Because of their versatile application potential, such as fuel cells and water electrolysis, boosting electrochemical half-cell reactions has been highlighted to realize energy conversion systems. However, sluggish multi-charge transfer reactions lower the energy efficiency for cell operation. Tailoring hierarchical catalyst nanostructures comprising heterogeneous crystalline phases allows for the improvement of limited activities and reaction performance. This study examines the controllable synthesis of heterogeneous rhenium oxide (ReOx) and rhenium sulfide (ReS2) nanoflakes vertically aligned on carbon nanofibers (CNFs) by thermal chemical vapor deposition (CVD). Their potential application as electrocatalysts in various electrochemical half-cell reactions for fuel cells and water electrolysis is elucidated. The phase portion of oxide and sulfide in the ReOx/ReS2 nanoflakedecorated CNF catalyst can be thermally tuned from an oxide-rich phase to a sulfide-rich phase, thereby optimizing the catalytic activities for hydrogen evolution (E-onset:-0.24 V) and oxygen reduction reactions (E-onset: 0.778 V, number of electron: 3.8), which is comparable to the performance of commercial Pt/C catalysts. The morphological and structural evolution mechanism of the ReOx/ReS2 nanoflake-decorated CNF catalyst materials is investigated using diverse material characterizations. This study suggests a synthetic method for temperature dependent heterogeneous phase control of non-precious-metal-based hierarchical materials and offers a basis for developing efficient catalyst alternatives for application to sustainable energy conversion and storage systems.

In this study, we report the electrochemical reaction mechanism and structural evolution of zirconium disulfide (ZrS2) electrode materials for Li-ion batteries, analogous to titanium disulfide (TiS2), known as the first intercalation compound. To minutely explore the electrochemical behaviors of the ZrS2 electrode in Li-ion cells, we conducted galvanostatic charge/discharge and cyclic voltammetry measurements at different depths of discharge, thereby observing the reaction change characteristics between the intercalation and conversion reactions. Furthermore, structural changes in the ZrS2 electrodes collected at different electrochemical states were investigated by ex-situ characterizations to identify the electrochemical reaction behaviors in detail. Our basic study on ZrS2 can provide important information and directions for those considering the electrochemical properties and design of ZrS2 for alkali-ion batteries.

Lithium-carbon dioxide (Li-CO2) batteries possess bifunctional applications in energy storage and greenhouse gases capture; however, the sluggish decomposition kinetics of discharge products during recharge impair battery lifespan, while severely raising Li-CO2 cells overpotentials. Hereby, we report a synthetic strategy for embedding iron (Fe) nanoparticles in nitrogen-doped carbon nanotubes (N-doped CNTs) (Fe NPs@N-CNTs) via capillary action of hemoglobin solution, and their potential as catalytic electrodes for efficient Li-CO2 cells. We elucidate under varying thermal conditions the conversion mechanisms by which Fe nanoparticles are incorporated into CNTs by capillary force. Compared with pristine cells, Li-CO2 cells employing Fe NPs@N-CNT catalysts deliver triple charge and discharge capacities, as well as stable cycle performance accompanied by lower charge polarization. By observing the reversible binding and disconnection between Fe and CO2 during ex situ characterization, it was revealed that Fe nanoparticles act as catalyst components. Our suggested method focuses on rational designing of catalyst-embedded nanotube composites and highlighting their potential applications in advanced energy and environmental devices.

