Meng Ding

Designed hybrid nanostructure with catalytic effect: beyond the theoretical capacity of SnO2 anode material for lithium ion batteries

Transition metal cobalt (Co) nanoparticle was designed as catalyst to promote the conversion reaction of Sn to SnO2 during the delithiation process which is deemed as an irreversible reaction. The designed nanocomposite, named as SnO2/Co3O4/reduced-graphene-oxide (rGO), was synthesized by a simple two-step method composed of hydrothermal (1st step) and solvothermal (2nd step) synthesis processes. Compared to the pristine SnO2/rGO and SnO2/Co3O4 electrodes, SnO2/Co3O4/rGO nanocomposites exhibit significantly enhanced electrochemical performance as the anode material of lithium-ion batteries (LIBs). The SnO2/Co3O4/rGO nanocomposites can deliver high specific capacities of 1038 and 712 mAh g−1 at the current densities of 100 and 1000 mA g−1, respectively. In addition, the SnO2/Co3O4/rGO nanocomposites also exhibit 641 mAh g−1 at a high current density of 1000 mA g−1 after 900 cycles, indicating an ultra-long cycling stability under high current density. Through ex-situ TEM analysis, the excellent electrochemical performance was attributed to the catalytic effect of Co nanoparticles to promote the conversion of Sn to SnO2 and the decomposition of Li2O during the delithiation process. Based on the results, herein we propose a new method in employing the catalyst to increase the capacity of alloying-dealloying type anode material to beyond its theoretical value and enhance the electrochemical performance.

Bimetallic metal–organic framework derived porous carbon nanostructures for high performance membrane capacitive desalination

Membrane-based capacitive deionization (MCDI) is a promising method for desalination that is expected to alleviate the problem of water shortage. Typical CDI processes show limited efficiency in salt removal and experimental results suggest that an improvement in electrode materials could be the cornerstone of MCDI. In this study, bimetallic metal–organic frameworks (BMOFs) have been used as precursors to develop porous carbons for MCDI electrodes. BMOFs are a unique class of MOFs that possess two types of metal ions with properties dependent on the ratio of the metal ions. In our work, we have synthesized a series of BMOFs with different molar ratios of Zn and Co based on ZIF-8 and ZIF-67. By controlling the molar ratio between Zn and Co, we are able to synthesize BMOF-derived porous carbons with different particle sizes and graphitization degrees. Furthermore, the porous carbon derived from a BMOF of Zn : Co = 3 : 1 exhibits a superior salt removal capacity of 45.62 mg g−1 in a 750 mg L−1 NaCl solution at 1.4 V. We attribute this performance to the large ion-accessible surface area and improved electrical conductivity of the carbon derived from the BMOF.

3D carbon foam-supported WS2 nanosheets for cable-shaped flexible sodium ion batteries

Sodium ion batteries (SIBs) are proposed as alternatives to the current widely used lithium ion batteries (LIBs) due to the abundance of battery-grade sodium sources in nature. However, the search for suitable high-performance electrode materials for SIBs continues to remain a significant challenge. Herein, we report a hybrid nanoarchitecture with nitrogen-doped graphene quantum dots (NGQDs)-decorated WS2 nanosheets anchored on a porous three-dimensional carbon foam (NGQDs-WS2/3DCF) scaffold as the anode that enables long-term cycling and high rate capability for SIBs. Benefiting from the 3D robust porous interpenetrating framework and the NGQDs decoration, the NGQDs-WS2/3DCF nanoarchitecture exhibits a high rate capability with a capacity of 268.4 mA h g−1 at 2000 mA g−1, and a long lifetime with an extraordinary capacity retention of 97.1% over 1000 cycles. Furthermore, the pseudocapacitance contributions of the NGQDs-WS2/3DCF nanoarchitecture are quantified by an in-depth kinetics analysis, which provides a better understanding of the excellent electrochemical performances. Remarkably, a cable-shaped flexible full SIB was also demonstrated using NGQDs-WS2/3DCF as the anode electrode, which exhibits high capacity and excellent flexibility. The nanoarchitecture fabrication approach and the surface engineering strategy as well as the demonstrated cable-shaped configuration may open an avenue for the development of wearable SIBs with high performance.

A high performance electrochemical deionization method to desalinate brackish water with an FePO4/RGO nanocomposite

Capacitive deionization (CDI) is a promising technique that may be applied in the desalination of brackish water. However, current CDI technologies suffer from low removal capacity and inapplicability for high concentration brine. Hence, here we introduce a new electrochemical deionization (EDI) method that achieves excellent deionization performance with a faradaic mechanism. In this work, a reduced graphene oxide supported amorphous FePO4 composite (FePO4@RGO) has been synthesized to work as the anode material due to its high capacity, good electrical conductivity and environmental benignity. Sodium ions in water will be intercalated/deintercalated into or out of the anode material during the charge and discharge process of batch mode experiments, which is different from the physical adsorption of traditional CDI by electrical double layers (EDLs). A high salt removal capacity of 100 mg g−1 has been achieved at a proper flow rate and a current density of 100 mA g−1 with the FePO4@RGO electrode. Meanwhile, a superior rate performance of 0.117 mg g−1 s−1 has been obtained with a current density of 1000 mA g−1. The energy consumption of EDI is 3.57 × 10−4 kW h g−1, which is comparable to those of other CDI technologies.

High-Performance Membrane Capacitive Deionization Based on Metal−Organic Framework-Derived Hierarchical Carbon Structures

Membrane capacitive deionization (MCDI) is a simple and highly energy efficient method to convert brackish water to clean water. In this work, a high-performance MCDI electrode architecture, which is composed of three-dimensional graphene networks and metal–organic frameworks (MOFs)–derived porous carbon rods, was prepared by a facile method. The obtained electrode material possesses not only the conducting networks for rapid electron transport but also the short diffusion length of ions, which exhibits excellent desalination performance with a high salt removal capacity, i.e., 37.6 mg g–1 at 1.2 V in 1000 mg L–1 NaCl solution. This strategy can be extended to other MOF-derived MCDI electrodes.