A Dielectric MXene-Induced Self-Built Electric Field in Polymer Electrolyte Triggering Fast Lithium-Ion Transport and High-Voltage Cycling Stability.

Quasi-solid polymer electrolyte (QPE) lithium (Li)-metal battery holds significant promise in the application of high-energy-density batteries, yet it suffers from low ionic conductivity and poor oxidation stability. Herein, a novel self-built electric field (SBEF) strategy is proposed to enhance Li+ transportation and accelerate the degradation dynamics of carbon-fluorine bond cleavage in LiTFSI by optimizing the termination of MXene. Among them, the SBEF induced by dielectric Nb4C3F2 MXene effectively constructs highly conductive LiF-enriched SEI and CEI stable interfaces, moreover, enhances the electrochemical performance of the QPE. The related Li-ion transfer mechanism and dual-reinforced stable interface are thoroughly investigated using ab initio molecular dynamics, COMSOL, XPS depth profiling, and ToF-SIMS. This comprehensive approach results in a high conductivity of 1.34 mS cm-1, leading to a small polarization of approximately 25 mV for Li//Li symmetric cell after 6000 h. Furthermore, it enables a prolonged cycle life at a high voltage of up to 4.6 V. Overall, this work not only broadens the application of MXene for QPE but also inspires the great potential of the self-built electric field in QPE-based high-voltage batteries.

Stabilizing Highly Active Ru Sites by Electron Reservoir in Acidic Oxygen Evolution.

Proton exchange membrane water electrolysis is hindered by the sluggish kinetics of the anodic oxygen evolution reaction. RuO2 is regarded as a promising alternative to IrO2 for the anode catalyst of proton exchange membrane water electrolyzers due to its superior activity and relatively lower cost compared to IrO2. However, the dissolution of Ru induced by its overoxidation under acidic oxygen evolution reaction (OER) conditions greatly hinders its durability. Herein, we developed a strategy for stabilizing RuO2 in acidic OER by the incorporation of high-valence metals with suitable ionic electronegativity. A molten salt method was employed to synthesize a series of high-valence metal-substituted RuO2 with large specific surface areas. The experimental results revealed that a high content of surface Ru4+ species promoted the OER intrinsic activity of high-valence doped RuO2. It was found that there was a linear relationship between the ratio of surface Ru4+/Ru3+ species and the ionic electronegativity of the dopant metals. By regulating the ratio of surface Ru4+/Ru3+ species, incorporating Re, with the highest ionic electronegativity, endowed Re0.1Ru0.9O2 with exceptional OER activity, exhibiting a low overpotential of 199 mV to reach 10 mA cm-2. More importantly, Re0.1Ru0.9O2 demonstrated outstanding stability at both 10 mA cm-2 (over 300 h) and 100 mA cm-2 (over 25 h). The characterization of post-stability Re0.1Ru0.9O2 revealed that Re promoted electron transfer to Ru, serving as an electron reservoir to mitigate excessive oxidation of Ru sites during the OER process and thus enhancing OER stability. We conclude that Re, with the highest ionic electronegativity, attracted a mass of electrons from Ru in the pre-catalyst and replenished electrons to Ru under the operating potential. This work spotlights an effective strategy for stabilizing cost-effective Ru-based catalysts for acidic OER.

Li ions traffic controller on thin lithium metal anode: Regulating deposition, optimizing and protecting solid electrolyte interphase.

The performance of thin lithium metal anodes is affected due to issues that weaken the electrode-electrolyte interphase. In this work, a coating layer serving as a Li+ traffic controller based on hexadecyl trimethyl ammonium bis(trifluoromethanesulphonyl)imide ([CTA][TFSI]) and poly (vinylidene difluoride co-hexafluoropropylene) (P(VDF-HFP)) is used to stabilize the thin lithium metal interface. The CTA+ ions in the coating layer can effectively regulate the distribution of Li+ concentration to promote uniform deposition of lithium. The anion of [CTA][TFSI] can optimize solid electrolyte interphase (SEI) with inorganic-rich components, which improve the ionic conductivity and reaction kinetics. Furthermore, the flexible polymer skeleton can fortify the fragile SEI, facilitating the consistent operation of the battery. Due to these improvements, a thin Li metal anode (4 mAh cm-2) with a coating layer in a Li||Li symmetric cell demonstrates a lifespan of 600 h at 1 mA cm-2 and 1 mAh cm-2. Notably, full cells with an ultra-low negative electrode/positive electrode = 1 (N/P = 1) demonstrate a stable performance over 200 cycles and 90 cycles at 0.5C and 1C (1C = 170 mA g-1), respectively.

