Tuning Main Group Element-based Metal-Organic Framework to Boost Electrocatalytic Nitrogen Reduction Under Ambient Conditions.

Main group element-based materials are emerging catalysts for ammonia (NH3 ) production via a sustainable electrochemical nitrogen reduction reaction (N2 RR) pathway under ambient conditions. However, their N2 RR performances are less explored due to the limited active behavior and unclear mechanism. Here, an aluminum-based defective metal-organic framework (MOF), aluminum-fumarate (Al-Fum), is investigated. As a proof of concept, the pristine Al-Fum MOF is synthesized by the solvothermal reaction process, and the defect engineering method namely solvent-assisted linker exchange, is applied to create the defective Al sites. The defective Al sites play an important role in ensuring the N2 RR activity for defective Al-Fum. It is found that only the defective Al-Fum enables stable and effective electrochemical N2 RR, in terms of the highest production rate of 53.9 µg(NH3 ) h-1 mgcat -1 (in 0.4 m K2 SO4 ) and the Faradaic efficiency of 73.8% (in 0.1 m K2 SO4 ) at -0.15 V vs reversible hydrogen electrode) under ambient conditions. Density functional theory calculations confirm that the N2 activation can be achieved on the defective Al sites. Such sites also allow the subsequent protonation process via the alternating associative mechanism. This defect characteristic gives the main group Al-based MOFs the ability to serve as promising electrocatalysts for N2 RR and other attractive applications.

Achieving Dendrite-Free Zinc Metal Anodes via Molecule Anchoring and lon-Transport Pumping.

The potential for scale-up application has been acknowledged by researchers for rechargeable aqueous zinc-ion batteries (ZIBs). Nonetheless, the progress of the development is significantly impeded due to the instability of the interface between the zinc anode and electrolyte. Herein, efficient and environmentally benign valine (Val) were introduced as aqueous electrolyte additive to stabilize the electrode/electrolyte interface (EEI) via functional groups in additive molecules, thus achieving reversible dendrite-free zinc anode. The amino groups present in Val molecules have a strong ability to adsorb on the surface of zinc metal, enabling the construction of anchored molecular layer on the surface of zinc anodes. The strongly polar carboxyl groups in Val molecules can act as ion-transport pumps to capture zinc ions in the electric double layer (EDL) through coordination chemistry. Therefore, this reconstructed EEI could modulate the zinc ion flux and simultaneously suppress side reactions and dendritic growth of Zn. Consequently, a long stable cycling up to 1400 h at a high current density of 20 mA cm-2 is achieved. Additionally, Zn//V2O5 full cell with Val additive exhibit enhanced cyclability, retaining 77 % capacity after 3000 cycles, displaying significant potential in promoting the commercialization of ZIBs.

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.

The Construction of Surface-Frustrated Lewis Pair Sites to Improve the Nitrogen Reduction Catalytic Activity of In2O3.

The construction of a surface-frustrated Lewis pairs (SFLPs) structure is expected to break the single electronic state restriction of catalytic centers of P-region element materials, due to the existence of acid-base and basic active canters without mutual quenching in the SFLPs system. Herein, we have constructed eight possible SFLPS structures on the In2O3 (110) surface by doping non-metallic elements and investigated their performance as electrocatalytic nitrogen reduction catalysts using density functional theory (DFT) calculations. The results show that P atom doping (P@In2O3) can effectively construct the structure of SFLPs, and the doped P atom and In atom near the vacancy act as Lewis base and acid, respectively. The P@In2O3 catalyst can effectively activate N2 molecules through the enzymatic mechanism with a limiting potential of -0.28 eV and can effectively suppress the hydrogen evolution reaction (HER). Electronic structure analysis also confirmed that the SFLPs site can efficiently capture N2 molecules and activate N≡N bonds through a unique "donation-acceptance" mechanism.

Reversible Al Metal Anodes Enabled by Amorphization for Aqueous Aluminum Batteries.

Aqueous aluminum metal batteries (AMBs) are regarded as one of the most sustainable energy storage systems among post-lithium-ion candidates, which is attributable to their highest theoretical volumetric capacity, inherent safe operation, and low cost. Yet, the development of aqueous AMBs is plagued by the incapable aluminum plating in an aqueous solution and severe parasitic reactions, which results in the limited discharge voltage, thus making the development of aqueous AMBs unsuccessful so far. Here, we demonstrate that amorphization is an effective strategy to tackle these critical issues of a metallic Al anode by shifting the reduction potential for Al deposition. The amorphous aluminum (a-Al) interfacial layer is triggered by an in situ lithium-ion alloying/dealloying process on a metallic Al substrate with low strength. Unveiled by experimental and theoretical investigations, the amorphous structure greatly lowers the Al nucleation energy barrier, which forces the Al deposition competitive to the electron-stealing hydrogen evolution reaction (HER). Simultaneously, the inhibited HER mitigates the passivation, promoting interfacial ion transfer kinetics and enabling steady aluminum plating/stripping for 800 h in the symmetric cell. The resultant multiple full cells using Al@a-Al anodes deliver approximately a 0.6 V increase in the discharge voltage plateau compared to that of bare Al-based cells, which far outperform all reported aqueous AMBs. In both symmetric cells and full cells, the excellent electrochemical performances are achieved in a noncorrosive, low-cost, and fluorine-free Al2(SO4)3 electrolyte, which is ecofriendly and can be easily adapted for sustainable large-scale applications. This work brings an intriguing picture of the design of metallic anodes for reversible and high-voltage AMBs.

