Constrained C2 adsorbate orientation enables CO-to-acetate electroreduction.

The carbon dioxide and carbon monoxide electroreduction reactions, when powered using low-carbon electricity, offer pathways to the decarbonization of chemical manufacture1,2. Copper (Cu) is relied on today for carbon-carbon coupling, in which it produces mixtures of more than ten C2+ chemicals3-6: a long-standing challenge lies in achieving selectivity to a single principal C2+ product7-9. Acetate is one such C2 compound on the path to the large but fossil-derived acetic acid market. Here we pursued dispersing a low concentration of Cu atoms in a host metal to favour the stabilization of ketenes10-chemical intermediates that are bound in monodentate fashion to the electrocatalyst. We synthesize Cu-in-Ag dilute (about 1 atomic per cent of Cu) alloy materials that we find to be highly selective for acetate electrosynthesis from CO at high *CO coverage, implemented at 10 atm pressure. Operando X-ray absorption spectroscopy indicates in situ-generated Cu clusters consisting of <4 atoms as active sites. We report a 12:1 ratio, an order of magnitude increase compared to the best previous reports, in the selectivity for acetate relative to all other products observed from the carbon monoxide electroreduction reaction. Combining catalyst design and reactor engineering, we achieve a CO-to-acetate Faradaic efficiency of 91% and report a Faradaic efficiency of 85% with an 820-h operating time. High selectivity benefits energy efficiency and downstream separation across all carbon-based electrochemical transformations, highlighting the importance of maximizing the Faradaic efficiency towards a single C2+ product11.

Fast-charging aluminium-chalcogen batteries resistant to dendritic shorting.

Although batteries fitted with a metal negative electrode are attractive for their higher energy density and lower complexity, the latter making them more easily recyclable, the threat of cell shorting by dendrites has stalled deployment of the technology1,2. Here we disclose a bidirectional, rapidly charging aluminium-chalcogen battery operating with a molten-salt electrolyte composed of NaCl-KCl-AlCl3. Formulated with high levels of AlCl3, these chloroaluminate melts contain catenated AlnCl3n+1- species, for example, Al2Cl7-, Al3Cl10- and Al4Cl13-, which with their Al-Cl-Al linkages confer facile Al3+ desolvation kinetics resulting in high faradaic exchange currents, to form the foundation for high-rate charging of the battery. This chemistry is distinguished from other aluminium batteries in the choice of a positive elemental-chalcogen electrode as opposed to various low-capacity compound formulations3-6, and in the choice of a molten-salt electrolyte as opposed to room-temperature ionic liquids that induce high polarization7-12. We show that the multi-step conversion pathway between aluminium and chalcogen allows rapid charging at up to 200C, and the battery endures hundreds of cycles at very high charging rates without aluminium dendrite formation. Importantly for scalability, the cell-level cost of the aluminium-sulfur battery is projected to be less than one-sixth that of current lithium-ion technologies. Composed of earth-abundant elements that can be ethically sourced and operated at moderately elevated temperatures just above the boiling point of water, this chemistry has all the requisites of a low-cost, rechargeable, fire-resistant, recyclable battery.

Vanadium Oxide: Phase Diagrams, Structures, Synthesis, and Applications.

Vanadium oxides with multioxidation states and various crystalline structures offer unique electrical, optical, optoelectronic and magnetic properties, which could be manipulated for various applications. For the past 30 years, significant efforts have been made to study the fundamental science and explore the potential for vanadium oxide materials in ion batteries, water splitting, smart windows, supercapacitors, sensors, and so on. This review focuses on the most recent progress in synthesis methods and applications of some thermodynamically stable and metastable vanadium oxides, including but not limited to V2O3, V3O5, VO2, V3O7, V2O5, V2O2, V6O13, and V4O9. We begin with a tutorial on the phase diagram of the V-O system. The second part is a detailed review covering the crystal structure, the synthesis protocols, and the applications of each vanadium oxide, especially in batteries, catalysts, smart windows, and supercapacitors. We conclude with a brief perspective on how material and device improvements can address current deficiencies. This comprehensive review could accelerate the development of novel vanadium oxide structures in related applications.