Constructing a Topologically Adaptable Solid Electrolyte Interphase for a Highly Reversible Zinc Anode.

The performance of aqueous zinc metal batteries is significantly compromised by the stability of the solid electrolyte interphase (SEI), which is intimately linked to the structure of the electrical double layer (EDL) between the zinc anode and electrolyte. Furthermore, understanding the mechanical behavior of SEI is crucial, as it governs its response to stress induced by volume changes, fracture, or deformation. In this study, we introduce l-glutamine (Gln) as an additive to regulate the adsorbed environment of the EDL and in situ produce a hybrid SEI consisting of ZnS and Gln-related species. The results of the nanoindentation test indicate that the hybrid SEI exhibits a low modulus and low hardness, alongside exceptional shape recovery capability, which effectively limits side reactions and enables topological adaptation to volume fluctuations in zinc anodes during zinc ion plating/stripping, thereby enabling Zn//Zn symmetric cells to exhibit an ultralong cycle life of 4000 h in coin cells and a high cumulative capacity of 18,000 mA h in pouch cells. More importantly, the superiority of the formulated strategy is further demonstrated in Zn//NH4V4O10 full cells at different N/P ratios of 5.2, 4.9, 3.5, and 2.4. This provides a promising approach for future interfacial modulation in aqueous battery chemistry.

Ammonia-Induced FCC Ru Nanocrystals for Efficient Alkaline Hydrogen Electrocatalysis.

The urgent development of effective electrocatalysts for hydrogen evolution and hydrogen oxidation reaction (HER/HOR) is needed due to the sluggish alkaline hydrogen electrocatalysis. Here, an unusual face-centered cubic (fcc) Ru nanocrystal with favorable HER/HOR performance is offered. Guided by the lower calculated surface energy of fcc Ru than that of hcp Ru in NH3, the carbon-supported fcc Ru electrocatalyst is facilely synthesized in the NH3 reducing atmosphere. The specific HOR kinetic current density of fcc Ru can reach 23.4 mA cmPGM -2, which is around 20 and 21 times greater than that of hexagonal close-packed (hcp) Ru and Pt/C, respectively. Additionally, the HER specific activity is enhanced more than six times in fcc Ru electrocatalyst when compared to Pt/C. Experimental and theoretical analysis indicate that the phase transition from hcp Ru to fcc Ru can negatively shift the d band center, weaken the interaction between catalysts and key intermediates and therefore enhances the HER/HOR kinetics.

Regulating Ir-O Covalency to Boost Acidic Oxygen Evolution Reaction.

The unsatisfactory oxygen evolution reaction (OER) activity of IrO2 has intensively raised the cost and energy consumption of hydrogen generation from proton exchange membrane water electrolyzers. Here, the acidic OER activity of the rutile IrO2 is significantly enhanced by the incorporation of trivalent metals (e.g., Gd, Nd, and Pr) to increase the Ir-O covalency, while the high-valence (pentavalent or higher) metal incorporation decreases the Ir-O covalency resulting in worse OER activity. Experimental and theoretical analyses indicate that enhanced Ir-O covalency activates lattice oxygen and triggers lattice oxygen-mediated mechanism to enhance OER kinetics, which is verified by the finding of a linear relationship between the natural logarithm of intrinsic activity and Ir-O covalency described by charge transfer energy. By regulating the Ir-O covalency, the obtained Gd-IrO2-δ merely needs 260 mV of overpotential to reach 10 mA cm-2 and shows impressive stability during a 200-h test in 0.5 м H2 SO4 . This work provides an effective strategy for significantly enhancing the OER activity of the widely used IrO2 electrocatalysts through the rational regulation of Ir-O covalency.

