Yttrium-preintercalated layered manganese oxide as a durable cathode for aqueous zinc-ion batteries.

Rechargeable aqueous zinc-ion batteries (RAZIBs) are regarded as competitive alternatives for large-scale energy storage on account of cost-effectiveness and inherent safety. In particular, rechargeable Zn-MnO2 batteries have drawn increasing attention due to high manufacturing readiness level. However, obtaining MnO2 with high electrochemical activity and high cyclic stability toward Zn2+/H+ storage still remains challenging. Herein, we reveal that incorporating yttrium ions (Y3+) into layered MnO2 can regulate the electronic structure of the MnO2 cathode by narrowing its band gap (from 3.25 to 2.50 eV), thus boosting the electrochemical performance in RAZIBs. Taking advantage of this feature, the optimized Y-MnO2 (YMO) sample exhibits greater capacity (212 vs. 152 mA h g-1 at 0.5 A g-1), better rate capability (94 vs. 61 mA h g-1 at 8 A g-1), reduced charge-transfer resistance (79 vs. 148 Ω), and promoted mass transfer kinetics (3.13 × 10-11vs. 2.37 × 10-11 cm2 s-1) in comparison with Y-free MnO2 (MO). More importantly, compared to MO, YMO-0.1 exhibits enhanced energy storage capability by nearly 40% (309 vs. 222 W h kg-1) and stable cycle performance (94 vs. 52 mA h g-1 after 3000 cycles). In situ Raman microscopy further reveals that the presence of Y3+ endows MnO2 with remarkable electrochemical reversibility during charge/discharge processes. This work highlights the importance of the Y3+ preintercalation strategy, which can be further developed to obtain better cathode materials for aqueous batteries.

Recent Development of Nickel-Based Electrocatalysts for Urea Electrolysis in Alkaline Solution.

Recently, urea electrolysis has been regarded as an up-and-coming pathway for the sustainability of hydrogen fuel production according to its far lower theoretical and thermodynamic electrolytic cell potential (0.37 V) compared to water electrolysis (1.23 V) and rectification of urea-rich wastewater pollution. The new era of the "hydrogen energy economy" involving urea electrolysis can efficiently promote the development of a low-carbon future. In recent decades, numerous inexpensive and fruitful nickel-based materials (metallic Ni, Ni-alloys, oxides/hydroxides, chalcogenides, nitrides and phosphides) have been explored as potential energy saving monofunctional and bifunctional electrocatalysts for urea electrolysis in alkaline solution. In this review, we start with a discussion about the basics and fundamentals of urea electrolysis, including the urea oxidation reaction (UOR) and the hydrogen evolution reaction (HER), and then discuss the strategies for designing electrocatalysts for the UOR, HER and both reactions (bifunctional). Next, the catalytic performance, mechanisms and factors including morphology, composition and electrode/electrolyte kinetics for the ameliorated and diminished activity of the various aforementioned nickel-based electrocatalysts for urea electrolysis, including monofunctional (UOR or HER) and bifunctional (UOR and HER) types, are summarized. Lastly, the features of persisting challenges, future prospects and expectations of unravelling the bifunctional electrocatalysts for urea-based energy conversion technologies, including urea electrolysis, urea fuel cells and photoelectrochemical urea splitting, are illuminated.

Defect regulated spinel Mn3O4 obtained by glycerol-assisted method for high-energy-density aqueous zinc-ion batteries.