Synchronous Redox Reactions in Copper Oxalate Enable High-Capacity Anode for Proton Battery.

Proton batteries are competitive due to their merits such as high safety, low cost, and fast kinetics. However, it is generally difficult for current studies of proton batteries to combine high capacity and high stability, while the research on proton storage mechanism and redox behavior is still in its infancy. Herein, the polyanionic layered copper oxalate is proposed as the anode for a high-capacity proton battery for the first time. The copper oxalate allows for reversible proton insertion/extraction through the layered space but also achieves high capacity through synchronous redox reactions of Cu2+ and C2O42-. During the discharge process, the bivalent Cu-ion is reduced, whereas the C═O of the oxalate group is partially converted to C-O. This synchronous behavior presents two units of charge transfer, enabling the embedding of two units of protons in the (110) crystal face. As a result, the copper oxalate anode demonstrates a high specific capacity of 226 mAh g-1 and maintains stable operation over 1000 cycles with a retention of 98%. This work offers new insights into the development of dual-redox electrode materials for high-capacity proton batteries.

What Makes On-Chip Microdevices Stand Out in Electrocatalysis?

Clean and sustainable energy conversion and storage through electrochemistry shows great promise as an alternative to traditional fuel or fossil-consumption energy systems. With regards to practical and high-efficient electrochemistry application, the rational design of active sites and the accurate description of mechanism remain a challenge. Toward this end, in this Perspective, a unique on-chip micro/nano device coupling nanofabrication and low-dimensional electrochemical materials is presented, in which material structure analysis, field-effect regulation, in situ monitoring, and simulation modeling are highlighted. The critical mechanisms that influence electrochemical response are discussed, and how on-chip micro/nano device distinguishes itself is emphasized. The key challenges and opportunities of on-chip electrochemical platforms are also provided through the Perspective.

Fluoride Doping Na3Al2/3V4/3(PO4)3 Microspheres As Cathode Materials for Sodium-Ion Batteries with Multielectron Redox.

Sodium-ion batteries (SIBs) are potential candidates for large energy storage usage because of the natural abundance and cheap sodium. Nevertheless, improving the energy density and cycling steadiness of SIB cathodes remains a challenge. In this work, F-doping Na3Al2/3V4/3(PO4)3(NAVP) microspheres (Na3Al2/3V4/3(PO4)2.9F0.3(NAVPF)) are synthesized via spray drying and investigated as SIB cathodes. XRD and Rietveld refinement reveal expanded lattice parameters for NAVPF compared to the undoped sample, and the successful cation doping into the Na superionic conductor (NASICON) framework improves Na+ diffusion channels. The NAVPF delivers an ultrahigh capacity of 148 mAh g-1 at 100 mA g-1 with 90.8% retention after 200 cycles, enabled by the activation of V2+/V5+ multielectron reaction. Notably, NAVPF delivers an ultrahigh rate performance, with a discharge capacity of 83.6 mAh g-1 at 5000 mA g-1. In situ XRD demonstrates solid-solution reactions occurred during charge-discharge of NAVPF without two-phase reactions, indicating enhanced structural stability after F-doped. The full cell with NAVPF cathode and Na+ preintercalated hard carbon anode shows a large discharge capacity of 100 mAh g-1 at 100 mA g-1 with 80.2% retention after 100 cycles. This anion doping strategy creates a promising SIB cathode candidate for future high-energy-density energy storage applications.

Charge-Separated Pdδ--Cuδ+ Atom Pairs Promote CO2 Reduction to C2.

Positively charged Cu sites have been confirmed to significantly promote the production of multicarbon (C2) products from an electrochemical CO2 reduction reaction (CO2RR). However, the positively charged Cu has difficulty in existing under a strong negative bias. In this work, we design a Pdδ--Cu3N catalyst containing charge-separated Pdδ--Cuδ+ atom pair that can stabilize the Cuδ+ sites. In situ characterizations and density functional theory reveal that the first reported negatively charged Pdδ- sites exhibited a superior CO binding capacity together with the adjacent Cuδ+ sites, synergistically promoting the CO dimerization process to produce C2 products. As a result, we achieve a 14-fold increase in the C2 product Faradaic efficiency (FE) on Pdδ--Cu3N, from 5.6% to 78.2%. This work provides a new strategy for synthesizing negative valence atom-pair catalysts and an atomic-level modulation approach of unstable Cuδ+ sites in the CO2RR.