Amorphous TiOx Stabilized Intermetallic Pt3Ti Nanocatalyst for Methanol Oxidation Reaction.

Intermetallic compounds, featuring atomically ordered structures, have emerged as a class of promising electrocatalysts for fuel cells. However, it remains a formidable challenge to controllably synthesize Pt-based intermetallics during the essential high-temperature annealing process as well as stabilize the nanoparticles (NPs) during the electrocatalytic process. Herein, we demonstrated a Ketjen black supported intermetallic Pt3Ti nanocatalyst coupled with amorphous TiOx species (Pt3Ti-TiOx/KB). The TiOx can not only confine Pt3Ti NPs during the synthesis and electrocatalytic process by a strong metal-oxide interaction but also promote the water dissociation for generating more OH species, thus facilitating the conversion of COad. The Pt3Ti-TiOx/KB showed a significantly enhanced mass activity (2.15 A mgPt-1) for the methanol oxidation reaction, compared with Pt3Ti/KB and Pt/C, and presented an impressively high mass activity retention (∼71%) after the durability test. This work provides an effective strategy of coupling Pt-based intermetallics with functional oxides for developing highly performed electrocatalysts.

A non-Newtonian fluid quasi-solid electrolyte designed for long life and high safety Li-O2 batteries.

The Li dendrite growth and the liquid electrolyte volatilization under semi-open architecture are intrinsic issues for Li-O2 battery. In this work, we propose a non-Newtonian fluid quasi-solid electrolyte (NNFQSE) SiO2-SO3Li/PVDF-HFP, which has both shear-thinning and shear-thickening properties. The component interactions among the sulfonated silica nanoparticles, liquid electrolyte, and polymer network are beneficial for decent Li+ conductivity and high liquid electrolyte retention without volatilization. Furthermore, NNFQSE exhibits shear-thinning property to eliminate the stress of dendrite growth during repeated cycling. Meanwhile, when the force suddenly increases, such as a high current rate, the NNFQSE may dynamically turn shear-thickening to respond and mechanically stiffen to inhibit the lithium dendrite penetration. By coupling with the NNFQSE, the lithium symmetrical battery can run over 2000 h under 1 mA cm-2 at room temperature, and the quasi-solid Li-O2 battery actualizes long life above 5000 h at 100 mA g-1.

Structurally integrated asymmetric polymer electrolyte with stable Janus interface properties for high-voltage lithium metal batteries.

Solid-state polymer electrolytes are outstanding candidates for next-generation lithium metal batteries in the realm of high specific energy densities, high safeties and tight contact with electrodes. However, their applications are still hindered by the limitations that no single polymer is electrochemically stable with the oxidizing high-voltage cathode and the highly reductive Li anode, simultaneously. Herein, a bilayer asymmetric polymer electrolyte (SL-SPE) without accessional interface resistance that using poly (ethylene glycol) diacrylate (PEGDA) as a "bridge" to connect the sulfonyl (OS = O)-contained oxidation-tolerated layer and polyether-derived reduction-tolerated layer (SPE), is proposed and synthesized by sequential two-step UV polymerizations. SL-SPE can provide widened electrochemical stability window up to 5 V, while simultaneously deploying a stable Janus interface property. Eventually, the superior high-voltage (4.4 V) cycling durability can be displayed in LiNi0.6Co0.2Mn0.2O2|SL-SPE|Li batteries. This finding provides a bran-new idea for designing multifunctional polymer electrolytes in the application of solid-state batteries.

Tuning the Interlayer Interactions of 2D Covalent Organic Frameworks Enables an Ultrastable Platform for Anhydrous Proton Transport.

