High‐entropy alloys combine multiple principal elements at a near equal fraction to form vast compositional spaces to achieve outstanding functionalities that are absent in alloys with one or two principal elements. Here, the prediction, synthesis, and multiscale characterization of 2D high‐entropy transition metal dichalcogenide (TMDC) alloys with four/five transition metals is reported. Of these, the electrochemical performance of a five‐component alloy with the highest configurational entropy, (MoWVNbTa)S2, is investigated for CO2 conversion to CO, revealing an excellent current density of 0.51 A cm−2 and a turnover frequency of 58.3 s−1 at ≈ −0.8 V versus reversible hydrogen electrode. First‐principles calculations show that the superior CO2 electroreduction is due to a multi‐site catalysis wherein the atomic‐scale disorder optimizes the rate‐limiting step of CO desorption by facilitating isolated transition metal edge sites with weak CO binding. 2D high‐entropy TMDC alloys provide a materials platform to design superior catalysts for many electrochemical systems.

Metal–organic frameworks (MOFs) are promising materials for electrocatalysis; however, lack of electrical conductivity in the majority of existing MOFs limits their effective utilization in the field. Herein, an excellent catalytic activity of a 2D copper (Cu)‐based conductive MOF, copper tetrahydroxyquinone (CuTHQ), is reported for aqueous CO2 reduction reaction (CO2RR) at low overpotentials. It is revealed that CuTHQ nanoflakes (NFs) with an average lateral size of 140 nm exhibit a negligible overpotential of 16 mV for the activation of this reaction, a high current density of ≈173 mA cm−2 at −0.45 V versus RHE, an average Faradaic efficiency (F.E.) of ≈91% toward CO production, and a remarkable turnover frequency as high as ≈20.82 s−1. In the low overpotential range, the obtained CO formation current density is more than 35 and 25 times higher compared to state‐of‐the‐art MOF and MOF‐derived catalysts, respectively. The operando Cu K‐edge X‐ray absorption near edge spectroscopy and density functional theory calculations reveal the existence of reduced Cu (Cu+) during CO2RR which reversibly returns to Cu2+ after the reaction. The outstanding CO2 catalytic functionality of conductive MOFs (c‐MOFs) can open a way toward high‐energy‐density electrochemical systems.

Conversion of CO2 to energy‐rich chemicals using renewable energy is of much interest to close the anthropogenic carbon cycle. However, the current photoelectrochemical systems are still far from being practically feasible. Here the successful demonstration of a continuous, energy efficient, and scalable solar‐driven CO2 reduction process based on earth‐abundant molybdenum disulfide (MoS2) catalyst, which works in synergy with an inexpensive hybrid electrolyte of choline chloride (a common food additive for livestock) and potassium hydroxide (KOH) is reported. The CO2 saturated hybrid electrolyte utilized in this study also acts as a buffer solution (pH ≈ 7.6) to adjust pH during the reactions. This study reveals that this system can efficiently convert CO2 to CO with solar‐to‐fuel and catalytic conversion efficiencies of 23% and 83%, respectively. Using density functional theory calculations, a new reaction mechanism in which the water molecules near the MoS2 cathode act as proton donors to facilitate the CO2 reduction process by MoS2 catalyst is proposed. This demonstration of a continuous, cost‐effective, and energy efficient solar driven CO2 conversion process is a key step toward the industrialization of this technology.

