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Bismuth (Bi) has been known as a highly efficient electrocatalyst for CO 2 reduction reaction. Stable free-standing two-dimensional Bi monolayer (Bismuthene) structures have been predicted theoretically, but never realized experimentally. Here, we show the first simple large-scale synthesis of free-standing Bismuthene, to our knowledge, and demonstrate its high electrocatalytic efficiency for formate (HCOO − ) formation from CO 2 reduction reaction. The catalytic performance is evident by the high Faradaic efficiency (99% at −580 mV vs. Reversible Hydrogen Electrode (RHE)), small onset overpotential (<90 mV) and high durability (no performance decay after 75 h and annealing at 400 °C). Density functional theory calculations show the structure-sensitivity of the CO 2 reduction reaction over Bismuthene and thicker nanosheets, suggesting that selective formation of HCOO − indeed can proceed easily on Bismuthene (111) facet due to the unique compressive strain. This work paves the way for the extensive experimental investigation of Bismuthene in many different fields. Stable free-standing two-dimensional Bi monolayer (Bismuthene) structures have been predicted theoretically, but never realized experimentally. Here, the authors show a large-scale synthesis of free-standing Bismuthene and its electrocatalytic activity for CO 2 reduction to formate.

Due to the high theoretical specific energy, the lithium–oxygen battery has been heralded as a promising energy storage system for applications such as electric vehicles. However, its large over-potentials during discharge–charge cycling lead to the formation of side-products, and short cycle life. Herein, we report an ionic liquid bearing the redox active 2,2,6,6-tetramethyl-1-piperidinyloxy moiety, which serves multiple functions as redox mediator, oxygen shuttle, lithium anode protector, as well as electrolyte solvent. The additive contributes a 33-fold increase of the discharge capacity in comparison to a pure ether-based electrolyte and lowers the over-potential to an exceptionally low value of 0.9 V. Meanwhile, its molecule facilitates smooth lithium plating/stripping, and promotes the formation of a stable solid electrolyte interface to suppress side-reactions. Moreover, the proportion of ionic liquid in the electrolyte influences the reaction mechanism, and a high proportion leads to the formation of amorphous lithium peroxide and a long cycling life (> 200 cycles). In particular, it enables an outstanding electrochemical performance when operated in air. Li-O 2 batteries are promising candidates for the next generation of rechargeable batteries, but the side reactions and poor cycling stability limit their applications. Here, the authors show a versatile ionic liquid with functional groups that can address both issues for cells operated in oxygen and air.

A robust electrode–electrolyte interface is the cornerstone for every battery system, as demonstrated in the meandering history of the development of Li‐ion batteries (LIBs). In the thrust to replace the graphite anode with more energetic ones in LIBs, the effectual strategy for stabilizing the original graphite–electrolyte interface becomes obsolete and a new anode–electrolyte interface needs reconfiguration. Unfortunately, this interface has become the Achilles' heel for those anodes, such as Li‐metal anode (LMA) and Si‐based anode owing to their excessive reductivity, enormous volume change, and so forth. Encouragingly, in the last decade, impressive progress has been made on taming these extremely unstable interfaces and on the solid‐state batteries (SSBs) that are reported to be less susceptible to parasitic reactions. One of the distinguished strategies is the application of artificial Li‐alloying intermetallic interphases onto the surface of LMA, via the direct introduction of foreign metals to the Li anode or indirect hetero‐cations doping in the electrolyte, to regulate the Li deposition/stripping behavior, which has markedly improved the stability of the LMA–electrolyte interface. In parallel, the intermetallic interphases are also witnessed to profoundly enhance the anode–solid electrolyte contact and the corresponding charge transfer kinetics in various SSBs. This review will provide a panoramic overview of the application of the intermetallic interphases at the anode–electrolyte interfaces in the lithium metal batteries (LMBs), SSBs, and also derivative works in the conventional LIBs, which will focus on different concepts, methodologies, and understandings from the encircled studies. In this review, we summarized the recent advances and achievements in the application of intermetallic interphases in regulating the anode–electrolyte interface in both the LMBs and LIBs, with the main emphasis laid onto the former, in both liquid‐electrolyte and solid‐state embodiments. It will concentrate on the ideas, methodologies, and interpretations of the working mechanisms behind different approaches.