The development of effective, stable anhydrous proton-conductive materials is vital but challenging. Covalent organic frameworks (COFs) are promising platforms for ion and molecule conduction owing to their pre-designable structures and tailor-made functionalities. However, their poor chemical stability is due to weak interlayer interactions and intrinsic reversibility of linkages. Herein, we present a strategy for enhancing the interlayer interactions of two-dimensional COFs via importing planar, rigid triazine units into the center of C3 -symmetric monomers. The developed triazine-core-based COF (denoted as TPT-COF) possesses a well-defined crystalline structure, ordered nanochannels, and prominent porosity. The proton conductivity was ≈10 times those of non-triazinyl COFs, even reaching up to 1.27×10-2  S cm-1 at 160 °C. Furthermore, the TPT-COF exhibited structural ultrastability, making it an effective proton transport platform with remarkable conductivity and long-term durability.

Ultrafast Carbothermal Shock Constructing Ni3Fe1-xCrx Intermetallic Integrated Electrodes for Efficient and Durable Overall Water Splitting.

The development of the electrocatalyst-integrated electrodes with HER/OER bifunctional activity is desirable to reduce the cost and simplify the system of the practical water electrolyzers. Herein, we construct a new type of Ni3Fe1-xCrx (0 ≤ x < 0.3) intermetallic integrated electrodes for overall water splitting via an ultrafast carbothermal shock method. The obtained Ni3Fe0.9Cr0.1/CACC electrode exhibits the optimum performance among all developed electrocatalyst electrodes in this work, and the overpotential is merely 239 mV for OER and 128 mV for HER at 10 mA cm-2. In addition, the Ni3Fe0.9Cr0.1/CACC electrode shows excellent durability during both OER and HER stability tests at a high current density of 100 mA cm-2. An electrolyzer, which was assembled with Ni3Fe0.9Cr0.1/CACC electrodes as both the anode and cathode, operates with a low cell voltage of 1.59 V at 10 mA cm-2. It has been found that the impressive OER activity of Ni3Fe0.9Cr0.1 nanoparticles (NPs) can be ascribed to the stimulative formation of the OER-active Ni3+/Fe3+ species by the substituted Cr, while the enhanced HER activity is caused by the Cr substitution, which decreases the water dissociation energy barrier. This work provides an ultrafast and facile strategy to develop electrocatalyst-integrated electrodes with low cost and impressive HER/OER bifunctional performance for overall water splitting.

Co4 N-Decorated 3D Wood-Derived Carbon Host Enables Enhanced Cathodic Electrocatalysis and Homogeneous Lithium Deposition for Lithium-Sulfur Full Cells.

The sluggish kinetics of sulfur conversion in the cathode and the nonuniform deposition of lithium metal at the anode result in severe capacity decay and poor cycle life for lithium-sulfur (Li-S) batteries. Resolving these deficiencies is the most direct route toward achieving practical cells of this chemistry. Herein, a vertically aligned wood-derived carbon plate decorated with Co4 N nanoparticles host (Co4 N/WCP) is proposed that can serve as a host for both the sulfur cathode and the metallic lithium anode. This Co4 N/WCP electrode host drastically enhances the reaction kinetics in the sulfur cathode and homogenizes the electric field at the anode for the uniform lithium plating. Density functional theory calculations confirm the experimental observations that Co4 N/WCP provides a lower energy barrier for the polysulfide redox reaction in the cathode and a low adsorption energy for lithium deposition at the anode. Employing the Co4 N/WCP host at both electrodes in a S@Co4 N/WCP||Li@Co4 N/WCP full cell delivers a specific capacity of 807.9 mAh g-1 after 500 cycles at a 1 C rate. Additional experiments are performed with high areal sulfur loading of 4 mg cm-2 to demonstrate the viability of this strategy for producing practical Li-S cells.

Recent Advances and Perspectives in Lithium-Sulfur Pouch Cells.