Developing an efficient and sustainable electrocatalyst for facilitating sluggish oxygen reduction reaction (ORR) is a key issue for the realization of metal-air batteries and fuel cells. The platinum deposited carbon (i.e., Pt/C) is the most popular and widely adopted catalyst system for enhancing the ORR kinetics. Unfortunately, the practical use of Pt/C is severely limited by low electrochemical oxidation resistance and subsequent structural collapse of the carbon-based support materials, especially during dynamic cell operations.[1] Recently, alternative inorganic metal oxides (TiO2, WO3, etc.) have been spotlighted as catalyst support due to higher electrochemical robustness than carbon. However, other properties such as electronic conductivity and electrochemical catalyst-support interactions should be considered to perform as a support material for achieving a prominent performance of supported catalyst.[2] Several methods for modulating the properties of metal oxides has been suggested to overcome their intrinsic limitation such as electronic and electrochemical features. Particularly, the off-stoichiometric metal oxides with oxygen-deficient structure have known to exhibit unique surface activity and electrical property. For example, tungsten oxide with low oxidation number, called black WO3-x, can offer several advantages such as (i) high electronic conductivity induced by reduced bandgap, (ii) high surface activity, (iii) improved ion mobility, and (iv) structural flexibility by generating free volumes.[3-7] However, the applicability and feasibility of WO3-x materials as a catalyst support have rarely been reported. In this work, we successfully synthesize the black WO3-x nanofiber (NF) via electrospinning and subsequent reducing thermal treatments, and elucidate their performance as a Pt catalyst support material. Morphological and structural characterizations of the black WO3-x NF are carried out to investigate unique features of the WO3-x NF. It is noted that the Pt catalysts supported on black WO3-x nanofibers (Pt/black WO3-xNF) outperform the Pt/white WO3 NF reference in electrochemical ORR and prolonged cycle tests. We also demonstrate the origin of high durability and catalytic functions of the black WO3-x NF as catalyst support by using various Ex-situ characterizations. [1] Lei Du, Yuyan Shao, Junming Sun, Geping Yin, Jun Liu, and Yong Wang, Nano Energy, 2016, 29, 314-322 [2] P. A. Shinde, S. C. Jun, ChemSusChem 2020, 13, 11. [3] Na-Won Lee, Ji-Won Jung, Jun-Seo Lee, Hye-Yeon Jang, Il-Doo Kim, and Won-Hee Ryu, Electrochimica Acta, 2018, 263, 417-425. [4] Na-Won Lee, Ki Ro Yoon, Jae Yun Lee, Yoonsu Park, Seongji Pyo, Ga-Yoon Kim, Don-Hyung Ha, and Won-Hee Ryu, ACS Applied Energy Materials, 2019, 2, 3513-3522. [5] Won-Hee Ryu, Hope Wilson, Sungwoo Sohn, Jinyang Li, Xiao Tong, Evyatar Shaulsky, Jan Schroers, Menachem Elimelech, André D. Taylor, ACS Nano, 2016, 10, 3, 3257-3266 [6] Ji-Yong Eom, Sung-Jin Lim, Sang-Min Lee, Won-Hee Ryu and Hyuk-Sang Kwon, J. Mater. Chem. A, 2015, 3, 11183-11188 [7] Jiajia Song, Zhen-Feng Huang, Lun Pan, Ji-Jun Zou, Xiangwen Zhang, and Li Wang, ACS Catalysis, 2015, 5, 6594-6599

Lithium-oxygen (Li-O2) batteries have been intensively investigated in recent decades for their utilization in electric vehicles. The intrinsic challenges arising from O2 (electro)chemistry have been mitigated by developing various types of catalysts, porous electrode materials, and stable electrolyte solutions. At the next stage, we face the need to reform batteries by substituting pure O2 gas with air from Earth's atmosphere. Thus, the key emerging challenges of Li-air batteries, which are related to the selective filtration of O2 gas from air and the suppression of undesired reactions with other constituents in air, such as N2, water vapor (H2O), and carbon dioxide (CO2), should be properly addressed. In this review, we discuss all key aspects for developing Li-air batteries that are optimized for operating in ambient air and highlight the crucial considerations and perspectives for future air-breathing batteries.

Hafnium oxide (HfO2), which is known as hafnia, is considered one of the best materials for various future applications such as neuromorphic computing systems and optical coatings. Although tetragonal phase (t-phase) in the multiple crystallographic structures of HfO2 outperforms monoclinic phase (m-phase) most common phase that can be formed at low temperature in physicochemical properties such as dielectric constant, bandgap, high resistance to corrosion and hardness, it is extremely hard to stabilize t-phase below 1670 degrees C. Herein, we synthesized oxygen-deficient tetragonal hafnium oxide nanofibers (t-HfO2-x NFs) using the electrospinning technique, which included the polymer-blended precursors and a magnesium-thermic reaction at a low processing temperature (< 600 degrees C). The small grain size (< 10 nm) of the t-HfO2-x NFs and oxygen vacancies (V-oxygen) synergistically stabilized t-phase in the nanofibrous structure. Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) performances of the t-HfO2-x NFs in alkaline and acid media were evaluated as a potential application, which were higher than those of the m-HfO2 NFs. Our straightforward approach to make t-phase in HfO2-based materials can be broadly applied for many future applications.

