Oxygen Plasma-Activated NiFe Prussian Blue Analogues Interconnected N‑Doped Carbon Nanotubes as a Bifunctional Electrocatalyst for a Rechargeable Zinc–Air Battery

Fabricating a robust and low-cost bifunctional electrocatalyst for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) becomes critical to realizing a high-performance rechargeable zinc–air battery (RZAB). Plasma treatment is a helpful way to preserve the uniformity of metal sites in the open framework of Prussian blue analogue (PBA) with highly active OER activity. Herein, we integrate the notable ORR performance of N-doped carbon nanotubes (N-CNT) with oxygen-plasma-activated NiFe PBA (O-PBA), which serves as an active OER catalyst, to realize the bifunctionality of the oxygen conversion reaction. Integrating N-CNT with O-NiFe PBA frameworks provides the individual active sites for ORR and OER with a stable performance. OER performance of O-PBA/N-CNT exhibited an overpotential of 280 mV at a current density of 10 mA/cm², outperforming the commercial RuO₂ due to the activated metal site of O-PBA anchored in conductive N-CNT. Even after the plasma treatment, the N-CNT still had its electrocatalytic ability to improve the ORR performance, and the structure of NiFe PBA was still maintained. The combined benefits of dual active electrocatalytic sites of O-PBA/N-CNT produced a low potential gap at the value of 0.83 V in the OER/ORR polarization curve, which also exhibited stable charge–discharge performance for 45 h with a negligible potential gap of 0.70 V in RZAB application. This study presents the exploration of producing a facile synthesis of a dual-active oxygen transformation electrocatalyst by utilizing the combination of surface engineering between surface doping and plasma activation.