Search

The development of Na-ion full cells (NIFCs) suffers from the issue that the solid electrolyte interphase formation on the carbon anode consumes the limited sodium from cathode and thus incurs the decreased energy density and poor cyclic stability. To address these issues, we herein report that Na2O2 could be used as a sacrificial Na source through spraying its slurry on the surface of cathode, and investigate its stability as well as electrochemical behavior toward NIFCs. The results show that Na2O2 has good chemical and storage stability under a dry atmosphere and has no negative effect on the electrochemical performance of the cathode. Compared with the pristine cathode, the Na2O2-decorated cathode exhibits higher discharge capacity, superior capacity retention, and rate capability in a full cell with a carbon anode. Our cathode Na compensation strategy provides an effective avenue to make up for the irreversible Na+ loss cause by the formation of solid electrolyte interphase on the anode, thereby promoting the electrochemical performance and energy density of NIFCs toward the large-scale application.

Metal-air batteries have attracted extensive research interests due to their high theoretical energy density. However, most of the previous studies were limited by applying pure oxygen in the cathode, sacrificing the gravimetric and volumetric energy density. Here, we develop a real sodium-"air" battery, in which the rechargeability of the battery relies on the reversible reaction of the formation of sodium peroxide dihydrate (Na2O2·2H2O). After an oxygen evolution reaction catalyst is applied, the charge overpotential is largely reduced to achieve a high energy efficiency. The sodium-air batteries deliver high areal capacity of 4.2 mAh·cm-2 and have a decent cycle life of 100 cycles. The oxygen crossover effect is largely suppressed by replacing the oxygen with air, whereas the dense solid electrolyte interphase formed on the sodium anode further prolongs the cycle life.

The development of Na–O2 batteries requires understanding the formation of reaction products, as different groups reported compounds such as sodium peroxide, sodium superoxide, and hydrated sodium peroxide as the main discharge products. In this study, we used in operando synchrotron radiation powder X-ray diffraction (SR-PXD) to (i) quantitatively track the formation of NaO2 in Na–O2 cells and (ii) measure how the growth of crystalline NaO2 is influenced by the choice of electrolyte salt. The results reveal that the discharge could be divided into two time regions and that the formation of NaO2 during the major part of the discharge reaction is highly efficient. The findings indicate that the cell with NaOTf salt exhibited higher capacity than the cell with NaPF6 salt, whereas the average domain size of NaO2 particles decreases during the discharge. This fundamental insight brings new information on the working mechanism of Na–O2 batteries.

23Na MAS NMR spectra of sodium–oxygen (Na–O2) cathodes reveals a combination of degradation species: newly observed sodium fluoride (NaF) and the expected sodium carbonate (Na2CO3), as well as the desired reaction product sodium peroxide (Na2O2). The initial reaction product, sodium superoxide (NaO2), is not present in a measurable quantity in the 23Na NMR spectra of the cycled electrodes. The reactivity of solid NaO2 is probed further, and NaF is found to be formed through a reaction between the electrochemically generated NaO2 and the electrode binder, polyvinylidene fluoride (PVDF). The instability of cell components in the presence of desired electrochemical reaction products is clearly problematic and bears further investigation.

The chemical nature of discharge products in nonaqueous Na–O2 batteries attracts attention due to the differing electrochemical behavior of seemingly similar battery cells forming either sodium peroxide (Na2O2) or sodium superoxide (NaO2). The experimental control parameters for the exclusive formation of one or the other phase during discharge are still unknown. In this paper, the important role of gas phase moisture on the chemical nature of these products is demonstrated by means of operando XRD. Operando XRD is rarely reported for alkali-O2 systems but provides valuable real time information about the solid discharge products, growth/decomposition rates, and side reactions in the cell. In addition, the discharge/charge mechanisms of Na2O2·2H2O are monitored in detail evidencing important differences from the cell reactions forming NaO2 and Li2O2 and refuting previous incorrect conclusions. Moreover, the effect of the applied potential window during cycling is discussed, as it provides valuable informa...

Understanding the oxygen reduction reaction kinetics in the presence of Na ions and the formation mechanism of discharge product(s) is key to enhancing Na-O2 battery performance. Here we show NaO2 as the only discharge product from Na-O2 cells with carbon nanotubes in 1,2-dimethoxyethane from X-ray diffraction and Raman spectroscopy. Sodium peroxide dihydrate was not detected in the discharged electrode with up to 6000 ppm of H2O added to the electrolyte, but it was detected with ambient air exposure. In addition, we show that the sizes and distributions of NaO2 can be highly dependent on the discharge rate, and we discuss the formation mechanisms responsible for this rate dependence. Micron-sized (∼500 nm) and nanometer-scale (∼50 nm) cubes were found on the top and bottom of a carbon nanotube (CNT) carpet electrode and along CNT sidewalls at 10 mA/g, while only micron-scale cubes (∼2 μm) were found on the top and bottom of the CNT carpet at 1000 mA/g, respectively.

The primary discharge product in sodium–air batteries has been reported in some experiments to be sodium peroxide, Na2O2, while in others sodium superoxide, NaO2, is observed. Importantly, cells that discharge to NaO2 exhibit low charging overpotentials, while those that discharge to Na2O2 do not. These differences could arise from a higher conductivity within the superoxide; however, this explanation remains speculative given that charge transport in superoxides is relatively unexplored. Here, density functional and quasi-particle GW methods are used to comparatively assess the conductivities of Na–O2 discharge phases by calculating the concentrations and mobilities of intrinsic charge carriers in Na2O2 and NaO2. Both compounds are predicted to be electrical insulators, with bandgaps in excess of 5 eV. In the case of sodium peroxide, the transport properties are similar to those reported previously for lithium peroxide, suggesting low bulk conductivity. Transport in the superoxide has some features in co...

