Novel application of sodium manganese oxide in removing acidic gases in ambient conditions

In this study, we have demonstrated the application of sodium manganese oxide for the chemisorption of toxic acidic gases at room temperature. The fabricated alkali ceramic has Na_0.4MnO₂, Na₂Mn₃O₇, and Na_xMnO₂ phases with a surface area of 2.6 m² g^-1. Na-Mn oxide was studied for oxidation of H₂S, SO₂, and NO₂ gases in the concentration range of 100-500 ppm. The material exhibited a high uptake capacity of 7.13, 0.75, and 0.53 mmol g^-1 for H₂S, SO₂, and NO₂ in wet conditions, respectively. The material was reusable when regenerated simply by soaking the spent oxide in a NaOH-H₂O₂ solution. While the H₂S chemisorption process was accompanied by sulfide, sulfur, and sulfate formation, the SO₂ chemisorption process yielded only sulfate ions. The NO₂ chemisorption process was accomplished by its conversion to nitrite and nitrate ions. Thus, the present work is one of the first reports on alkali ceramic utilization for room-temperature mineralization of acidic gases.

Fabrication of Na0.4MnO2 Microrods for Room-Temperature Oxidation of Sulfurous Gases

Phase pure Na_0.4MnO₂ microrods crystallized in the orthorhombic symmetry were fabricated for the wet oxidation of H₂S and SO₂ gases at room temperature. The material was found highly effective for the mineralization of low concentrations of acidic gases. The material was fully regenerable after soaking in a basic H₂O₂ solution.

Advanced cobalt-free cathode materials for sodium-ion batteries

Attempts to utilize lithium-ion batteries (LIBs) in large-scale electrochemical energy storage systems have achieved initial success, and solid-state LIBs using metallic lithium as the anode have also been well developed. However, the sharply increased demands/costs and the limited reserves of the two most important metal elements (Li & Co) for LIBs have raised concerns about future development. Sodium-ion batteries (SIBs) equipped with advanced cobalt-free cathodes show great potential in solving both "lithium panic" and "cobalt panic", and have made remarkable progress in recent years. In this review, we comprehensively summarize the recent advances of high-performance cobalt-free cathode materials for advanced SIBs, systematically analyze the conflicts of structural/electrochemical stability with intrinsic insufficiencies of cobalt-free cathode materials, and extensively discuss the strategies of constructing stable cobalt-free cathode materials by making full use of non-cobalt transition-metal elements and suitable crystal structures, all of which aim to provide insights into the key factors (e.g., phase transformation, particle cracks, crystal defects, lattice distortion, lattice oxygen oxidation, morphology, transition-metal migration/dissolution, and the synergistic effects of composite structures) that can determine the stability of cobalt-free cathode materials, provide guidelines for future research, and stimulate more interest on constructing high-performance cobalt-free cathode materials.

Faradaic Electrodes Open a New Era for Capacitive Deionization

Capacitive deionization (CDI) is an emerging desalination technology for effective removal of ionic species from aqueous solutions. Compared to conventional CDI, which is based on carbon electrodes and struggles with high salinity streams due to a limited salt removal capacity by ion electrosorption and excessive co-ion expulsion, the emerging Faradaic electrodes provide unique opportunities to upgrade the CDI performance, i.e., achieving much higher salt removal capacities and energy-efficient desalination for high salinity streams, due to the Faradaic reaction for ion capture. This article presents a comprehensive overview on the current developments of Faradaic electrode materials for CDI. Here, the fundamentals of Faradaic electrode-based CDI are first introduced in detail, including novel CDI cell architectures, key CDI performance metrics, ion capture mechanisms, and the design principles of Faradaic electrode materials. Three main categories of Faradaic electrode materials are summarized and discussed regarding their crystal structure, physicochemical characteristics, and desalination performance. In particular, the ion capture mechanisms in Faradaic electrode materials are highlighted to obtain a better understanding of the CDI process. Moreover, novel tailored applications, including selective ion removal and contaminant removal, are specifically introduced. Finally, the remaining challenges and research directions are also outlined to provide guidelines for future research.

A High-Performance Primary Nanosheet Heterojunction Cathode Composed of Na0.44 MnO2 Tunnels and Layered Na2 Mn3 O7 for Na-Ion Batteries

Owing to its large capacity and high average potential, the structure and reversible O-redox compensation mechanism of Na₂ Mn₃ O₇ have recently been analyzed. However, capacity fade and low coulombic efficiency over multiple cycles have also been found to be a problem, which result from oxygen evolution at high charge voltages. Herein, a Na_0.44 MnO₂ ⋅Na₂ Mn₃ O₇ heterojunction of primary nanosheets was prepared by a sol-gel-assisted high-temperature sintering method. In the nanodomain regions, the close contact of Na_0.44 MnO₂ not only supplies multidimensional channels to improve the rate performance of the composite, but also plays the role of pillars for enhancing the cycling stability and coulombic efficiency; this is accomplished by suppressing oxygen evolution, which is confirmed by high-resolution (HR)TEM, cyclic voltammetry, and charge/discharge curves. As the cathode of a Na-ion battery, at 200 mA g^-1 after 100 cycles, the Na_0.44 MnO₂ ⋅Na₂ Mn₃ O₇ heterojunction retains an 88 % capacity and the coulombic efficiency approaches 100 % during the cycles. At 1000 mA g^-1 , the Na_0.44 MnO₂ ⋅Na₂ Mn₃ O₇ heterojunction has a discharge capacity of 72 mAh g^-1 . In addition, the average potential is as high as 2.7 V in the range 1.5-4.6 V. The above good performances indicate that heterojunctions are an effective strategy for addressing oxygen evolution by disturbing the long-range order distribution of manganese vacancies in the Mn-O layer.