Facile synthesis of carbon co-doped with nitrogen and phosphorus as metal-free electrocatalyst with precisely controlled pore structure and dual heteroatoms for oxygen reduction reaction

Abstract

Electrocatalysts used in sustainable energy conversion devices, such as fuel cells and air-metal batteries, have been widely investigated. Pt-based catalysts are widely used in the oxygen reduction reaction (ORR), which is a key reaction in these devices; however, these catalysts are highly expensive and unstable, thus impeding commercialization. Therefore, metal-free catalysts have attracted significant research interest as alternatives to noble-metal-based catalysts. We synthesized N and P co-doped carbon using a mixture of glycine and phytic acid, followed by CO2 activation to improve porosity. The optimized catalyst (CNP-act825-4) exhibited onset and half-wave potentials of 0.925 V vs. reversible hydrogen electrode (RHE) and 0.838 V vs. RHE, respectively. Density functional theory calculations revealed that the catalytic performance was attributed to the synergistic effects between graphitic-N and oxidized graphitic-P, in addition to the suitable porosity for ORR. This study provides a simple method for synthesizing N and P co-doped carbon and describes the effects of introducing N and P in electron distribution for ORR activity. This study demonstrates that N and P co-doping facilitates the effective preparation of highly active metal-free N and P co-doped catalysts. This study unlocks the possibility of maximizing the potential of metal-free multi-heteroatom-doped carbons for electrocatalytic processes via precise nanoscale control of the chemical states of multi-heteroatoms and pore structures.