A Highly Stable and Non-Flammable Deep Eutectic Electrolyte for High-Performance Lithium Metal Batteries.

Deep eutectic electrolytes (DEEs) are regarded as one of the next-generation electrolytes to promote the development of lithium metal batteries (LMBs) due to their unparalleled advantages compared to both liquid electrolytes and solid electrolytes. However, its application in LMBs is limited by electrode interface compatibility. Here, we introduce a novel solid dimethylmalononitrile (DMMN)-based DEE induced by N coordination to dissociate LiTFSI. We confirmed that the DMMN molecule can promote the dissociation of LiTFSI by the interaction between the N atom and Li+, and form the hydrogen bond with TFSI- anion, which can promote the dissociation of LiTFSI to form DEE. More importantly, due to the absence of active α-hydrogen, DMMN exhibits greatly enhanced reduction stability with Li metal, resulting in favorable electrode/electrolyte interface compatibility. Polymer electrolytes based on this DEE exhibit high ionic conductivity (0.67 mS cm-1 at 25 ℃), high oxidation voltage (5.0 V vs. Li+/Li), favorable interfacial stability and nonflammability. Li‖LFP and Li‖NCM811 full batteries utilizing this DEE polymer electrolyte exhibit excellent long-term cycling stability and excellent rate performance at high rates. Therefore, the new DMMN-based DEE overcomes the limitations of traditional electrolytes in electrode interface compatibility and opens new possibilities for improving the performance of LMBs.

The Role of the Molecular Encapsulation Effect in Stabilizing Hydrogen-Bond-Rich Gel-State Lithium Metal Batteries.

Gel-state polymer electrolytes with superior mechanical properties, self-healing abilities and high Li+ transference numbers can be obtained by in situ polymerization of monomers with hydrogen-bonding moieties. However, it is overlooked that the active hydrogen atoms in hydrogen-bond donors experience displacement reactions with lithium metal in lithium metal batteries (LMBs), leading to corrosion of the lithium metal. Herein, it is discovered that the addition of hydrogen-bond acceptors to hydrogen-bond-rich gel-state electrolytes modulates the chemical activity of the active hydrogen atoms via the formation of hydrogen-bonded intermolecular interactions. The characterizations reveal that the added hydrogen-bond acceptors encapsulate the active hydrogen atoms to suppress the interfacial chemical corrosions of lithium metals, thereby enhancing the chemical stability of the polymer structure and interphase. With the employment of this strategy, a 1.1 Ah LiNi0.8Co0.1Mn0.1O2/Li metal pouch cell achieves stable cycling with 96.3 % capacity retention at 100 cycles. This new approach indicates a feasible path for achieving in situ polymerization of highly stable gel-state-based LMBs.

Regulating reconstruction-engineered active sites for accelerated electrocatalytic conversion of urea.

Reconstruction-engineered electrocatalysts with enriched high active Ni species for urea oxidation reaction (UOR) have recently become promising candidates for energy conversion. However, to inhibit the over-oxidation of urea brought by the high valence state of Ni, tremendous efforts are devoted to obtaining low-value products of nitrogen gas to avoid toxic nitrite formation, undesirably causing inefficient utilization of the nitrogen cycle. Herein, we proposed a mediation engineering strategy to significantly boost high-value nitrite formation to help close a loop for the employment of a nitrogen economy. Specifically, platinum-loaded nickel phosphides (Pt-Ni2P) catalysts exhibit a promising nitrite production rate (0.82 mol kWh-1 cm-2), high stability over 66 h of Zn-urea-air battery operation, and 135 h of co-production of nitrite and hydrogen under 200 mA cm-2 in a zero-gap membrane electrode assembly (MEA) system. The in situ spectroscopic characterizations and computational calculations demonstrated that the urea oxidation kinetics is facilitated by enriched dynamic Ni3+ active sites, thus augmenting the "cyanate" UOR pathway. The *NOO desorption was further verified as the rate-determining step for nitrite generation.

