SSE) limits the rate capability and cycling stability of ASSBs. The main issue is the formation of voids at the Li/SSE interface during Li stripping due to the slow diffusion of Li within the bulk Li metal, then increasing internal cell resistance and inducing the formation of lithium dendrites. To address these issues, a composite Li anode (LAO) composed by Li-Ag alloy and Li2O is constructed by mixing the stoichiometric metal Li and Ag2O directly. LAO anode is capable of improving bulk Li diffusion kinetics and inhibiting the formation of interfacial voids effectively, achieving a high critical current density over 1.5 mA cm-2 and long stable cycling over 1000 h at 1 mA cm-2. The ASSBs, employing LAO as the anode, Li6PS5Cl as the SSE, and LiCoO2 as the cathode, exhibit superior rate capability and stable cycling over 4000 cycles at 5 C. Moreover, ASSBs can operate stably with a high LiCoO2 loading of 17.8 mg cm-2 for more than 100 cycles at 0.2 C.

Competitive Li+ Coordination in Ionogel Electrolytes for Enhanced Li-Ion Transport Kinetics.

Developing ionogel electrolytes based on ionic liquid instead of volatile liquid in gel polymer electrolytes is regarded to be effective to diminish safety concerns in terms of overheating and fire. Herein, a zwitterion-based copolymer matrix based on the copolymerization of trimethylolpropane ethoxylate triacrylate (ETPTA) and 2-methacryloyloxyethylphosphorylcholine (MPC, one typical zwitterion) is developed. It is shown that introducing zwitterions into ionogel electrolytes can effectively optimize local lithium-ion (Li+ ) coordination environment to improve Li+ transport kinetics. The interactions between Li+ and bis(trifluoromethanesulfonyl)imide (TFSI- )/MPC lead to the formation of Li+ coordination shell jointly occupied by MPC and TFSI- . Benefiting from the competitive Li+ attraction of TFSI- and MPC, the energy barrier of Li+ desolvation is sharply decreased and thus the room-temperature ionic conductivity can reach a value of 4.4 × 10-4 S cm-1 . Besides, the coulombic interaction between TFSI- and MPC can greatly decrease the reduction stability of TFSI- , boosting in situ derivation of LiF-enriched solid electrolyte interface  layer on lithium metal surface. As expected, the assembled Li||LiFePO4 cells deliver a high reversible discharge capacity of 139 mAh g-1 at 0.5 C and good cycling stability. Besides, the pouch cells exhibit a steady open-circuit voltage and can operate normally under abuse testing (fold, cut), showing its outstanding safety performance.

Electron Acceptor Molecule Doping Induced π-π Interaction to Promote Charge Transport Kinetics for Efficient and Stable 2D/3D Perovskite Solar Cells.

Although the incorporation of 2D perovskite into 3D perovskite can greatly enhance intrinsic stability, power conversion efficiency (PCE) of 2D/3D perovskite is still inferior to its 3D counterpart due to poor carrier transport kinetics resulted from the quantum and dielectric confinement of 2D component. To overcome this issue, the electron acceptor molecule 1,2,4,5-tetracyanobenzene (TCNB) was introduced to trigger intermolecular π-π interaction in 2D perovskite along with the electronic doping of 2D/3D perovskite to improve charge transfer efficiency. By virtue of high electron affinity, TCNB can undergo electron transfer reaction and subsequently establish π-π interaction with 1-naphthalenemethylammonium (NMA) cations, greatly strengthening lattice rigidity and reducing exciton binding energy. Transmission electron microscopy results demonstrate that 2D phases are mainly distributed at grain boundaries, reducing defect density and weakening nonradiative recombination. Meanwhile, the p-type doping of perovskite by TCNB optimizes energy level alignment at perovskite/hole transport layer interface. Consequently, PCE of champion device is significantly boosted to 24.01 %. The unencapsulated device retains an initial efficiency close to 94 % after exposure to ambient environment for over 1000 h. This work paves a novel path for designing new mixed-dimensional perovskite solar cells with high PCE and superior stability.

Intrinsic Dipole Arrangement to Coordinate Energy Levels for Efficient and Stable Perovskite Solar Cells.

