Three-Dimensional Nanofibrous Air Electrode Assembled With Carbon Nanotubes-Bridged Hollow Fe₂O₃ Nanoparticles for High-Performance Lithium–Oxygen Batteries

Lithium–oxygen batteries have been considered as one of the most viable energy source options for electric vehicles due to their high energy density. However, they are still faced with technical challenges, such as low round-trip efficiency and short cycle life, which mainly originate from the cathode part of the battery. In this work, we designed a three-dimensional nanofibrous air electrode consisted of hierarchically structured carbon nanotube-bridged hollow Fe₂O₃ nanoparticles (H-Fe₂O₃/CNT NFs). Composite nanofibers consisted of hollow Fe₂O₃ NPs anchored by multiple CNTs offered enhanced catalytic sites (interconnected hollow Fe₂O₃ NPs) and fast charge-transport highway (bridged CNTs) for facile formation and decomposition of Li₂O₂, leading to outstanding cell performance: (1) Swagelok cell exhibited highly reversible cycling characteristics for 250 cycles with a fixed capacity of 1000 mAh g^–1 at a current density of 500 mA g^–1. (2) A module composed of two pouch-type cells stably powered an light-emitting diode lamp operated at 5.0 V

Rational Design of Efficient Electrocatalysts for Hydrogen Evolution Reaction: Single Layers of WS₂ Nanoplates Anchored to Hollow Nitrogen-Doped Carbon Nanofibers

To exploit the benefits of nanostructuring for enhanced hydrogen evolution reaction (HER), we employed coaxial electrospinning to synthesize single-layered WS₂ nanoplates anchored to hollow nitrogen-doped carbon nanofibers (WS₂@HNCNFs) as efficient electrocatalysts. For comparison, bulk WS₂ powder and single layers of WS₂ embedded in nitrogen-doped carbon nanofibers (WS₂@NCNFs) were synthesized and electrochemically tested. The distinctive design of the WS₂@HNCNFs enables remarkable electrochemical performances showing a low overpotential with reduced charge transfer resistance, a small Tafel slope, and excellent durability. The experimental results highlight the importance of nanostructure engineering in electrocatalysts for enhanced HER

One-Dimensional RuO₂/Mn₂O₃ Hollow Architectures as Efficient Bifunctional Catalysts for Lithium–Oxygen Batteries

Rational design and massive production of bifunctional catalysts with fast oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics are critical to the realization of highly efficient lithium–oxygen (Li–O₂) batteries. Here, we first exploit two types of double-walled RuO₂ and Mn₂O₃ composite fibers, i.e., (i) phase separated RuO₂/Mn₂O₃ fiber-in-tube (RM-FIT) and (ii) multicomposite RuO₂/Mn₂O₃ tube-in-tube (RM-TIT), by controlling ramping rate during electrospinning process. Both RM-FIT and RM-TIT exhibited excellent bifunctional electrocatalytic activities in alkaline media. The air electrodes using RM-FIT and RM-TIT showed enhanced overpotential characteristics and stable cyclability over 100 cycles in the Li–O₂ cells, demonstrating high potential as efficient OER and ORR catalysts

Brush-Like Cobalt Nitride Anchored Carbon Nanofiber Membrane: Current Collector-Catalyst Integrated Cathode for Long Cycle Li–O₂ Batteries

To achieve a high reversibility and long cycle life for lithium–oxygen (Li–O₂) batteries, the irreversible formation of Li₂O₂, inevitable side reactions, and poor charge transport at the cathode interfaces should be overcome. Here, we report a rational design of air cathode using a cobalt nitride (Co₄N) functionalized carbon nanofiber (CNF) membrane as current collector-catalyst integrated air cathode. Brush-like Co₄N nanorods are uniformly anchored on conductive electrospun CNF papers via hydrothermal growth of Co­(OH)F nanorods followed by nitridation step. Co₄N-decorated CNF (Co₄N/CNF) cathode exhibited excellent electrochemical performance with outstanding stability for over 177 cycles in Li–O₂ cells. During cycling, metallic Co₄N nanorods provide sufficient accessible reaction sites as well as facile electron transport pathway throughout the continuously networked CNF. Furthermore, thin oxide layer (<10 nm) formed on the surface of Co₄N nanorods promote reversible formation/decomposition of film-type Li₂O₂, leading to significant reduction in overpotential gap (∼1.23 V at 700 mAh g^–1). Moreover, pouch-type Li-air cells using Co₄N/CNF cathode stably operated in real air atmosphere even under 180° bending. The results demonstrate that the favorable formation/decomposition of reaction products and mediation of side reactions are hugely governed by the suitable surface chemistry and tailored structure of cathode materials, which are essential for real Li–air battery applications

Conducting Nanopaper: A Carbon-Free Cathode Platform for Li–O₂ Batteries

For a lithium–oxygen (Li–O₂) battery air electrode, we have developed a new all-in-one platform for designing a porous, carbon-free conducting nanopaper (CNp), which has dual functions as catalyst and current-collector, composed of one-dimensional conductive nanowires bound by a chitin binder. The CNp platform is fabricated by a liquid diffusion-induced crystallization and vacuum filtration methods. Employing less than 1 wt % chitin to connect the conductive skeleton, pores and active sites for reactions have become maximized in self-standing CNp. The carbon-free CNp enables the Li–O₂ air electrode to be more stably operated compared to carbon nanofibers and other CNps bound by PVDF and PMMA; side reactions are largely suppressed on the CNp. The versatile chitin is highlighted for diverse conducting nanopapers that can be used in various applications