Integrating PtNi nanoparticles on NiFe layered double hydroxide nanosheets as a bifunctional catalyst for hybrid sodium–air batteries

Abstract

Hybrid sodium–air batteries (HSABs) are emerging systems for next-generation energy storage owing to their high theoretical energy density, high specific capacity, low cost, and environmental friendliness. However, the ungratified energy efficiency, large overpotential, and poor cycling stability associated with the sluggish oxygen reduction reaction/oxygen evolution reaction (ORR/OER) at air electrodes hamper their further development. Herein, we report a facile electrodeposition method to construct three-dimensional nickel defect-rich nickel–iron layered double hydroxide nanosheets decorated with platinum–nickel alloyed nanoparticles grown on macroporous nickel foam substrates (PtNi/Ni_xFe LDHs) as a binder-free electrocatalyst. The optimal catalyst (Pt₃Ni₁/Ni_xFe LDHs) demonstrates a low overpotential (265 mV at the current density of 10 mA cm⁻²), a small Tafel slope (22.2 mV dec⁻¹) towards the OER and a high half-wave potential (0.852 V) for ORR, as well as superior long-term stability in comparison to commercial catalysts. Theoretical calculations revealed that the Ni-top site of Pt₃Ni₁/Ni_xFe LDHs works as an active site for enhanced OER/ORR activities. The fabricated HSAB with Pt₃Ni₁/Ni_xFe LDHs as the air cathode displayed not only an initial low overpotential gap (0.50 V) but also superior rechargeability and structure stability with high round-trip efficiency (∼79.9%) of over 300 cycles. These results provide a novel design of bifunctional and binder-free catalyst as the cathode for metal–air batteries.