Despite great progress in perovskite photovoltaics, it should be noted that the intrinsic disorder dipolar cations in organic-inorganic hybrid perovskites exert negative effects on the energy band structure as well as the carrier separation and transfer dynamics. However, oriented polarization achieved by applying an external electric field may cause irreversible damage to perovskites. Herein, a unique and efficient strategy is developed to modulate the intrinsic dipole arrangement in perovskite films for high-performance and stable perovskite solar cells (PSCs). The spontaneous reorientation of dipolar cation methylamine is triggered by a polar molecule, constructing a vertical polarization during crystallization regulation. The oriented dipole determines a gradient energy-level arrangement in PSCs and more favorable energetics at interfaces, effectively enhancing the built-in electric field and suppressing the nonradiative recombination. Besides, the dipole reorientation induces a local dielectric environment to remarkably reduce exciton binding energy, leading to an ultralong carrier diffusion length of up to 1708 nm. Accordingly, the n-i-p PSCs achieve a significant increase in power conversion efficiency, reaching 24.63% with negligible hysteresis and exhibiting outstanding stabilities. This strategy also provides a facile route to eliminate the mismatched energetics and enhance carrier dynamics for other novel photovoltaic devices.

Hexaindium Heptasulfide/Nitrogen and Sulfur Co-Doped Carbon Hollow Microspindles with Ultrahigh-Rate Sodium Storage through Stable Conversion and Alloying Reactions.

Group IIIA-VA metal sulfides (GMSs) have attracted increasing attention because of their unique Na-storage mechanisms through combined conversion and alloying reactions, thus delivering large theoretical capacities and low working potentials. However, Na+ diffusion within GMSs anodes leads to severe volume change, generally representing a fundamental limitation to rate capability and cycling stability. Here, monodispersed In6 S7 /nitrogen and sulfur co-doped carbon hollow microspindles (In6 S7 /NSC HMS) are produced by morphology-preserved thermal sulfurization of spindle-like and porous indium-based metal organic frameworks. The resulting In6 S7 /NSC HMS anode exhibits theoretical-value-close specific capacity (546.2 mAh g-1 at 0.1 A g-1 ), ultrahigh rate capability (267.5 mAh g-1 at 30.0 A g-1 ), high initial coulombic efficiency (≈93.5%), and ≈92.6% capacity retention after 4000 cycles. This kinetically favored In6 S7 /NSC HMS anode fills up the kinetics gap with a capacitive porous carbon cathode, enabling a sodium-ion capacitor to deliver an ultrahigh energy density of 136.3 Wh kg-1 and a maximum power density of 47.5 kW kg-1 . The in situ/ex situ analytical techniques and theoretical calculation both show that the robust and fast Na+ charge storage of In6 S7 /NSC HMS arises from the multi-electron redox mechanism, buffered volume expansion, negligible morphological change, and surface-controlled solid-state Na+ transport.

New Conceptual Catalyst on Spatial High-Entropy Alloy Heterostructures for High-Performance Li-O2 Batteries.

High-entropy alloys (HEAs) are attracting increased attention as an alternative to noble metals for various catalytic reactions. However, it is of great challenge and fundamental importance to develop spatial HEA heterostructures to manipulate d-band center of interfacial metal atoms and modulate electron-distribution to enhance electrocatalytic activity of HEA catalysts. Herein, an efficient strategy is demonstrated to construct unique well-designed HEAs spatial heterostructure electrocatalyst (HEA@Pt) as bifunctional cathode to accelerate oxygen reduction and evolution reaction (ORR/OER) kinetics for Li-O2 batteries, where uniform Pt dendrites grow on PtRuFeCoNi HEA at a low angle boundary. Such atomically connected HEA spatial interfaces engender efficient electrons from HEA to Pt due to discrepancy of work functions, modulating electron distribution for fast interfacial electron transfer, and abundant active sites. Theoretical calculations reveal that electron redistribution manipulates d-band center of interfacial metal atoms, allowing appropriate adsorption energy of oxygen species to lower ORR/OER reaction barriers. Hence, Li-O2 battery based on HEA@Pt electrocatalyst delivers a minimal polarization potential (0.37 V) and long-term cyclability (210 cycles) under a cut-off capacity of 1000 mAh g-1 , surpassing most previously reported noble metal-based catalysts. This work provides significant insights on electron-modulation and d-band center optimization for advanced electrocatalysts.

A Silica-Reinforced Composite Electrolyte with Greatly Enhanced Interfacial Lithium-Ion Transfer Kinetics for High-Performance Lithium Metal Batteries.

