Deactivation of carbon electrode for elimination of carbon dioxide evolution from rechargeable lithium-oxygen cells

Carbon has unfaired advantages in material properties to be used as electrodes. It offers a low cost, light weight cathode that minimizes the loss in specific energy of lithium-oxygen batteries as well. To date, however, carbon dioxide evolution has been an unavoidable event during the operation of non-aqueous lithium-oxygen batteries with carbon electrodes, due to the reactivity of carbon against self-decomposition and catalytic decomposition of electrolyte. Here we report a simple but potent approach to eliminate carbon dioxide evolution by using an ionic solvate of dimethoxyethane and lithium nitrate. We show that the solvate leads to deactivation of the carbon against parasitic reactions by electrochemical doping of nitrogen into carbon. This work demonstrates that one could take full advantage of carbon by mitigating the undesired activity. © 2014 Macmillan Publishers Limited. All rights reserved.open8

Hierarchical urchin-shaped alpha-MnO2 on graphene-coated carbon microfibers: a binder-free electrode for rechargeable aqueous Na-air battery

With the increasing demand of cost-effective and high-energy devices, sodium-air (Na-air) batteries have attracted immense interest due to the natural abundance of sodium in contrast to lithium. In particular, an aqueous Na-air battery has fundamental advantage over non-aqueous batteries due to the formation of highly water-soluble discharge product, which improve the overall performance of the system in terms of energy density, cyclic stability and round-trip efficiency. Despite these advantages, the rechargeability of aqueous Na-air batteries has not yet been demonstrated when using non-precious metal catalysts. In this work, we rationally synthesized a binder-free and robust electrode by directly growing urchin-shaped MnO2 nanowires on porous reduced graphene oxide-coated carbon microfiber (MGC) mats and fabricated an aqueous Na-air cell using the MGC as an air electrode to demonstrate the rechargeability of an aqueous Na-air battery. The fabricated aqueous Na-air cell exhibited excellent rechargeability and rate capability with a low overpotential gap (0.7 V) and high round-trip efficiency (81%). We believe that our approach opens a new avenue for synthesizing robust and binder-free electrodes that can be utilized to build not only metal-air batteries but also other energy systems such as supercapacitors, metal-ion batteries and fuel cells.ope

Tuning the Catalytic Activity of Graphene Nanosheets for Oxygen Reduction Reaction via Size and Thickness Reduction

Currently, the fundamental factors that control the oxygen reduction reaction (ORR) activity of graphene itself, in particular the dependence of the ORR activity on the number of exposed edge sites remain elusive, mainly due to limited synthesis routes of achieving small size graphene. In this work, the synthesis of low oxygen content (< 2.5 +/-0.2 at %), few layer graphene nanosheets with lateral dimensions smaller than a few hundred nm was achieved using a combination of ionic liquid assisted grinding of high purity graphite coupled with sequential centrifugation. We show for the first time, that the graphene nanosheets possessing a plethora of edges exhibited considerably higher electron transfer numbers compared to the thicker graphene nanoplatelets. This enhanced ORR activity was accomplished by successfully exploiting the plethora of edges of the nanosized graphene as well as the efficient electron communication between the active edge sites and the electrode substrate. The graphene nanosheets were characterized by an onset potential of -0.13 V vs. Ag/AgCl and a current density of -3.85 mA/cm2 at -1 V, which represent the best ORR performance ever achieved from an undoped carbon based catalyst. This work demonstrates how low oxygen content nanosized graphene synthesized by a simple route can considerably impact the ORR catalytic activity and hence it is of significance in designing and optimizing advanced metal-free ORR electrocatalysts.Comment: corresponding author: [email protected], ACS Applied Materials and Interfaces 201

Synergistic effect of quinary molten salts and Ruthenium catalyst for high-power-density Lithium-carbon dioxide cell

With a recent increase in interest in metal-gas batteries, the lithium-carbon dioxide cell has attracted considerable attention because of its extraordinary carbon dioxide-capture ability during the discharge process and its potential application as a power source for Mars exploration. However, owing to the stable lithium carbonate discharge product, the cell enables operation only at low current densities, which significantly limits the application of lithium-carbon dioxide batteries and effective carbon dioxide-capture cells. Here, we investigate a high-performance lithium-carbon dioxide cell using a quinary molten salt electrolyte and ruthenium nanoparticles on the carbon cathode. The nitrate-based molten salt electrolyte allows us to observe the enhanced carbon dioxide-capture rate and the reduced discharge-charge over-potential gap with that of conventional lithium-carbon dioxide cells. Furthermore, owing to the ruthernium catalyst, the cell sustains its performance over more than 300 cycles at a current density of 10.0Ag(-1) and exhibits a peak power density of 33.4mWcm(-2). Lithium-carbon dioxide cells are challenging due to the sluggish electron transfer in the Lithium carbonate in aprotic electrolyte. Here, the authors report synergistic effect of molten salt electrolyte and Ruthenium catalyst to enhance the electrochemical performance of Lithium-carbon dioxide batterie

