With the rapidly increasing interests on wearable electronics over the past decades, the limited energy density and nondeformable configuration of conventional 2D lithium-ion batteries (LIBs) have already become the dominant obstacles that are hindering the roads of wearable consumer electronics toward ubiquity. [1][2][3][4][5] Hence, it is urgent to develop an alternative highperformance flexible energy storage device to break through the inherent restrictions of rigid LIBs. [6][7][8] The Li-CO 2 battery, a newly conceptual metal-gas battery, has been considered as a promising candidate for the next-generation high-performance electrochemical energy storage system recently. [9,10] It possesses a high theoretical energy density via the four-electrons transfer reaction (4Li + + 3CO 2 + 4e − → 2Li 2 CO 3 + C, E° = 2.80 V vs Li + /Li) and provides a novel environmentally friendly approach to CO 2 fixing which is of great benefit to alleviate global warming. [11][12][13] Interestingly, the Li-CO 2 battery is also very attractive for aerospace exploration; for example, it may be a possible energy system for providing electricity on Mars where the atmosphere consists of 96% CO 2 gas. [14] In spite of the aforementioned favorable factors, very few reports in the literature related to flexible Li-CO 2 battery devices for wearable electronics have been reported so far. After systematical investigations, it is found that the main challenges of fabricating high-performance flexible Li-CO 2 battery devices lie in the following three aspects: (1) carbon nanophases (e.g., Ketjenblack, [9,10,15] CNTs, [11,16] graphene [17,18] ), which dominate those known Li-CO 2 battery catalysts, induce the formation of Li 2 CO 3 , a wide-bandgap insulator. [19,20] It results in a sluggish kinetics for CO 2 evolution so that a high charge potential of 4.2-4.6 V was commonly required to drive the degradation of Li 2 CO 3 in most previous Li-CO 2 batteries. [10,11,17] Such high potential not only increases the risk of electrolyte decomposition but also accelerates the oxidation of electrodes. [21,22] Meanwhile, originated from the incomplete decomposition, more and more solid carbonate species accumulated in the surface of cathode during cycling, leading to a distinct decrease on catalytic performance and even the rapid extension of impedance up to a "sudden death" of the battery. [20,23,24] Consequently, the majority of those reported Li-CO 2 batteries showed a negligibleThe rapid development of wearable electronics requires a revolution of power accessories regarding flexibility and energy density. The Li-CO 2 battery was recently proposed as a novel and promising candidate for nextgeneration energy-storage systems. However, the current Li-CO 2 batteries usually suffer from the difficulties of poor stability, low energy efficiency, and leakage of liquid electrolyte, and few flexible Li-CO 2 batteries for wearable electronics have been reported so far. Herein, a quasi-solidstate flexible fiber-shaped Li-CO 2 battery with low overpotential and ...

First-principles density functional theory calculations are first used to study possible reaction mechanisms of molybdenum carbide (Mo2C) as cathode catalysts in Li-CO2 batteries. By systematically investigating the Gibbs free energy changes of different intermediates during lithium oxalate (Li2C2O4) and lithium carbonate (Li2CO3) nucleations, it is theoretically demonstrated that Li2C2O4 could be stabilized as the final discharge product, preventing the further formation of Li2CO3. The surface charge distributions of Li2C2O4 adsorbing onto catalytic surfaces are studied by using Bader charge analysis, given that electron transfers are found between Li2C2O4 and Mo2C surfaces. The catalytic activities of catalysts are intensively evaluated toward the discharge and charge processes by calculating the electrochemical free energy diagrams to identify the overpotentials. Our studies promote the understanding of electrochemical processes and shed more light on the design and optimization of cathode catalysts for Li-CO2 batteries.

