Scalable synthesis of nitrogen and nitrogen–silicon co-doped graphene: SiC4 and SiN1C3 as new active centers for boosting ORR performance

Abstract

Innovations in energy storage and conversion technologies are closely dependent on developing superior materials that can be used in this field. Here, we present an industrially scalable and low-cost solvothermal method for synthesizing Si-N-co-doped (Si-N-GN) and N-doped graphene (N-GN) with a high specific surface area of 523 m2 g−1 and 1289 m2 g−1, respectively. Silicon atoms were successfully incorporated into the 2D graphene at a doping rate of 2.28 at.% via Si-C, Si-N, and Si-O bonds, thanks to the decarbonylation of N,N-dimethyl formamide (DMF) into dimethylamine and highly reactive carbonyl at the solvothermal conditions. The Si-N-GN exhibited an average electron transfer number of 3.83 e− per mole of O2 in a wide potential range with similar on-set potential (0.988 V vs. 1.012 V), greater methanol tolerance capability, and higher diffusion limiting current density (7.2 vs. 6.5 mA cm−2 at 0.4 V) for oxygen reduction reaction (ORR) in alkaline electrolytes compared to the commercial Pt/C catalyst. The improved ORR performance of Si-N-GN was attributed to the effectively decreased adsorption energy of O2 on SiC4 and SiN1C3 type bondings supported by the density functional theory (DFT) calculations based on the model created according to the XPS results. The promising electrocatalytic activity of Si-N-GN for ORR could also be enlarged to other electrochemical applications, including metal-air batteries.