Low-Temperature Pyrolysis: A Universal Route to High-Loading Single-Atom Catalysts for Fuel Cells.

Abstract

High-temperature pyrolysis (HTP, ≥900 °C) is a widely used method for synthesizing single-atom catalysts (SACs). However, the high operational temperatures required for HTP pose significant challenges in achieving high single-atom loading, primarily due to the Ostwald ripening effect. In this work, a low-temperature trans-metalation synthesis approach is developed which involves the exchange of cation between transition metal ions (M = Fe, Co, Cu, Ni, Mn, etc) and Zn²⁺ ions on a nitrogen-doped carbon (NC) matrix within a molten salt medium. This strategy effectively avoids phase transformations and enables the direct formation of high mass loading (3.7-4.7 wt.%) of atomically dispersed M-N₄ sites. Both experimental and theoretical analyses confirm that this cation-exchange occurs at a lower temperature threshold of 450 °C, significantly reducing the energy barriers for SACs synthesis. Furthermore, the synthesized catalyst with atomically dispersed Fe sites demonstrate excellent performance toward oxygen reduction reaction and fuel cell with a peak power density of 1.12 W cm^-2 in an H₂─O₂ fuel cell at 1.0 bar and 80 °C.