Hierarchical graphitic carbon nitride-polypyrrole on metal-organic framework-derived carbon nanorod: Metal-Free electrocatalyst for solid-state flexible zinc-air batteries

Rechargeable Zn-air batteries (ZABs) offer high energy density and environmental friendliness but require durable, nonprecious bifunctional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) to enhance oxygen electrocatalysis, improving reaction kinetics and performance in practical applications. Herein, a unique metal-free throne-like hierarchical ternary electrocatalyst containing graphitic carbon nitrides-polypyrrole on carbon nanorod (g-C₃N₄-PPy@CNR) is synthesized by depositing g-C₃N₄-PPy on the surface of a metal-organic framework-derived carbon nanorod (CNR). g-C₃N₄-PPy@CNR catalyst exhibits outstanding ORR and OER in alkaline media with a low potential gap of 0.63 V, more efficient than commercial catalysts like the mixture of Platinum on Carbon (Pt-C) and ruthenium dioxide (RuO₂). Moreover, the g-C₃N₄-PPy@CNR catalyst is utilized to assemble the ZABs with solution and solid-state electrolytes. The ZAB comprised of g-C₃N₄-PPy@CNR cathode reveals a high energy density of 620 Wh/kg, a specific capacity of 541.2 mAh/g with an open circuit potential of 1.39 V. Assembled solid-state ZAB outperforms the commercial Pt-C and RuO₂-based ZAB with impressive energy density, capacity, and high charge-discharge stability and is used efficiently as the energy sources for green hydrogen generation through overall water splitting, light emitting diode (LED) panel and wearable electronics.