Designing Switchable Transition Metal Nitrides/Carbides from High-Entropy PBA Derivative As Bifunctional Oxygen Electrocatalyst for Rechargeable Zinc-Air Batteries

Abstract

In response to the growing energy and environmental challenges, considerable endeavors have been directed towards the development of sustainable and eco-friendly energy technologies as alternatives to fossil fuels. Moreover, rechargeable zinc-air batteries (RZABs) stand out due to their high energy density and environmental friendliness, although the sluggish cathode oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics restrict RZABs performance. Prussian blue analogues (PBAs), owing to their highly porous structure and tunable morphology, are often utilized as the precursors of the materials. Particularly, high-entropy PBAs (HEPBAs), formed by blending five or more metals in a random lattice, have achieved enhanced thermal and chemical stability via a robust structure with multiple transition metal ions. Meanwhile, transition metal carbides (TMCs) were investigated for ZAB applications due to their higher catalytic activity. Herein, we introduced CNT into HEPBA nanoparticles, followed by calcination processes, resulting in the synthesis of high-entropy metal carbides on CNT (HE-TMCs/CNT) which are effective for the bifunctional OER and ORR performance. HE-TMCs/CNT demonstrate superior activity towards the ORR (E1/2 = 0.77 V) in a 0.1 M KOH solution and OER (η = 330 mV @10 mA cm−2) in a 1 M KOH solution. The ZAB with HE-TMCs/CNT as the cathode demonstrated an open-circuit voltage of 1.39 V, providing a high energy density of 71 mW cm-2 under a current density of 102 mA cm-2. It exhibited the ability to be charged and discharged in cycles for up to 40 hours, revealing good stability under an applied current density of 5 mA cm-2. These results offer a straightforward pathway for the development of efficient bifunctional electrocatalysts for high-performance RZABs. Figure 1