Improvement of Electrochemical Properties of Lithium–Oxygen Batteries Using a Silver Electrode

Silver (Ag) electrodes are prepared by an electrodeposition method at −0.25 V versus SCE. To evaluate the effect of particle size on Li–air cells, deposition times are 3, 10, 30, and 300 s. When cycled at a current density of 0.032 mA cm^–2, the Ag-deposited electrode for 300 s shows very low polarization corresponding to the oxygen evolution reaction potential at 3.6 V. X-ray diffraction studies confirm that the main discharge product is Li₂O₂, and the results of scanning electron microscopy and transmission electron microscopy of the discharged electrodes show lithium peroxides at different positions due to the limitation of active sites on silver particles

Thermodynamic Destabilization of Magnesium Hydride Using Mg-Based Solid Solution Alloys

Thermodynamic destabilization of magnesium hydride is a difficult task that has challenged researchers of metal hydrides for decades. In this work, solid solution alloys of magnesium were exploited as a way to destabilize magnesium hydride thermodynamically. Various elements were alloyed with magnesium to form solid solutions, including: indium (In), aluminum (Al), gallium (Ga), and zinc (Zn). Thermodynamic properties of the reactions between the magnesium solid solution alloys and hydrogen were investigated. Equilibrium pressures were determined by pressure–composition–isothermal (PCI) measurements, showing that all the solid solution alloys that were investigated in this work have higher equilibrium hydrogen pressures than that of pure magnesium. Compared to magnesium hydride, the enthalpy (Δ<i>H</i>) of decomposition to form hydrogen and the magnesium alloy can be reduced from 78.60 kJ/(mol H₂) to 69.04 kJ/(mol H₂), and the temperature of 1 bar hydrogen pressure can be reduced to 262.33 °C, from 282.78 °C, for the decomposition of pure magnesium hydride. Further, <i>in situ</i> XRD analysis confirmed that magnesium solid solutions were indeed formed after the dehydrogenation of high-energy ball-milled MgH₂ with the addition of the solute element(s). XRD results also indicated that intermetallic phases of Mg with the solute elements were present along with MgH₂ in the rehydrogenated magnesium solid solution alloys, providing a reversible hydrogen absorption/desorption reaction pathway. However, the alloys were shown to have lower hydrogen storage capacity than that of pure MgH₂

Mesocarbon Microbead Carbon-Supported Magnesium Hydroxide Nanoparticles: Turning Spent Li-ion Battery Anode into a Highly Efficient Phosphate Adsorbent for Wastewater Treatment

Phosphorus in water eutrophication has become a serious problem threatening the environment. However, the development of efficient adsorbents for phosphate removal from water is lagging. In this work, we recovered the waste material, graphitized carbon, from spent lithium ion batteries and modified it with nanostructured Mg­(OH)₂ on the surface to treat excess phosphate. This phosphate adsorbent shows one of the highest phosphate adsorption capacities to date, 588.4 mg/g (1 order of magnitude higher than previously reported carbon-based adsorbents), and exhibits decent stability. A heterogeneous multilayer adsorption mechanism was proposed on the basis of multiple adsorption results. This highly efficient adsorbent from spent Li-ion batteries displays great potential to be utilized in industry, and the mechanism study paved a way for further design of the adsorbent for phosphate adsorption

Study on the Catalytic Activity of Noble Metal Nanoparticles on Reduced Graphene Oxide for Oxygen Evolution Reactions in Lithium–Air Batteries

Among many challenges present in Li–air batteries, one of the main reasons of low efficiency is the high charge overpotential due to the slow oxygen evolution reaction (OER). Here, we present systematic evaluation of Pt, Pd, and Ru nanoparticles supported on rGO as OER electrocatalysts in Li–air cell cathodes with LiCF₃SO₃–tetra­(ethylene glycol) dimethyl ether (TEGDME) salt-electrolyte system. All of the noble metals explored could lower the charge overpotentials, and among them, Ru-rGO hybrids exhibited the most stable cycling performance and the lowest charge overpotentials. Role of Ru nanoparticles in boosting oxidation kinetics of the discharge products were investigated. Apparent behavior of Ru nanoparticles was different from the conventional electrocatalysts that lower activation barrier through electron transfer, because the major contribution of Ru nanoparticles in lowering charge overpotential is to control the nature of the discharge products. Ru nanoparticles facilitated thin film-like or nanoparticulate Li₂O₂ formation during oxygen reduction reaction (ORR), which decomposes at lower potentials during charge, although the conventional role as electrocatalysts during OER cannot be ruled out. Pt-and Pd-rGO hybrids showed fluctuating potential profiles during the cycling. Although Pt- and Pd-rGO decomposed the electrolyte after electrochemical cycling, no electrolyte instability was observed with Ru-rGO hybrids. This study provides the possibility of screening selective electrocatalysts for Li–air cells while maintaining electrolyte stability

Synthesis of Porous Carbon Supported Palladium Nanoparticle Catalysts by Atomic Layer Deposition: Application for Rechargeable Lithium–O₂ Battery

In this study, atomic layer deposition (ALD) was used to deposit nanostructured palladium on porous carbon as the cathode material for Li–O₂ cells. Scanning transmission electron microscopy showed discrete crystalline nanoparticles decorating the surface of the porous carbon support, where the size could be controlled in the range of 2–8 nm and depended on the number of Pd ALD cycles performed. X-ray absorption spectroscopy at the Pd K-edge revealed that the carbon supported Pd existed in a mixed phase of metallic palladium and palladium oxide. The conformality of ALD allowed us to uniformly disperse the Pd catalyst onto the carbon support while preserving the initial porous structure. As a result, the charging and discharging performance of the oxygen cathode in a Li–O₂ cell was improved. Our results suggest that ALD is a promising technique for tailoring the surface composition and structure of nanoporous supports in energy storage devices

Lithium Superoxide Hydrolysis and Relevance to Li–O₂ Batteries

Fundamental understanding of reactions of lithium peroxides and superoxides is essential for the development of Li–O₂ batteries. In this context, an investigation is reported of the hydrolysis of lithium superoxide, which has recently been synthesized in a Li–O₂ battery. Surprisingly, the hydrolysis of solid LiO₂ is significantly different from that of NaO₂ and KO₂. Unlike KO₂ and NaO₂, the hydrolysis of LiO₂ does not produce H₂O₂. Similarly, the reactivity of Li₂O₂ toward water differs from LiO₂, in that Li₂O₂ results in H₂O₂ as a product. The difference in the LiO₂ reactivity with water is due to the more exothermic nature of the formation of LiOH and O₂ compared with the corresponding reactions of NaO₂ and KO₂. We also show that a titration method used in this study, based on reaction of the discharge product with a Ti­(IV)­OSO₄ solution, provides a useful diagnostic technique to provide information on the composition of a discharge product in a Li–O₂ battery