Ultra-High Proportion of Grain Boundaries in Zinc Metal Anode Spontaneously Inhibiting Dendrites Growth.

Aqueous Zn-ion batteries are an attractive electrochemical energy storage solution for their budget and safe properties. However, dendrites and uncontrolled side reactions in anodes detract the cycle life and energy density of the batteries. Grain boundaries in metals are generally considered as the source of the above problems but we present a diverse result. This study introduces an ultra-high proportion of grain boundaries on zinc electrodes through femtosecond laser bombardment to enhance stability of zinc metal/electrolyte interface. The ultra-high proportion of grain boundaries promotes the homogenization of zinc growth potential, to achieve uniform nucleation and growth, thereby suppressing dendrite formation. Additionally, the abundant active sites mitigate the side reactions during the electrochemical process. Consequently, the 15 µm Fs-Zn||MnO2 pouch cell achieves an energy density of 249.4 Wh kg-1 and operates for over 60 cycles at a depth-of-discharge of 23 %. The recognition of the favorable influence exerted by UP-GBs paves a new way for other metal batteries.

Boosting the Hydrogen Evolution Reaction Performance of P-Doped PtTe2 Nanocages via Spontaneous Defects Formation.

PtTe2 , a member of the noble metal dichalcogenides (NMDs), has aroused great interest in exploring its behavior in the hydrogen evolution reaction (HER) due to the unique type-II topological semimetallic nature. In this work, a simple template-free hydrothermal method to obtain the phosphorus-doped (P-doped) PtTe2 nanocages with abundant amorphous and crystalline interface (A/C-P-PtTe2 ) is developed. Revealed by density functional theory calculations, the atomic Te vacancies can spontaneously form on the basal planes of PtTe2 by the P doping, which results in the unsaturated Pt atoms exposed as the active sites in the amorphous layer for HER. Owing to the defective structure, the A/C-P-PtTe2 catalysts have the fast Tafel step determined kinetics in HER, which contributes to an ultralow overpotential (η = 28 mV at 10 mA cm-2 ) and a small Tafel slope of 37 mV dec-1 . More importantly, benefiting from the inner stable crystalline P-PtTe2 nanosheets, limited decay of the performance is observed after chronopotentiometry test. This work reveals the important role of the inherent relationship between structure and activity in PtTe2 for HER, which may bring another enlightenment for the design of efficient catalysts based on NMDs in the near future.

Amine-Aldehyde Condensation-Derived N-Doped Hard Carbon Microspheres for High-Capacity and Robust Sodium Storage.

Hard carbon is generally accepted as the choice of anode material for sodium-ion batteries. However, integrating high capacity, high initial Coulombic efficiency (ICE), and good durability in hard carbon materials remains challenging. Herein, N-doped hard carbon microspheres (NHCMs) with abundant Na+ adsorption sites and tunable interlayer distance are constructed based on the amine-aldehyde condensation reaction using m-phenylenediamine and formaldehyde as the precursors. The optimized NHCM-1400 with a considerable N content (4.64%) demonstrates a high ICE (87%), high reversible capacity with ideal durability (399 mAh g-1 at 30 mA g-1 and 98.5% retention over 120 cycles), and decent rate capability (297 mAh g-1 at 2000 mA g-1 ). In situ characterizations elucidate the adsorption-intercalation-filling sodium storage mechanism of NHCMs. Theoretical calculation reveals that the N-doping decreases the Na+ adsorption energy on hard carbon.

Ni Single Atoms on MoS2 Nanosheets Enabling Enhanced Kinetics of Li-S Batteries.