Developing quasi-solid-state electrolytes with superior ionic conductivity and high mechanical strength is urgently desired to improve the safety and cycling stability of lithium-metal batteries. Herein, a novel solid-like electrolyte (SLE) with enhanced Li+ interfacial transfer kinetics is rationally designed by soaking bulk nanostructured silica-polymer composites in liquid electrolytes. Benefiting from the high content of inorganic silica and abundant interfaces for fast Li+ -transport channels, the prepared SLE exhibits superb ionic conductivity and high mechanical strength. Furthermore, fumed silica with a high specific area in the SLE can homogenize Li+ flux and electrical field gradient. More importantly, a Li2 S-rich solid electrolyte interphase (SEI) is constructed on the lithium metal due to the intimate ion coordination in the SLE. Therefore, the lithium-metal anode exhibits excellent electrochemical performance in symmetric Li-Li cells due to the merits of superior ionic conductivity, high modulus, Li2 S-rich SEI, as well as the homogeneous Li+ flux. Full cells with LiFePO4 cathode can still display a capacity retention of 98% at 0.2 C after 400 cycles. The proposed strategy on quasi-solid-state electrolytes provides a promising avenue for next-generation metal-based batteries.

Simultaneous removal of arsenite and arsenate from mining wastewater using ZIF-8 embedded with iron nanoparticles.

Arsenic contamination is an increasing global environmental problem, especially in mining industry wastewater where both arsenite (As(III)) and arsenate (As(V)) have been routinely detected. In this paper, a novel porous metal-organic framework material (ZIF-8) was composited with iron nanoparticles (FeNPs) to form a functional material (ZIF-8@FeNPs) for the simultaneous removal of As(III)/(V) from wastewater. The material effectively removed both As(III) and As(V) with removal efficiencies of 99.9 and 71.2%, respectively. Advanced characterization techniques including X-ray photoelectron spectroscopy (XPS) and Fourier infrared (FTIR) indicated that removal of As(III) and As(V) involved complex formation. Adsorption kinetics followed a pseudo-second order kinetics indicating adsorption involved chemisorption. After four cycles of reuse the he removal rate of As species was still relatively high at > 60% When ZIF-8@FeNPs were used to remove As from real wastewater from acid mines the removal efficiency was 94.27%. Finally, a As(III) and As(V) removal mechanism was proposed.

Pseudohalide Anions to Suppress Oxidative Degradation for Efficient Formamidinium-Based Sn-Pb Halide Perovskite Solar Cells.

Although binary Sn-Pb perovskites possess optimal band gap approaching to the Shockley-Queisser limit efficiency, the enhancement on power conversion efficiency (PCE) of Sn-Pb perovskite solar cells (PSCs) is impeded by the detrimental oxidation of Sn2+. Herein, a novel and effective strategy is developed to introduce pseudohalide anion thiocyanate (SCN-) with similar ionic radius to iodide to occupy the X-site of the perovskite lattice, thus restraining the rapid oxidation of Sn2+ to Sn4+. The incorporation of SCN- into perovskite stabilizes the perovskite crystal structure thermodynamically and increases the adsorption-energy-barrier of oxygen molecules. The coordination between Sn2+ and SCN- can reduce the defect density by healing the undercoordinated Sn2+ and suppressing the Sn and I vacancies. With the incorporation of SCN-, the ion migration behavior and lattice strain associated with the defects are remarkably relaxed. The study on carrier dynamics based on steady-state and time-resolved photoluminescence suggests that the carrier lifetime and non-radiative recombination rate of SCN- PSCs can be remarkably prolonged and depressed, respectively. As a result, FASn0.5Pb0.5I3-based PSCs achieve a 14.5% increase in PCE, reaching 13.74% under AM 1.5G illumination. This strategy takes a noteworthy step toward high efficiency and high stability FA-based Sn-Pb PSCs.

Achieve Stable Lithium Metal Anode by Sulfurized-Polyacrylonitrile Modified Separator for High-Performance Lithium Batteries.

To develop a high-energy-density lithium battery, there still are several severe challenges for Li metal anode: low Coulombic efficiency caused by its high chemical reactivity, Li dendrite formation, and "dead" Li accumulation during repeated plating/stripping processes. Especially, lithium dendrite growth imposes inferior cycling stability and serious safety issues. Herein, we propose a facile but effective strategy to suppress lithium dendrite growth through an artificial inorganic-polymer protective layer derived from sulfurized polyacrylonitrile on a polyethylene separator. Benefiting from the lithiated sulfurized polyacrylonitrile and poly(acrylic acid), the flexible and ion-conductive protective layer could regulate Li+ flux and facilitate dendrite-free lithium deposition. Consequently, lithium metal with the meritorious protective layer can achieve a long-term cycling with negligible overpotential rise in Li-Li symmetric cells, even at a high areal capacity of 5 mAh cm-2. Remarkably, such a protective layer enables stable cycling performance of Li-S cell with a high areal capacity (∼9 mAh cm-2). This work provides a valuable exploration strategy for potential industrial applications of high-performance lithium metal batteries.