electrochemical reactions. [1][2][3][4][5][6][7][8][9][10][11] In particular, molybdenum disulfide (MoS 2 ) and a few members of transition metal dichalcogenides (TMDCs) in contact with ionic-liquid (IL) electrolyte have recently shown a great promise to overcome fundamental electronic and thermokinetic limitations for CO 2 reduction reaction, as well as the oxygen reduction and evolution reactions (ORR/OER). [7][8][9][10] These studies have been conducted on a limited number of TMDCs, and the majority of other TMDCs with a wide range of electronic and potentially catalytic properties have not been investigated. In this study, we report synthesis and characterization of a wide range of TMDCs including sulfides, selenides, and tellurides of group V and VI transition metals and study their electrochemical performance in aprotic medium with Li salts. We employ a wide suite of characterization techniques, such as scanning transmission electron microscopy (STEM), energy dispersive spectroscopy (EDS), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), dynamic light scattering (DLS), and atomic forceThe optimization of traditional electrocatalysts has reached a point where progress is impeded by fundamental physical factors including inherent scaling relations among thermokinetic characteristics of different elementary reaction steps, non-Nernstian behavior, and electronic structure of the catalyst. This indicates that the currently utilized classes of electrocatalysts may not be adequate for future needs. This study reports on synthesis and characterization of a new class of materials based on 2D transition metal dichalcogenides including sulfides, selenides, and tellurides of group V and VI transition metals that exhibit excellent catalytic performance for both oxygen reduction and evolution reactions in an aprotic medium with Li salts. The reaction rates are much higher for these materials than previously reported catalysts for these reactions. The reasons for the high activity are found to be the metal edges with adiabatic electron transfer capability and a cocatalyst effect involving an ionic-liquid electrolyte. These new materials are expected to have high activity for other core electrocatalytic reactions and open the way for advances in energy storage and catalysis. ElectrocatalystsThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.

with applications in health monitoring and diagnostics, [1][2][3][4][5] human-machine interface devices, [6,7] cell phones and laptops, [8,9] internet of things, [10] and athletics applications. [11,12] Among various alternative energy storage systems, Li-Oxygen (Li-O 2 ) batteries are promising candidates to meet the requirements of modern flexible electronics with a long-time operation due to their ultrahigh theoretical energy density of ≈3500 Wh kg −1 which is about one order of magnitude higher than that of Li-ion batteries (≈400 Wh kg −1 ). [13][14][15] However, most flexible Li-O 2 batteries operate with a current density in the range of 100-500 mA g −1 , [16][17][18][19][20][21][22][23][24][25] which is far from practical applications of flexible electronics. In addition, the majority of these batteries operate in a pure oxygen environment. Thus, it is imperative that these batteries operate at much higher current rates in an air-like atmosphere since it enables a much higher volumetric energy density compared to its operation in a pure oxygen environment. It also provides a safe and cost-effective approach. Nevertheless, in the presence of all components of air (e.g., nitrogen (N 2 ), carbon dioxide (CO 2 ), and moisture), the Li-O 2 battery operation becomes more complex and serious issues are imposed on the battery including: i) degradation of anode due to its reaction with air compounds, ii) clogging of the cathode due to formation of poorly reversible side products such as lithium hydroxide (LiOH), and iii) degradation of the electrolyte due to sides reactions. [26][27][28] These issues negatively affect the round-trip efficiency and cause other problems, such as parasitic reactions, which lead to poor cyclability and early death of the battery. [29][30][31][32] To resolve these issues, in this study, we designed, fabricated, and tested a new architecture for sheet-type flexible Li-O 2 batteries that operate in ambient air with an open system (flow in and out) where unlike closed systems, no gas storage chamber is needed. In addition, our system is comprised of a Fomblin-based protection layer to filter unwanted air species, such as H 2 O, [33] and an electrolyte blend of 1 m bis(trifluoromethanesulfonyl) imide (LiTFSI) salt, redox mediator (RM) of indium bromide (InBr 3 ) to simultaneously reduce the charge potential and protect the anode from parasitic reactions, [34] and dimethyl sulfoxide (DMSO) and ionic liquid of 1-Ethyl-3-methylimidazolium tetrafluoroborate EMIM-BF4 Lithium-oxygen (Li-O 2 ) batteries possess the highest theoretical energy density (3500 Wh kg −1 ), which makes them attractive candidates for modern electronics and transportation applications. In this work, an inexpensive, flexible, and wearable Li-O 2 battery based on the bifunctional redox mediator of InBr 3 , MoS 2 cathode catalyst, and Fomblin-based oxygen permeable membrane that enable long-cycle-life operation of the battery in pure oxygen, dry air, and ambient air is designed, fabricated, and tested. The battery operates in...

