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The role of the alkali metal cations in halide perovskite solar cells is not well understood. Using synchrotron-based nano–x-ray fluorescence and complementary measurements, we found that the halide distribution becomes homogenized upon addition of cesium iodide, either alone or with rubidium iodide, for substoichiometric, stoichiometric, and overstoichiometric preparations, where the lead halide is varied with respect to organic halide precursors. Halide homogenization coincides with long-lived charge carrier decays, spatially homogeneous carrier dynamics (as visualized by ultrafast microscopy), and improved photovoltaic device performance. We found that rubidium and potassium phase-segregate in highly concentrated clusters. Alkali metals are beneficial at low concentrations, where they homogenize the halide distribution, but at higher concentrations, they form recombination-active second-phase clusters.

K-containing polyanion compounds hold great potential as anodes for sodium-ion batteries considering their large ion transport channels and stable open frameworks; however, sodium storage behavior has rarely been studied, and the mechanism remains unclear. Here, using a noninterference KTiOPO 4 thin-film model, the Na + storage mechanism is comprehensively revealed by in situ/operando spectroscopy, aberration-corrected electron microscopy and density functional theory calculations. We find that incomplete K + /Na + ion exchange occurs and eventually 0.15 K + remains as a pillar to stabilize the tunnel structure. The pillar effect substantially maintains the volume change within 3.9%, much smaller than that of K + (Na + ) insertion into KTiOPO 4 (NaTiOPO 4 ) (9.5%; 5%), thus enabling 10,000 cycles. The powder electrode demonstrates comparable capacity and can work efficiently at commercial-level areal capacity of 2.47 mAh cm −2 . The quasi-solid-state pouch cell with high safety under extreme abuse also manifests long-term cycling stability. This pillar chemistry will inspire alkali metal ion storage in hosts containing heterogeneous cations. The sodium storage mechanism of K-containing polyanion compounds is intricate and unclear. Here, the authors reveal that the residual K + pillars uphold K-containing polyanion structure upon sodium storage, enabling long-term cycling stability.

The classic models of metal electrode–electrolyte interfaces generally focus on either covalent interactions between adsorbates and solid surfaces or on long-range electrolyte–metal electrostatic interactions. Here we demonstrate that these traditional models are insufficient. To understand electrocatalytic trends in the oxygen reduction reaction (ORR), the hydrogen oxidation reaction (HOR) and the oxidation of methanol on platinum surfaces in alkaline electrolytes, non-covalent interactions must be considered. We find that non-covalent interactions between hydrated alkali metal cations M + (H 2 O) x and adsorbed OH (OH ad ) species increase in the same order as the hydration energies of the corresponding cations (Li +  >> Na +  > K +  > Cs + ) and also correspond to an increase in the concentration of OH ad –M + (H 2 O) x clusters at the interface. These trends are inversely proportional to the activities of the ORR, the HOR and the oxidation of methanol on platinum (Cs +  > K +  > Na +  >> Li + ), which suggests that the clusters block the platinum active sites for electrocatalytic reactions. Better understanding of the fundamental bonding interactions at electrified metal–liquid interfaces is critical for improving the electrochemical reactions of fuel cells, but now traditional models are shown to be insufficient. Using experimental measurements of various electrocatalytic reactions on platinum and density functional theory it is shown that non-covalent interactions must be considered.

The electronic and optical properties of alkali-metal-adsorbed graphene-like gallium nitride (g-GaN) have been investigated using density functional theory. The results denote that alkali-metal-adsorbed g-GaN systems are stable compounds, with the most stable adsorption site being the center of the hexagonal ring. In addition, because of charge transfer from the alkali-metal atom to the host, the g-GaN layer shows clear n-type doping behavior. The adsorption of alkali metal atoms on g-GaN occurs via chemisorption. More importantly, the work function of g-GaN is substantially reduced following the adsorption of alkali-metal atoms. Specifically, the Cs-adsorbed g-GaN system shows an ultralow work function of 0.84 eV, which has great potential application in field-emission devices. In addition, the alkali-metal adsorption can lead to an increase in the static dielectric constant and extend the absorption spectrum of g-GaN.