Superimposed Effect of La Doping and Structural Engineering to Achieve Oxygen-Deficient TiNb2O7 for Ultrafast Li-Ion Storage.

TiNb2O7 (TNO) is a competitive candidate of a fast-charging anode due to its high specific capacity. However, the insulator nature seriously hinders its rate performance. Herein, the La3+-doped mesoporous TiNb2O7 materials (La-M-TNO) were first synthesized via a facile one-step solvothermal method with the assistance of polyvinyl pyrrolidone (PVP). The synergic effect of La3+ doping and the mesoporous structure enables a dual improvement on the electronic conductivity and ionic diffusion coefficient, which delivers an impressive specific capacity of 213 mAh g-1 at 30 C. The capacity retention (@30C/@1C) increases from 33 to 53 and 74% for TNO, M-TNO, and La-M-TNO (0.03), respectively, demonstrating a step-by-step improvement of rate performance by making porous structures and intrinsic conductivity enhancement. DFT calculations verify that the enhancement in electronic conductivity due to La3+ doping and oxygen vacancy, which induce localized energy levels via slight hybridization of O 2p, Ti 3d, and Nb 4d orbits. Meanwhile, the GITT result indicates that PVP-induced self-assembly of TNO accelerates the lithium ion diffusion rate by shortening the Li+ diffusion path. This work verifies the effectiveness of the porous structure and highlights the significance of electronic conductivity to rate performance, especially at >30C. It provides a general approach to low-conductivity electrode materials for fast Li-ion storage.

Oxide Nanoclusters on Ti3 C2 MXenes to Deactivate Defects for Enhanced Lithium Ion Storage Performance.

The commercialization of MXenes as anodes for lithium-ion batteries is largely impeded by low initial coulombic efficiency (ICE) and unfavorable cycling stability, which are closely associated with defects such as Ti vacancies (VTi ) in Ti3 C2 MXenes. Herein, an effective strategy is developed to deactivate VTi defects by in situ growing Al2 O3 nanoclusters on MXenes to alleviate the irreversible electrolyte decomposition and Li dendrites formation trend induced by defects, improving ICE and cycling stability. Furthermore, it is revealed that excessively lithiophilic VTi defects would impede Li ions diffusion due to their strong adsorption, leading to a locally nonuniform Li flux to these "hot spots," setting scene for the formation of Li dendrites. The Al2 O3 nanoclusters anchored on VTi sites can not only improve Li diffusion kinetics but also promote the homogeneous solid electrolyte interphase formation with small charge transfer resistance, achieving uniform Li deposition in a smaller overpotential without formation of Li dendrites. As expected, Ti3 C2 @Al2 O3 -11 electrode delivers a high ICE of 76.6% and an outstanding specific capacity of 285.5 mAh g-1 after 500 cycles, which is much higher than that of pristine Ti3 C2 sample. This work sheds light on modulating defects for high-performance energy storage materials.

Stiffening the Pb-X Framework through a π-Conjugated Small-Molecule Cross-Linker for High-Performance Inorganic CsPbI2Br Perovskite Solar Cells.

Inorganic CsPbI2Br perovskites have witnessed incredible advances as a promising representative for translucent and tandem solar cells, but unfortunately, they are still plagued by serious energy losses and undesired phase instability. Herein, a new type of π-conjugated small molecule of 4-guanidinobenzoic-acid-hydrochloride (4-GBACl) is demonstrated to effectively cross-link the Pb-X framework of perovskites. The strong coordination between 4-GBACl and the [PbX6]4- octahedron of perovskites effectively stiffens the Pb-X framework to suppress the ion migration, thus stabilizing the perovskite phase structure against light and thermal conditions. Apart from the physical barrier for phase instability resulting from the hydrophobic benzene ring at grain boundaries (GBs), guanidinium cations and -COOH and Cl- groups can simultaneously afford the passivation of positively and negatively charged defects at the GBs and surface, including undercoordinated halide species and undercoordinated Pb2+ ions, thereby effectively inhibiting the charge trapping/recombination centers. Two-dimensional confocal-fluorescence mapping images provide a visualized sight into the significantly suppressed nonradiative recombination and the prolonged carrier lifetime. It is suggested that the 4-GBACl additive plays multiple roles in grain cross-linking to regulate crystallization, distinctly reducing the trap-state density, ion migration inhibition, and moisture barrier in CsPbI2Br films. Consequently, the 4-GBACl-treated device exhibits a champion power conversion efficiency (PCE) of 15.59% accompanied with a considerably improved Voc of 1.28 V and maintains 88% of the initial PCE value after 1200 h aging under 20% relative humidity.

