Multilayer graphene crystals with enhanced performances in oxygen reduction and zinc–air batteries via interlayer carbon promoted OO bond dissociation

Abstract

OO bond activation determines activities of oxygen reduction reaction (ORR) catalysts, and developing metal-free catalysts that outperform precious metals remains challenging. Herein, we demonstrate the mechanochemical polymerization of pyrrole tandem carbonization for designing nitrogen-containing, micropore-penetrated multilayer graphene crystals (NM-MGCs) with abundant barrier-free nanochannels for O₂, leading to high exposure of carbon atoms adjacent to graphitic nitrogen. Due to the ordered multilayer structure with steady layer-by-layer van der Waals interaction, the resultant exposed interlayer carbon atoms exhibit much improved ability to activate O₂ through adsorption-configuration-induced OO bond dissociation in the ORR with approximately zero energy barrier. Thus, the NM-MGCs show record-breaking ORR performance among metal-free catalysts, which can be fabricated as air cathodes for both flow and flexible Zn–air batteries, exhibiting high maximum power density, high specific capacity (815.30 mA h g_Zn⁻¹ at 5 mA cm⁻²), and extraordinary long-term cycling durability (>800 h) and round-trip energy efficiency (63.7%). The overall performance of Zn–air batteries assembled using the NM-MGCs surpass those of commercial Pt/C (20 wt%) and many literature-reported metal and/or metal-free electrocatalysts.