Enhancing adsorption capacity and structural stability of Li1.6Mn1.6O4 adsorbents by anion/cation co-doping.

Modifying the structure of Li1.6Mn1.6O4 (LMO) to enhance its structural stability and adsorption capacity is an effective method to generate materials to recover Li+ ions from mixed solution. Herein, the co-doping of trace non-metal ion (S) and metal ion (Al) into Li1.6Mn1.6O4 (LMO-SAl) is established and shows excellent Li+ adsorption capacity and Mn anti-dissolution properties. The adsorption capacity (when [Li+] is 6 mmol L-1) is increased from 26.1 mg g-1 to 33.7 mg g-1. This is attributed to improved charge density via substitution of S at O sites, which facilitates the adsorption/desorption process. The Mn dissolution is also reduced from 5.4% to 3.0% for LMO-SAl, which may result from the stronger Al-O bonds compared to Li-O bonds that enhance the structural stability of the LMO. The ion-sieving ability of the co-doped material goes by the order of K d (Li+ > Ca2+ > Mg2+ > Na+ > K+), indicating that Li+ can be efficiently separated from Lagoco Salt Lake brine. These results predict that lithium ions are effectively adsorbed from brine by the co-doped LMO material, which manifests the feasibility of lithium recovery and provides basic data for further industrial applications of adsorption.

Mesopore-Rich Fe-N-C Catalyst with FeN4 -O-NC Single-Atom Sites Delivers Remarkable Oxygen Reduction Reaction Performance in Alkaline Media.

Fe-N-C catalysts offer excellent performance for the oxygen reduction reaction (ORR) in alkaline media. With a view toward boosting the intrinsic ORR activity of Fe single-atom sites in Fe-N-C catalysts, fine-tuning the local coordination of the Fe sites to optimize the binding energies of ORR intermediates is imperative. Herein, a porous FeN4 -O-NCR electrocatalyst rich in catalytically accessible FeN4 -O sites (wherein the Fe single atoms are coordinated to four in-plane nitrogen atoms and one subsurface axial oxygen atom) supported on N-doped carbon nanorods (NCR) is reported. Fe K-edge X-ray absorption spectroscopy (XAS) verifies the presence of FeN4 -O active sites in FeN4 -O-NCR, while density functional theory calculations reveal that the FeN4 -O coordination offers a lower energy and more selective 4-electron/4-proton ORR pathway compared to traditional FeN4 sites. Electrochemical tests validate the outstanding intrinsic activity of FeN4 -O-NCR for alkaline ORR, outperforming Pt/C and almost all other M-N-C catalysts reported to date. A primary zinc-air battery constructed using FeN4 -O-NCR delivers a peak power density of 214.2 mW cm-2 at a current density of 334.1 mA cm-2 , highlighting the benefits of optimizing the local coordination of iron single atoms.

Hydrothermal synthesis and adsorption behavior of H4Ti5O12 nanorods along [100] as lithium ion-sieves.

The adsorption method is a promising route to recover Li+ from waste lithium batteries and lithium-containing brines. To achieve this goal, it is vital to synthesize a stable and high adsorption capacity adsorbent. In this work, Li4Ti5O12 nanorods are prepared by two hydrothermal processes followed by a calcination process. Then the prepared Li4Ti5O12 nanorods are treated with different HCl concentrations to obtain a H4Ti5O12 adsorbent with 5 µm length along the [100] direction. The maximum amount of extracted lithium can reach 90% and the extracted titanium only 2.5%. The batch adsorption experiments indicate that the H4Ti5O12 nanorod maximum adsorption capacity can reach 23.20 mg g-1 in 24 mM LiCl solution. The adsorption isotherms and kinetics fit a Langmuir model and pseudo-second-order model, respectively. Meanwhile, the real adsorption selectivity experiments show that the maximum Li+ adsorption capacity reaches 1.99 mmol g-1, which is far higher than Mg2+ (0.03 mmol g-1) and Ca2+ (0.02 mmol g-1), implying these nanorods have higher adsorption selectivity for Li+ from Lagoco Salt Lake brine. The adsorption capacity for Li+ remains 91% after five cycles. With the help of XPS analyses, the adsorption mechanism of Li+ on the H4Ti5O12 nanorods is an ion exchange reaction. Therefore, this nanorod adsorbent has a potential application for Li+ recovery from aqueous lithium resources.

K-gradient doping to stabilize the spinel structure of Li1.6Mn1.6O4 for Li+ recovery.

Lithium-rich spinel lithium manganese oxide (LMO) compounds are one kind of promising adsorbents for lithium recovery from brine due to their high capacity and low Mn dissolution; Li1.6Mn1.6O4 is one of them. However, Mn3+ exists in the Li1.6Mn1.6O4 precursor due to incomplete reaction during syntheses, and the disproportionation reaction of Mn3+ inevitably results in Mn dissolution during lithium adsorption and desorption. The stable recycling and structural stability of Li1.6Mn1.6O4 were improved in aqueous lithium resources through K-gradient doping (LMO-K). The dissolution of Mn is reduced to 4.0% from 5.4% (before doping) and the adsorption capacity is kept at high capacity (31.6 mg g-1) at a low Li+ concentration of 12 mmol L-1. In addition, first-principles calculations further confirm that K substitutes for Li at 16d sites, leading to the stabilization of the Mn cations in the compound. With the help of K doping, the undesired dissolution of Mn in the cycle process is inhibited, which may be due to the reduction in the content of Mn3+ and improvement in the structural stability of the adsorbent.