Rechargeable Aqueous Aluminum-Ion Battery: Progress and Outlook.

The high cost and scarcity of lithium resources have prompted researchers to seek alternatives to lithium-ion batteries. Among emerging "Beyond Lithium" batteries, rechargeable aluminum-ion batteries (AIBs) are yet another attractive electrochemical storage device due to their high specific capacity and the abundance of aluminum. Although the current electrochemical performance of nonaqueous AIBs is better than aqueous AIBs (AAIBs), AAIBs have recently gained attention due to their low cost and enhanced safety. Extensive efforts are devoted to developing AAIBs in the last few years. Yet, it is still challenging to achieve stable electrodes with good electrochemical performance and electrolytes without side reactions. This review summarizes the recent progress in the exploration of anode and cathode materials and the selection of electrolytes of AAIBs. Lastly, the main challenges and future research outlook of high-performance AAIBs are also presented.

Architecting a Stable High-Energy Aqueous Al-Ion Battery.

Aqueous Al-ion batteries (AAIBs) are the subject of great interest due to the inherent safety and high theoretical capacity of aluminum. The high abundancy and easy accessibility of aluminum raw materials further make AAIBs appealing for grid-scale energy storage. However, the passivating oxide film formation and hydrogen side reactions at the aluminum anode as well as limited availability of the cathode lead to low discharge voltage and poor cycling stability. Here, we proposed a new AAIB system consisting of an AlxMnO2 cathode, a zinc substrate-supported Zn-Al alloy anode, and an Al(OTF)3 aqueous electrolyte. Through the in situ electrochemical activation of MnO, the cathode was synthesized to incorporate a two-electron reaction, thus enabling its high theoretical capacity. The anode was realized by a simple deposition process of Al3+ onto Zn foil substrate. The featured alloy interface layer can effectively alleviate the passivation and suppress the dendrite growth, ensuring ultralong-term stable aluminum stripping/plating. The architected cell delivers a record-high discharge voltage plateau near 1.6 V and specific capacity of 460 mAh g-1 for over 80 cycles. This work provides new opportunities for the development of high-performance and low-cost AAIBs for practical applications.

A 1D Honeycomb-Like Amorphous Zincic Vanadate for Stable and Fast Sodium-Ion Storage.

Developing nanomaterials with synergistic effects of various structural merits is considered to be an effective strategy to improve the sluggish ion kinetics and severe structural degradation of sodium-ion battery (SIB) anodes. Herein, honeycomb-like amorphous Zn2 V2 O7 (ZVO-AH) nanofibers as SIBs anode material with plentiful defective sites, complex cavities, and good mechanical flexibility are reported. The fabrication strategy relies on the expansive and volatile nature of the organic vanadium source, based on a simple electrospinning with subsequent calcination. Originating from the synergies of amorphous nature and honeycomb-like cavities, ZVO-AH shows increased electrochemical activity, accelerated Na-ion diffusion, and robust structure. Impressively, the ZVO-AH anode delivers superior cycle stability (112% retention at 5 A g-1 after 5000 cycles) and high rate capability (150 mAh g-1 at 10 A g-1 ). The synthetic versatility is able to synergistically promote the practical application of more potential materials in sodium-ion storage.

An All-Organic D-A System for Visible-Light-Driven Overall Water Splitting.

Direct water splitting over photocatalysts is a prospective strategy to convert solar energy into hydrogen energy. Nevertheless, because of the undesirable electron accumulation at the surface, the overall water-splitting efficiency is seriously restricted by the poor charge separation/transfer ability. Here, an all-organic donor-acceptor (D-A) system through crafting carbon rings units-conjugated tubular graphitic carbon nitride (C-TCN) is proposed. Through a range of characterizations and theoretical calculations, the incorporation of carbon rings units via continuous π-conjugated bond builds a D-A system, which can drive intramolecular charge transfer to realize highly efficient charge separation. More importantly, the tubular structure and the incorporated carbon rings units cause a significant downshift of the valence band, of which the potential is beneficial to the activation for O2 evolution. When serving as photocatalyst for overall water splitting, C-TCN displays considerable performance with H2 and O2 production rates of 204.6 and 100.8 µmol g-1 h-1 , respectively. The corresponding external quantum efficiency reaches 2.6% at 405 nm, and still remains 1.7% at 420 nm. This work demonstrates that the all-organic D-A system conceptualized from organic solar cell can offer promotional effect for overall water splitting by addressing the charge accumulation problem rooted in the hydrogen evolution reaction.