Rechargeable aqueous zinc-ion batteries (RAZIBs) show great potential as a competitive candidate for reliable energy storage by virtue of cost-effectiveness, high safety, and environmental friendliness. However, unsatisfactory cycle stability of cathode material impedes the development of high-performance RAZIBs. This study reveals a strategic polyol-mediated process by using glycerol as the solvent for solvothermal reaction. After heat treatment in air, Mn-deficient Mn3O4 spinel (D-Mn3O4) can be obtained with rich Mn valence states (Mn2+/Mn3+/Mn4+), expanded crystal structure, high surface area, and good electrolyte compatability. Compared to well-crystallized Mn3O4, the presence of manganese vacancies in D-Mn3O4 enables lower charge-transfer resistance (86.0 vs 196.5 Ω), reduced activation energy for ion insertion (30.9 vs 50.4 kJ mol-1), and boosted solid-state ion diffusivity (9.45 × 10-12 vs 4.61 × 10-14 cm2 s-1). Therefore, D-Mn3O4 exhibits promising electrochemical performance with high capacity (284 mAh g-1), high specific energy (388.5 Wh kg-1) and stable cycle retention (87% after 200 cyclesat 0.3 A g-1). On the contrary, the well-crystallized Mn3O4 sample suffers from severe capacity fading with only 48% capacity retention. Moreover, the specific energies obtained after 200 cycles are 336.1 and 166.0 Wh kg-1 for D-Mn3O4 and Mn3O4, respectively. The drastic differences between the electrochemical performance of D-Mn3O4 and Mn3O4 manifest that the existing manganese vacancies in Mn3O4 spinel structure enhance energy storage capability.

Expanded spinel ZnxMn2O4 induced by electrochemical activation of glucose - mediated manganese oxide for stable cycle performance in zinc - ion batteries.

Rechargeable aqueous Zn - MnOx batteries show great potential for grid - scale storage due to cost - effectiveness and high safety. However, most of MnOx cathodes suffer from irreversible phase transformation into spinel ZnMn2O4 with reduced electrochemical activity after repeated charge/discharge cycles, leading to severe capacity decay. Herein, we reveal a strategic design utilizing glucose as the mediating agent to prepare nanostructured MnO/Mn3O4 material, which can be then transformed into lattice - expanded ZnxMn2O4 nanoparticles by electrochemical activation. The expanded structure of ZnxMn2O4 allows better accommodation of Zn2+ and H+ ions and undergoes reversible lattice expansion/contraction during charge/discharge process. Therefore, the lattice - expanded ZnxMn2O4 retains 121 mAh g-1 after 2000 cycles at 1 A g-1, exhibiting stable cycle performance in comparison with the parent MnO2 (63 mAh g-1) and well - crystalline ZnMn2O4 (58 mAh g-1). Moreover, through the comparison of MnO/Mn3O4, Mn3O4/MnO2, and pure Mn3O4 samples, MnO is found to play an important role in forming lattice - expanded spinel structure during the activation process.

Vanadium oxides obtained by chimie douce reactions: The influences of transition metal species on crystal structures and electrochemical behaviors in zinc-ion batteries.

Rechargeable aqueous zinc-ion batteries (RAZIBs) have received increasing attention due to cost-effectiveness and inherent safety. A wide variety of advanced cathode materials have been revealed with promising performance in RAZIBs. However, these materials usually require sophisticated procedures at high temperatures, which greatly limit further practical application. Herein, a chimie douce approach is adopted to prepare vanadium oxides from V2O5 suspension with the addition of various transition metal cations (Mn2+, Zn2+, Ag+, and Fe3+) by simple liquid-solid mixing under ambient conditions. For the cases of Mn2+ and Zn2+, the dissolution-recrystallization process takes place leading to layered Mn0.31V3O7·1.40H2O (MnVO) and Zn0.32V3O7·1.52H2O (ZnVO). The use of Ag+ forms tunneled Ag0.33V2O5 (AgVO), and the present of Fe3+ stays mainly unreacted V2O5. The underlying reaction chemistries are proposed, for which the pH values of precursor solutions are found to be a key factor. Among the prepared materials, layered vanadium oxides exhibit promising battery performance. Particularly, MnVO delivers 340 and 217 mAh g-1 at 1 and 8 A g-1, respectively. A specific capacity of 164 mAh g-1 can be retained after 500 cycles at 1 A g-1. By contrast, AgVO and FeVO demonstrate inferior performance with retaining only 89 and 20 mAh g-1 after 500 cycles.

Reduced Intercalation Energy Barrier by Rich Structural Water in Spinel ZnMn2O4 for High-Rate Zinc-Ion Batteries.

