N-, P-, and O-doped porous carbon as advanced trifunctional metal-free electrocatalysts

Abstract

Electrocatalytic oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) play crucial roles in the development of green and sustainable energy systems. Metal-based electrocatalysts are extensively investigated in these core reactions. Nevertheless, such electrocatalysts usually suffer from high costs, resource scarcity, and inferior stability. To break through this obstacle, we prepared nitrogen, phosphorus, and oxygen-doped carbon with a cross-linked 3D porous nanostructure (named the NPOCs) via a simple two-step annealing method. The obtained NPOCs can act as a trifunctional electrocatalyst for HER, OER, and ORR. Thereinto, NPOCs show comparable electrocatalytic activity and reaction kinetics to commercial IrO₂ toward alkaline OER. Moreover, the NPOCs could deliver faster reaction kinetics compared to that of the benchmark Pt/C under high current densities for alkaline HER. For ORR, the NPOCs can display a closed half-wave potential to Pt/C and great CH₃OH tolerance. Meanwhile, the NPOCs acting as air cathodes for zinc–air batteries displayed a higher specific capacity than that of Pt/C + IrO₂-based zinc–air batteries.