A template-free assembly of Cu,N-codoped hollow carbon nanospheres as low-cost and highly efficient peroxidase nanozymes.

Developing carbon-based materials with high catalytic performance and sensitivity has significance in low-cost and highly efficient nanozymes. Herein, for the first time, Cu,N-codoped hollow carbon nanospheres (CuNHCNs) with highly active Cu-Nx sites were successfully assembled through a template-free strategy, in which Cu2+-poly(m-phenylenediamine) (Cu-PmPD) nanospheres were utilized as the source of Cu, N and C. Benefiting from the synergistic effect of the hollow spherical structure and optimized composition, the CuNHCN exhibits high affinity for 3,3',5,5'-tetramethylbenzidine and H2O2 with 0.0655 mM and 0.918 mM, respectively, which are superior to those of HRP and most metal-based nanozymes. Moreover, by employing glucose and ascorbic acid (AA) as biomolecule models, a CuNHCN-based colorimetric detection platform is developed. The CuNHCN exhibits superior peroxidase mimicking activity and sensitivity in detecting glucose and AA with a detection limit of 0.187 µM and 68.9 nM (S/N = 3), respectively. Also, the colorimetric detection based on the CuNHCN towards glucose and AA in human serum presents superior practicability and accuracy. The assay provides a new avenue for designing and fabricating low-cost peroxidase nanozymes with high performance in bioassays.

Construction of Li3PO4 nanoshells for the improved electrochemical performance of a Ni-rich cathode material.

A Li3PO4 nanocoating around a nickel-rich cathode material was successfully constructed via controlling the reaction between the electrode material and a preformed phosphorus-containing polymeric nanoshell; this not only effectively tackles the alkali residue challenge, but it also contributes to much-improved electrochemical performance being shown by a high-energy cathode.

High-Performance Cathode Materials for Potassium-Ion Batteries: Structural Design and Electrochemical Properties.

Due to the obvious advantage in potassium reserves, potassium-ion batteries (PIBs) are now receiving increasing research attention as an alternative energy storage system for lithium-ion batteries (LIBs). Unfortunately, the large size of K+ makes it a challenging task to identify suitable electrode materials, particularly cathode ones that determine the energy density of PIBs, capable of tolerating the serious structural deformation during the continuous intercalation/deintercalation of K+ . It is therefore of paramount importance that proper design principles of cathode materials be followed to ensure stable electrochemical performance if a practical application of PIBs is expected. Herein, the current knowledge on the structural engineering of cathode materials acquired during the battle against its performance degradation is summarized. The K+ storage behavior of different types of cathodes is discussed in detail and the structure-performance relationship of materials sensitive to their different lattice frameworks is highlighted. The key issues facing the future development of different categories of cathode materials are also highlighted and perspectives for potential approaches and strategies to promote the further development of PIBs are provided.

High-Performance Cathode of Sodium-Ion Batteries Enabled by a Potassium-Containing Framework of K0.5Mn0.7Fe0.2Ti0.1O2.

Sodium-ion batteries (SIBs) are promising candidates for large-scale electric energy storage with abundant sodium resources. However, their development is challenged by the availability of satisfactory cathode materials with stable framework to accommodate the transportation of large-sized Na+ (1.02 Å), whose continuous insertion/extraction can easily cause irreversible volumetric deformation in the crystalline material, leading to inevitable structural failure and capacity fading. Here, different from the previous synthesis efforts targeting at Na+ containing compounds, we unveil the possibility of achieving a highly reversible sodiation/desodiation process by resorting to a K+-based layered metal oxide formulated as K0.5Mn0.7Fe0.2Ti0.1O2 (KMFT), which is a P2 type in structure with a wide interlayer spacing to sit K+ (1.38 Å). We demonstrate that an initial K+/Na+ exchange can introduce Na+ into the lattice while a small amount of K+ remains inside, which plays a significant role in ensuring enlarged channels for a fast and stable Na+ diffusion. The KMFT electrode delivers a high initial discharge capacity of 147.1 mA h g-1 at 10 mA g-1 and outstanding long cycling stability with capacity retention of 71.5% after 1000 cycles at 500 mA g-1. These results provide a new design strategy for the development of stable SIBs cathodes to facilitate their future applications.

Facile Synthesis of Hollow Carbon Nanospheres and Their Potential as Stable Anode Materials in Potassium-Ion Batteries.

Hollow carbon nanospheres (HCNs) have found broad applications in a large variety of application fields. Unfortunately, HCNs are known for their tedious operations and are incompetent for scalable synthesis for those widely adopted nanocasting-based routes. Here, we report a facile and highly efficient method for the creation of hollow carbon structures by tuning the growth kinetics of its polymeric precursor. We identified that a controlled polymerization of Cu2+-poly(m-phenylenediamine) (Cu-PmPD) could form nanospheres with modulated inner chemical inhomogeneity, where the core of the particles was low in polymerization degree and water soluble, whereas the outer part was water insoluble. Therefore, a simple water washing of the prepared polymeric particles directly formed hollow nanospheres with a good control on the structural features including their cavity size and shell thickness. HCNs were formed through a following heat treatment and were able to exhibit promising potential as a stable anode material when tested in potassium-ion batteries.

Phase Control on Surface for the Stabilization of High Energy Cathode Materials of Lithium Ion Batteries.

The development of high energy electrode materials for lithium ion batteries is challenged by their inherent instabilities, which become more aggravated as the energy densities continue to climb, accordingly causing increasing concerns on battery safety and reliability. Here, taking the high voltage cathode of LiNi0.5Mn1.5O4 as an example, we demonstrate a protocol to stabilize this cathode through a systematic phase modulating on its particle surface. We are able to transfer the spinel surface into a 30 nm shell composed of two functional phases including a rock-salt one and a layered one. The former is electrochemically inert for surface stabilization while the latter is designated to provide necessary electrochemical activity. The precise synthesis control enables us to tune the ratio of these two phases, and achieve an optimized balance between improved stability against structural degradation without sacrificing its capacity. This study highlights the critical importance of well-tailored surface phase property for the cathode stabilization of high energy lithium ion batteries.

Construction of uniform ZrO2 nanoshells by buffer solutions.

We identified that the growth kinetics of ZrO2 could be well-tuned in a CH3COOH-CH3COONa based buffer solution, which provided an efficient way to build uniform ZrO2 nanoshells on various substrates. Using this synthetic strategy, yolk-shell structured Pd@ZrO2 is demonstrated as a promising catalyst for methane oxidation.

Surface Zn doped LiMn2O4 for an improved high temperature performance.

A surface doping strategy is demonstrated for the stabilization of LiMn2O4, which is achieved by the surface solid reaction between the LiMn2O4 particle and its ZnO nanoshell. The surface treated sample shows a much improved high temperature performance with evidently suppressed Mn dissolution.

Designed synthesis of SnO2-C hollow microspheres as an anode material for lithium-ion batteries.

We report a simple and facile synthetic protocol to prepare an SnO2-C hollow composite, which shows improved battery performance when used as an anode material in lithium ion batteries.