Unlocking Four-electron Conversion in Tellurium Cathodes for Advanced Magnesium-based Dual-ion Batteries.

Magnesium (Mg) batteries hold promise as a large-scale energy storage solution, but their progress has been hindered by the lack of high-performance cathodes. Here, we address this challenge by unlocking the reversible four-electron Te0/Te4+ conversion in elemental Te, enabling the demonstration of superior Mg//Te dual-ion batteries. Specifically, the classic magnesium aluminum chloride complex (MACC) electrolyte is tailored by introducing Mg bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2), which initiates the Te0/Te4+ conversion with two distinct charge-storage steps. Te cathode undergoes Te/TeCl4 conversion involving Cl- as charge carriers, during which a tellurium subchloride phase is presented as an intermediate. Significantly, the Te cathode achieves a high specific capacity of 543 mAh gTe -1 and an outstanding energy density of 850 Wh kgTe -1, outperforming most of the previously reported cathodes. Our electrolyte analysis indicates that the addition of Mg(TFSI)2 reduces the overall ion-molecule interaction and mitigates the strength of ion-solvent aggregation within the MACC electrolyte, which implies the facilized Cl- dissociation from the electrolyte. Besides, Mg(TFSI)2 is verified as an essential buffer to mitigate the corrosion and passivation of Mg anodes caused by the consumption of the electrolyte MgCl2 in Mg//Te dual-ion cells. These findings provide crucial insights into the development of advanced Mg-based dual-ion batteries.

Proton-selective coating enables fast-kinetics high-mass-loading cathodes for sustainable zinc batteries.

The pressing demand for sustainable energy storage solutions has spurred the burgeoning development of aqueous zinc batteries. However, kinetics-sluggish Zn2+ as the dominant charge carriers in cathodes leads to suboptimal charge-storage capacity and durability of aqueous zinc batteries. Here, we discover that an ultrathin two-dimensional polyimine membrane, featured by dual ion-transport nanochannels and rich proton-conduction groups, facilitates rapid and selective proton passing. Subsequently, a distinctive electrochemistry transition shifting from sluggish Zn2+-dominated to fast-kinetics H+-dominated Faradic reactions is achieved for high-mass-loading cathodes by using the polyimine membrane as an interfacial coating. Notably, the NaV3O8·1.5H2O cathode (10 mg cm-2) with this interfacial coating exhibits an ultrahigh areal capacity of 4.5 mAh cm-2 and a state-of-the-art energy density of 33.8 Wh m-2, along with apparently enhanced cycling stability. Additionally, we showcase the applicability of the interfacial proton-selective coating to different cathodes and aqueous electrolytes, validating its universality for developing reliable aqueous batteries.

A High-Energy Tellurium Redox-Amphoteric Conversion Cathode Chemistry for Aqueous Zinc Batteries.

Rechargeable aqueous zinc batteries are potential candidates for sustainable energy storage systems at a grid scale, owing to their high safety and low cost. However, the existing cathode chemistries exhibit restricted energy density, which hinders their extensive applications. Here, a tellurium redox-amphoteric conversion cathode chemistry is presented for aqueous zinc batteries, which delivers a specific capacity of 1223.9 mAh gTe -1 and a high energy density of 1028.0 Wh kgTe -1. A highly concentrated electrolyte (30 mol kg-1 ZnCl2) is revealed crucial for initiating the Te redox-amphoteric conversion as it suppresses the H2O reactivity and inhibits undesirable hydrolysis of the Te4+ product. By carrying out multiple operando/ex situ characterizations, the reversible six-electron Te2-/Te0/Te4+ conversion with TeCl4 is identified as the fully charged product and ZnTe as the fully discharged product. This finding not only enriches the conversion-type battery chemistries but also establishes a critical step in exploring redox-amphoteric materials for aqueous zinc batteries and beyond.

Giant Blue Energy Harvesting in Two-Dimensional Polymer Membranes with Spatially Aligned Charges.