UWB/Binocular VO Fusion Algorithm Based on Adaptive Kalman Filter.

Among the existing wireless indoor positioning systems, UWB (ultra-wideband) is one of the most promising solutions. However, the single UWB positioning system is affected by factors such as non-line of sight and multipath, and the navigation accuracy will decrease. In order to make up for the shortcomings of a single UWB positioning system, this paper proposes a scheme based on binocular VO (visual odometer) and UWB sensor fusion. In this paper, the original distance measurement data of UWB and the position information of binocular VO are merged by adaptive Kalman filter, and the structural design of the fusion system and the realization of the fusion algorithm are elaborated. The experimental results show that compared with a single positioning system, the proposed data fusion method can significantly improve the positioning accuracy.

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.

An Amorphous Noble-Metal-Free Electrocatalyst that Enables Nitrogen Fixation under Ambient Conditions.

N2 fixation by the electrocatalytic nitrogen reduction reaction (NRR) under ambient conditions is regarded as a potential approach to achieve NH3 production, which still heavily relies on the Haber-Bosch process at the cost of huge energy and massive production of CO2 . A noble-metal-free Bi4 V2 O11 /CeO2 hybrid with an amorphous phase (BVC-A) is used as the cathode for electrocatalytic NRR. The amorphous Bi4 V2 O11 contains significant defects, which play a role as active sites. The CeO2 not only serves as a trigger to induce the amorphous structure, but also establishes band alignment with Bi4 V2 O11 for rapid interfacial charge transfer. Remarkably, BVC-A shows outstanding electrocatalytic NRR performance with high average yield (NH3 : 23.21 µg h-1 mg-1cat. , Faradaic efficiency: 10.16 %) under ambient conditions, which is superior to the Bi4 V2 O11 /CeO2 hybrid with crystalline phase (BVC-C) counterpart.

Engineering Mesoporous Single Crystals Co-Doped Fe2O3 for High-Performance Lithium Ion Batteries.

To achieve high-efficiency lithium ion batteries (LIBs), an effective active electrode material is vital. For the first time, mesoporous single crystals cobalt-doped Fe2O3 (MSCs Co-Fe2O3) is synthesized using formamide as a pore forming agent, through a solvothermal process followed by calcination. Compared with mesoporous single crystals Fe2O3 (MSCs Fe2O3) and cobalt-doped Fe2O3 (Co-Fe2O3), MSCs Co-Fe2O3 exhibits a significantly improved electrochemical performance with high reversible capacity, excellent rate capability, and cycling life as anode materials for LIBs. The superior performance of MSCs Co-Fe2O3 can be ascribed to the combined structure characteristics, including Co-doping and mesoporous single-crystals structure, which endow Fe2O3 with rapid Li+ diffusion rate and tolerance for volume change.

Construction of α-ß Phase Junction on Bi4V2O11 via Electrospinning Retardation Effect and Its Promoted Photocatalytic Performance.

The creation of a phase junction structure in photocatalysts is a wise approach to promote photocatalytic performance, as phase junctions possess the potential to inhibit the recombination of photoinduced charge carriers. Here, Bi4V2O11 nanofibers with an α-ß phase junction are fabricated via electrospinning with subsequent calcination. Electrospinning offers the opportunity to keep α-Bi4V2O11 from transforming into ß-Bi4V2O11 completely due to an electrospinning retardation effect, leading to the formation of an α-ß Bi4V2O11 phase junction. Furthermore, the α-ß Bi4V2O11 phase junction realizes a well-established type-II band alignment. Photoelectrochemical measurements and photoluminescence spectroscopic investigations demonstrate that the phase junction structure has a significant impact on the separation and transfer of photogenerated electrons and holes. Thus, the α-ß phase junction on Bi4V2O11 holds the key to achieving promoted efficiency in the photocatalysis process.

A novel anode comprised of C&N co-doped Co3O4 hollow nanofibres with excellent performance for lithium-ion batteries.

C&N co-doped Co3O4 hollow nanofibres are prepared by combining the electrospinning technique and the hydrothermal method, which show a high reversible capacity and excellent cycling stability as anode materials for Li-ion batteries. DFT calculations give a good explanation for the experimentally enhanced conductivity in C&N co-doped Co3O4 hollow nanofibres.