The superoxide based Na–O2 battery has circumvented the issue of large charge overpotential in Li–O2 batteries; however, the one-electron process leads to limited capacity. Herein, a sodium peroxide based low-overpotential (∼0.5 V) Na–O2 battery with a capacity as high as 7.5 mAh/cm2 is developed with Pd nanoparticles as catalysts on the cathode.

Plutonium oxide (PuO2) calcined at >900 °C resists dissolution in nitric acid (HNO3)-potassium fluoride (KF) solutions commonly used for their dissolution. The Savannah River National Laboratory (S...

The anion of 2-aryl acetonitrile derivatives reacted with a variety of heteroaryl chlorides or bromides in an S(N)Ar manifold to afford intermediate anions which were susceptible to oxidation. The addition of sodium peroxide and aqueous NH(4)OAc solution effected oxidation to afford aryl heteroaryl ketones in good yields. Aryl acetonitrile derivatives are thus umpolung-type synthons of the corresponding aryl carbonyl functionality.

A combined procedure for separating Lu, Hf, Sm, Nd, and rare earth elements (REEs) from a single sample digest is presented. The procedure consists of the following five steps: (1) sample dissolution via sodium peroxide sintering; (2) separation of the high field strength elements from the REEs and other matrix elements by a HF-free anion-exchange column procedure; (3) purification of Hf on a cation-exchange resin; (4) separation of REEs from other matrix elements by cation exchange; (5) Lu, Sm, and Nd separation from the other REEs by reversed-phase ion chromatography. Analytical reproducibilities of Sm-Nd and Lu-Hf isotope systematics are demonstrated for standard solutions and international rock reference materials. Results show overall good reproducibilities for Sm-Nd systematics independent of the rock type analyzed. For the Lu-Hf systematics, the reproducibility of the parent/daughter ratio is much better for JB-1 (basalt) than for two analyzed felsic crustal rocks (DR-N and an Archaean granitoid). It is demonstrated that this poorer reproducibility of the Lu/Hf ratio is truly caused by sample heterogeneity; thus, results are geologically reasonable.

Uranium (U) was successfully removed from contaminated soils from the Fernald Environmental Management Project (FEMP) site near Fernald, Ohio. The laboratory column leach process, referred to as the simulated heap leach process, using 0.5 M sodium bicarbonate as the dominant reagent, was able to achieve uranium removals of 75−90%, corresponding approximately to the percentage of uranium in the oxidized state. Parametric optimization studies are reported. The dissolution of uranium took place in two stages: a rapid desorption associated with soil surfaces and a slow step associated with diffusion of uranium toward solid surfaces. In addition, use of the oxidizing agent, sodium peroxide, improved uranium removal due to oxidation of U(IV), enhancing the solubility of the uranium. The results suggest that the process will be effective for field scale remediation of uranium-contaminated soils because of the efficiency, mild complexing agent employed, lack of prescreening of the soil and the simple equipment n...

An alternative procedure to the classical fire assay method for determining Pt and Pd in sulfide ores, concentrates, and furnace mattes is presented. A suitable amount of sample is digested with aqua regla and filtered and any remaining gangue is digested with a mixture of HF and HClO/sub 4/. The solution is filtered and the residue fused with sodium peroxide granules. The fused salts are dissolved in a dilute HCl acid solution and all three solutions combined. The resultant solution is passed through a Bio-Rad AG 50W-X8 cation exchange resin in the H/sup +/ form. The chlorocomplex anions of Pt and Pd are not retained by the cation exchange resin while the base metal cations are efficiently removed from the eluent. Pt and Pd concentrations are subsequently determined with an inductively coupled plasma (ICP). Preliminary experiments showing the method's potential expandability to Au are included.

In a search for a rapid and accurate method for determining sulfur in rubber it was found that oxidation of the sample by means of sodium peroxide in the Parr bomb is unsatisfactory when the sulfur content of the rubber is low because the samples that can be used for this purpose are too small for accurate results, or, if larger samples are used, the oxidation is incomplete. The use of a mixture of nitric and perchloric acids, as described by Kahane, is also unsatisfactory; but with certain modifications the method may be made to yield very good results, and if fusions are unnecessary, it will save time and labor. The chief modifications recommended are the use of a more dilute solution of nitric acid (equal volumes of the concentrated acid and water), allowing the rubber to dissolve completely on the steam bath before heating more strongly, then heating to gentle boiling until oxidation is complete, and finally destroying the residual nitric acid by means of hydrochloric acid. The use of a large...

n/a

n/a

n/a

The extraction of 24 elements by tri-n-butylphosphine sulfide was investigated. Only two metal ions among those tested extracted well, Ag(I) (D = 825) and Hg(II) (D = 282). Elements that were partially extracted are border region acceptors and included Bi (D = 0.56), Cu(II) (D = 0.026 from 0.1 M HCl), Pb (D = 0.27), and Zn (D = 0.27). It proved difficult to strip Hg(II) from the organic phase with common reagents such as nitric acid, aqua regia, or sodium peroxide. (P.C.H.)

Demonstrations described involve gunpowder, the combustion of sulfur dioxide, zirconium, nitric acid, sodium peroxide, hot iron, ammonium nitrate, organic chlorates and nitrates, and zinc stearate.