Blue energy between seawater and river water is attracting increasing interest, as one of the sustainable and renewable energy resources that can be harvested from water. Within the reverse electrodialysis applied in blue energy conversion, novel membranes with nanoscale confinement that function as selective ion transport mediums are currently in high demand for realizing higher power density. The primary challenge lies in constructing well-defined nanochannels that allow for low-energy barrier transport. This work proposes a concept for nanofluidic channels with a simultaneous dual electrostatic effect that can enhance both ion selectivity and flux. To actualize this, this work has synthesized propidium iodide-based two-dimensional polymer (PI-2DP) membranes possessing both skeleton charge and intrinsic space charge, which are spatially aligned along the ion transport pathway. The dual charge design of PI-2DP significantly enhances the electrostatic interaction between the translocating anions and the cationic polymer framework, and a high anion selectivity coefficient (≈0.8) is reached. When mixing standard artificial seawater and river water, this work achieves a considerable power density of 48.4 W m-2, outperforming most state-of-the-art nanofluidic membranes. Moreover, when applied between the Mediterranean Sea and the Elbe River, an output power density of 42.2 W m-2 is achieved by the PI-2DP. This nanofluidic membrane design with dual-layer charges will inspire more innovative development of ion-selective channels for blue energy conversion that will contribute to global energy consumption.

A General Synthesis of Nanostructured Conductive Metal-Organic Frameworks from Insulating MOF Precursors for Supercapacitors and Chemiresistive Sensors.

Two-dimensional conjugated metal-organic frameworks (2D c-MOFs) are emerging as a unique subclass of layer-stacked crystalline coordination polymers that simultaneously possess porous and conductive properties, and have broad application potential in energy and electronic devices. However, to make the best use of the intrinsic electronic properties and structural features of 2D c-MOFs, the controlled synthesis of hierarchically nanostructured 2D c-MOFs with high crystallinity and customized morphologies is essential, which remains a great challenge. Herein, we present a template strategy to synthesize a library of 2D c-MOFs with controlled morphologies and dimensions via insulating MOFs-to-c-MOFs transformations. The resultant hierarchically nanostructured 2D c-MOFs feature intrinsic electrical conductivity and higher surface areas than the reported bulk-type 2D c-MOFs, which are beneficial for improved access to active sites and enhanced mass transport. As proof-of-concept applications, the hierarchically nanostructured 2D c-MOFs exhibit a superior performance for electrical properties related applications (hollow Cu-BHT nanocubes-based supercapacitor and Cu-HHB nanoflowers-based chemiresistive gas sensor), achieving over 225 % and 250 % improvement in specific capacity and response intensity over the corresponding bulk type c-MOFs, respectively.

Accessing parity-forbidden d-d transitions for photocatalytic CO2 reduction driven by infrared light.

A general approach to promote IR light-driven CO2 reduction within ultrathin Cu-based hydrotalcite-like hydroxy salts is presented. Associated band structures and optical properties of the Cu-based materials are first predicted by theory. Subsequently, Cu4(SO4)(OH)6 nanosheets were synthesized and are found to undergo cascaded electron transfer processes based on d-d orbital transitions under infrared light irradiation. The obtained samples exhibit excellent activity for IR light-driven CO2 reduction, with a production rate of 21.95 and 4.11 µmol g-1 h-1 for CO and CH4, respectively, surpassing most reported catalysts under the same reaction conditions. X-ray absorption spectroscopy and in situ Fourier-transform infrared spectroscopy are used to track the evolution of the catalytic sites and intermediates to understand the photocatalytic mechanism. Similar ultrathin catalysts are also investigated to explore the generality of the proposed electron transfer approach. Our findings illustrate that abundant transition metal complexes hold great promise for IR light-responsive photocatalysis.

An Anode-Free Zn-Graphite Battery.

The anode-free battery concept is proposed to pursue the aspiration of energy-dense, rechargeable metal batteries, but this has not been achieved with dual-ion batteries. Herein, the first anode-free Zn-graphite battery enabled by efficient Zn plating-stripping onto a silver-coated Cu substrate is demonstrated. The silver coating guides uniform Zn deposition without dendrite formation or side reaction over a wide range of electrolyte concentrations, enabling the construction of anode-free Zn cells. In addition, the graphite cathode operates efficiently under reversible bis(trifluoromethanesulfonyl)imide anion (TFSI- ) intercalation without anodic corrosion. An extra high-potential TFSI- intercalation plateau is recognized at 2.75 V, contributing to the high capacity of graphite cathode. Thanks to efficient Zn plating-stripping and TFSI- intercalation-deintercalation, an anode-free Zn-graphite dual-ion battery that exhibits impressive cycling stability with 82% capacity retention after 1000 cycles is constructed. At the same time, a specific energy of 79 Wh kg-1 based on the mass of cathode and electrolyte is achieved, which is over two times higher than conventional Zn-graphite batteries (<30 Wh kg-1 ).

