A Deep Dive Into the Study of Nitrogen-Doped Carbons as Electrocatalysts for the Oxygen Reduction Reaction via Design of Experiments

Abstract

A design of experiments (DoE) approach is applied to the study of nitrogen (N)-doped carbons prepared via a molten salt templating method using the eutectic salt lithium chloride/potassium chloride (LiCl/KCl) and the precursors sucrose and melamine (N precursor). This approach is used to deconvolute effects from surface composition and porosity on the electrocatalytic performance of N-doped carbons as oxygen reduction reaction (ORR) electrocatalysts. Additionally, DoE is implemented to reveal the synthesis-structure-function relationship for the prepared materials over an entire design space. From this work, it is evident that the N precursor content has the greatest impact on the tunability of material properties (e.g., N-content, pyridinic N content, surface area, pore size distribution, etc.) followed by pyrolysis temperature and salt mass. Additionally, without adequate porosity (surface area ≥ 500 m² g⁻¹, micropore volume > 0.15 cc g⁻¹, etc.) and electrochemically active surface area, activity and selectivity for the ORR via N-functionalization is significantly reduced. Optimization of the studied design space indicates that an N precursor content of 35 wt.%–38 wt.%, pyrolysis temperature ≤ 900 °C, and a salt mass < 15 g would garner the necessary N-content (∼7–8 at%) and porosity to achieve the most active and selective N-doped carbon ORR electrocatalysts.