The non-aqueous Li–air (O 2 ) battery is receiving intense interest because its theoretical specific energy exceeds that of Li-ion batteries. Recharging the Li–O 2 battery depends on oxidizing solid lithium peroxide (Li 2 O 2 ), which is formed on discharge within the porous cathode. However, transporting charge between Li 2 O 2 particles and the solid electrode surface is at best very difficult and leads to voltage polarization on charging, even at modest rates. This is a significant problem facing the non-aqueous Li–O 2 battery. Here we show that incorporation of a redox mediator, tetrathiafulvalene (TTF), enables recharging at rates that are impossible for the cell in the absence of the mediator. On charging, TTF is oxidized to TTF + at the cathode surface; TTF + in turn oxidizes the solid Li 2 O 2 , which results in the regeneration of TTF. The mediator acts as an electron–hole transfer agent that permits efficient oxidation of solid Li 2 O 2 . The cell with the mediator demonstrated 100 charge/discharge cycles. Recharging Li–O 2 batteries requires oxidation of the discharge product solid Li 2 O 2 . Now a redox-mediating molecule is shown to assist this process by transferring electron–holes between solid Li 2 O 2 and the positive electrode in a non-aqueous Li–O 2 cell. This allows the cell to be charged at rates that are otherwise impossible.

Rechargeable lithium–air (O 2 ) batteries are receiving intense interest because their high theoretical specific energy exceeds that of lithium-ion batteries. If the Li–O 2 battery is ever to succeed, highly reversible formation/decomposition of Li 2 O 2 must take place at the cathode on cycling. However, carbon, used ubiquitously as the basis of the cathode, decomposes during Li 2 O 2 oxidation on charge and actively promotes electrolyte decomposition on cycling. Replacing carbon with a nanoporous gold cathode, when in contact with a dimethyl sulphoxide-based electrolyte, does seem to demonstrate better stability. However, nanoporous gold is not a suitable cathode; its high mass destroys the key advantage of Li–O 2 over Li ion (specific energy), it is too expensive and too difficult to fabricate. Identifying a suitable cathode material for the Li–O 2 cell is one of the greatest challenges at present. Here we show that a TiC-based cathode reduces greatly side reactions (arising from the electrolyte and electrode degradation) compared with carbon and exhibits better reversible formation/decomposition of Li 2 O 2 even than nanoporous gold (>98% capacity retention after 100 cycles, compared with 95% for nanoporous gold); it is also four times lighter, of lower cost and easier to fabricate. The stability may originate from the presence of TiO 2 (along with some TiOC) on the surface of TiC. In contrast to carbon or nanoporous gold, TiC seems to represent a more viable, stable, cathode for aprotic Li–O 2 cells. Although rechargeable lithium–air batteries are receiving significant attention because of their high theoretical specific energy, carbon cathodes that are currently used decompose during oxidation and promote electrolyte decomposition on cycling. A titanium carbide-based cathode is now shown to reduce side-reactions, and exhibits enhanced reversible formation and decomposition of Li 2 O 2 .

Among various efficient electrocatalysts for water splitting, CoFe and NiFe-based oxides/hydroxides are typically promising candidates thanks to their extraordinary activities towards oxygen evolution reaction (OER). However, the endeavor to advance their performance towards overall water splitting has been largely impeded by the limited activities for hydrogen evolution reaction (HER). Herein, we present a CoFeNi ternary metal-based oxide (CoFeNi-O) with impressive hierarchical bimodal channel nanostructures, which was synthesized via a facile one-step dealloying strategy. The oxide shows superior catalytic activities towards both HER and OER in alkaline solution due to the alloying effect and the intrinsic hierarchical porous structure. CoFeNi-O loaded on glass carbon electrodes only requires the overpotentials as low as 230 and 278 mV to achieve the OER current densities of 10 and 100 mA·cm −2 , respectively. In particular, extremely low overpotentials of 200 and 57.9 mV are sufficient enough for Ni foam-supported CoFeNi-O to drive the current density of 10 mA·cm −2 towards OER and HER respectively, which is comparable with or even better than the already-developed state-of-the-art non-noble metal oxide based catalysts. Benefiting from the bifunctionalities of CoFeNi-O, an alkaline electrolyzer constructed by the Ni foam-supported CoFeNi-O electrodes as both the anode and the cathode can deliver a current density of 10 mA·cm −2 at a fairly low cell-voltage of 1.558 V. In view of its electrocatalytic merits together with the facile and cost-effective dealloying route, CoFeNi-O is envisioned as a promising catalyst for future production of sustainable energy resources.