Hard carbon, a prominent member of carbonaceous materials, shows immense potential as a high-performance anode for energy storage in batteries, attracting significant attention. Its structural diversity offers superior performance and high tunability, making it ideal for use as an anode in lithium-ion batteries, sodium-ion batteries, and potassium-ion batteries. To develop higher-performance hard carbon anode materials, extensive research has been conducted to understand the storage mechanisms of alkali metal ions in hard carbon. Building on this foundation, this paper provides an in-depth review of the relationship between the structure of hard carbon and its electrochemical properties with alkali metal ions. It emphasizes the structural design and characterization of hard carbon, the storage mechanisms of alkali metal ions, and key strategies for structural modulation. Additionally, it offers a forward-looking perspective on the future potential of hard carbon. This review aims to provide a comprehensive overview of the current state of hard carbon anodes in battery research and highlights the promising future of this rapidly evolving field in advancing the development of next-generation alkali metal-ion batteries. Graphical Abstract This review comprehensively summarizes the origin, characterization, and precise design and regulation of diverse hard carbon structures, and explores their specific applications in lithium/sodium/potassium-ion batteries and future development prospects.

As the only stable binary compound formed between an alkali metal and nitrogen, lithium nitride possesses remarkable properties and is a model material for energy applications involving the transport of lithium ions. Following a materials design principle drawn from broad structural analogies to hexagonal graphene and boron nitride, we demonstrate that such low dimensional structures can also be formed from an s-block element and nitrogen. Both one- and two-dimensional nanostructures of lithium nitride, Li 3 N, can be grown despite the absence of an equivalent van der Waals gap. Lithium-ion diffusion is enhanced compared to the bulk compound, yielding materials with exceptional ionic mobility. Li 3 N demonstrates the conceptual assembly of ionic inorganic nanostructures from monolayers without the requirement of a van der Waals gap. Computational studies reveal an electronic structure mediated by the number of Li-N layers, with a transition from a bulk narrow-bandgap semiconductor to a metal at the nanoscale. Lithium nitride is the only stable binary alkali metal-nitrogen compound and shows promise for energy applications involving the transport of lithium ions. Here, the authors demonstrate that lithium nitride nanostructures can be grown as fibres and sheets despite the absence of a van der Waals gap.

In recent years, climate change has increasingly become one of the major challenges facing mankind today, seriously threatening the survival and sustainable development of mankind. Dramatically increasing carbon dioxide concentrations are thought to cause a severe greenhouse effect, leading to severe and sustained global warming, associated climate instability and unwelcome natural disasters, melting glaciers and extreme weather patterns. The treatment of flue gas from thermal power plants uses carbon capture, utilization, and storage (CCUS) technology, one of the most promising current methods to accomplish significant CO 2 emission reduction. In order to implement the technological and financial system of CO 2 capture, which is the key technology of CCUS technology and accounts for 70–80% of the overall cost of CCUS technology, it is crucial to create more effective adsorbents. Nowadays, with the development and application of various carbon dioxide capture materials, it is necessary to review and summarize carbon dioxide capture materials in time. In this paper, the main technologies of CO 2 capture are reviewed, with emphasis on the latest research status of CO 2 capture materials, such as amines, zeolites, alkali metals, as well as emerging MOFs and carbon nanomaterials. More and more research on CO 2 capture materials has used a variety of improved methods, which have achieved high CO 2 capture performance. For example, doping of layered double hydroxides (LDH) with metal atoms significantly increases the active site on the surface of the material, which has a significant impact on improving the CO 2 capture capacity and performance stability of LDH. Although many carbon capture materials have been developed, high cost and low technology scale remain major obstacles to CO 2 capture. Future research should focus on designing low-cost, high-availability carbon capture materials.

The catalytic oxidation of formaldehyde to CO 2 and H 2 O under low temperature is of great significance and insistent demand for indoor air purification. In this work, through alkali metal doping, we significantly improved the formaldehyde oxidation activity of Mn-based catalysts. At a temperature as low as 97 °C, 300 ppm of formaldehyde can be completely eliminated over 5%Cs/MnO x . The results showed that the presence of alkali metals markedly increased the redox ability of MnO x catalyst and the proportion of reactive oxygen species. The adsorption and reaction path of formaldehyde on the surface of the catalysts were studied by in-situ infrared spectroscopy. It was found that the adsorption form of formaldehyde on the surface of alkali metals doped MnO x catalyst was different from that of MnO x , except for monodentate formate detected over MnO x , more easily decomposed bridged adsorbed formate was another prominent adsorbed species over 5%Na/MnO x and 5%Cs/MnO x catalysts. The difference in reaction paths may be the key to the higher activities of alkali doped MnO x catalysts. This finding may provide some new ideas for the design of low temperature formaldehyde oxidation catalysts. Graphical Abstract The intermediate species during formaldehyde oxidation on MnO x and Na + /Cs + -doped MnO x are different, which may be the key reason why the latter exhibit higher activities than MnO x .

