Ionic liquid-derived Fe–N/C catalysts for highly efficient oxygen reduction reaction without any supports, templates, or multi-step pyrolysis

Abstract

The development of efficient and low-cost non-precious-metal electrocatalysts such as Fe–N/C for the oxygen reduction reaction (ORR) is crucial for fuel cells and metal–air batteries. Here, we report a class of highly efficient Fe–N/C electrocatalysts derived from versatile imidazolium-based ionic liquids (ILs) with a halogen-coordinated iron anion. Without any supports, templates, or multi-step pyrolysis, the as-prepared Fe–N/C catalysts exhibited superior activity in the ORR to the state-of-the-art Pt/C in alkaline electrolytes by 44 mV in half-wave potential. More interestingly, owing to the versatile configuration of the imidazolium-based IL precursors, a diverse range of catalyst structures was successfully modulated. Based on this, it was clearly revealed that the electrical conductivity, type/amount of N dopants, and “effective porosity” (not the conventional total surface area) jointly determined the electrocatalytic activity. A pivotal radar chart is further proposed to successfully predict activity in the ORR merely from the structures of Fe–N/C catalysts. The proposed ILs platform would provide a valuable toolbox for the molecular design of precursors to tune the structures of Fe–N/C electrocatalysts towards excellent activity in the ORR in a highly flexible manner, and facilitate the long-term challenging study of relationships between processing, structure and activity.