Transition-metal dichalcogenides （TMDs） exhibit immense potential as lithium/ sodium-ion electrode materials owing to their sandwich-like layered structures. To optimize their lithium/sodium-storage performance, two issues should be addressed： fundamentally understanding the chemical reaction occurring in TMD electrodes and developing novel TMDs. In this study, WSe2 hexagonal nanoplates were synthesized as lithium/sodium-ion battery （LIB/SIB） electrode materials. For LIBs, the WSe2-nanoplate electrodes achieved a stable reversible capacity and a high rate capability, as well as an ultralong cycle life of up to 1,500 cycles at 1,000 mA·g^-1. Most importantly, in situ Raman spectroscopy, ex situ X-ray diffraction （XRD）, transmission electron microscopy, and electrochemical impedance spectroscopy measurements performed during the discharge-charge process clearly verified the reversible conversion mechanism, which can be summarized as follows： WSe2 ＋ 4Li^＋ ＋ 4e^- ←→ W ＋ 2Li2Se. The WSe2 nanoplates also exhibited excellent cycling performance and a high rate capability as SIB electrodes. Ex situ XRD and Raman spectroscopy results demonstrate that WSe2 reacted with Na^＋ more easily and thoroughly than with Li^＋ and converted to Na2Se and tungsten in the Ist sodiated state. The subsequent charging reaction can be expressed as Na2Se → Se ＋ 2Na^＋＋ 2e^-, which differs from the traditional conversion mechanism for LIBs. To our knowledge, this is the first systematic exploration of the lithium/sodium-storage performance of WSe2 and the mechanism involved.

Closed pores are widely accepted as the critical structure for hard carbon negative electrodes in sodium-ion batteries. However, the lack of a clear definition and design principle of closed pores leads to the undesirable electrochemical performance of hard carbon negative electrodes. Herein, we reveal how the evolution of pore mouth sizes determines the solvation structure and thereby redefine the closed pores. The precise and uniform control of the pore mouth sizes is achieved by using carbon molecular sieves as a model material. We show when the pore mouth is inaccessible to N 2 but accessible to CO 2 molecular probes, only a portion of solvent shells is removed before entering the pores and contact ion pairs dominate inside pores. When the pore mouth is inaccessible to CO 2 molecular probes, namely smaller than 0.35 nm, solvent shells are mostly sieved and dominated anion aggregates produce a thin and inorganic NaF-rich solid electrolyte interphase inside pores. Closed pores are accordingly redefined, and initial coulombic efficiency, cycling and low-temperature performance are largely improved. Furthermore, we show that intrinsic defects inside the redefined closed pores are effectively shielded from the interfacial passivation and contribute to the increased low-potential plateau capacity. Closed pores govern sodium-ion storage performance of hard carbon negative electrodes. Here, authors link pore mouth size evolution of the closed pores to the solvation structure and propose design principles for optimizing both closed pores and intrinsic defects.

Magnesium ion batteries are emerging as promising alternatives to lithium ion batteries because of their advantages including high energy density, dendrite-free features and low cost. Nevertheless, one of the major challenges for magnesium ion batteries is the kinetically sluggish magnesium insertion/extraction and diffusion in electrode materials. Aiming at this issue, biphase eutectic-like bismuth-tin film is designed herein to construct a self-supporting anode with interdigitated phase distribution and hierarchically porous structure, and further fabricated by a facile one-step magnetron cosputtering route. As benchmarked with single-phase bismuth or tin film, the biphase bismuth-tin film delivers high specific capacity (538 mAh/g at 50 mA/g), excellent rate performance (417 mAh/g at 1,000 mA/g) and good cycling stability (233 mAh/g at the 200th cycle). The superior magnesium storage performance of the sputtered bismuth-tin film could be attributed to the synergetic effect of the interdigitated bismuth/tin phase distribution, hierarchically porous structure and biphase buffering matrices, which could increase ionic transport channels, shorten diffusion lengths and reduce total volume changes.

Li‐CO2 batteries could skillfully combine the reduction of “greenhouse effect” with energy storage systems. However, Li‐CO2 batteries still suffer from unsatisfactory electrochemical performances and their rechargeability is challenged. Here, it is reported that a composite of Ni nanoparticles highly dispersed on N‐doped graphene (Ni‐NG) with 3D porous structure, exhibits a superior discharge capacity of 17 625 mA h g−1, as the air cathode for Li‐CO2 batteries. The batteries with these highly efficient cathodes could sustain 100 cycles at a cutoff capacity of 1000 mA h g−1 with low overpotentials at the current density of 100 mA g−1. Particularly, the Ni‐NG cathodes allow to observe the appearance/disappearance of agglomerated Li2CO3 particles and carbon thin films directly upon discharge/charge processes. In addition, the recycle of CO2 is detected through in situ differential electrochemical mass spectrometry. This is a critical step to verify the electrochemical rechargeability of Li‐CO2 batteries. Also, first‐principles computations further prove that Ni nanoparticles are active sites for the reaction of Li and CO2, which could guide to design more advantageous catalysts for rechargeable Li‐CO2 batteries. A composite of Ni nanoparticles highly dispersed on N‐doped graphene is prepared as the air cathode for Li‐CO2 batteries, with high discharge capacity and excellent cyclic stability. The cathode allows to observe the morphological evolution of discharge products directly and reversible consumption and evolution of CO2, and then the reversibility of electrochemical reactions could well be understood in Li‐CO2 batteries.