A Pyrolysis-Free Method Toward Large-Scale Synthesis of Ultra-Highly Efficient Bifunctional Oxygen Electrocatalyst for Zinc-Air Flow Batteries.

The transition-metal nitrogen-carbon (M-N-C) catalysts, as one of the optimal bifunctional oxygen catalysts, are vital for cathodic oxygen electrode of Zn-based air flow batteries (ZAFBs). However, chemical complexity of M-N-C catalysts prepared via the traditional pyrolytic process increases the difficulties of precise control toward configuration and repeatability, especially in large-scale synthesis. Herein, a bifunctional oxygen catalyst via a pyrolysis-free approach based on closed π-conjugated covalent organic polymers (COPs, microwave synthesis) is developed, which inherits the advantage of the well-defined configuration in an atomic manner. Profited from distinct catalytic centers and strong electronic coupling at the interface between COP and layered double hydroxides, the as-synthesized catalyst not only more easily permits large quantity production (>1 kg per batch), but also maintains an ultrahigh bifunctional activity and a long cycle stability even after scale synthesis (ΔE [Ej - E ] = 591 mV; energy efficiency drops by only 2.02% after 1200 cycles), which overwhelmingly exceeds the benchmark Pt/C+IrO and the state-of-the-art pyrolytic bifunctional M-N-C oxygen catalysts.