Mn3O4@NiAl-layered double hydroxide as cathode electrocatalysts for aqueous and flexible zinc-air battery applications.

This work focuses on the preparation of nanostructured Mn3O4 by reducing a zeolite imidazole framework and integrating it with hydrothermally synthesized nickel aluminum-layered double hydroxide (NiAl-LDH) nanosheets. Morphological analysis reveals that the electrocatalysts exhibit nanostructures, with the oxide showing a spherule-like morphology and the LDH presenting a sheet-like morphology. Additionally, high-resolution transmission electron microscopy has been used to study their structure. Electrochemical studies conducted in an alkaline medium reveal that the Mn3O4@NiAl-LDH exhibits a bi-functional capability for the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR), with a potential difference of 0.72 V between OER and ORR. Furthermore, the nanostructured Mn3O4@NiAl-LDH exhibited excellent stability, with a relative current of 98 % for OER and 79 % for ORR over a period of 24 h and 12 h, respectively. To support the obtained electrochemical performance, in-situ Raman analysis is carried out to explain the electron transfer mechanism in detail. Furthermore, the fabricated zinc-air battery (ZAB), with Mn₃O₄@NiAl-LDH as air cathode, undergoes various assessments, including specific capacity, multi-step current input, reversibility, and stability under different current densities. The ZAB demonstrated impressive endurance, lasting over 300 h at 2 mA/cm2 and 190 h at 5 mA/cm2. To meet the requirements of wearable technology, the ZAB is made flexible by employing a polymer gel electrolyte, resulting in a flexible ZAB. This flexible version achieved an excellent working potential of 1.34 V and a power density of 84 mW/cm2, exhibiting stable performance for 24 h. Additionally, the flexible ZAB performance is analyzed in conjunction with other environmental conditions, including negative temperatures. Finally, a practical demonstration was conducted by connecting two ZABs in series, successfully powering an LED, and running miniature fans. These results highlight Mn₃O₄@NiAl-LDH as an efficient electrocatalyst for air cathode applications in ZABs.