Single-step Synthesis of Highly Porous Nitrogen-doped Carbon by Solid–gas Mechanochemical Treatment as an Oxygen Reduction Electrocatalyst (Supporting Information)

Herein, we report a single-step mechanochemical synthesis of highly porous nitrogen-doped carbon and its electrocatalytic oxygen reduction activity. X-ray diffraction and X-ray photoelectron spectroscopy measurements revealed that solid–gas mechanochemical treatment (MT) using a planetary ball mill cleaved the C–C bonds in carbon black (CB) and simultaneously incorporated nitrogen atoms with a high proportion of quaternary N into the carbon network. MT at a milling speed of 600 rpm yielded nitrogen-doped porous carbon (N-PC) with an optimal combination of nitrogen content of 2.20 at% and surface area of 516 m² g⁻¹, which is 10 times larger than that of CB (51.1 m² g⁻¹). Owing to the high nitrogen content and large surface area, N-PC synthesized by MT at a milling speed of 600 rpm exhibited higher oxygen reduction activity than N-PC synthesized by MT at a milling speed of 800 rpm and porous carbon synthesized by MT at a milling speed of 300 rpm.