Water-Salt Oligomers Enable Supersoluble Electrolytes for High-Performance Aqueous Batteries.

Aqueous rechargeable batteries are highly safe, low-cost, and environmentally friendly, but restricted by low energy density. One of the most efficient solutions is to improve the concentration of the aqueous electrolytes. However, each salt is limited by its physical solubility, generally below 21-32 mol kg-1 (m). Here, a ZnCl2 /ZnBr2 /Zn(OAc)2 aqueous electrolyte with a record super-solubility up to 75 m is reported, which breaks through the physical solubility limit. This is attributed to the formation of acetate-capped water-salt oligomers bridged by Br- /Cl- -H and Br- /Cl- /O-Zn2+ interactions. Mass spectrometry indicates that acetate anions containing nonpolarized protons prohibit the overgrowth and precipitation of ionic oligomers. The polymer-like glass transition temperature of such inorganic electrolytes is found at ≈-70 to -60 °C, without the observation of peaks for salt-crystallization and water-freezing from 40 to -80 °C. This supersoluble electrolyte enables high-performance aqueous dual-ion batteries that exhibit a reversible capacity of 605.7 mAh g-1 , corresponding to an energy density of 908.5 Wh kg-1 , with a coulombic efficiency of 98.07%. In situ X-ray diffraction and Raman technologies reveal that such high ionic concentrations of the supersoluble electrolyte enable a stage-1 intercalation of bromine into macroscopically assembled graphene cathode.

A polyimide-pyrolyzed carbon waste approach for the scalable and controlled electrochemical preparation of size-tunable graphene.

Carbon materials are widely used in numerous fields, thus changing our lives. With the increasing consumption of carbon-based products, the disposal of consequent wastes has become a challenge due to their inert nature, which is hard to degrade, burn, or melt. Here, a recyclable strategy is proposed to deal with the explosive growth of carbon wastes. Through a fast and clean electrochemical method, carbon wastes are converted into functional building blocks of high value, such as graphene and graphene quantum dots (GQDs). For typical polyimide-pyrolyzed carbon (PPC), we establish the relationship between the chemical structure of raw materials and the characteristics of graphene products, including size and yield. The size-tunable graphene ranging from 3 nm to tens of micrometers is prepared by tuning the sp3/sp2 carbon ratio of PPC from 0.5 to 0 at adjustable temperatures (800 °C-2800 °C). Significantly, PPC with a bicontinuous structure (comprising sp2 and sp3) was efficiently cut into GQDs in 2 h with a high yield of 98%. Our protocol offers great potential for the scale-up preparations and applications of GQDs. Besides, we demonstrate that the GQDs performed well as dispersants to disperse hydrophobic carbon nanotubes (0.6 mg mL-1) in water and improved the gravimetric capacitance of graphene-based supercapacitors by 79.4% with 3% GQDs added as nano-fillers.

Heavy Water Enables High-Voltage Aqueous Electrochemistry via the Deuterium Isotope Effect.

Aqueous electrolytes, which possess the advantages of nonflammability and high ionic conductivity for safe and sustainable energy storage systems, are restricted by their narrow potential windows due to water electrolysis. The recent study of high-voltage aqueous electrolytes has mainly focused on the molecular-level hydration structure of electrolyte salts, while the influence from subatomic-scale neutrons of the water solvent has never been considered. Here, for the first time, we report an electrochemical isotope effect in which the numerically increased neutrons in the water solvent extend the potential window of aqueous electrolytes. This effect is caused by the following factors: the lower zero-point energy of the deuterium compound, the smaller ion product, and the larger dehydration energy of heavy water. It is affected by ion species, electrolyte concentrations, and the ratio of deuterium to protium. Our finding provides the new insight into aqueous electrochemistry that the isotope in molecular water improves the performance of aqueous electrolytes.