Biomass derived N-doped carbon aerogel/NiFe-prussian blue analogue as robust bifunctional oxygen electrocatalyst for rechargeable zinc-air batteries

Prussian Blue Analogues (PBAs) with bimetallic transition metals have emerged as promising bifunctional electrocatalysts for oxygen reduction (ORR) and oxygen evolution (OER) reactions in rechargeable zinc–air batteries (ZABs), although their low intrinsic conductivity remains a major limitation. Herein, we report a sustainable, high-performance NiFe-PBA–carbon composite (NiFe-PBA-C) engineered from oil palm empty fruit bunches (PEFB) and metallic iron as renewable carbon and iron sources. NiFe-PBA nanoparticles were synthesized via a facile electrochemical iron-dissolution route in a Ni²⁺/[Fe(CN)₆]³⁻ electrolyte and subsequently integrated with a biomass-derived N-doped carbon aerogel (NCA) prepared through freeze-drying and pyrolysis. The optimized NiFe-PBA-C3 exhibits uniformly dispersed nanoparticles (∼13.1 nm) embedded within a conductive porous carbon network, enabling efficient charge transport and active-site exposure. XPS analysis reveals pronounced binding energy shifts in the N 1 s and Ni/Fe 2p spectra, indicating strong electronic coupling and metal–nitrogen coordination at the PBA–carbon interface, which compensates for the reduced pyridinic-N content and promotes favorable O₂ adsorption and activation. Consequently, NiFe-PBA-C3 delivers a half-wave potential of 0.77 V (vs. RHE), a kinetic current density of 0.41 mA cm⁻², and an electron transfer number of 3.61, confirming a dominant four-electron ORR pathway, along with low charge-transfer resistance (21.18 Ω) and excellent OER activity. When employed as an air cathode in a ZAB pouch cell, the catalyst demonstrates stable cycling over 120 h, a high specific capacity of 765.12 mAh g⁻¹, and an energy density of 718.89 mWh g⁻¹. This work highlights the synergistic role of PBA frameworks and nitrogen-enriched biomass carbon in tuning interfacial electronic structures, offering an eco-friendly and scalable strategy for advanced metal–air battery electrocatalysts.