The design of a nanoporous cathode for Li–O2 batteries that can achieve high chemical stability and superior electrochemical performance remains a formidable challenge. A novel approach for the fabrication of nanoengineered PdNi alloys directly coated onto Ni nonwoven fabric (PdNi/NiNF) obtained through electrospinning has been proposed. On the basis of the contributions of the porous structure, the prepared metal-based cathodes can exhibit high chemical and mechanical stabilities, high catalytic activity, and high conductivity. In this design, the major side reactions were excluded when compared with popularly used carbon cathodes, and excellent cycling stability (266 cycles) could be achieved. The proposed cathode exhibited a high discharge capacity of 15 700 mA h g−1 at 500 mA g−1, which was 5 times higher than those reported for carbon-free cathodes.
Proton-coupled electrocatalytic reactions, such as the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) in acidic media, are very important half-reactions of fuel cells and water electrolysis. Aiming at increasing the interfacial proton concentration to improve the ORR/HER activity, we synthesize PdNi alloy nanostructures (PdNi-ANSs)–polyethyleneimine (PEI) inorganic–organic nanocomposites (PdNi-ANSs@PEI) by a PEI assisted cyanogel-reduction strategy. Various physical characterization techniques show that PdNi-ANSs are successfully functionalized by the PEI polymer during the synthesis of PdNi-ANSs@PEI because of the N–Pd interaction. Thanks to the increased interfacial proton concentration caused by the protonation of amine groups at PEI in acidic media, the molecular weight optimized PdNi-ANSs@PEI exhibit enhanced ORR/HER activity compared to PdNi-ANSs without PEI and commercial electrocatalysts, which indicates that the electrocatalytic activity of metal nanostructures can be remarkably improved by reasonable interface design.
A novel free-standing and binder-free air electrode with excellent electrochemical performance was designed for highly reversible Li–O2 batteries. The 3D hierarchically N, S co-doped macro–mesoporous carbon (NSMmC) was deposited on carbon paper (CP) via a template method, and then uniformly decorated with PdNi nanoparticles. The macropores of the porous carbon can provide enough space to accommodate discharge products, while the interconnected pores and channels efficiently facilitate oxygen and electrolyte diffusion. The introduction of PdNi nanoparticles greatly reduce the charge transfer resistance, resulting in the improvement of electron mobility of the whole cathode. Compared with Pd–NSMmC/CP and NSMmC/CP cathodes, the PdNi–NSMmC/CP cathode shows considerable enhancement of Li–O2 battery performance. The ultrafine and evenly distributed PdNi nanoparticles can not only provide enough catalytic sites, but can also tailor the discharge products into a cage-like morphology, which provides enough channels for electron and lithium ion transport. Moreover, the smaller size of the cage-like Li2O2 makes it decompose more easily, resulting in lower charge overpotential. This study provides a promising strategy to design 3D structured air cathodes for Li–O2 batteries with high electrocatalytic performance.
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