Niobium oxide (Nb₂O₅) is a promising material in photocatalytic, solar cell, electronic like electron field emitters, and especially lithium-ion batteries (LIBs) because of its adjustable morphologies, controllable crystal type, stable structure, and environmental friendliness. However, its low electrical conductivity lowers the rate performance and limits the practical applications in LIBs. Herein, we present a one-step solid-state synthesis of orthogonal Nb₂O₅ nanocrystals/graphene composites (Nb₂O₅/G) as high-performance anode materials in LIBs. Benefiting from the nanoscale crystalline structure Nb₂O₅ and highly-conductive graphene substrate, the as-prepared Nb₂O₅/G exhibits excellent electrochemical performances. Impressively, a reversible structural phase transition between orthogonal Nb₂O₅ and tetragonal Li_1−xNbO₂ (0 < x < 1) was verified by ex-situ transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). After coupling with graphite cathode based on PF₆⁻ intercalation/deintercalation mechanisms, Nb₂O₅/G||graphite dual-ion batteries (DIBs) full cell delivers good electrochemical performance in terms of cyclic performance and rate capability. We believe this work can provide a clear route towards developing advanced transition metal oxide/graphene composite anode and a comprehension of its electrochemical reaction mechanism.

Abnormal expression of hydrogen peroxide (H₂O₂) indicates the disorder of cell functions and is able to induce the occurrence and deterioration of numerous diseases. However, limited by its low concentration under pathophysiological conditions, intracellular H₂O₂ is still difficult to be determined to date. Herein, to achieve sensitive quantification of H₂O₂ in cells, CIS/ZnS/ZnS quantum dots (CIS/d-ZnS QDs) are retrofitted with ZnO shells via self-passivation. Different from the traditional self-passivation of QDs, self-passivation of CIS/d-ZnS QDs is realized facilely without the assistance of additional cation ions, which improves optical properties of QDs and equips the QDs with a sensing layer. As a result, the CIS/d-ZnS/ZnO QDs exhibit enhanced fluorescence emission and stability. Relying on the decomposition of ZnO and ZnS shells in the presence of H₂O₂, aggregated QDs reveal exciton energy transfer effect, resulting in fluorescence quenching. On a basis of this principle, a fluorescence H₂O₂ sensor is further established with the CIS/d-ZnS/ZnO QDs. To be noted, since the equipped ZnO shells are more susceptible to H₂O₂ than original ZnS shells, analytical performance of the fluorescence sensor is remarkably promoted by the self-passivation of QDs. Accordingly, H₂O₂ can be measured in 5 orders of magnitude with a limit of detection (LOD) of 0.46 nM. Furthermore, because the ZnO shells improve H₂O₂-responsive selectivity and sensitivity, variation of H₂O₂ in cells can also be quantified with the CIS/d-ZnS/ZnO QDs. In this work, sensitive detection of intracellular H₂O₂ is enabled by equipping QDs with a sensing layer, which provides an alternative perspective of functionalizing nanomaterials for analytical applications.