Facile synthesis of mesoporous carbon materials with a three-dimensional ordered mesostructure and rich FeNX/C-S-C sites for efficient electrocatalytic oxygen reduction

Abstract

Incorporation of sulfur (S) atoms into iron/nitrogen co-doped (FeNX) carbon materials is attractive for developing efficient electrocatalysts for the oxygen reduction reaction (ORR). Synthesis of such materials with suitable pore structures and rich active sites are important to improve the ORR performance. In this study, we demonstrate the facile synthesis of novel N/S co-doped ordered mesoporous carbon materials with a three-dimensional (3D) ordered bicontinuous cubic mesopore structure and rich FeNX and carbon-sulfur-carbon (C-S-C) sites (denoted as FeNX@NSOMCs) using the solvent-free nanocasting method. The 3D ordered bicontinuous cubic mesopore structure is replicated in the FeNX@NSOMCs from the mesoporous silica hard template KIT-6. The uniform N/S dopants in the carbon matrix is derived from the confined pyrolysis of a single amino acid methionine (Met). The creation of the FeNX sites is enabled by using anhydrous FeCl3 as the precursor. The absence of solvent and the coordination between FeCl3 and Met can reduce metal hydrolysis and aggregation, reduce N loss, and thus promote the formation of FeNX sites. The FeNX@NSOMCs possess high surface areas (830–938 m2/g), large pore volumes (0.97–1.36 cm3/g), disordered macropores and ordered mesopores (3.5–3.6 nm), and well-graphitized carbon walls. They are promising for ORR. The represent sample shows superior performance under alkaline conditions, achieving a high half-wave potential of 0.9 V, a high kinetic current density of 4.2 mA/cm2, a low Tafel slope of 55.3 mV/dec, a near four-electron process with a low H2O2 yield and a high stability. A comparative study using various control samples reveals that the FeNX sites, the S doping and the ordered mesopore structure are crucial to achieve the high ORR performance.