The practical application of Li-S batteries is seriously hindered due to its shuttle effect and sluggish redox reaction, which requires a better functional separator to solve the problems. Herein, polypropylene separators modified by MoS2 nanosheets with atomically dispersed nickel (Ni-MoS2 ) are prepared to prevent the shuttle effect and facilitate the redox kinetics for Li-S batteries. Compared with pristine MoS2 nanosheets, Ni-MoS2 nanosheets exhibit both excellent adsorption and catalysis performance for overcoming the shuttle effect. Assembled with this novel separator, the Li-S batteries exhibit an admirable cycling stability at 2 C over 400 cycles with 0.01% per cycle decaying. In addition, even with a high sulfur loading of 7.5 mg cm-2 , the battery still provides an initial capacity of 6.9 mAh cm-2 and remains 5.9 mAh cm-2 after 50 cycles because of the fast convention of polysulfides catalyzed by Ni-MoS2 nanosheets, which is further confirmed by the density functional theory (DFT) calculations. Therefore, the proposed strategy is expected to offer a new thought for single atom catalyst applying in Li-S batteries.

Toward the High-Performance Lithium Primary Batteries by Chemically Modified Fluorinate Carbon with δ-MnO2.

Li/CFx battery is one of the most promising lithium primary batteries (LPBs) which yields the highest energy density but with poor rate capability. This Achilles'' heel hinders the large-scale applications of Li/CFx batteries. This work first reports a facile chemical modification method of CFx with δ-MnO2 . Having benefited from the chemical bonding, the electrochemical performance at high-rate discharge is remarkably enhanced without compromising the specific capacity. The coin cells exhibit an energy density of 1.94 × 103  Wh kg-1 at 0.2 C, which is approaching the theoretical energy density of commercial fluorinated graphite (2.07 × 103  Wh kg-1 ). A power density of 5.49 × 104  W kg-1 at 40 C associated with an energy density of 4.39 × 102  Wh kg-1 , which is among the highest value of Li/CFx batteries, are obtained. Besides, the punch batteries achieve an ultrahigh power density of 4.39 × 104  W kg-1 with an energy density of 7.60 × 102  Wh kg-1 at 30 C. The intrinsic reasons for this outstanding electrochemical performance, which are known as the fast Li+ diffusion kinetics guided by thin δ-MnO2 flakes and the low formation energy barrier caused by chemical bonding, are explored by the galvanostatic intermittent titration technique (GITT) and theoretical calculations.

Amine-aldehyde resin derived porous N-doped hollow carbon nanorods for high-energy capacitive energy storage.

Electrochemical double layer capacitors (EDLCs) are known for their high power density but hampered by low energy density. Herein, N-doped hollow carbon nanorods (NHCRs) have been constructed by a hard templating method using MnO2nanorods as the hard templates andm-phenylenediamine-formaldehyde resin as the carbon precursor. The NHCRs after activation (NHCRs-A) manifest abundant micropores/mesopores and an ultrahigh surface area (2166 m2g-1). When employed in ionic liquid (IL) electrolyte-based EDLCs, the NHCRs-A delivers a high specific capacitance (220 F g-1at 1 A g-1), an impressive energy density (110 Wh kg-1), and decent cyclability (97% retention over 15 000 cycles). The impressive energy density is derived from the abundant ion-available micropores, while the decent power density is originated from the hollow ion-diffusion channels as well as excellent wettability in ILs.In situinfrared spectroscopy together within situRaman unveil that both counter-ion adsorption and ion exchange are involved in the charge storage of NHCRs-A. This study provides insight into the construction of porous carbon materials for EDLCs.

A High-Energy NASICON-Type Na3.2 MnTi0.8 V0.2 (PO4 )3 Cathode Material with Reversible 3.2-Electron Redox Reaction for Sodium-Ion Batteries.

Na superionic conductor (NASICON) structured cathode materials with robust structural stability and large Na+ diffusion channels have aroused great interest in sodium-ion batteries (SIBs). However, most of NASICON-type cathode materials exhibit redox reaction of no more than three electrons per formula, which strictly limits capacity and energy density. Herein, a series of NASICON-type Na3+x MnTi1-x Vx (PO4 )3 cathode materials are designed, which demonstrate not only a multi-electron reaction but also high voltage platform. With five redox couples from V5+/4+ (≈4.1 V), Mn4+/3+ (≈4.0 V), Mn3+/2+ (≈3.6 V), V4+/3+ (≈3.4 V), and Ti4+/3+ (≈2.1 V), the optimized material, Na3.2 MnTi0.8 V0.2 (PO4 )3 , realizes a reversible 3.2-electron redox reaction, enabling a high discharge capacity (172.5 mAh g-1 ) and an ultrahigh energy density (527.2 Wh kg-1 ). This work sheds light on the rational construction of NASICON-type cathode materials with multi-electron redox reaction for high-energy SIBs.