Metal-Organic Framework-Derived Nitrogen-Doped Cobalt Nanocluster Inlaid Porous Carbon as High-Efficiency Catalyst for Advanced Potassium-Sulfur Batteries.

Despite high theoretical capacity and earth-abundant resources, the potential industrialization of potassium-sulfur (K-S) batteries is severely plagued by poor electrochemical reaction kinetics and a parasitic shuttle effect. Herein, a facile low-temperature pyrolysis strategy is developed to synthesize N-doped Co nanocluster inlaid porous N-doped carbon derived from ZIF-67 as catalytic cathodes for K-S batteries. To maximize the utilization efficiency, the size of Co nanoparticles can be tuned from 7 nm to homogeneously distributed 3 nm clusters to create more active sites to regulate affinity for S/polysulfides, improving the conversion reaction kinetics between captured polysulfides and K2S3/S, fundamentally suppressing the shuttle effect. Cyclic voltammetry curves, Tafel plots, electrochemical impedance spectroscopy, and density functional theory calculations ascertain that 3 nm Co clusters in S-N-Cos-C cathodes exhibit superior catalytic activity to ensure low charge transfer resistance and energy barriers, enhanced exchange current density, and improved conversion reaction rate. The constructed S-N-Cos-C cathode delivers a superior reversible capacity of 453 mAh g-1 at 50 mA g-1 after 50 cycles, a dramatic rate capacity of 415 mAh g-1 at 400 mA g-1, and a long cycling stability. This work provides an avenue to make full use of high catalytic Co nanoclusters derived from metal-organic frameworks.

Encapsulating Ultrafine Sb Nanoparticles in Na+ Pre-Intercalated 3D Porous Ti3C2Tx MXene Nanostructures for Enhanced Potassium Storage Performance.

Taking into consideration the advantages of the highly theoretical capacity of antimony (Sb) and abundant surface redox reaction sites of Na+ pre-intercalated 3D porous Ti3C2Tx (Na-Ti3C2Tx) architectures, we elaborately designed the Sb/Na-Ti3C2Tx hybrid with Sb nanoparticles homogeneously distributed in 3D porous Na-Ti3C2Tx architectures through a facile electrostatic attraction and carbothermic reduction process. Na-Ti3C2Tx architectures with more open structures and larger active specific surface area not only could certainly alleviate volume changes and hinder the aggregation of Sb nanoparticles in the cycling process to improve the structural stability but also significantly strengthen the electron-transfer kinetics and provide unblocked K+ diffusion channels to promote ionic/electronic transport rate. Furthermore, the ultrafine Sb nanoparticles could efficiently shorten K+ transport distance and expose more accessible active sites to improve capacity utilization. DFT calculations further indicate that the Sb/Na-Ti3C2Tx anode effectively decreases the adsorption energy of K+ and accelerates the potassiation process. Benefiting from the synergistic effect, it exhibits an outstanding specific capacity of 392.2 mAh g-1 at 0.1 A g-1 after 450 cycles and a stable capacity reservation with a capacity fading rate of 0.03% per cycle at 0.5 A g-1. Our work may encourage further research on advanced MXene-based hybrid materials for high-performance PIBs.

Atomically dispersed cobalt catalyst anchored on nitrogen-doped carbon nanosheets for lithium-oxygen batteries.

Developing single-site catalysts featuring maximum atom utilization efficiency is urgently desired to improve oxidation-reduction efficiency and cycling capability of lithium-oxygen batteries. Here, we report a green method to synthesize isolated cobalt atoms embedded ultrathin nitrogen-rich carbon as a dual-catalyst for lithium-oxygen batteries. The achieved electrode with maximized exposed atomic active sites is beneficial for tailoring formation/decomposition mechanisms of uniformly distributed nano-sized lithium peroxide during oxygen reduction/evolution reactions due to abundant cobalt-nitrogen coordinate catalytic sites, thus demonstrating greatly enhanced redox kinetics and efficiently ameliorated over-potentials. Critically, theoretical simulations disclose that rich cobalt-nitrogen moieties as the driving force centers can drastically enhance the intrinsic affinity of intermediate species and thus fundamentally tune the evolution mechanism of the size and distribution of final lithium peroxide. In the lithium-oxygen battery, the electrode affords remarkably decreased charge/discharge polarization (0.40 V) and long-term cyclability (260 cycles at 400 mA g-1).