Effect of Surface Ionization of Doped MnO2 on Capacitive Deionization Efficiency

3D grape string-like heterostructures enable high-efficiency sodium ion capture in Ti3C2Tx MXene/fungi-derived carbon nanoribbon hybrids

2D transition metal carbides and carbonitrides (MXenes) have emerged as promising electrode materials for electrochemistry ion capture but always suffer from severe layer-restacking and irreversible oxidation that restrains their electrochemical performance. Here we design a dual strategy of microstructure tailoring and heterostructure construction to synthesize a unique 3D grape string-like heterostructure consisting of Ti3C2Tx MXene hollow microspheres wrapped by fungi-derived N-doping carbon nanoribbons (denoted as GMNC). The 3D grape string-like heterostructure effectively avoids the aggregation of Ti3C2Tx MXene sheets and enhances the stability of MXenes, providing abundant active sites for ion capture, and an interconnected conductive bionic nanofiber network for high-rate electron transport. In consequence, GMNC achieves a superior adsorption capacity for sodium ions (Na+) in capacitive deionization (CDI) (162.37 mg gNaCl-1) with an ultra-high instantaneous adsorption rate (30.52 mg g-1 min-1) at an applied voltage of 1.6 V and satisfactory cycle stability over 100 cycles, which is a strong performer among the state-of-the-art values for MXene-based CDI electrodes. In addition, in situ electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) measurement combined with density functional theory (DFT) reveals the mechanisms of the Na+ capture process in the GMNC heterostructure. This work opens a new avenue for designing high-performance MXenes with a 3D hierarchical heterostructure for advanced electrochemical applications.

Upgrading Waste Activated Carbon by Equipping Micro-/Mesopore-Dominant Microstructures from the Perspective of Circular Economy

Equipping wastes with interesting properties in response to the circular economy could release environmental burdens by reducing resource exploitation and material manufacturing. In this study, we demonstrated that the waste regenerated activated carbon (RAC) could become micro-/mesopore-dominant through a simple surfactant/gel modification. This was achieved by associating carbon precursors, such as commercially available low-cost surfactants/methyl cellulose thickening reagents, with the pores of RAC. Following heat treatment, associated carbon precursors were carbonized, hence modifying the microstructure of RAC to be micro-/mesopore-dominant. The surfactant modification gave rise to a micropore-dominant RAC by increasing the micropore volume (PVmicro) together with significantly decreasing the mesopore volume (PVmeso) and macropore volume (PVmacro). In contrast, gel modification led to mesopore-rich RAC by blocking micropores with carbonized methyl cellulose and a surfactant matrix. Interestingly, both surfactant/gel modifications were insensitive to the properties of the surfactant applied, which provided a new alternative for waste/low-grade surfactant mixture disposal. Our results provide an important demonstration that waste could be effectively upgraded with a rational design by exhibiting new properties in response to the circular economy.

Oriented-Redox Induced Uniform MnO2 Coating on Ni3S2 Nanorod Arrays as a Stable Anode for Enhanced Performances of Lithium Ion Battery

Cost-effective transition metal chalcogenides have aroused wide consideration as alternative anode materials in lithium ion batteries (LIBs) on account of their elevated lithium activity and considerable theoretical capacity. However, the significant challenge caused by the large volume change and shuttle effect of polysulfides during Li ion insertion/extraction severely restricts their practical application. In this work, the uniform MnO₂ coating layer with a tunable thickness on Ni₃S₂ nanorod arrays has been achieved through a mild oriented-redox reaction by taking advantage of the mixing valence of Ni in Ni₃S₂ [(Ni²⁺)₂(Ni⁰)(S^2-)₂]. The core/shell structured nanorod arrays directly used as anode materials of LIBs demonstrate remarkably improved lithium storage performance including high rate capacity and long cycle life, which deliver a discharge capacity of 662 mA h g^-1 for 150 cycles at 0.5 C, corresponding to an elevated capacity retention of 90.7%. The improved electrochemical performances can be assigned to the generation of stable solid electrolyte interface films and suppression of the shuttle behavior with the protection of the MnO₂ coating layer on Ni₃S₂ nanorod arrays.