Nanoporous silicon is a promising anode material for high energy density batteries due to its high cycling stability and high tap density compared to other nanostructured anode materials. However, the high cost of synthesis and low yield of nanoporous silicon limit its practical application. Here, we develop a scalable, low-cost top-down process of controlled oxidation of Mg₂Si in the air, followed by HCl removal of MgO to generate nanoporous silicon without the use of HF. By controlling the synthesis conditions, the oxygen content, grain size and yield of the porous silicon are simultaneously optimized from commercial standpoints. In situ environmental transmission electron microscopy reveals the reaction mechanism; the Mg₂Si microparticle reacts with O₂ to form MgO and Si, while preventing SiO₂ formation. Owing to the low oxygen content and microscale secondary structure, the nanoporous silicon delivers a higher initial reversible capacity and initial Coulombic efficiency compared to commercial Si nanoparticles (3,033 mAh/g vs. 2,418 mAh/g, 84.3% vs. 73.1%). Synthesis is highly scalable, and a yield of 90.4% is achieved for the porous Si nanostructure with the capability to make an excess of 10 g per batch. Our synthetic nanoporous silicon is promising for practical applications in next generation lithium-ion batteries.

Lithium-ion batteries are approaching their theoretical limit and can no longer keep up with the increasing demands of human society. Lithium-sulfur batteries, with a high theoretical specific energy, are promising candidates for next generation energy storage. However, the use of Li metal in Li-S batteries compromises both safety and performance, enabling dendrite formation and causing fast capacity degradation. Previous studies have probed alternative battery systems to replace the metallic Li in Li-S system, such as a Si/Li₂S couple, with limited success in performance. Recently, there is a focus on red P as a favorable anode material to host Li. Here, we establish a novel battery scheme by utilizing a P/C nanocomposite anode and pairing it with a Li₂S coated carbon nanofiber cathode. We find that red P anode can be compatible in ether-based electrolyte systems and can be successfully coupled to a Li₂S cathode. Our proof of concept full-cell displays remarkable specific capacity, rate and cycling performances. We expect our work will provide a useful alternative system and valuable insight in the quest for next generation energy storage devices.

Particulate matter (PM) pollution has become a major environmental concern in many developing countries. PM pollution control remains a great challenge owing to the complex sources and evolution processes of PM particles. There are two categories of PM, i.e., primary and secondary PM particles, and the primary PM emissions play a key role in the formation of PM pollution. Knowledge of primary PM particle compositions, sources, and evolution processes is of great importance to the effective control of PM pollution. In order to characterize PM particles effectively, their fundamental properties including the morphology, concentration distribution, surface chemistry, and composition must be systematically investigated. In this study, we collected and analyzed six types of PM₁₀ and PM_2.5 particles from different sources using an in situ sampling approach. The concentration distributions of PM particles were analyzed and comparative analysis of the morphologies, distributions, capture mechanisms, and compositions of PM particles was conducted using scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and energy-dispersive X-ray spectroscopy. We found that there were significant differences in the structures, morphologies, and capture mechanisms of PM_2.5 and PM₁₀ particles. The systematic comparative investigation in this work will benefit the study of evolution processes and the effective control of PM pollution in the future.

Developing advanced technologies to stabilize positive electrodes of lithium ion batteries under high-voltage operation is becoming increasingly important, owing to the potential to achieve substantially enhanced energy density for applications such as portable electronics and electrical vehicles. Here, we deposited chemically inert and ionically conductive LiAlO₂ interfacial layers on LiCoO₂ electrodes using the atomic layer deposition technique. During prolonged cycling at high-voltage, the LiAlO₂ coating not only prevented interfacial reactions between the LiCoO₂ electrode and electrolyte, as confirmed by electrochemical impedance spectroscopy and Raman characterizations, but also allowed lithium ions to freely diffuse into LiCoO₂ without sacrificing the power density. As a result, a capacity value close to 200 mA·h·g^–1 was achieved for the LiCoO₂ electrodes with commercial level loading densities, cycled at the cut-off potential of 4.6 V vs. Li⁺/Li for 50 stable cycles; this represents a 40% capacity gain, compared with the values obtained for commercial samples cycled at the cut-off potential of 4.2 V vs. Li⁺/Li.

Li metal chemistry is a promising alternative with a much higher energy density than that of state-of-the-art Li-ion counterparts. However, significant challenges including safety issues and poor cyclability have severely impeded Li metal technology from becoming viable. In recent years, nanotechnologies have become increasingly important in materials design and fabrication for Li metal anodes, contributing to major progress in the field. In this review, we first introduce the main achievements in Li metal battery systems fulfilled by nanotechnologies, particularly regarding Li metal anode design and protection, ultrastrong separator engineering, safety monitoring, and smart functions. Next, we introduce recent studies on nanoscale Li nucleation/deposition. Finally, we discuss possible future research directions. We hope this review delivers an overall picture of the role of nanoscale approaches in the recent progress of Li metal battery technology and inspires more research in the future.