Electrochemical Li-CO2 cells, which provide a sustainable and environmentally friendly pathway away from greenhouse gases, often suffer from sluggish kinetics for the growth and evolution of the cathode species on an electrode. The problematic irreversibility of the solid-to-gas conversion reactions can be addressed by the introduction of efficient catalysts into the Li-CO2 cell. Here, we report the direct utilization of hemoglobin proteins, which are plentiful bioresources extracted from blood wastes, to effectively boost two-way Li-CO2 reactions. The hemoglobin was immobilized on a cathodic electrode and showed excellent catalytic activity and improved capacity for CO2 reduction and evolution reactions with a desirable weight ratio between the conductive carbons and the hemoglobin catalysts. We also verified the structural characteristics of lithium carbonate product species and the reversibility of the Li-CO2 reaction by ex situ studies. The iron ion active site in a heterocyclic porphyrin ring of hemoglobin can participate in the Li-CO2 reaction as a redox component.

Nature-inspired molecules present a family of affordable, environmentally friendly catalysts to enable and enhance next-generation energy storage systems. In this study, we report the use of cobalt-based polyoxometalates (Co-POMs) with an oxo-bridged tetracobalt active site, which is reminiscent of the natural oxygen-evolving complex, as an efficient and stable redox catalyst for Li-O-2 batteries. Interestingly, Co-POMs exhibit catalytic activity for both oxygen evolution and reduction reactions (OER and ORR, respectively) under a certain condition when it forms a stable dispersion of molecular aggregates, which can be controlled by the types of electrolyte solvents and exposure to light. As a result of the optimized OER/ORR bifunctional activity, Li-O-2 cells facilitated by Co-POM redox reactions successfully achieve improved efficiency and a longer cycle life in comparison to reference cells. The reversibility of the Li-O-2 reactions in the presence of the bifunctional Co-POM catalysts is confirmed by ex situ characterizations.

Lithium-oxygen (Li-O 2 ) batteries employing a lightweight and gaseous oxygen cathode have been spotlighted because of their exceptional high-energy density (practically 2~3 times higher than lithium-ion cells). [1-2] However, their poor efficiency and cyclability originating from the sluggish kinetics for the formation and decomposition of lithium oxide products (i.e., LiO 2 , Li 2 O 2 ) necessitate utilization of efficient catalysts. Although loading of the solid catalysts on the electrode effectively facilitates the Li-O 2 cell reactions, they are quickly deactivated upon cycling due to accumulating product residues. [3-4] Incorporation of soluble redox molecules into an electrolyte has been considered an effective alternative strategy to address the deactivation issues. [5] Their redox properties enable rapid electron transfer from/to the electrode through their self-diffusion and subsequent redox reactions instead of a slow electron movement through the insulating discharge products. Development of potential redox catalysts for Li-O 2 cells should meet the following requirements: (i) high mobility in electrolyte; (ii) reversible redox properties for fast electron transfer; (iii) robust stability; and (iv) environmental friendliness. In this work, we report a class of nature-inspired molecules as an efficient and stable redox catalyst for Li-O 2 batteries. Interestingly, the catalyst molecules exhibits catalytic activity for both oxygen evolution and reduction reactions under a certain condition when it forms a stable dispersion of molecular aggregates, which can be controlled by types of electrolyte solvents and exposure to light. As a result of the optimized catalytic activity, the Li-O 2 cells facilitated by redox reactions successfully achieve improved efficiency and a longer cycle life compared to reference cells. The reversibility of the Li-O 2 reactions in the presence of the molecular catalysts is confirmed by ex-situ characterizations. [1] Ryu, W. H.; Yoon, T. H.; Song, S. H.; Jeon, S.; Park, Y. J.; Kim, I. D. Nano Lett 2013, 13, 4190-7. [2] Gittleson, F. S.; Yao, K. P. C.; Kwabi, D. G.; Sayed; Ryu, W.-H.; Shao-Horn, Y.; Taylor, A. D., ChemElectroChem 2015 , 2, 1446-1457. [3] Ryu, W. H.; Gittleson, F. S.; Schwab, M.; Goh, T.; Taylor, A. D., Nano Lett 2015, 15 , 434-441 [4] Ryu, W. H.; Gittleson, F. S.; Li, J.; Tong, X.; Taylor, A. D., Nano Lett 2016, 16, 4799-4806 [5] Ryu, W. H.; Gittleson, F. S.; Thomsen, J.; Li, J.; Schwab, M.; Brudvig, G.; Taylor, A. D., Nature Commun. , 2016, 7, 12925.

