Lamellar-assembled PdNi super-nanosheets as effective oxygen redox dual-electrocatalysts for rechargeable Zn-air batteries

Exploration of bifunctional electrocatalysts toward effective oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is pivotal for developing high-efficiency and rechargeable metal-air batteries but remains great challenging. Here we elaborately synthesize lamellar-assembled PdNi super-nanosheets (SNSs) with an optimized Pd/Ni molar ratio to serve as attractive ORR and OER bifunctional electrocatalysts for rechargeable high-powered Zn-air batteries (ZABs). The products are layer-by-layer stackings of ultrathin PdNi nanosheet motifs. On the drastically extended two-dimensional (2D) surface, the inserted Ni atoms can substantially lower down the d-band center of surface Pd toward improved ORR kinetics and concurrently create oxytropic NiO_x sites to adsorb –OH groups for promoting the reverse OER electrocatalysis. Specifically, the ORR mass activity and specific activity of the primary Pd₉₂Ni₈ SNSs attain 2.5 A·mg⁻¹ and 3.15 mA·cm⁻², which are respectively 14 and 9 times those of commercial Pt/C. Meanwhile, the OER activity and stability of Pd₉₂Ni₈ SNSs/C distinctly outperform those of the RuO₂ benchmark, suggesting excellent reversible oxygen electrocatalysis. The power density of the ZAB with Pd₉₂Ni₈ SNSs/C as the air cathode is 2.7 times higher than that by Pt/C benchmark. Significantly, it can last for over 150 h without significant performance degradation during the charge–discharge cycle test. This work showcases a feasible strategy for developing self-assembled multimetallic 2D nanomaterials with excellent bifunctional catalytic performances toward energy conversion applications.