Binder-free NiCoFe layered double hydroxide nanosheets for flexible energy storage devices with high-rate-retention characteristics

Enhanced oxygen evolution and power density of Co/Zn@NC@MWCNTs for the application of zinc-air batteries

Rechargeable zinc-air batteries (ZABs) are viewed as a promising solution for electric vehicles due to their potential to provide a clean, cost-effective, and sustainable energy storage system for the next generation. Nevertheless, sluggish kinetics of the oxygen evolution reaction (OER), the oxygen reduction reaction (ORR) at the air electrode, and low power density are significant challenges that hinder the practical application of ZABs. The key to resolving the development of ZABs is developing an affordable, efficient, and stable catalyst with bifunctional catalytic. In this study, we present a series of bifunctional catalysts composed of Co/Zn nanoparticles uniformly embedded in nitrogen-doped carbon (NC) and multi-walled carbon nanotubes (MWCNTs) denoted as Co/Zn@NC@MWCNTs. The incorporation of MWCNTs using a facile and non-toxic method significantly decreased the overpotential of the OER from 570 to 430 mV at 10 mA cm-2 and the peak power density from 226 to 263 mW cm-2. Besides, the electrochemical surface area measurements and electrochemical impedance spectroscopy indicate that the three-dimensional (3D) network structure of MWCNTs facilitates mass transport for ORR and reduces electron transfer resistance during OER, leading to a small potential gap of 0.86 V between OER and ORR, high electron transfer number (3.92-3.98) of the ORR, and lowest Tafel slope (47.8 mV dec-1) of the OER in aqueous ZABs. In addition, in-situ Raman spectroscopy revealed a notable decrease in the ID/IG ratio for the optimally configured Co/Zn@NC@MWCNTs (75:25), indicating a reduction in defect density and improved structural ordering during the electrochemical process, which directly contributes to enhanced ORR activity. Hence, this study provides an excellent strategy for constructing a bifunctional catalyst material with a 3D MWCNTs conductive network for the development of advanced ZAB systems for sustainable energy applications.

Formation of MXene-Derived/NiCoFe-LDH Heterostructures for Supercapacitor Applications

In this study, MXene-derived/NiCoFe-LDH heterostructures with three-dimensional interconnected porous network microstructures were prepared, leveraging the excellent electrical conductivity and growth platform provided by the MXene material. The remarkable specific capacitance of metal oxides was fully exploited. The composite exhibited high specific capacitance and excellent stability, with a specific capacitance of 1305 F g^-1 at 1 A g^-1 and a capacitance of 85.7% of the initial performance after 6000 charge/discharge tests at 10 A g^-1. A two-electrode assembly was constructed using activated carbon as the negative electrode material corresponding to 49.5 Wh kg^-1 at 800 W kg^-1, indicating that the electrodes could achieve rapid charge/discharge. The findings of this study indicate that the composite material comprising LDH/MXene has significant potential for supercapacitor applications.