Developing high-performance nonprecious-metal electrocatalysts for the oxygen reduction reaction (ORR) is crucial for a variety of renewable energy conversion and storage systems. Toward that end, rational catalyst design principles that lead to highly active catalytic centers and enhanced active site accessibility are undoubtedly of paramount importance. Here, we used Prussian blue nanoparticles to anchor Fe/Fe₃C species to nitrogen-doped reduced graphene oxide aerogels as ORR catalysts. The strong interaction between nanosized Fe₃C and the graphitic carbon shell led to synergistic effects in the ORR, and the protection of the carbon shell guaranteed stability of the catalyst. As a result, the aerogel electrocatalyst displayed outstanding activity in the ORR on par with the state-of-the-art Pt/C catalyst at the same mass loading in alkaline media, good performance in acidic media, and excellent stability and crossover tolerance that rivaled that of the best nonprecious-metal ORR electrocatalysts reported to date.

Highly active and low-cost catalysts for electrochemical reactions such as the hydrogen evolution reaction (HER) are crucial for the development of efficient energy conversion and storage technologies. Theoretical simulations have been instrumental in revealing the correlations between the electronic structure of materials and their catalytic activity, and guide the prediction and development of improved catalysts. However, difficulties in accurately engineering the desired atomic sites lead to challenges in making direct comparisons between experimental and theoretical results. In MoS₂, the Mo-edge has been demonstrated to be active for HER whereas the S-edge is inert. Using a computational descriptor-based approach, we predict that by incorporating transition metal atoms (Fe, Co, Ni, or Cu) the S-edge site should also become HER active. Vertically standing, edge-terminated MoS₂ nanofilms provide a well-defined model system for verifying these predictions. The transition metal doped MoS₂ nanofilms show an increase in exchange current densities by at least two-fold, in agreement with the theoretical calculations. This work opens up further opportunities for improving electrochemical catalysts by incorporating promoters into particular atomic sites, and for using well-defined systems in order to understand the origin of the promotion effects.

Metal–organic frameworks (MOFs) and silicon nanowires (SiNWs) have been extensively studied due to their unique properties; MOFs have high porosity and specific surface area with well-defined nanoporous structure, while SiNWs have valuable one-dimensional electronic properties. Integration of the two materials into one composite could synergistically combine the advantages of both materials and lead to new applications. We report the first example of a MOF synthesized on surface-modified SiNWs. The synthesis of polycrystalline MOF-199 (also known as HKUST-1) on SiNWs was performed at room temperature using a step-by-step (SBS) approach, and X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy dispersive spectroscopy elemental mapping were used to characterize the material. Matching of the SiNW surface functional groups with the MOF organic linker coordinating groups was found to be critical for the growth. Additionally, the MOF morphology can by tuned by changing the soaking time, synthesis temperature and precursor solution concentration. This SiNW/MOF hybrid structure opens new avenues for rational design of materials with novel functionalities.

Hydrogenated amorphous Si (α-Si: H) is a promising material for photovoltaic applications due to its low cost, high abundance, long lifetime, and non-toxicity. We demonstrate a device designed to investigate the effect of nanostructured back reflectors on quantum efficiency in photovoltaic devices. We adopt a superstrate configuration so that we may use conventional industrial light trapping strategies for thin film solar cells as a reference for comparison. We controlled the nanostructure parameters via a wafer-scale self-assembly technique and systematically studied the relation between nanostructure size and photocurrent generation. The gain/loss transition at short wavelengths showed red-shifts with decreasing nanostructure scale. In the infrared region the nanostructured back reflector shows large photocurrent enhancement with a modified feature scale. This device geometry is a useful archetype for investigating absorption enhancement by nanostructures.

Wearable electronics offer the combined advantages of both electronics and fabrics. In this article, we report the fabrication of wearable supercapacitors using cotton fabric as an essential component. Carbon nanotubes are conformally coated onto the cotton fibers, leading to a highly electrically conductive interconnecting network. The porous carbon nanotube coating functions as both active material and current collector in the supercapacitor. Aqueous lithium sulfate is used as the electrolyte in the devices, because it presents no safety concerns for human use. The supercapacitor shows high specific capacitance (~70–80 F·g⁻¹ at 0.1 A·g⁻¹) and cycling stability (negligible decay after 35, 000 cycles). The extremely simple design and fabrication process make it applicable for providing power in practical electronic devices.