Comparative study of the implementation of tin and titanium oxide nanoparticles as electrodes materials in Li-ion batteries

Transition metal oxides potentially present higher specific capacities than the current anodes based on carbon, providing an increasing energy density as compared to commercial Li-ion batteries. However, many parameters could influence the performance of the batteries, which depend on the processing of the electrode materials leading to different surface properties, sizes or crystalline phases. In this work a comparative study of tin and titanium oxide nanoparticles synthesized by different methods, undoped or Li doped, used as single components or in mixed ratio, or alternatively forming a composite with graphene oxide have been tested demonstrating an enhancement in capacity with Li doping and better cyclability for mixed phases and composite anodes

Geometric Algorithms for Optimal Airspace Design and Air Traffic Controller Workload Balancing

The National Airspace System (NAS) is designed to accommodate a large number of flights over North America. For purposes of workload limitations for air traffic controllers, the airspace is partitioned into approximately 600 sectors; each sector is observed by one or more controllers. In order to satisfy workload limitations for controllers, it is important that sectors be designed carefully according to the traffic patterns of flights, so that no sector becomes overloaded. We formulate and study the airspace sectorization problem from an algorithmic point of view, modeling the problem of optimal sectorization as a geometric partition problem with constraints. The novelty of the problem is that it partitions data consisting of trajectories of moving points, rather than static point set partitioning that is commonly studied. First, we formulate and solve the 1D version of the problem, showing how to partition a line into “sectors ” (intervals) according to historical trajectory data. Then, we apply the 1D solution framework to design a 2D sectorization heuristic based on binary space partitions. We also devise partitions based on balanced “pie partitions” of a convex polygon. We evaluate our 2D algorithms experimentally. We conduct experiments using actual historical flight track data for the NAS as the basis of our partitioning. We compare the workload balance of our methods to that of the existing set of sectors for the NAS and find that our resectorization yields competitive and improved workload balancing. In particular, our methods yield an improvement by a factor between 2 and 3 over the current sectorization in terms of the time-average and the worst-case workloads of the maximum workload sector. An even better improvement is seen in the standard deviations (over all sectors) of both time-average and worst-case workloads.

Distributed Localization Using Noisy Distance and Angle Information

Localization is an important and extensively studied problem in ad-hoc wireless sensor networks. Given the connectivity graph of the sensor nodes, along with additional local information (e.g. distances, angles, orientations etc.), the goal is to reconstruct the global geometry of the network. In this paper, we study the problem of localization with noisy distance and angle information. With no noise at all, the localization problem with both angle (with orientation) and distance information is trivial. However, in the presence of even a small amount of noise, we prove that the localization problem is NP-hard. Localization with accurate distance information and relative angle information is also hard. These hardness results motivate our study of approximation schemes. We relax the non-convex constraints to approximating convex constraints and propose linear programs (LP) for two formulations of the resulting localization problem, which we call the weak deployment and strong deployment problems. These two formulations give upper and lower bounds on the location uncertainty respectively: No sensor is located outside its weak deployment region, and each sensor can be anywhere in its strong deployment region without violating the approximate distance and angle constraints. Though LP-based algorithms are usually solved by centralized methods, we propose distributed, iterative methods, which are provably convergent to the centralized algorithm solutions. We give simulation results for the distributed algorithms, evaluating the convergence rate, dependence on measurement noises, and robustness to link dynamics

A false aneurysm

AbstractObjective: We report a case of a remaining hemi-thyroid following laryngectomy, which was misinterpreted as a pseudoaneurysm.Methods: Case report and comment on this understandable error which is easily avoidable.Results: A 59-year-old man had undergone salvage laryngectomy for recurrent squamous cell carcinoma of the larynx, which had previously been treated with radiotherapy. Three months after his laryngectomy, he presented with a sore neck and subcutaneous collections. Computed tomography revealed a unilateral mass with high signal contrast uptake anterior to the left common carotid artery, which was thought initially to be a carotid pseudoaneurysm. Further investigation, including ultrasonography and a review by the senior head and neck radiologist, demonstrated that this mass was actually the remnant hemi-thyroid preserved at laryngectomy (which is often misshapen compared with a normal hemi-thyroid). The collections were found to be recurrent tumour, and unnecessary further interventions were avoided.Conclusion: Ultrasonography easily distinguishes between a thyroid remnant and a pseudoaneurysm. Furthermore, the opinion of an experienced head and neck radiologist may be vital when interpreting complex post-surgical head and neck radiology