is inevitable in Li-CO 2 batteries, [11,12] Li-CO 2 /O 2 batteries, [8,13] and even Li-air batteries. [14] Exception is that the discharge products could be different without the generation of Li 2 CO 3 under specific conditions including protected anodes and effective electrolytes. [15,16] Li 2 CO 3 decomposes to CO 2 when the potential is higher than 3.8 V versus Li/Li + . Notably, O 2 evolution is not detected, as is expected according to the decomposition reaction 2Li 2 CO 3 → 4Li + + 4 e -+ 2CO 2 + O 2 . Instead, superoxide radicals or "nascent oxygen" form during the self-decomposition of Li 2 CO 3 . [12,17] More accurate verification was performed through chemical probes, which qualitatively detected the existence of singlet oxygen ( 1 O 2 ). [18] Parasitic reactions of electrolytes and catalyst degradation were then induced by Li 2 CO 3 oxidation. [12,18] Therefore, efficient air cathodes are expected to change this situation.The introduction of metal nanoparticles could limit side reactions and promote the interaction between Li 2 CO 3 and C. [11,[19][20][21] Beyond this, metal-organic frameworks or surface modified carbon materials also brought unexpected electrochemical performance. [22,23] Therefore, catalysts play important roles in Li-CO 2 batteries. [24][25][26][27][28][29] As mentioned above, self-decomposition of Li 2 CO 3 induced a series of parasitic reactions, and further influenced the stability of catalysts during the operation of Li-CO 2 batteries. Only by clarifying the changes of catalysts in this process can we design more stable Li-CO 2 batteries. In previous reports, mono metal catalysts (Ru, Cu, Au, and Ni) exhibited outstanding activity toward Li-CO 2 batteries and revealed some changes in electrochemical processes. [19][20][21] Nevertheless, there exist shortcomings with mono metal catalysts from materials preparation to electrochemical processes. First, for example, the preparation for monodispersed Ru nanoparticles was often achieved under mild experimental conditions without the generation of stable crystal surfaces, further affecting catalytic activity in Li-CO 2 batteries. [21,30] Second, the incompatibility between the discharge products and mono metal nanomaterials might lead to severe agglomeration and dropping during long cycles. [20,31] In this work, we designed a composite of ruthenium-copper nanoparticles highly co-dispersed on graphene (Ru-Cu-G), and this composite cathode endows Li-CO 2 batteries with low overpotential and excellent cyclability through their synergistic Li-CO 2 batteries are attractive electrical energy storage devices; however, they still suffer from unsatisfactory electrochemical performance, and the kinetics of CO 2 reduction and evolution reactions must be improved significantly. Herein, a composite of ruthenium-copper nanoparticles highly co-dispersed on graphene (Ru-Cu-G) as efficient air cathodes for Li-CO 2 batteries is designed. The Li-CO 2 batteries with Ru-Cu-G cathodes exhibit ultra-low overpotential and can be operated for 100 cycles with ...

Noble metals, especially gold, have been widely used in plasmon resonance applications. Although silver has a larger optical cross section and lower cost than gold, it has attracted much less attention because of its easy corrosion, thereby degrading plasmonic signals and limiting its applications. To circumvent this problem, we report the facile synthesis of superstable AgCu@graphene (ACG) nanoparticles (NPs). The growth of several layers of graphene onto the surface of AgCu alloy NPs effectively protects the Ag surface from contamination, even in the presence of hydrogen peroxide, hydrogen sulfide, and nitric acid. The ACG NPs have been utilized to enhance the unique Raman signals from the graphitic shell, making ACG an ideal candidate for cell labeling, rapid Raman imaging, and SERS detection. ACG is further functionalized with alkyne-polyethylene glycol, which has strong Raman vibrations in the Raman-silent region of the cell, leading to more accurate colocalization inside cells. In sum, this work provides a simple approach to fabricate corrosion-resistant, water-soluble, and graphene-protected AgCu NPs having a strong surface plasmon resonance effect suitable for sensing and imaging.

Ceria has conventionally been thought to have a cubic fluorite structure with stable geometric and electronic properties over a wide temperature range. Here we report a reversible tetragonal (P42/nmc) to cubic (Fm-3m) phase transition in nanosized ceria, which triggers negative thermal expansion in the temperature range of −25 °C–75 °C. Local structure investigations using neutron pair distribution function and Raman scatterings reveal that the tetragonal phase involves a continuous displacement of O2− anions along the fourfold axis, while the first-principles calculations clearly show oxygen vacancies play a pivotal role in stabilizing the tetragonal ceria. Further experiments provide evidence of a charge transfer between oxygen vacancies and 4f orbitals in ceria, which is inferred to be the mechanism behind this anomalous phase transition.