Structural and electronic modification of titanium oxide (TiO2) nanomaterials induced by the co-introduction of fully disordered glass phase and oxygen vacancies can lead to remarkable advances in the electrode performance in emerging energy storage systems. We report on the effective co-creation of fully amorphous nanofibers (NFs) composed of black TiO2-x and conductive carbons throughout the NF structure, and evaluate the materials as potential anodes in sodium-ion batteries. The black TiO2-x nanofiber is successfully fabricated by electrospinning a precursor solution followed by a two-step sequential thermal treatment in an air and reducing atmosphere. The NF electrode could deliver approximately two-fold higher 2nd discharge capacity and an excellent kinetic performance even under high rates compared to that delivered by anatase-structured white TiO2 NFs used as reference, because of (i) an inherent free volume in the glass phase corresponding to the enlarged Na+ sites, (ii) increased electrical conductivity (low bandgap) resulting from the presence of Ti3+, (iii) introduction of conductive carbon agents around the TiO2-x domain, and (iv) one-dimensional NF feature allowing numerous Na+ reaction sites at the electrochemical interface. We also elucidate the morphological and structural changes in the nanofibers after discharge and charge by ex-situ characterizations.

Two-dimensional (2D) materials have opened up a field for developing the next generation of optoelectronic devices thanks to their novel properties such as ultrafast charge injection/extraction, strong light-matter interactions (despite being atomically thin) and quantum confinement(1). In addition, recent advancements in liquid phase exfoliation has revealed a new scalable route to investigate these materials(2). A good example is the fabrication of graphene oxide (GO) where the high resistive precursor of graphene that has to be reduced to recover its favorable optoelectronic properties. In most cases, ultra-high temperature (>1000ºC) and toxic chemicals (hydrazine) have to be used. In this talk, we will present a novel solution-processed film containing T3C2Tx monolayers, a 2D crystal from the recently discovered family of MXenes(3). This new MXene 2D family can be synthetized by selectively etching the A element of the MAX phase and formed into stacks of transition metal carbides and carbonitrides. Indeed, MXenes have recently gained attention due their a hydrophilic behavior, high metallic conductivity and excellent mechanical properties(4). Herein, we explore the use of freestanding nanometer-thin films of T3C2Tx for solution-processed transparent conductive electrodes. We demonstrate that our T3C2Tx films possess half of the sheet resistance (437 Ohm/sq) of the best reduced graphene oxide by produced solution-processed methods(5) while preserving an 80% of its transmission. In this talk, we will show that by using a simple spin-coating technique we can control the number of flakes forming the film (Figure 1a) and optimize the optoelectronic properties of our films so that they exhibit a figure of merit twice as large as reduced-GO (Figure 1b). The novelty of our approach is our in deep understanding of the limiting factors in the resistivity of the films such as heat treatments and functional end-groups. In addition, we will illustrate their metallic behavior by on-chip measurements and report for the first time the experimental measurement of their work function, which is crucial for advanced device design. This demonstration of a novel metallic and solution-processed 2D material with high conductivity using T3C2Txflakes with low-temperature fabrication provides a new possible pathway towards scalable manufacturing of ultrathin film devices. 1. F. Bonaccorso et al., Graphene, related two-dimensional crystals, and hybrid systems for energy conversion and storage. Science 347, 1246501 (2015). 2. V. Nicolosi, M. Chhowalla, M. G. Kanatzidis, M. S. Strano, J. N. Coleman, Liquid Exfoliation of Layered Materials. Science 340, 1226419 (2013). 3. M. Naguib, V. N. Mochalin, M. W. Barsoum, Y. Gogotsi, 25th Anniversary Article: MXenes: A New Family of Two-Dimensional Materials. Advanced Materials 26, 992-1005 (2014). 4. M. Naguib, Y. Gogotsi, Synthesis of Two-Dimensional Materials by Selective Extraction. Accounts of Chemical Research 48, 128-135 (2015). 5. H. A. Becerril et al., Evaluation of Solution-Processed Reduced Graphene Oxide Films as Transparent Conductors. ACS Nano 2, 463-470 (2008). Figure 1

