5.1 µm Ion-Regulated Rigid Quasi-Solid Electrolyte Constructed by Bridging Fast Li-Ion Transfer Channels for Lithium Metal Batteries.

An ultra-thin quasi-solid electrolyte (QSE) with dendrite-inhibiting properties is a requirement for achieving high energy density quasi-solid lithium metal batteries (LMBs). Here, a 5.1 µm rigid QSE layer is directly designed on the cathode, in which Kevlar (poly(p-phenylene terephthalate)) nanofibers (KANFs) with negatively charged groups bridging metal-organic framework (MOF) particles are served as a rigid skeleton, and non-flammable deep eutectic solvent is selected to be encapsulated into the MOF channels, combined with in situ polymerization to complete safe electrolyte system with high rigidness and stability. The QSE with constructed topological network demonstrates high rigidity (5.4 GPa), high ionic conductivity (0.73 mS cm-1 at room temperature), good ion-regulated properties, and improved structural stability, contributing to homogenized Li-ion flux, excellent dendrite suppression, and prolonged cyclic performance for LMB. Additionally, ion regulation influences the Li deposition behavior, exhibiting a uniform morphology on the Li-metal surface after cycling. According to density-functional theory, KANFs bridging MOFs as hosts play a vital function in the free-state and fast diffusion dynamics of Li-ions. This work provides an effective strategy for constructing ultrathin robust electrolytes with a novel ionic conduction mode.

Oxygen-regulated carbon quantum dots as an efficient metal-free electrocatalyst for nitrogen reduction.

An electrocatalytic nitrogen reduction reaction under ambient conditions provides a wonderful blueprint for the conversion of nitrogen to ammonia. However, current research on ammonia synthesis is mainly focused on metal-based catalysts. It is still a great challenge to realize the effective activation of N2 on non-metallic catalysts. Herein, carbon quantum dots are reported to reduce dinitrogen to ammonia under ambient conditions. Benefiting from its numerous defect sites, this metal-free catalyst shows excellent catalytic performance in 0.1 M HCl with a faradaic efficiency of 17.59%. In addition, both experimental and theoretical results confirm that the catalytic performance of the catalyst can be improved by appropriately controlling the oxygen content of samples at different temperatures, and the utmost ammonia yield is 134.08 µg h-1 mg-1cat., which is almost three times higher than that of a reported metal-free material. The proposed oxygen regulation provides a new method to optimize the surface properties of metal-free catalysts for ammonia synthesis.

Ti3C2Tx MXene-derived TiO2/C-QDs as oxidase mimics for the efficient diagnosis of glutathione in human serum.

Nanozyme-based colorimetry was suggested to be a rapid method for biomarker (e.g. glutathione) detection, but this method suffers from lack of efficiency and low-toxicity nanozymes till now. Herein, quantum dots of TiO2 loaded on carbon (TiO2/C-QDs) oxidase-like nanozymes were prepared via a hydrothermal treatment of tiny and few-layered Ti3C2Tx MXene nanosheets, which possess abundant thermodynamic metastable Ti atoms on MXene margins as raw materials for the preparation of TiO2/C-QDs. The oxygen vacancy in TiO2 on the surface of the carbon matrix can facilitate O2 adsorption in the solution and generate reactive oxygen species (ROS), thereby quickly oxidizing 3,3',5,5'-tetramethylbenzidine (TMB) to its oxidized form (TMBox) in the absence of H2O2. After adding glutathione (GSH), TMBox was able to be restored to TMB, which resulted in a corresponding decrease in the UV-vis absorbance value at 652 nm. Furthermore, this assay possesses good selectivity, excellent specificity and high sensitivity (limit of detection: 0.2 µM), which made it possible to efficiently detect GSH in complex biological samples such as human serum.

Spinel LiMn2O4 Nanofiber: An Efficient Electrocatalyst for N2 Reduction to NH3 under Ambient Conditions.