Aqueous zinc-ion batteries are considered promising next-generation systems for large-scale energy storage due to low cost, environmental friendliness, and high reversibility of the Zn anode. However, the interfacial charge-transfer resistance for the insertion of divalent Zn2+ into cathode materials is normally high, which limits the kinetics of Zn2+ transfer at the cathode/electrolyte interface. This study reveals the presence of rich structural water in spinel ZnMn2O4 (ZnMn2O4·0.94H2O, denoted as ZMO), synthesized by a scalable and low-temperature process, significantly overcoming the great interfacial charge-transfer resistance. ZMO exhibits excellent electrochemical performance toward Zn storage, that is, high capacity (230 and 101 mA h g-1 at 0.5 and 8 A g-1), high specific energy/specific power (329 W h kg-1/706 W kg-1 and 134 W h kg-1/11,160 W kg-1), and stable cycle retention (75% after 2000 cycles at 4 A g-1) can be achieved. On the contrary, the controlled sample ZMO-450 with deficient structural water, prepared by post-heat treatment of ZMO at 450 °C, demonstrates limited discharge capacity (45 and 15 mA h g-1 at 0.5 and 8 A g-1). As examined by electrochemical impedance spectroscopy, rich structural water in ZMO effectively reduces the activation energy barrier upon Zn2+ insertion, rendering fast interfacial kinetics for Zn storage. Benefiting from rich structural water in ZMO, the involvement of Zn2+ during the charge/discharge process exhibits good reversibility, as characterized by X-ray diffraction and X-ray photoelectron spectroscopy.

Polypropylene Carbonate-Based Adaptive Buffer Layer for Stable Interfaces of Solid Polymer Lithium Metal Batteries.

Solid polymer electrolytes (SPEs) have the potential to enhance the safety and energy density of lithium batteries. However, poor interfacial contact between the lithium metal anode and SPE leads to high interfacial resistance and low specific capacity of the battery. In this work, we present a novel strategy to improve this solid-solid interface problem and maintain good interfacial contact during battery cycling by introducing an adaptive buffer layer (ABL) between the Li metal anode and SPE. The ABL consists of low molecular-weight polypropylene carbonate , poly(ethylene oxide) (PEO), and lithium salt. Rheological experiments indicate that ABL is viscoelastic and that it flows with a higher viscosity compared to PEO-only SPE. ABL also has higher ionic conductivity than PEO-only SPE. In the presence of ABL, the interface resistance of the Li/ABL/SPE/LiFePO4 battery only increased 20% after 150 cycles, whereas that of the battery without ABL increased by 117%. In addition, because ABL makes a good solid-solid interface contact between the Li metal anode and SPE, the battery with ABL delivered an initial discharge specific capacity of >110 mA·h/g, which is nearly twice that of the battery without ABL, which is 60 mA·h/g. Moreover, ABL is able to maintain electrode-electrolyte interfacial contact during battery cycling, which stabilizes the battery Coulombic efficiency.

Electroless deposition of RuO2-based nanoparticles for energy conversion applications.

This study reports a delicate electroless approach for the deposition of RuO2·nH2O nanoparticles on the VO x ·mH2O nanowires and this method can be extended to deposit RuO2·nH2O nanoparticles on various material surfaces. Electrochemical characterizations, including linear sweep voltammetry (LSV), electrochemical quartz crystal microbalance (QCM) analysis and rotating ring-disc electrode (RRDE) voltammetry, were carried out to investigate the growth mechanism. The deposition involves the catalytic reduction of dissolved oxygen by the V4+ species of VO x ·mH2O, which drives the oxidation of RuCl3 to proceed with the growth of RuO2·nH2O. This core/shell VO x ·mH2O/RuO2·nH2O shows a better catalytic activity of the oxygen reduction reaction (ORR) than RuO2·nH2O, which is ascribed to the pronounced dispersion of RuO2·nH2O. Such an electroless approach was applicable to the preparation of a RuO2-based nanoparticle suspension as well as the deposition of nanocrystalline RuO2·nH2O on other functional supports like TiO2 nanowires. The thus-obtained RuO2-decorated TiO2 nanorods exhibit significantly an enhanced photoactivity toward photoelectrochemical water oxidation. The versatility of the current electroless approach may facilitate the widespread deployment of nanocrystalline RuO2·nH2O in a variety of energy-related applications.