MXenes, a recently discovered family of two-dimensional materials, have obtained a large consideration since they exhibit properties with potential applications. Among them, their hydrophilic and metallic conductivity have opened a way to deposit them by solution process techniques. We will present Ti3C2Tx delaminated monolayers forming ultra thin films as transparent electrodes with properties exceeding comparable reduced graphene oxide films. Our films deposited by spin-coating show a low sheet resistance of 437 Omega/sq with 77 % transmittance at 550 nm light. Finally, FET transistors fabricated with our films confirmed the metallic behavior of them. These results demonstrate the presence of a novel and solution-processed two-dimensional material with both high conductivity and transparency.

In this study, we present a facile and scalable approach to fabricate omniphobic nanofiber membranes by constructing multilevel re-entrant structures with low surface energy. We first prepared positively charged nanofiber mats by electrospinning a blend polymer surfactant solution of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and cationic surfactant (benzyltriethylammonium). Negatively charged silica nanoparticles (SiNPs) were grafted on the positively charged electrospun nanofibers via dip-coating to achieve multilevel re-entrant structures. Grafted SiNPs were then coated with fluoroalkylsilane to lower the surface energy of the membrane. The fabricated membrane showed excellent omniphobicity, as demonstrated by its wetting resistance to various low surface tension liquids, including ethanol with a surface tension of 22.1 mN/m. As a promising application, the prepared omniphobic membrane was tested in direct contact membrane distillation to extract water from highly saline feed solutions containing low surface tension substances, mimicking emerging industrial wastewaters (e.g., from shale gas production). While a control hydrophobic PVDF-HFP nanofiber membrane failed in the desalination/separation process due to low wetting resistance, our fabricated omniphobic membrane exhibited a stable desalination performance for 8 h of operation, successfully demonstrating clean water production from the low surface tension feedwater.

Experimental Section Preparation of GNFs and dispersed solution: The graphite intercalation compound (GIC) was manufactured by following the method previously reported in ref.[33]. Briefly, a ternary eutectic system (KCl, NaCl, and ZnCl2) was used for GIC at 350 °C and the prepared GIC was exfoliated in a pyridine solution. For the functionalized GNFs, 1-pyrenebutyric acid (20 mg) was added to GNFs (20 mg) dispersed in pyridine (40 ml) and then these mixtures were mildly sonicated for 12 h. The mixtures were subsequently stored at 70 °C for 24 h. The mixture was filtered and washed with de-ionized water using a 0.1 micron Anodisc filter to remove the salts and residual pyridine. The product was dried under 100 °C in a furnace. The GNFs (10 mg) were dispersed in 10 ml of ethanol with sonication for 3 h.