Highlights Host–guest inversion engineering is proposed to create poly(vinylidene fluoride-hexafluoropropylene) (PVH)-in-SiO 2 composite solid electrolytes with an original “polymer guest-in-ceramic host” architecture, exhibiting optimized interfacial contacts and comprehensive properties. The PVH-in-SiO 2 exhibits an overwhelming ionic conductivity of 1.32 × 10 −3  S cm −1 at 25 °C, with an ultralow residual solvent content of 2.9 wt%. In addition, the LiFePO 4 |PVH-in-SiO 2 |Li full cells deliver a significant capacity retention of 92.9% at an ultrahigh rate of 3C after 300 cycles at 25 °C. The host–guest inversion engineering is a versatile strategy, as proved by preparing Na + and K + -based PVH-in-SiO 2 composite solid electrolytes, delivering excellent ionic conductivity of 10 −4  S cm −1 at 25 °C (vs. 10 −6 –10 −5  S cm −1 of previous reports). Composite solid electrolytes (CSEs) are promising for solid-state Li metal batteries but suffer from inferior room-temperature ionic conductivity due to sluggish ion transport and high cost due to expensive active ceramic fillers. Here, a host–guest inversion engineering strategy is proposed to develop superionic CSEs using cost-effective SiO 2 nanoparticles as passive ceramic hosts and poly(vinylidene fluoride-hexafluoropropylene) (PVH) microspheres as polymer guests, forming an unprecedented “polymer guest-in-ceramic host” (i.e., PVH-in-SiO 2 ) architecture differing from the traditional “ceramic guest-in-polymer host”. The PVH-in-SiO 2 exhibits excellent Li-salt dissociation, achieving high-concentration free Li + . Owing to the low diffusion energy barriers and high diffusion coefficient, the free Li + is thermodynamically and kinetically favorable to migrate to and transport at the SiO 2 /PVH interfaces. Consequently, the PVH-in-SiO 2 delivers an exceptional ionic conductivity of 1.32 × 10 −3  S cm −1 at 25 °C (vs . typically 10 −5 –10 −4  S cm −1 using high-cost active ceramics), achieved under an ultralow residual solvent content of 2.9 wt% (vs . 8–15 wt% in other CSEs). Additionally, PVH-in-SiO 2 is electrochemically stable with Li anode and various cathodes. Therefore, the PVH-in-SiO 2 demonstrates excellent high-rate cyclability in LiFePO 4 |Li full cells (92.9% capacity-retention at 3C after 300 cycles under 25 °C) and outstanding stability with high-mass-loading LiFePO 4 (9.2 mg cm −1 ) and high-voltage NCM622 (147.1 mAh g −1 ). Furthermore, we verify the versatility of the host–guest inversion engineering strategy by fabricating Na-ion and K-ion-based PVH-in-SiO 2 CSEs with similarly excellent promotions in ionic conductivity. Our strategy offers a simple, low-cost approach to fabricating superionic CSEs for large-scale application of solid-state Li metal batteries and beyond.

This study aimed to clarify the effect of wire structure and alkaline elements in wire composition on metal transfer behavior in metal-cored arc welding (MCAW). A comparison of metal transfer in pure argon gas was carried out using a solid wire (wire 1), a metal-cored wire without an alkaline element (wire 2), and another metal-cored wire with 0.084 mass% of sodium (wire 3). The experiments were conducted under 280 and 320 A welding currents, observed by high-speed imaging techniques equipped with laser assistance and bandpass filters. At 280 A, wire 1 showed a streaming transfer mode, while the others showed a projected one. When the current was 320 A, the metal transfer of wire 2 changed to streaming, while wire 3 remained projected. As sodium has a lower ionization energy than iron, the mixing of sodium vapor into the iron plasma increases its electrical conductivity, raising the proportion of current flowing through metal vapor plasma. As a result, the current flows to the upper region of the molten metal on the wire tip, with the resulting electromagnetic force causing droplet detachment. Consequently, the metal transfer mode in wire 3 remained projected. Furthermore, weld bead formation is the best for wire 3.