Revealing the Interfacial Chemistry of Fluoride Alkyl Magnesium Salts in Magnesium Metal Batteries.

Exploring promising electrolyte-system with high reversible Mg plating/stripping and excellent stability is essential for rechargeable magnesium batteries (RMBs). Fluoride alkyl magnesium salts (Mg(ORF )2 ) not only possess high solubility in ether solvents but also compatible with Mg metal anode, thus holding a vast application prospect. Herein, a series of diverse Mg(ORF )2 were synthesized, among them, perfluoro-tert-butanol magnesium (Mg(PFTB)2 )/AlCl3 /MgCl2 based electrolyte demonstrates highest oxidation stability, and promotes the in situ formation of robust solid electrolyte interface. Consequently, the fabricated symmetric cell sustains a long-term cycling over 2000 h, and the asymmetric cell exhibits a stable Coulombic efficiency of 99.5 % over 3000 cycles. Furthermore, the Mg||Mo6 S8 full cell maintains a stable cycling over 500 cycles. This work presents guidance for understanding structure-property relationships and electrolyte applications of fluoride alkyl magnesium salts.

NH4 + Deprotonation at Interfaces Induced Reversible H3 O+ /NH4 + Co-insertion/Extraction.

Ion insertions always involve electrode-electrolyte interface process, desolvation for instance, which determines the electrochemical kinetics. However, it's still a challenge to achieve fast ion insertion and investigate ion transformation at interface. Herein, the interface deprotonation of NH4 + and the introduced dissociation of H2 O molecules to provide sufficient H3 O+ to insert into materials' structure for fast energy storages are revealed. Lewis acidic ion-NH4 + can, on one hand provide H3 O+ itself via deprotonation, and on the other hand hydrolyze with H2 O molecules to produce H3 O+ . In situ attenuated total reflection-Fourier transform infrared ray method probed the interface accumulation and deprotonation of NH4 + , and density functional theory calculations manifested that NH4 + tend to thermodynamically adsorb on the surface of monoclinic VO2 , and deprotonate to provide H3 O+ . In addition, the inserted NH4 + has a positive effect for stabilizing the VO2 (B) structure. Therefore, high specific capacity (>300 mAh g-1 ) and fast ionic insertion/extraction (<20 s) can be realized in VO2 (B) anode. This interface derivation proposes a new path for designing proton ion insertion/extraction in mild electrolyte.

Proton/Mg2+ Co-Insertion Chemistry in Aqueous Mg-Ion Batteries: From the Interface to the Inner.

Co-insertion of protons happens widely and enables divalent-ion aqueous batteries to achieve high performances. However, detailed investigations and comprehensive understandings of proton co-insertion are scarce. Herein, we demonstrate that proton co-insertion into tunnel materials is determined jointly by interface derivation and inner diffusion: at the interface, hdrated Mg2+ has poor insertion kinetics, and therefore accumulates and hydrolyzes to produce protons; in the tunnels, co-inserted/lattice H2 O molecules block the Mg2+ diffusion while facilitate the proton diffusion. When monoclinic vanadium dioxide (VO2 (B)) anode is tested in Mg(CH3 COO)2 aqueous solution, the formation of Mg-rich solid electrolyte interphase on the VO2 (B) electrode and co-insertion of derived protons are probed; in the tunnels, the diffusion energy barrier of Mg2+ +H2 O is 2.7 eV, while that of the protons is 0.37 eV. Thus, protons dominate the subsequent insertion and inner diffusion. As a consequence, the VO2 (B) achieves a high capacity of 257.0 mAh g-1 at 1 A g-1 , a high rate retention of 59.1 % from 1 to 8 A g-1 , and stable cyclability of 3000 times with a capacity retention of 81.5 %. This work provides an in-depth understanding of the proton co-insertion and may promote the development of rechargeable aqueous batteries.