A considerable amount of effort has been devoted to developing innovative and economical energy storage systems, including methods that are optimized for application to large-scale energy storage systems such as smart grids and electric vehicles. Sodium ion batteries have been spotlighted recently owing to lower material costs, the abundance of sodium resources, and analogous electrochemical components with existing Li-ion battery systems. However, unlike Li-ion batteries, current studies on Na-ion batteries have often confronted problems related to the insufficient Na storage capacities of electrode materials, especially anode materials, originating from the larger ionic radius of Na compared with Li (e.g. Li+: 0.76 Å, Na+: 1.02 Å). Therefore, the development of high capacity anode materials that enable facile insertion/extraction of large Na ions is essential for high performance Na-ion batteries. In recent years, metal sulfides have been considered as functional electrode materials for diverse applications such as electronic devices, energy conversion and storage systems due to their unique electronic properties and structural characteristics, compared to metal oxides. Metal disulfides (MoS2 and WS2) have also shown their possibility as a high capacity anode material (>700 mAh/g) because of (i) the large slab space between their 2-D planes, (ii) their reversible conversion reaction characteristics (MS2 + 4Na+ + 4e- → 2 Na2S + M, M = Mo, W), and (iii) the higher conductivity of Na2S products (metal sulfides) compared to Na2O (metal oxides). Similarly, amorphous metal trisulfides (MS3, M = Mo, W) could be considered as high capacity anode materials due to the structural flexibility of their glassy phase and the excess sulfur as an active component (MS3 + 6Na+ + 6e- → 3Na2S + M). Moreover, the electronic conductivity of MS3 can be improved by excess sulfur in the trisulfide structure. However, Na battery performance of metal trisulfides has not been thoroughly introduced thus far. Moreover, an effective solution is required for the sulfur dissolution issue originating from soluble polysulfide intermediates during the Na2S formation/decomposition process, thereby losing sulfur components and consequently degrading capacity. To address complex concerns, designing hierarchical architecture of the metal sulfide strucutre with a functional coating layer can offer considerable improvement in sodium battery performance. Reducing the size-dimension to the nanoscale and tailoring their morphologies can also afford an increased number of reaction sites and reduced Na ion diffusion. In this presentation, we report a tailored synthetic strategy used to create heterogeneous metal sulfide (e.g. MoS2, WSx)/oxide core-shell nanofiber materials with hierachical features, and we evaluate them as potential anode materials for high performance Na-ion batteries. The sulfide nanofibers are successfully prepared by electrospinning and subsequent calcination in a reducing atmosphere. Conformal oxide coating is applied to prevent capacity degradation of the metal sulfide anodes originating from sulfur dissolution. [1] W.-H. Ryu, J.-W. Jung, K. Park, S.-J. Kim, I.-D. Kim, Nanoscale, 2014, 6, 10975-10981 [2] W.-H. Ryu, H. Wilson, S. Sohn, J. Li, X. Tong, E. Shaulsky, J. Schroers, M. Elimelech, A. D. Taylor, ACS Nano, 2016, 10, 3257–3266 [3] S.-J. Lim, D.-W. Han, D.-H. Nam, K.-S. Hong, J.-Y. Eom, W.-H. Ryu and H.-S. Kwon, J. Mater. Chem. A, 2014, 2, 19623-19632

Amorphous silicon (a-Si) has been intensively explored as one of the most attractive candidates for high-capacity and long-cycle-life anode in Li-ion batteries (LIBs) primarily because of its reduced volume expansion characteristic (∼280%) compared to crystalline Si anodes (∼400%) after full Li(+) insertion. Here, we report one-dimensional (1-D) electrospun Si-based metallic glass alloy nanofibers (NFs) with an optimized composition of Si60Sn12Ce18Fe5Al3Ti2. On the basis of careful compositional tailoring of Si alloy NFs, we found that Ce plays the most important role as a glass former in the formation of the metallic glass alloy. Moreover, Si-based metallic glass alloy NFs were wrapped by reduced graphene oxide sheets (specifically Si60Sn12Ce18Fe5Al3Ti2 NFs@rGO), which can prevent the direct exposure of a-Si alloy NFs to the liquid electrolyte and stabilize the solid-electrolyte interphase (SEI) layers on the surfaces of rGO sheets while facilitating electron transport. The metallic glass nanofibers exhibited superior electrochemical cell performance as an anode: (i) Si60Sn12Ce18Fe5Al3Ti2 NFs show a high specific capacity of 1017 mAh g(-1) up to 400 cycles at 0.05C with negligible capacity loss as well as superior cycling performance (nearly 99.9% capacity retention even after 2000 cycles at 0.5C); (ii) Si60Sn12Ce18Fe5Al3Ti2 NFs@rGO reveals outstanding rate behavior (569.77 mAh g(-1) after 2000 cycles at 0.5C and a reversible capacity of around 370 mAh g(-1) at 4C). We demonstrate the potential suitability of multicomponent a-Si alloy NFs as a long-cycling anode material.