promising solution since it offers the highest theoretical energy density, that can substantially outperform Li-ion batteries. [1][2][3][4][5][6] Recently, Li-O 2 batteries have attracted a significant attention in various applications such as electrified transportation and smart grid systems; however, on the path of their practical use, there still remain many obstacles. The sluggish kinetics of the governing reactions during discharge and charge impose high overpotentials that result in low round trip efficiency. [7,8] Moreover, an inefficient decomposition of solid discharge products (Li 2 O 2 ) and its accumulation on the surface of the cathode lead to poor cycling (early failure) in these systems. [9,10] To address these issues, discovery of new cathode materials with outstanding functionalities is essential. In this context, metal organic frameworks (MOFs) are promising platforms owing to their high porosity, large surface area, highly ordered structure, and tunable chemical composition. These characteristics make MOFs an ideal candidate to be investigated as electrode materials in electrochemical energy applications [11][12][13] and especially rechargeable batteries. [14][15][16] However, traditional MOFs are still far from practical cathode materials due to their insulating nature stemming from the redox-inactive organic ligands and low-energy electron transfer pathways. [15,[17][18][19] Lithium-oxygen batteries are among the most attractive alternatives for future electrified transportation. However, their practical application is hindered by many obstacles. Due to the insulating nature of Li 2 O 2 product and the slow kinetics of reactions, attaining sustainable low charge overpotentials at high rates becomes a challenge resulting in the battery's early failure and low round trip efficiency. Herein, outstanding characteristics are discovered of a conductive metal organic framework (c-MOF) that promotes the growth of nanocrystalline Li 2 O 2 with amorphous regions. This provides a platform for the continuous growth of Li 2 O 2 units away from framework, enabling a fast discharge at high current rates. Moreover, the Li 2 O 2 structure works in synergy with the redox mediator (RM). The conductivity of the amorphous regions of the Li 2 O 2 allows the RM to act directly on the Li 2 O 2 surface instead of catalyst edges and then transport through the electrolyte to the Li 2 O 2 surface. This direct charge transfer enables a small charge potential of <3.7 V under high current densities (1-2 A g −1 ) sustained for a long cycle life (100-300 cycles) for large capacities (1000-2000 mAh g −1 ). These results open a new direction for utilizing c-MOFs towards advanced energy storage systems.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smll.202102902.

Transition metal dichalcogenides (TMDCs) have garnered much attention recently due to their remarkable performance for different electrochemical systems. In this study, we report on the synthesis and catalysis of less studied TMDC nanoflakes (NFs) with a design space comprised of three transition metals (rhenium, ruthenium, and iridium) and three chalcogens (sulfur, selenium, and tellurium) for the oxygen reduction and evolution reactions (ORR and OER) in an aprotic hybrid electrolyte containing 0.1 M lithium bis­(trifluoromethanesulfonyl)­imide salt in 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid and dimethyl sulfoxide. Our results indicate that among the tested catalysts, ReS2 exhibits the highest current density for both ORR and OER, beyond those of the state-of-the-art catalysts used in aprotic media with Li salts. We performed density functional calculations to provide a mechanistic understanding of the reactions in the ReS2 NFs/ionic liquid system. These novel bifunctional catalyst results could open a way for exploiting the unique properties of these materials in Li–O2 batteries as well as other important electrochemical systems.

Gallium-based room-temperature liquid metals possess extremely valuable properties, such as low toxicity, low vapor pressure, and high thermal and electrical conductivity enabling them to become suitable substitutes for mercury and beyond in wide range of applications. When exposed to air, a native oxide layer forms on the surface of gallium-based liquid metals which mechanically stabilizes the liquid. By removing or reconstructing the oxide skin, shape and state of liquid metal droplets and flows can be manipulated/actuated desirably. This can occur manually or in the presence/absence of a magnetic/electric field. These methods lead to numerous useful applications such as soft electronics, reconfigurable devices, and soft robots. In this mini-review, we summarize the most recent progresses achieved on liquid metal droplet generation and actuation of gallium-based liquid metals with/without an external force.