Lithium-sulfur batteries (LSBs) are considered one of the most promising candidates for next-generation energy storage owing to their large energy capacity. Tremendous effort has been devoted to overcoming the inherent problems of LSBs to facilitate their commercialization, such as polysulfide shuttling and dendritic lithium growth. Pouch cells present additional challenges for LSBs as they require greater electrode active material utilization, a lower electrolyte-sulfur ratio, and more mechanically robust electrode architectures to ensure long-term cycling stability. In this review, the critical challenges facing practical Li-S pouch cells that dictate their energy density and long-term cyclability are summarized. Strategies and perspectives for every major pouch cell component-cathode/anode active materials and electrode construction, separator design, and electrolyte-are discussed with emphasis placed on approaches aimed at improving the reversible electrochemical conversion of sulfur and lithium anode protection for high-energy Li-S pouch cells.

Facile Room-Temperature Synthesis of a Highly Active and Robust Single-Crystal Pt Multipod Catalyst for Oxygen Reduction Reaction.

Economical production of highly active and robust Pt catalysts on a large scale is vital to the broad commercialization of polymer electrolyte membrane fuel cells. Here, we report a low-cost, one-pot process for large-scale synthesis of single-crystal Pt multipods with abundant high-index facets, in an aqueous solution without any template or surfactant. A composite consisting of the Pt multipods (40 wt %) and carbon displays a specific activity of 0.242 mA/cm2 and a mass activity of 0.109 A/mg at 0.9 V (versus a reversible hydrogen electrode) for oxygen reduction reaction, corresponding to ∼124% and ∼100% enhancement compared with those of the state-of-the-art commercial Pt/C catalyst (0.108 mA/cm2 and 0.054 A/mg). The single-crystal Pt multipods also show excellent stability when tested for 4500 cycles in a potential range of 0.6-1.1 V and another 2000 cycles in 0-1.2 V. More importantly, the superior performance of the Pt multipods/C catalyst is also demonstrated in a membrane electrode assembly (MEA), achieving a power density of 774 mW/cm2 (1.29 A/cm2) at 0.6 V and a peak power density of ∼1 W/cm2, representing 34% and 20% enhancement compared with those of a MEA based on the state-of-the-art commercial Pt/C catalyst (576 and 834 mW/cm2).

An Efficient Bifunctional Electrocatalyst of Phosphorous Carbon Co-doped MOFs.

It is eager to develop high-performance and cheap bifunctional electrochemical catalysts for both of the oxygen reduction reaction (ORR) or oxygen evolution reaction (OER) for the energy crisis and environmental problems. Herein, we report a series of ZIF-derived Co-P-C co-doped polyhedral materials with a well-defined morphology. The optimized catalyst Co/P/MOFs-CNTs-700 exhibited favorable electrochemical activities with the lowest overpotential of 420 mV to achieve the current density of 10 mA cm-2 for OER and the half potential of 0.8 V for ORR in 0.1 M NaOH. The performance can be well improved by doping phosphorous resource which greatly changed its morphology. Meanwhile, the doped carbon resources also improve the conductivity, which makes it a promising bifunctional electrochemical catalyst and can be comparable with the commercial electrocatalysts.

La(OH)3-modified magnetic sodium carboxymethyl cellulose for sequential removal of pollutants: adsorption of phosphate and subsequent photocatalytical reduction of Cr(VI).

In this study, La(OH)3-modified magnetic sodium carboxymethyl cellulose (La-MC) was prepared as adsorbents for phosphate, which exhibited excellent adsorption performance up to 62.98 mg P/g and magnetic property for easy recovery. The recovered adsorbents after phosphate sorption were subsequently used for photocatalytic reduction of Cr(VI) and possessed good photocatalytic activity. This work provided an excellent reference for developing a new way of extending life cycle of adsorbents by combining phosphate adsorption with photocatalysis for sequential removal of pollutants from water in the future.

Stable and active Pt colloid preparation by modified citrate reduction and a mechanism analysis of inorganic additives.