In recent years lithium-oxygen (Li-O2) batteries have drawn much attention due to their exceptionally high energy density, which could exceed the capable value of conventional Li-ion batteries.1, 2 Li-O2 batteries operate via surface reactions that form (discharging) and evolve (charging) solid oxide products.3, 4 To facilitate reaction reversibility, the oxygen electrode for Li-O2 cells often requires an efficient catalyst. Yet insulating solid products formed during discharging often deactivate the catalyst surface, making product evolution difficult.5 Soluble catalysts have recently been shown to improve charge transfer with isolated or poorly conductive products near the electrode/electrolyte interface.6 Choosing proper catalytic molecules is essential to reduce the barrier to oxygen evolution in the Li-O2 cell. The redox molecules directly transport the generated electrons to/from the electrode substrate, consequently lowering overpotential. While a few redox molecules (e.g. Li iodide (LiI), tetrathiafulvalene (TTF), iron phthalocyanine (FePc), and 2,2,6,6-tetramethylpinperdinyloxyl (TEMPO)) have been investigated so far,6-9 seeking a low cost and environmentally friendly alternative is desirable. In this presentation, we report the use of a common biomolecule as a soluble, eco-friendly catalyst to promote Li-O2 reactions with reduced overpotentials. We also elucidate the chemical reaction mechanism of its operation during oxide formation and evolution. In situ observations of chemical structure in the redox molecule are essential to establish the catalytic function and further design molecules for high performance Li-O2 battery systems. Here, we discuss the catalytic effects of the redox biomolecule on the significantly improved electrochemical characteristics of a practical Li-O2 battery. 1. D. G. Kwabi, N. Ortiz-Vitoriano, S. A. Freunberger, Y. Chen, N. Imanishi, P. G. Bruce and Y. Shao-Horn, Mrs Bull, 2014, 39, 443-452. 2. K. G. Gallagher, S. Goebel, T. Greszler, M. Mathias, W. Oelerich, D. Eroglu and V. Srinivasan, Energy & Environmental Science, 2014, 7, 1555-1563. 3. W. H. Ryu, F. S. Gittleson, M. Schwab, T. Goh and A. D. Taylor, Nano Lett, 2015, 15, 434-441. 4. W. H. Ryu, T. H. Yoon, S. H. Song, S. Jeon, Y. J. Park and I. D. Kim, Nano Lett, 2013, 13, 4190-4197. 5. F. S. Gittleson, W. H. Ryu and A. D. Taylor, ACS Appl Mater Interfaces, 2014, 6, 19017-19025. 6. Y. H. Chen, S. A. Freunberger, Z. Q. Peng, O. Fontaine and P. G. Bruce, Nat Chem, 2013, 5, 489-494. 7. H. D. Lim, H. Song, J. Kim, H. Gwon, Y. Bae, K. Y. Park, J. Hong, H. Kim, T. Kim, Y. H. Kim, X. Lepro, R. Ovalle-Robles, R. H. Baughman and K. Kang, Angew Chem Int Edit, 2014, 53, 3926-3931. 8. B. J. Bergner, A. Schurmann, K. Peppler, A. Garsuch and J. Janek, J Am Chem Soc, 2014, 136, 15054-15064. 9. D. Sun, Y. Shen, W. Zhang, L. Yu, Z. Q. Yi, W. Yin, D. Wang, Y. H. Huang, J. Wang, D. L. Wang and J. B. Goodenough, Journal of the American Chemical Society, 2014, 136, 8941-8946.

Dumbbell-like microsphere carbonate precursors including multi-transition metal components (Ni1/3Mn1/3Co1/3CO3) assembled with nano-building blocks were synthesized by urea-assisted solvo/hydrothermal method, and layered cathode materials (LiNi1/3Mn1/3Co1/3O2) were subsequently prepared using the similarly shaped carbonate precursors for Li-ion batteries. For the synthesis of hierarchical microsphere structures, the partial addition of viscous organic solvent (e.g. ethylene glycol) in aqueous solution played a crucial role, not only in suppressing the sudden particle growth but also in regulating the directional crystallization of carbonate particles on the surface. The dumbbell-like LiNi1/3Mn1/3Co1/3O2 assembled with nanocubes prepared via the urea-assisted solvo/hydrothermal method exhibited better electrochemical characteristics, such as initial discharge capacity, cyclic performance, and rate-capability as a cathode material of Li-ion batteries, compared with the LiNi1/3Mn1/3Co1/3O2 materials prepared via the conventional co-precipitation method.