The production of ammonia (NH3) in the industrial scale basically relies on the traditional technology of Haber-Bosch, which is operated under harsh conditions with high energy consumption and a huge number of greenhouse gas emissions. Electrochemical N2 reduction reaction (NRR) is a promising route for artificial N2-to-NH3 fixation with less energy consumption. However, an effective electrocatalyst, as a prerequisite of the NRR, is of significance. Here, we report that a spinel LiMn2O4 nanofiber acts as a noble-metal-free electrocatalyst for NH3 synthesis with excellent performance under ambient conditions. The electrocatalyst, which was tested in 0.1 M HCl, has an excellent Faradaic efficiency of 7.44% and a NH3 yield of 15.83 µg h-1 mgcat.-1 at -0.50 V versus reversible hydrogen electrode. Moreover, it also possesses excellent electrochemical and structure stability.

WO3 nanosheets rich in oxygen vacancies for enhanced electrocatalytic N2 reduction to NH3.

The Haber-Bosch process for industrial-scale NH3 production suffers from harsh conditions and serious CO2 release. Electrochemical N2 reduction is an alternative approach to synthesize NH3 under ambient conditions, but it requires highly-efficient electrocatalysts for the N2 reduction reaction (NRR). In this Communication, we demonstrate that WO3 nanosheets rich in oxygen vacancies (R-WO3 NSs) exhibit greatly enhanced NRR performances. In 0.1 M HCl, such R-WO3 NSs achieve a large NH3 yield of 17.28 µg h-1 mgcat.-1 and a high faradaic efficiency of 7.0% at -0.3 V vs. a reversible hydrogen electrode, much superior to the WO3 nanosheets deficient in oxygen vacancies (6.47 µg h-1 mgcat.-1 and 1.02%). Remarkably, R-WO3 NSs also show high electrochemical stability.

Electrocatalytic N2-to-NH3 conversion with high faradaic efficiency enabled using a Bi nanosheet array.

Electrocatalytic N2 reduction represents a promising alternative to the conventional Haber-Bosch process for ambient N2-to-NH3 fixation, but it is severely challenged by competitive hydrogen evolution, which limits the current efficiency for NH3 formation. In this work, a nanosheet array of metallic Bi, an environmentally benign elemental substance previously predicted theoretically to have low hydrogen-evolving activity, is proposed as a superior catalyst for N2 reduction electrocatalysis. Electrochemical tests show that the Bi nanosheet array on Cu foil as a stable 3D catalyst electrode achieves a high faradaic efficiency of 10.26% with an NH3 yield rate of 6.89 × 10-11 mol s-1 cm-2 at -0.50 V vs. the reversible hydrogen electrode in 0.1 M HCl, rivalling the performances of most reported noble-metal-free catalysts operating in acids. Density functional theory calculations suggest that Bi effectively activates the N[triple bond, length as m-dash]N bond and the alternating mechanism is energetically favourable.

Biomass-derived oxygen-doped hollow carbon microtubes for electrocatalytic N2-to-NH3 fixation under ambient conditions.

Electrocatalytic N2 reduction as an alternative approach to the energy-intensive and large CO2-producing Haber-Bosch process for NH3 synthesis under mild conditions has attracted extensive attention. Current research efforts on N2 reduction have mainly focused on metal-based catalysts, but metal-free alternatives can avoid the issue of metal ion release. In this work, oxygen-doped hollow carbon microtubes (O-KFCNTs) derived from natural kapok fibers are reported as a metal-free NRR electrocatalyst for N2-to-NH3 conversion with excellent selectivity. In 0.1 M HCl, the O-KFCNTs achieve a high faradaic efficiency of 9.1% at -0.80 V vs. a reversible hydrogen electrode (RHE) and a NH3 yield rate of 25.12 µg h-1 mgcat.-1 at -0.85 V vs. RHE under ambient conditions. Notably, this catalyst also demonstrates high stability.