Durability, inactivation and regeneration of silver tetratantalate in photocatalytic H2 evolution.

The prepared Ag2Ta4O11 photocatalyst exhibits durable activity for H2 production from water. We investigated the durability, inactivation and regeneration mechanism in depth. This work provides a new perspective and makes an important step for the research on Ag-based photocatalysts.

An advanced Ag-based photocatalyst Ag2Ta4O11 with outstanding activity, durability and universality for removing organic dyes.

Constructing Ag-based photocatalysts by the incorporation of Ag(+) ions into metal/nonmetal oxides for removing organic pollutants is a recently developed strategy, but overcoming their own photocorrosion is still a tremendous challenge. In this work, an advanced Ag-based photocatalyst Ag2Ta4O11 is obtained by this strategy, which exhibits improved photocatalytic activity compared with Ta2O5 and the universality for degrading several organic dyes. Importantly, the Ag2Ta4O11 photocatalyst has outstanding durability and reusability, which indicates that it has potential application prospects for organic wastewater treatment in the printing and dyeing industry.

Interface engineering enabled by sodium dodecyl sulfonate surfactant for stable Zn metal batteries.

Aqueous zinc-ion batteries are emerging as powerful candidates for large-scale energy storage, due to their inherent high safety and high theoretical capacity. However, the inevitable hydrogen evolution and side effects of the deposition process limit their lifespan, which requires rational engineering of the interface between anode and aqueous electrolyte. In this paper, an anionic surfactant as electrolyte additive, sodium dodecyl sulfonate (SDS), is introduced to deliver highly reversible zinc metal batteries. Unlike traditional surfactants, the solvation structure is not affected by SDS, which tends to adsorb on the (002) crystal plane of Zn with the purpose of effectively limiting the water molecules adsorption. Attributed to the natural hydrophobic part of SDS, a dynamic electrostatic shielding layer and a unique hydrophobic interface are constructed on the anode. Assisted by the above merits, the adverse surface corrosion, hydrogen evolution and dendrite growth are significantly inhibited without the sacrifice in the deposition kinetics of Zn ions. As a result, the Zn||Zn symmetric batteries demonstrate an increased cycle life of 2000 h (1 mA cm-2, 1 mA h cm-2) with the presence of SDS additive. Such strategy provides a new avenue for the developing advanced electrolytes to be applied in aqueous energy storage systems.

Nitroxyl radical triggered the construction of a molecular protective layer for achieving durable Zn metal anodes.

The issues of dendrite growth, hydrogen evolution reaction, and zinc anode corrosion have significantly hindered the widespread implementation of aqueous zinc-ion batteries (AZIBs). Herein, trace amounts of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) additive is introduced into AZIBs to protect the zinc metal anode. Trace amounts of the TEMPO additive with nitroxyl radical can provide fast Zn2+ transport and anode protection ability by forming an adsorbed molecular layer via Zn-O bond. This interface not only provides strong interfacial compatibility and promotes dynamic transport of Zn2+, but also induces deposition of Zn2+ along Zn (002) plane. Additionally, the molecular protective layer significantly inhibits hydrogen evolution reaction (HER) and corrosion. The Zn anodes achieve high Coulombic efficiency of up to 99.75 % and long-term plating/stripping of more than 1400 h at 1 mA cm-2 and 0.5 mAh cm-2. The Zn//Zn symmetric cell can operate continuously for 2500 h at a current density of 1 mA cm-2 and 1 mAh cm-2, and it can still last for nearly 1400 h even when the current density is increased to 5 mA cm-2. Furthermore, the Zn//V2O5 full cell using TEMPO/ZnSO4 electrolyte effectively maintains a maximum capacity retention rate of 53.4 % even after 1500 cycles at 5 A/g. This innovative strategy introduces trace additive with free radicals into the electrolyte, which may help to achieve large-scale, ultra-long-life, and low-cost AZIBs.

Interface Engineering for Aqueous Aluminum Metal Batteries: Current Progresses and Future Prospects.

Aqueous aluminum metal batteries (AMBs) have attracted numerous attention because of the abundant reserves, low cost, high theoretical capacity, and high safety. Nevertheless, the poor thermodynamics stability of metallic Al anode in aqueous solution, which is caused by the self-corrosion, surface passivation, or hydrogen evolution reaction, dramatically limits the electrochemical performance and hampers the further development of AMBs. In this comprehensive review, the key scientific challenges of Al anode/electrolyte interface (AEI) are highlighted. A systematic overview is also provided about the recent progress on the rational interface engineering principles toward a relatively stable AEI. Finally, suggestions and perspectives for future research are offered on the optimization of Al anode and aqueous electrolytes to enable a stable and durable AEI, which may pave the way for developing high-performance AMBs.