Ultra-small and monodispersed Pt nanoparticles (NPs) have been successfully synthesized in polymer electrolyte membrane fuel cells. The process normally involves the use of capping agents, organic species, templates, and substrates and is thus complex. Hence, obtaining Pt NPs with a clean surface is challenging. In this study, a method for preparing stable and highly dispersed Pt NPs with clean surfaces is proposed. The method involves the use of a modified Na3C6H5O7 reduction process assisted by NaNO3 stabilization. The specific complexations of NO2- ions possibly alter the reaction kinetics and lower the growth rate of Pt NPs by retarding the reduction reaction. The optimized Pt/carbon nanotube (CNT) catalysts exhibit high mass activity and moderate activity decay after 10,000 times of potential cycling compared with commercially available Pt/C catalysts. Then, membrane electrode assemblies based on the resultant catalysts are characterized. The cell performance of 744 mW cm-2 (maximum power density) is achieved after the optimized Pt/CNT catalysts are used in carbon black.

Dendrite-Free Composite Li Anode Assisted by Ag Nanoparticles in a Wood-Derived Carbon Frame.

Using lithium metal as anode in lithium batteries has attracted great attention due to its ultrahigh theoretical capacity of 3860 mA h g-1. However, the uneven deposition of lithium will cause dendrites, resulting in a poor cycling performance. Herein, a dendrite-free Li composite anode is developed by anchoring Ag nanoparticles in a wood-derived carbon (WDC) frame. The composite anode is integrally formed and has enough room for Li deposition due to the aligned open channels preserved from natural wood, which can decrease anode volume change greatly during cycling. The Ag nanoparticles, serving as seeds of lithium deposition, can help in the even deposition of lithium in the channels of carbon matrix due to their lithiophilicity and then avoid lithium dendrite formation. The composite anode exhibits excellent cyclic performance over 450 h at 1 mA cm-2 and over 300 h at 3 mA cm-2. The full cell of Ag-WDC@LFP also exhibits the smallest electrochemical polarization from 0.2 to 5 C, and a stable specific capacity and a high Coulombic efficiency at 1 C after a long time cycle. These results indicate that Ag nanoparticles play an important role in restraining dendrite formation during lithium plating/stripping. The wood-derived composite cathode can achieve no lithium dendrite formation and can be applied in other storage batteries.

La(OH)3-modified magnetic pineapple biochar as novel adsorbents for efficient phosphate removal.

A series of La(OH)3-modified magnetic pineapple biochar (Lax-MC) with different contents of La(OH)3 were prepared and used as phosphate adsorbents for the first time. With the increase of La(OH)3 content, the adsorption capacity for phosphate increased while the magnetic property decreased. La10-MC exhibited excellent magnetic property for easy recovery and high adsorption capacity up to 101.16 mg P/g, which was 27 times that of pineapple biochar and much higher than most phosphate adsorbents. Adsorption isotherm and adsorption kinetics were better fitted by Langmuir model and pseudo second-order model, respectively. The removal efficiency >96.04% in coexisting ions indicated its high selectivity to phosphate. Little decrease in removal efficiency after three adsorption-desorption cycles suggested its excellent stability and cyclic utilization. Leaching study demonstrated the negligible risk of La3+ and Fe3+ leakage during adsorption process. Mechanism study revealed that the adsorption mechanism involved precipitation, electrostatic interaction, ligand exchange and inner-sphere complexation.

Template-Free Preparation of 3D Porous Co-Doped VN Nanosheet-Assembled Microflowers with Enhanced Oxygen Reduction Activity.

Developing cheap and stable electrocatalysts is considered the key factor to achieve the large-scale application of fuel cells. In this paper, three-dimensional (3D) porous Co-doped vanadium nitride (VN) nanosheet-assembled microflowers are prepared with a facile solvothermal approach followed by nitridation at 500 °C in NH3. It is found that the microflower morphology and the Co doping both significantly enhance the oxygen reduction reaction (ORR) performance of the materials. Because the unique 3D porous structure provides higher specific surface area and more active sites as well as enriching the d electrons of V via doping, Co also improves the intrinsic activity of VN. Our optimal V0.95Co0.05N microflowers achieve a half-wave potential for the ORR of up to 0.80 V in 0.1 M KOH solution, which is almost comparable to that of commercial 20% Pt/C. More importantly, the catalysts show superior durability with little current decline (less than 12%) during chronoamperometric evaluation for over 25 000 s. These features make the V0.95Co0.05N microflowers attractive for fuel cell applications.